Spring. Data access using JDBC
Chapter 11. Data access using JDBC
11.1. Introduction
The value-add provided by the Spring Framework's JDBC abstraction framework is perhaps best shown by the following list (note that only the italicized lines need to be coded by an application developer):
-
Define connection parameters
-
Open the connection
-
Specify the statement
-
Prepare and execute the statement
-
Set up the loop to iterate through the results (if any)
-
Do the work for each iteration
-
Process any exception
-
Handle transactions
-
Close the connection
The Spring Framework takes care of all the grungy, low-level details that can make JDBC such a tedious API to develop with.
11.1.1. Choosing a style
There are a number of options for selecting an approach to form the basis for your JDBC database access. There are three flavors of the JdbcTemplate, a new "SimpleJdbc" approach taking advantage of database metadata, and there is also the "RDBMS Object" style for a more object oriented approach similar in style to the JDO Query design. We'll briefly list the primary reasons why you would pick one of these approaches. Keep in mind that even if you start using one of these approaches, you can still mix and match if there is a feature in a different approach that you would like to take advantage of. All approaches requires a JDBC 2.0 compliant driver and some advanced features require a JDBC 3.0 driver.
-
JdbcTemplate - this is the classic Spring JDBC approach and the most widely used. This is the "lowest level" approach and all other approaches use a JdbcTemplate under the covers. Works well in a JDK 1.4 and higher environment.
-
NamedParameterJdbcTemplate - wraps a JdbcTemplate to provide more convenient usage with named parameters instead of the traditional JDBC "?" place holders. This provides better documentation and ease of use when you have multiple parameters for an SQL statement. Works with JDK 1.4 and up.
-
SimpleJdbcTemplate - this class combines the most frequently used features of both JdbcTemplate and NamedParameterJdbcTemplate plus it adds additional convenience by taking advantage of some Java 5 features like varargs, autoboxing and generics to provide an easier to use API. Requires JDK 5 or higher.
-
SimpleJdbcInsert and SimpleJdbcCall - designed to take advantage of database metadata to limit the amount of configuration needed. This will simplify the coding to a point where you only need to provide the name of the table or procedure and provide a Map of parameters matching the column names. Designed to work together with the SimpleJdbcTemplate. Requires JDK 5 or higher and a database that provides adequate metadata.
-
RDBMS Objects including MappingSqlQuery, SqlUpdate and StoredProcedure - an approach where you create reusable and thread safe objects during initialization of your data access layer. This approach is modeled after JDO Query where you define your query string, declare parameters and compile the query. Once that is done any execute methods can be called multiple times with various parameter values passed in. Works with JDK 1.4 and higher.
11.1.2. The package hierarchy
The Spring Framework's JDBC abstraction framework consists of four different packages, namely core, datasource, object, and support.
The org.springframework.jdbc.core package contains the JdbcTemplate class and its various callback interfaces, plus a variety of related classes. A sub-package named org.springframework.jdbc.core.simple contains the SimpleJdbcTemplate class and the related SimpleJdbcInsert and SimpleJdbcCall classes. Another sub-package named org.springframework.jdbc.core.namedparam contains the NamedParameterJdbcTemplate class and the related support classes.
The org.springframework.jdbc.datasource package contains a utility class for easy DataSource access, and various simple DataSource implementations that can be used for testing and running unmodified JDBC code outside of a J2EE container. The utility class provides static methods to obtain connections from JNDI and to close connections if necessary. It has support for thread-bound connections, e.g. for use with DataSourceTransactionManager.
Next, the org.springframework.jdbc.object package contains classes that represent RDBMS queries, updates, and stored procedures as thread safe, reusable objects. This approach is modeled by JDO, although of course objects returned by queries are “disconnected” from the database. This higher level of JDBC abstraction depends on the lower-level abstraction in the org.springframework.jdbc.core package.
Finally the org.springframework.jdbc.support package is where you find the SQLException translation functionality and some utility classes.
Exceptions thrown during JDBC processing are translated to exceptions defined in the org.springframework.dao package. This means that code using the Spring JDBC abstraction layer does not need to implement JDBC or RDBMS-specific error handling. All translated exceptions are unchecked giving you the option of catching the exceptions that you can recover from while allowing other exceptions to be propagated to the caller.
11.2. Using the JDBC Core classes to control basic JDBC processing and error handling
11.2.1. JdbcTemplate
The JdbcTemplate class is the central class in the JDBC core package. It simplifies the use of JDBC since it handles the creation and release of resources. This helps to avoid common errors such as forgetting to always close the connection. It executes the core JDBC workflow like statement creation and execution, leaving application code to provide SQL and extract results. This class executes SQL queries, update statements or stored procedure calls, imitating iteration over ResultSets and extraction of returned parameter values. It also catches JDBC exceptions and translates them to the generic, more informative, exception hierarchy defined in the org.springframework.dao package.
Code using the JdbcTemplate only need to implement callback interfaces, giving them a clearly defined contract. The PreparedStatementCreator callback interface creates a prepared statement given a Connection provided by this class, providing SQL and any necessary parameters. The same is true for the CallableStatementCreator interface which creates callable statement. The RowCallbackHandler interface extracts values from each row of a ResultSet.
The JdbcTemplate can be used within a DAO implementation via direct instantiation with a DataSource reference, or be configured in a Spring IOC container and given to DAOs as a bean reference. Note: the DataSource should always be configured as a bean in the Spring IoC container, in the first case given to the service directly, in the second case to the prepared template.
Finally, all of the SQL issued by this class is logged at the 'DEBUG' level under the category corresponding to the fully qualified class name of the template instance (typically JdbcTemplate, but it may be different if a custom subclass of the JdbcTemplate class is being used).
11.2.1.1. Examples
Find below some examples of using the JdbcTemplate class. (These examples are not an exhaustive list of all of the functionality exposed by the JdbcTemplate; see the attendant Javadocs for that).
11.2.1.1.1. Querying (SELECT)
A simple query for getting the number of rows in a relation.
int rowCount = this.jdbcTemplate.queryForInt("select count(0) from t_accrual");
A simple query using a bind variable.
int countOfActorsNamedJoe = this.jdbcTemplate.queryForInt(
"select count(0) from t_actors where first_name = ?", new Object[]{"Joe"});
Querying for a String.
String surname = (String) this.jdbcTemplate.queryForObject(
"select surname from t_actor where id = ?",
new Object[]{new Long(1212)}, String.class);
Querying and populating a single domain object.
Actor actor = (Actor) this.jdbcTemplate.queryForObject(
"select first_name, surname from t_actor where id = ?",
new Object[]{new Long(1212)},
new RowMapper() {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setFirstName(rs.getString("first_name"));
actor.setSurname(rs.getString("surname"));
return actor;
}
});
Querying and populating a number of domain objects.
Collection actors = this.jdbcTemplate.query(
"select first_name, surname from t_actor",
new RowMapper() {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setFirstName(rs.getString("first_name"));
actor.setSurname(rs.getString("surname"));
return actor;
}
});
If the last two snippets of code actually existed in the same application, it would make sense to remove the duplication present in the two RowMapper anonymous inner classes, and extract them out into a single class (typically a static inner class) that can then be referenced by DAO methods as needed. For example, the last code snippet might be better off written like so:
public Collection findAllActors() {
return this.jdbcTemplate.query( "select first_name, surname from t_actor", new ActorMapper());
}
private static final class ActorMapper implements RowMapper {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setFirstName(rs.getString("first_name"));
actor.setSurname(rs.getString("surname"));
return actor;
}
}
11.2.1.1.2. Updating (INSERT/UPDATE/DELETE)
this.jdbcTemplate.update(
"insert into t_actor (first_name, surname) values (?, ?)",
new Object[] {"Leonor", "Watling"});
this.jdbcTemplate.update(
"update t_actor set weapon = ? where id = ?",
new Object[] {"Banjo", new Long(5276)});
this.jdbcTemplate.update(
"delete from actor where id = ?",
new Object[] {new Long.valueOf(actorId)});
11.2.1.1.3. Other operations
The execute(..) method can be used to execute any arbitrary SQL, and as such is often used for DDL statements. It is heavily overloaded with variants taking callback interfaces, binding variable arrays, and suchlike.
this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");
Invoking a simple stored procedure (more sophisticated stored procedure support is covered later).
this.jdbcTemplate.update(
"call SUPPORT.REFRESH_ACTORS_SUMMARY(?)",
new Object[]{Long.valueOf(unionId)});
11.2.1.2. JdbcTemplate idioms (best practices)
Instances of the JdbcTemplate class are threadsafe once configured. This is important because it means that you can configure a single instance of a JdbcTemplate and then safely inject this shared reference into multiple DAOs (or repositories). To be clear, the JdbcTemplate is stateful, in that it maintains a reference to a DataSource, but this state is not conversational state.
A common idiom when using the JdbcTemplate class (and the associated SimpleJdbcTemplate and NamedParameterJdbcTemplate classes) is to configure a DataSource in your Spring configuration file, and then dependency inject that shared DataSource bean into your DAO classes; the JdbcTemplate is created in the setter for the DataSource. This leads to DAOs that look in part like this:
public class JdbcCorporateEventDao implements CorporateEventDao {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
// JDBC-backed implementations of the methods on the CorporateEventDao follow...
}
The attendant configuration might look like this.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="corporateEventDao" class="com.example.JdbcCorporateEventDao">
<property name="dataSource" ref="dataSource"/>
</bean>
<!-- the DataSource (parameterized for configuration via a PropertyPlaceHolderConfigurer) -->
<bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</bean>
</beans>
If you are using Spring's JdbcDaoSupport class, and your various JDBC-backed DAO classes extend from it, then you inherit a setDataSource(..) method for free from said superclass. It is totally up to you as to whether or not you inherit from said class, you certainly are not forced to. If you look at the source for the JdbcDaoSupport class you will see that there is not a whole lot to it... it is provided as a convenience only.
Regardless of which of the above template initialization styles you choose to use (or not), there is (almost) certainly no need to create a brand new instance of a JdbcTemplate class each and every time you wish to execute some SQL... remember, once configured, a JdbcTemplate instance is threadsafe. A reason for wanting multiple JdbcTemplate instances would be when you have an application that accesses multiple databases, which requires multiple DataSources, and subsequently multiple differently configured JdbcTemplates.
11.2.2. NamedParameterJdbcTemplate
The NamedParameterJdbcTemplate class adds support for programming JDBC statements using named parameters (as opposed to programming JDBC statements using only classic placeholder ('?') arguments. The NamedParameterJdbcTemplate class wraps a JdbcTemplate, and delegates to the wrapped JdbcTemplate to do much of its work. This section will describe only those areas of the NamedParameterJdbcTemplate class that differ from the JdbcTemplate itself; namely, programming JDBC statements using named parameters.
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActorsByFirstName(String firstName) {
String sql = "select count(0) from T_ACTOR where first_name = :first_name";
SqlParameterSource namedParameters = new MapSqlParameterSource("first_name", firstName);
return namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Notice the use of the named parameter notation in the value assigned to the 'sql' variable, and the corresponding value that is plugged into the 'namedParameters' variable (of type MapSqlParameterSource).
If you like, you can also pass along named parameters (and their corresponding values) to a NamedParameterJdbcTemplate instance using the (perhaps more familiar) Map-based style. (The rest of the methods exposed by the NamedParameterJdbcOperations - and implemented by the NamedParameterJdbcTemplate class) follow a similar pattern and will not be covered here.)
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActorsByFirstName(String firstName) {
String sql = "select count(0) from T_ACTOR where first_name = :first_name";
Map namedParameters = Collections.singletonMap("first_name", firstName);
return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Another nice feature related to the NamedParameterJdbcTemplate (and existing in the same Java package) is the SqlParameterSource interface. You have already seen an example of an implementation of this interface in one of the preceding code snippets (the MapSqlParameterSource class). The entire point of the SqlParameterSource is to serve as a source of named parameter values to a NamedParameterJdbcTemplate. The MapSqlParameterSource class is a very simple implementation, that is simply an adapter around a java.util.Map, where the keys are the parameter names and the values are the parameter values.
Another SqlParameterSource implementation is the BeanPropertySqlParameterSource class. This class wraps an arbitrary JavaBean (that is, an instance of a class that adheres to the JavaBean conventions), and uses the properties of the wrapped JavaBean as the source of named parameter values.
public class Actor {
private Long id;
private String firstName;
private String lastName;
public String getFirstName() {
return this.firstName;
}
public String getLastName() {
return this.lastName;
}
public Long getId() {
return this.id;
}
// setters omitted...
}
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActors(Actor exampleActor) {
// notice how the named parameters match the properties of the above 'Actor' class
String sql = "select count(0) from T_ACTOR where first_name = :firstName and last_name = :lastName";
SqlParameterSource namedParameters = new BeanPropertySqlParameterSource(exampleActor);
return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Remember that the NamedParameterJdbcTemplate class wraps a classic JdbcTemplate template; if you need access to the wrapped JdbcTemplate instance (to access some of the functionality only present in the JdbcTemplate class), then you can use the getJdbcOperations() method to access the wrapped JdbcTemplate via the JdbcOperations interface.
See also the section entitled Section 11.2.1.2, “JdbcTemplate idioms (best practices)” for some advice on how to best use the NamedParameterJdbcTemplate class in the context of an application.
11.2.3. SimpleJdbcTemplate
![[Note]](http://static.springsource.org/images/admons/note.png)
Note
The functionality offered by the SimpleJdbcTemplate is only available to you if you are using Java 5 or later.
The SimpleJdbcTemplate class is a wrapper around the classic JdbcTemplate that takes advantage of Java 5 language features such as varargs and autoboxing. The SimpleJdbcTemplate class is somewhat of a sop to the syntactic-sugar-like features of Java 5, but as anyone who has developed on Java 5 and then had to move back to developing on a previous version of the JDK will know, those syntactic-sugar-like features sure are nice.
The value-add of the SimpleJdbcTemplate class in the area of syntactic-sugar is best illustrated with a 'before and after' example. The following code snippet shows first some data access code using the classic JdbcTemplate, followed immediately thereafter by a code snippet that does the same job, only this time using the SimpleJdbcTemplate.
// classic JdbcTemplate-style...
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public Actor findActor(long id) {
String sql = "select id, first_name, last_name from T_ACTOR where id = ?";
RowMapper mapper = new RowMapper() {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setId(rs.getLong("id"));
actor.setFirstName(rs.getString("first_name"));
actor.setLastName(rs.getString("last_name"));
return actor;
}
};
// notice the cast, the wrapping up of the 'id' argument
// in an array, and the boxing of the 'id' argument as a reference type
return (Actor) jdbcTemplate.queryForObject(sql, mapper, new Object[] {Long.valueOf(id)});
}
Here is the same method, only this time using the SimpleJdbcTemplate; notice how much 'cleaner' the code is.
// SimpleJdbcTemplate-style...
private SimpleJdbcTemplate simpleJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
}
public Actor findActor(long id) {
String sql = "select id, first_name, last_name from T_ACTOR where id = ?";
ParameterizedRowMapper<Actor> mapper = new ParameterizedRowMapper<Actor>() {
// notice the return type with respect to Java 5 covariant return types
public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setId(rs.getLong("id"));
actor.setFirstName(rs.getString("first_name"));
actor.setLastName(rs.getString("last_name"));
return actor;
}
};
return this.simpleJdbcTemplate.queryForObject(sql, mapper, id);
}
See also the section entitled Section 11.2.1.2, “JdbcTemplate idioms (best practices)” for some advice on how to best use the SimpleJdbcTemplate class in the context of an application.
Note
The SimpleJdbcTemplate class only offers a subset of the methods exposed on the JdbcTemplate class. If you need to use a method from the JdbcTemplate that is not defined on the SimpleJdbcTemplate, you can always access the underlying JdbcTemplate by calling the getJdbcOperations() method on the SimpleJdbcTemplate, which will then allow you to invoke the method that you want. The only downside is that the methods on the JdbcOperations interface are not generified, so you are back to casting and such again.
11.2.4. DataSource
In order to work with data from a database, one needs to obtain a connection to the database. The way Spring does this is through a DataSource. A DataSource is part of the JDBC specification and can be seen as a generalized connection factory. It allows a container or a framework to hide connection pooling and transaction management issues from the application code. As a developer, you don not need to know any details about how to connect to the database, that is the responsibility for the administrator that sets up the datasource. You will most likely have to fulfill both roles while you are developing and testing you code though, but you will not necessarily have to know how the production data source is configured.
When using Spring's JDBC layer, you can either obtain a data source from JNDI or you can configure your own, using an implementation that is provided in the Spring distribution. The latter comes in handy for unit testing outside of a web container. We will use the DriverManagerDataSource implementation for this section but there are several additional implementations that will be covered later on. The DriverManagerDataSource works the same way that you probably are used to work when you obtain a JDBC connection. You have to specify the fully qualified class name of the JDBC driver that you are using so that the DriverManager can load the driver class. Then you have to provide a URL that varies between JDBC drivers. You have to consult the documentation for your driver for the correct value to use here. Finally you must provide a username and a password that will be used to connect to the database. Here is an example of how to configure a DriverManagerDataSource:
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName("org.hsqldb.jdbcDriver");
dataSource.setUrl("jdbc:hsqldb:hsql://localhost:");
dataSource.setUsername("sa");
dataSource.setPassword("");
11.2.5. SQLExceptionTranslator
SQLExceptionTranslator is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnostic org.springframework.dao.DataAccessException. Implementations can be generic (for example, using SQLState codes for JDBC) or proprietary (for example, using Oracle error codes) for greater precision.
SQLErrorCodeSQLExceptionTranslator is the implementation of SQLExceptionTranslator that is used by default. This implementation uses specific vendor codes. More precise than SQLState implementation, but vendor specific. The error code translations are based on codes held in a JavaBean type class named SQLErrorCodes. This class is created and populated by an SQLErrorCodesFactory which as the name suggests is a factory for creating SQLErrorCodes based on the contents of a configuration file named 'sql-error-codes.xml'. This file is populated with vendor codes and based on the DatabaseProductName taken from the DatabaseMetaData, the codes for the current database are used.
The SQLErrorCodeSQLExceptionTranslator applies the following matching rules:
-
Try custom translation implemented by any subclass. Note that this class is concrete and is typically used itself, in which case this rule does not apply.
-
Apply error code matching. Error codes are obtained from the SQLErrorCodesFactory by default. This looks up error codes from the classpath and keys into them from the database name from the database metadata.
-
Use the fallback translator. SQLStateSQLExceptionTranslator is the default fallback translator.
SQLErrorCodeSQLExceptionTranslator can be extended the following way:
public class MySQLErrorCodesTranslator extends SQLErrorCodeSQLExceptionTranslator {
protected DataAccessException customTranslate(String task, String sql, SQLException sqlex) {
if (sqlex.getErrorCode() == -12345) {
return new DeadlockLoserDataAccessException(task, sqlex);
}
return null;
}
}
In this example the specific error code '-12345' is translated and any other errors are simply left to be translated by the default translator implementation. To use this custom translator, it is necessary to pass it to the JdbcTemplate using the method setExceptionTranslator and to use this JdbcTemplate for all of the data access processing where this translator is needed. Here is an example of how this custom translator can be used:
// create a JdbcTemplate and set data source
JdbcTemplate jt = new JdbcTemplate();
jt.setDataSource(dataSource);
// create a custom translator and set the DataSource for the default translation lookup
MySQLErrorCodesTransalator tr = new MySQLErrorCodesTransalator();
tr.setDataSource(dataSource);
jt.setExceptionTranslator(tr);
// use the JdbcTemplate for this SqlUpdate
SqlUpdate su = new SqlUpdate();
su.setJdbcTemplate(jt);
su.setSql("update orders set shipping_charge = shipping_charge * 1.05");
su.compile();
su.update();
The custom translator is passed a data source because we still want the default translation to look up the error codes in sql-error-codes.xml.
11.2.6. Executing statements
To execute an SQL statement, there is very little code needed. All you need is a DataSource and a JdbcTemplate. Once you have that, you can use a number of convenience methods that are provided with the JdbcTemplate. Here is a short example showing what you need to include for a minimal but fully functional class that creates a new table.
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;
public class ExecuteAStatement {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public void doExecute() {
this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");
}
}
11.2.7. Running Queries
In addition to the execute methods, there is a large number of query methods. Some of these methods are intended to be used for queries that return a single value. Maybe you want to retrieve a count or a specific value from one row. If that is the case then you can use queryForInt(..), queryForLong(..) or queryForObject(..). The latter will convert the returned JDBC Type to the Java class that is passed in as an argument. If the type conversion is invalid, then an InvalidDataAccessApiUsageException will be thrown. Here is an example that contains two query methods, one for an int and one that queries for a String.
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;
public class RunAQuery {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public int getCount() {
return this.jdbcTemplate.queryForInt("select count(*) from mytable");
}
public String getName() {
return (String) this.jdbcTemplate.queryForObject("select name from mytable", String.class);
}
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
}
}
In addition to the single results query methods there are several methods that return a List with an entry for each row that the query returned. The most generic method is queryForList(..) which returns a List where each entry is a Map with each entry in the map representing the column value for that row. If we add a method to the above example to retrieve a list of all the rows, it would look like this:
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public List getList() {
return this.jdbcTemplate.queryForList("select * from mytable");
}
The list returned would look something like this:
[{name=Bob, id=1}, {name=Mary, id=2}]
11.2.8. Updating the database
There are also a number of update methods that you can use. Find below an example where a column is updated for a certain primary key. In this example an SQL statement is used that has place holders for row parameters. Note that the parameter values are passed in as an array of objects (and thus primitives have to be wrapped in the primitive wrapper classes).
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;
public class ExecuteAnUpdate {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public void setName(int id, String name) {
this.jdbcTemplate.update(
"update mytable set name = ? where id = ?",
new Object[] {name, new Integer(id)});
}
}
11.2.9. Retrieving auto-generated keys
One of the update convenience methods provides support for acquiring the primary keys generated by the database (part of the JDBC 3.0 standard - see chapter 13.6 of the specification for details). The method takes a PreparedStatementCreator as its first argument, and this is the way the required insert statement is specified. The other argument is a KeyHolder, which will contain the generated key on successful return from the update. There is not a standard single way to create an appropriate PreparedStatement (which explains why the method signature is the way it is). An example that works on Oracle and may not work on other platforms is:
final String INSERT_SQL = "insert into my_test (name) values(?)";
final String name = "Rob";
KeyHolder keyHolder = new GeneratedKeyHolder();
jdbcTemplate.update(
new PreparedStatementCreator() {
public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
PreparedStatement ps =
connection.prepareStatement(INSERT_SQL, new String[] {"id"});
ps.setString(1, name);
return ps;
}
},
keyHolder);
// keyHolder.getKey() now contains the generated key
11.3. Controlling database connections
11.3.1. DataSourceUtils
The DataSourceUtils class is a convenient and powerful helper class that provides static methods to obtain connections from JNDI and close connections if necessary. It has support for thread-bound connections, for example for use with DataSourceTransactionManager.
11.3.2. SmartDataSource
The SmartDataSource interface is to be implemented by classes that can provide a connection to a relational database. Extends the DataSource interface to allow classes using it to query whether or not the connection should be closed after a given operation. This can sometimes be useful for efficiency, in the cases where one knows that one wants to reuse a connection.
11.3.3. AbstractDataSource
This is an abstract base class for Spring's DataSource implementations, that takes care of the "uninteresting" glue. This is the class one would extend if one was writing one's own DataSource implementation.
11.3.4. SingleConnectionDataSource
The SingleConnectionDataSource class is an implementation of the SmartDataSource interface that wraps a single Connection that is not closed after use. Obviously, this is not multi-threading capable.
If client code will call close in the assumption of a pooled connection, like when using persistence tools, set suppressClose to true. This will return a close-suppressing proxy instead of the physical connection. Be aware that you will not be able to cast this to a native Oracle Connection or the like anymore.
This is primarily a test class. For example, it enables easy testing of code outside an application server, in conjunction with a simple JNDI environment. In contrast to DriverManagerDataSource, it reuses the same connection all the time, avoiding excessive creation of physical connections.
11.3.5. DriverManagerDataSource
The DriverManagerDataSource class is an implementation of the standard DataSource interface that configures a plain old JDBC Driver via bean properties, and returns a new Connection every time.
This is potentially useful for test or standalone environments outside of a J2EE container, either as a DataSource bean in a Spring IoC container, or in conjunction with a simple JNDI environment. Pool-assuming Connection.close() calls will simply close the connection, so any DataSource-aware persistence code should work. However, using JavaBean style connection pools such as commons-dbcp is so easy, even in a test environment, that it is almost always preferable to use such a connection pool over DriverManagerDataSource.
11.3.6. TransactionAwareDataSourceProxy
TransactionAwareDataSourceProxy is a proxy for a target DataSource, which wraps that target DataSource to add awareness of Spring-managed transactions. In this respect it is similar to a transactional JNDI DataSource as provided by a J2EE server.
Note
It should almost never be necessary or desirable to use this class, except when existing code exists which must be called and passed a standard JDBC DataSource interface implementation. In this case, it's possible to still have this code be usable, but participating in Spring managed transactions. It is generally preferable to write your own new code using the higher level abstractions for resource management, such as JdbcTemplate or DataSourceUtils.
(See the TransactionAwareDataSourceProxy Javadocs for more details.)
11.3.7. DataSourceTransactionManager
The DataSourceTransactionManager class is a PlatformTransactionManager implementation for single JDBC datasources. It binds a JDBC connection from the specified data source to the currently executing thread, potentially allowing for one thread connection per data source.
Application code is required to retrieve the JDBC connection via DataSourceUtils.getConnection(DataSource) instead of J2EE's standard DataSource.getConnection. This is recommended anyway, as it throws unchecked org.springframework.dao exceptions instead of checked SQLExceptions. All framework classes like JdbcTemplate use this strategy implicitly. If not used with this transaction manager, the lookup strategy behaves exactly like the common one - it can thus be used in any case.
The DataSourceTransactionManager class supports custom isolation levels, and timeouts that get applied as appropriate JDBC statement query timeouts. To support the latter, application code must either use JdbcTemplate or call DataSourceUtils.applyTransactionTimeout(..) method for each created statement.
This implementation can be used instead of JtaTransactionManager in the single resource case, as it does not require the container to support JTA. Switching between both is just a matter of configuration, if you stick to the required connection lookup pattern. Note that JTA does not support custom isolation levels!
11.3.8. NativeJdbcExtractor
There are times when we need to access vendor specific JDBC methods that differ from the standard JDBC API. This can be problematic if we are running in an application server or with a DataSource that wraps the Connection, Statement and ResultSet objects with its own wrapper objects. To gain access to the native objects you can configure your JdbcTemplate or OracleLobHandler with a NativeJdbcExtractor.
The NativeJdbcExtractor comes in a variety of flavors to match your execution environment:
-
SimpleNativeJdbcExtractor
-
C3P0NativeJdbcExtractor
-
CommonsDbcpNativeJdbcExtractor
-
JBossNativeJdbcExtractor
-
WebLogicNativeJdbcExtractor
-
WebSphereNativeJdbcExtractor
-
XAPoolNativeJdbcExtractor
Usually the SimpleNativeJdbcExtractor is sufficient for unwrapping a Connection object in most environments. See the Java Docs for more details.
11.4. JDBC batch operations
Most JDBC drivers provide improved performance if you batch multiple calls to the same prepared statement. By grouping updates into batches you limit the number of round trips to the database. This section will cover batch processing using both the JdbcTemplate and the SimpleJdbcTemplate.
11.4.1. Batch operations with the JdbcTemplate
Using the JdbcTemplate batch processing is accomplished by implementing a special interface, BatchPreparedStatementSetter, and passing that in as the second parameter in your batchUpdate method call. This interface has two methods you must implement. One is named getBatchSize and here you provide the size of the current batch. The other method is setValues and it allows you to set the values for the parameters of the prepared statement and. This method will get called the number of times that you specified in the getBatchSize call. Here is an example of this where we update the actor table based on entries in a list. The entire list is used as the batch in his example.
public class JdbcActorDao implements ActorDao {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public int[] batchUpdate(final List actors) {
int[] updateCounts = jdbcTemplate.batchUpdate(
"update t_actor set first_name = ?, last_name = ? where id = ?",
new BatchPreparedStatementSetter() {
public void setValues(PreparedStatement ps, int i) throws SQLException {
ps.setString(1, ((Actor)actors.get(i)).getFirstName());
ps.setString(2, ((Actor)actors.get(i)).getLastName());
ps.setLong(3, ((Actor)actors.get(i)).getId().longValue());
}
public int getBatchSize() {
return actors.size();
}
} );
return updateCounts;
}
// ... additional methods
}
If you are processing stream of updates or reading from a file then you might have a preferred batch size, but the last batch might not have that number of entries. In this case you can use the InterruptibleBatchPreparedStatementSetter interface which allows you to interrupt a batch once the input source is exhausted. The isBatchExhausted method allows you to signal the end of the batch.
11.4.2. Batch operations with the SimpleJdbcTemplate
The SimpleJdbcTemplate provides an alternate way of providing the batch update. Instead of implementing a special batch interface, you simply provide all parameter values in the call and the framework will loop over these values and use an internal prepared statement setter. The API varies depending on whether you use named parameters or not. For the named parameters you provide an array of SqlParameterSource, one entry for each member of the batch. You can use the SqlParameterSource.createBatch method to create this array, passing in either an array of JavaBeans or an array of Maps containing the parameter values.
This example shows a batch update using named parameters:
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
}
public int[] batchUpdate(final List<Actor> actors) {
SqlParameterSource[] batch = SqlParameterSourceUtils.createBatch(actors.toArray());
int[] updateCounts = simpleJdbcTemplate.batchUpdate(
"update t_actor set first_name = :firstName, last_name = :lastName where id = :id",
batch);
return updateCounts;
}
// ... additional methods
}
For an SQL statement using the classic "?" place holders you pass in a List containing an object array with the update values. This object array must have one entry for each placeholder in the SQL statement and they must be in the same order as they are defined in the SQL statement.
The same example using classic JDBC "?" place holders:
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
}
public int[] batchUpdate(final List<Actor> actors) {
List<Object[]> batch = new ArrayList<Object[]>();
for (Actor actor : actors) {
Object[] values = new Object[] {
actor.getFirstName(),
actor.getLastName(),
actor.getId()};
batch.add(values);
}
int[] updateCounts = simpleJdbcTemplate.batchUpdate(
"update t_actor set first_name = ?, last_name = ? where id = ?",
batch);
return updateCounts;
}
// ... additional methods
}
All batch update methods return an int array containing the number of affected rows for each batch entry. This count is reported by the JDBC driver and it's not always available in which case the JDBC driver simply returns a -2 value.
11.5. Simplifying JDBC operations with the SimpleJdbc classes
The SimpleJdbcInsert and SimpleJdbcCall classes provide simplified configuration by taking advantage of database metadata that can be retrieved via the JDBC driver. This means there is less to configure up front, although you can override or turn off the metadata processing if you prefer to provide all the details in your code.
11.5.1. Inserting data using SimpleJdbcInsert
Let's start by looking at the SimpleJdbcInsert class first. We will use the minimal amount of configuration options to start with. The SimpleJdbcInsert should be instantiated in the data access layer's initialization method. For this example, the initializing method is the setDataSource method. There is no need to subclass the SimpleJdbcInsert class, just create a new instance and set the table name using the withTableName method. Configuration methods for this class follows the "fluid" style returning the instance of the SimpleJdbcInsert which allows you to chain all configuration methods. In this case there is only one configuration method used but we will see examples of multiple ones soon.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcInsert insertActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.insertActor =
new SimpleJdbcInsert(dataSource).withTableName("t_actor");
}
public void add(Actor actor) {
Map<String, Object> parameters = new HashMap<String, Object>(3);
parameters.put("id", actor.getId());
parameters.put("first_name", actor.getFirstName());
parameters.put("last_name", actor.getLastName());
insertActor.execute(parameters);
}
// ... additional methods
}
The execute method used here takes a plain java.utils.Map as its only parameter. The important thing to note here is that the keys used for the Map must match the column names of the table as defined in the database. This is because we read the metadata in order to construct the actual insert statement.
11.5.2. Retrieving auto-generated keys using SimpleJdbcInsert
Next we'll look at the same insert, but instead of passing in the id we will retrieve the auto-generated key and set it on the new Actor object. When we create the SimpleJdbcInsert, in addition to specifying the table name, we specify the name of the generated key column using the usingGeneratedKeyColumns method.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcInsert insertActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.insertActor =
new SimpleJdbcInsert(dataSource)
.withTableName("t_actor")
.usingGeneratedKeyColumns("id");
}
public void add(Actor actor) {
Map<String, Object> parameters = new HashMap<String, Object>(2);
parameters.put("first_name", actor.getFirstName());
parameters.put("last_name", actor.getLastName());
Number newId = insertActor.executeAndReturnKey(parameters);
actor.setId(newId.longValue());
}
// ... additional methods
}
Here we can see the main difference when executing the insert is that we don't add the id to the Map and we call the executeReturningKey method. This returns a java.lang.Number object that we can use to create an instance of the numerical type that is used in our domain class. It's important to note that we can't rely on all databases to return a specific Java class here, java.lang.Number is the base class that we can rely on. If you have multiple auto-generated columns or the generated values are non-numeric then you can use a KeyHolder that is returned from the executeReturningKeyHolder method.
11.5.3. Specifying the columns to use for a SimpleJdbcInsert
It's possible to limit the columns used for the insert by specifying a list of column names to be used. This is accomplished using the usingColumns method.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcInsert insertActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.insertActor =
new SimpleJdbcInsert(dataSource)
.withTableName("t_actor")
.usingColumns("first_name", "last_name")
.usingGeneratedKeyColumns("id");
}
public void add(Actor actor) {
Map<String, Object> parameters = new HashMap<String, Object>(2);
parameters.put("first_name", actor.getFirstName());
parameters.put("last_name", actor.getLastName());
Number newId = insertActor.executeAndReturnKey(parameters);
actor.setId(newId.longValue());
}
// ... additional methods
}
The execution of the insert is the same as if we had relied on the metadata for determining what columns to use.
11.5.4. Using SqlParameterSource to provide parameter values
Using a Map to provide parameter values works fine, but it's not the most convenient class to use. Spring provides a couple of implementations of the SqlParameterSource interface that can be used instead. The first one we'll look at is BeanPropertySqlParameterSource which is a very convenient class as long as you have a JavaBean compliant class that contains your values. It will use the corresponding getter method to extract the parameter values. Here is an example:
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcInsert insertActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.insertActor =
new SimpleJdbcInsert(dataSource)
.withTableName("t_actor")
.usingGeneratedKeyColumns("id");
}
public void add(Actor actor) {
SqlParameterSource parameters = new BeanPropertySqlParameterSource(actor);
Number newId = insertActor.executeAndReturnKey(parameters);
actor.setId(newId.longValue());
}
// ... additional methods
}
Another option is the MapSqlParameterSource that resembles a Map but provides a more convenient addValue method that can be chained.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcInsert insertActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.insertActor =
new SimpleJdbcInsert(dataSource)
.withTableName("t_actor")
.usingGeneratedKeyColumns("id");
}
public void add(Actor actor) {
SqlParameterSource parameters = new MapSqlParameterSource()
.addValue("first_name", actor.getFirstName())
.addValue("last_name", actor.getLastName());
Number newId = insertActor.executeAndReturnKey(parameters);
actor.setId(newId.longValue());
}
// ... additional methods
}
As you can see, the configuration is the same, it;s just the executing code that has to change to use these alternative input classes.
11.5.5. Calling a stored procedure using SimpleJdbcCall
Let's now turn our attention to calling stored procedures using the SimpleJdbcCall class. This class is designed to make it as simple as possible to call a stored procedure. It takes advantage of metadata present in the database to look up names of in and out parameters. This means that you don't have to explicitly declare parameters. You can of course still declare them if you prefer to do that or if you have parameters that don't have an automatic mapping to a Java class like ARRAY or STRUCT parameters. In our first example we will look at a plain vanilla procedure that only returns scalar values in form of VARCHAR and DATE. I have added a birthDate property to the Actor class to get some variety in terms of return values. The example procedure reads a specified actor entry and returns first_name, last_name, and birth_date columns in the form of out parameters. Here is the source for the procedure as it would look when using MySQL as the database:
CREATE PROCEDURE read_actor ( IN in_id INTEGER, OUT out_first_name VARCHAR(100), OUT out_last_name VARCHAR(100), OUT out_birth_date DATE) BEGIN SELECT first_name, last_name, birth_date INTO out_first_name, out_last_name, out_birth_date FROM t_actor where id = in_id; END;
As you can see there are four parameters. One is an in parameter "in_id" containing the id of the Actor we are looking up. The remaining parameters are out parameters and they will be used to return the data read from the table.
The SimpleJdbcCall is declared in a similar manner to the SimpleJdbcInsert, no need to subclass and we declare it in the initialization method. For this example, all we need to specify is the name of the procedure.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcCall procReadActor;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
this.procReadActor =
new SimpleJdbcCall(dataSource)
.withProcedureName("read_actor");
}
public Actor readActor(Long id) {
SqlParameterSource in = new MapSqlParameterSource()
.addValue("in_id", id);
Map out = procReadActor.execute(in);
Actor actor = new Actor();
actor.setId(id);
actor.setFirstName((String) out.get("out_first_name"));
actor.setLastName((String) out.get("out_last_name"));
actor.setBirthDate((Date) out.get("out_birth_date"));
return actor;
}
// ... additional methods
}
The execution of the call involves creating an SqlParameterSource containing the in parameter. It's important to match the name of the parameter declared in the stored procedure. The case doesn't have to match since we use metadata to determine how database objects should be referred to - what you specify in your source for the stored procedure is not necessarily the way it is stored in the database, some databases transform names to all upper case while others use lower case or the case as specified.
The execute method takes the in parameters and returns a Map containing any out parameters keyed by the name as specified in the stored procedure. In this case they are out_first_name, out_last_name and out_birth_date.
The last part of the execute method just creates an Actor instance to use to return the data retrieved. Again, it's important to match the names of the out parameters here. Also, the case used for the names of the out parameters stored in the results map are as they were defined in the database. You will either have to do a case-insensitive lookup or instruct Spring to use a CaseInsensitiveMap from the Jakarta Commons project. The way you do that is by creating your own JdbcTemplate and setting the setResultsMapCaseInsensitive property to true. Then you pass this customized JdbcTemplate instance into the constructor of your SimpleJdbcCall. You also have to include the commons-collections.jar on your classpath for this to work. Here is an example of this configuration:
public class JdbcActorDao implements ActorDao {
private SimpleJdbcCall procReadActor;
public void setDataSource(DataSource dataSource) {
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate.setResultsMapCaseInsensitive(true);
this.procReadActor =
new SimpleJdbcCall(jdbcTemplate)
.withProcedureName("read_actor");
}
// ... additional methods
}
By doing this, you don't have to worry about the case used for the names of your returned out parameters.
11.5.6. Declaring parameters to use for a SimpleJdbcCall
We have seen how the parameters are deduced based on metadata, but you can declare then explicitly if you wish. This is done when the SimpleJdbcCall is created and configured using the declareParameters method that takes a variable number of SqlParameter objects as input. See the next section for details on how to define an SqlParameter.
We can opt to declare one, some or all of the parameters explicitly. The parameter metadata is still being used. By calling the method withoutProcedureColumnMetaDataAccess we can specify that we would like to bypass any processing of the metadata lookups for potential parameters and only use the declared ones. Another situation that can arise is that one or more in parameters have default values and we would like to leave them out of the call. To do that we will just call the useInParameterNames to specify the list of in parameter names to include.
This is what a fully declared procedure call declaration of our earlier example would look like:
public class JdbcActorDao implements ActorDao {
private SimpleJdbcCall procReadActor;
public void setDataSource(DataSource dataSource) {
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate.setResultsMapCaseInsensitive(true);
this.procReadActor =
new SimpleJdbcCall(jdbcTemplate)
.withProcedureName("read_actor")
.withoutProcedureColumnMetaDataAccess()
.useInParameterNames("in_id")
.declareParameters(
new SqlParameter("in_id", Types.NUMERIC),
new SqlOutParameter("out_first_name", Types.VARCHAR),
new SqlOutParameter("out_last_name", Types.VARCHAR),
new SqlOutParameter("out_birth_date", Types.DATE)
);
}
// ... additional methods
}
The execution and end results are the same, we are just specifying all the details explicitly rather than relying on metadata. This will be necessary if the database we use is not part of the supported databases. Currently we support metadata lookup of stored procedure calls for the following databases: Apache Derby, DB2, MySQL, Microsoft SQL Server, Oracle and Sybase. We also support metadata lookup of stored functions for: MySQL, Microsoft SQL Server and Oracle.
11.5.7. How to define SqlParameters
To define a parameter to be used for the SimpleJdbc classes, and also for the RDBMS operations classes covered in the following section, you use an SqlParameter or one of its subclasses. You typically specify the parameter name and SQL type in the constructor. The SQL type is specified using the java.sql.Types constants. We have already seen declarations like:
new SqlParameter("in_id", Types.NUMERIC),
new SqlOutParameter("out_first_name", Types.VARCHAR),
The first line with the SqlParameter declares an in parameter. In parameters can be used for both stored procedure calls and for queries using the SqlQuery and its subclasses covered in the following section.
The second line with the SqlOutParameter declares an out parameter to be used in a stored procedure call. There is also an SqlInOutParameter for inout parameters, parameters that provide an in value to the procedure and that also return a value
Note
Only parameters declared as SqlParameter and SqlInOutParameter will be used to provide input values. This is different from the StoredProcedure class which for backwards compatibility reasons allows input values to be provided for parameters declared as SqlOutParameter.
In addition to the name and the SQL type you can specify additional options. For in parameters you can specify a scale for numeric data or a type name for custom database types. For out parameters you can provide a RowMapper to handle mapping of rows returned from a REF cursor. Another option is to specify an SqlReturnType that provides and opportunity to define customized handling of the return values.
11.5.8. Calling a stored function using SimpleJdbcCall
Calling a stored function is done almost exactly the same way as calling a stored procedure. The only difference is that you need to provide a function name rather than a procedure name. This is done by using the withFunctionName method. Using this method indicates that your call is to a function and the corresponding call string for a function call will be generated. There is also a specialized execute call executeFunction that will return the function return value as an object of a specified type. This way you don't have to retrieve the return value from the results map. A similar convenience method named executeObject is also available for stored procedures that only have one out parameter. The following example is based on a stored function named get_actor_name that returns an actor's full name. Here is the MySQL source for this function:
CREATE FUNCTION get_actor_name (in_id INTEGER)
RETURNS VARCHAR(200) READS SQL DATA
BEGIN
DECLARE out_name VARCHAR(200);
SELECT concat(first_name, ' ', last_name)
INTO out_name
FROM t_actor where id = in_id;
RETURN out_name;
END;
To call this function we again create a SimpleJdbcCall in the initialization method.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcCall funcGetActorName;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate.setResultsMapCaseInsensitive(true);
this.funcGetActorName =
new SimpleJdbcCall(jdbcTemplate)
.withFunctionName("get_actor_name");
}
public String getActorName(Long id) {
SqlParameterSource in = new MapSqlParameterSource()
.addValue("in_id", id);
String name = funcGetActorName.executeFunction(String.class, in);
return name;
}
// ... additional methods
}
The execute method used returns a String containing the return value from the function call.
11.5.9. Returning ResultSet/REF Cursor from a SimpleJdbcCall
Calling a stored procedure or function that returns a result set has always been a bit tricky. Some databases return result sets during the JDBC results processing while others require an explicitly registered out parameter of a specific type. Both approaches still needs some additional processing to loop over the result set and process the returned rows. With the SimpleJdbcCall you use the returningResultSet method and declare a RowMapper implementation to be used for a specific parameter. In the case where the result set is returned during the results processing, there are no names defined, so the returned results will have to match the order you declare the RowMapper implementations. The name specified will still be used to store the processed list of results in the results map returned from the execute statement.
For this example we will use a stored procedure that takes no in parameters and returns all rows from the t_actor table. Here is the MySQL source for this procedure:
CREATE PROCEDURE read_all_actors() BEGIN SELECT a.id, a.first_name, a.last_name, a.birth_date FROM t_actor a; END;
In order to call this procedure we need to declare the RowMapper to be used. Since the class we want to map to follows the JavaBean rules, we can use a ParameterizedBeanPropertyRowMapper that is created by passing in the required class to map to in the newInstance method.
public class JdbcActorDao implements ActorDao {
private SimpleJdbcTemplate simpleJdbcTemplate;
private SimpleJdbcCall procReadAllActors;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate.setResultsMapCaseInsensitive(true);
this.procReadAllActors =
new SimpleJdbcCall(jdbcTemplate)
.withProcedureName("read_all_actors")
.returningResultSet("actors",
ParameterizedBeanPropertyRowMapper.newInstance(Actor.class));
}
public List getActorsList() {
Map m = procReadAllActors.execute(new HashMap<String, Object>(0));
return (List) m.get("actors");
}
// ... additional methods
}
The execute call passes in an empty Map since this call doesn't take any parameters. The list of Actors is then retrieved from the results map and returned to the caller.
11.6. Modeling JDBC operations as Java objects
The org.springframework.jdbc.object package contains classes that allow one to access the database in a more object-oriented manner. By way of an example, one can execute queries and get the results back as a list containing business objects with the relational column data mapped to the properties of the business object. One can also execute stored procedures and run update, delete and insert statements.
Note
There is a view borne from experience acquired in the field amongst some of the Spring developers that the various RDBMS operation classes described below (with the exception of the StoredProcedure class) can often be replaced with straight JdbcTemplate calls... often it is simpler to use and plain easier to read a DAO method that simply calls a method on a JdbcTemplate direct (as opposed to encapsulating a query as a full-blown class).
It must be stressed however that this is just a view... if you feel that you are getting measurable value from using the RDBMS operation classes, feel free to continue using these classes.
11.6.1. SqlQuery
SqlQuery is a reusable, threadsafe class that encapsulates an SQL query. Subclasses must implement the newRowMapper(..) method to provide a RowMapper instance that can create one object per row obtained from iterating over the ResultSet that is created during the execution of the query. The SqlQuery class is rarely used directly since the MappingSqlQuery subclass provides a much more convenient implementation for mapping rows to Java classes. Other implementations that extend SqlQuery are MappingSqlQueryWithParameters and UpdatableSqlQuery.
11.6.2. MappingSqlQuery
MappingSqlQuery is a reusable query in which concrete subclasses must implement the abstract mapRow(..) method to convert each row of the supplied ResultSet into an object. Find below a brief example of a custom query that maps the data from the customer relation to an instance of the Customer class.
private class CustomerMappingQuery extends MappingSqlQuery {
public CustomerMappingQuery(DataSource ds) {
super(ds, "SELECT id, name FROM customer WHERE id = ?");
super.declareParameter(new SqlParameter("id", Types.INTEGER));
compile();
}
public Object mapRow(ResultSet rs, int rowNumber) throws SQLException {
Customer cust = new Customer();
cust.setId((Integer) rs.getObject("id"));
cust.setName(rs.getString("name"));
return cust;
}
}
We provide a constructor for this customer query that takes the DataSource as the only parameter. In this constructor we call the constructor on the superclass with the DataSource and the SQL that should be executed to retrieve the rows for this query. This SQL will be used to create a PreparedStatement so it may contain place holders for any parameters to be passed in during execution. Each parameter must be declared using the declareParameter method passing in an SqlParameter. The SqlParameter takes a name and the JDBC type as defined in java.sql.Types. After all parameters have been defined we call the compile() method so the statement can be prepared and later be executed.
public Customer getCustomer(Integer id) {
CustomerMappingQuery custQry = new CustomerMappingQuery(dataSource);
Object[] parms = new Object[1];
parms[0] = id;
List customers = custQry.execute(parms);
if (customers.size() > 0) {
return (Customer) customers.get(0);
}
else {
return null;
}
}
The method in this example retrieves the customer with the id that is passed in as the only parameter. After creating an instance of the CustomerMappingQuery class we create an array of objects that will contain all parameters that are passed in. In this case there is only one parameter and it is passed in as an Integer. Now we are ready to execute the query using this array of parameters and we get a List that contains a Customer object for each row that was returned for our query. In this case it will only be one entry if there was a match.
11.6.3. SqlUpdate
The SqlUpdate class encapsulates an SQL update. Like a query, an update object is reusable, and like all RdbmsOperation classes, an update can have parameters and is defined in SQL. This class provides a number of update(..) methods analogous to the execute(..) methods of query objects. This class is concrete. Although it can be subclassed (for example to add a custom update method) it can easily be parameterized by setting SQL and declaring parameters.
import java.sql.Types;
import javax.sql.DataSource;
import org.springframework.jdbc.core.SqlParameter;
import org.springframework.jdbc.object.SqlUpdate;
public class UpdateCreditRating extends SqlUpdate {
public UpdateCreditRating(DataSource ds) {
setDataSource(ds);
setSql("update customer set credit_rating = ? where id = ?");
declareParameter(new SqlParameter(Types.NUMERIC));
declareParameter(new SqlParameter(Types.NUMERIC));
compile();
}
/**
* @param id for the Customer to be updated
* @param rating the new value for credit rating
* @return number of rows updated
*/
public int run(int id, int rating) {
Object[] params =
new Object[] {
new Integer(rating),
new Integer(id)};
return update(params);
}
}
11.6.4. StoredProcedure
The StoredProcedure class is a superclass for object abstractions of RDBMS stored procedures. This class is abstract, and its various execute(..) methods have protected access, preventing use other than through a subclass that offers tighter typing.
The inherited sql property will be the name of the stored procedure in the RDBMS.
To define a parameter to be used for the StoredProcedure classe, you use an SqlParameter or one of its subclasses. You must specify the parameter name and SQL type in the constructor. The SQL type is specified using the java.sql.Types constants. We have already seen declarations like:
new SqlParameter("in_id", Types.NUMERIC),
new SqlOutParameter("out_first_name", Types.VARCHAR),
The first line with the SqlParameter declares an in parameter. In parameters can be used for both stored procedure calls and for queries using the SqlQuery and its subclasses covered in the following section.
The second line with the SqlOutParameter declares an out parameter to be used in the stored procedure call. There is also an SqlInOutParameter for inout parameters, parameters that provide an in value to the procedure and that also return a value
Note
Parameters declared as SqlParameter and SqlInOutParameter will always be used to provide input values. In addition to this any parameter declared as SqlOutParameter where an non-null input value is provided will also be used as an input paraneter.
In addition to the name and the SQL type you can specify additional options. For in parameters you can specify a scale for numeric data or a type name for custom database types. For out parameters you can provide a RowMapper to handle mapping of rows returned from a REF cursor. Another option is to specify an SqlReturnType that provides and opportunity to define customized handling of the return values.
Here is an example of a program that calls a function, sysdate(), that comes with any Oracle database. To use the stored procedure functionality one has to create a class that extends StoredProcedure. There are no input parameters, but there is an output parameter that is declared as a date type using the class SqlOutParameter. The execute() method returns a map with an entry for each declared output parameter using the parameter name as the key.
import java.sql.Types;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import javax.sql.DataSource;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.datasource.*;
import org.springframework.jdbc.object.StoredProcedure;
public class TestStoredProcedure {
public static void main(String[] args) {
TestStoredProcedure t = new TestStoredProcedure();
t.test();
System.out.println("Done!");
}
void test() {
DriverManagerDataSource ds = new DriverManagerDataSource();
ds.setDriverClassName("oracle.jdbc.OracleDriver");
ds.setUrl("jdbc:oracle:thin:@localhost:1521:mydb");
ds.setUsername("scott");
ds.setPassword("tiger");
MyStoredProcedure sproc = new MyStoredProcedure(ds);
Map results = sproc.execute();
printMap(results);
}
private class MyStoredProcedure extends StoredProcedure {
private static final String SQL = "sysdate";
public MyStoredProcedure(DataSource ds) {
setDataSource(ds);
setFunction(true);
setSql(SQL);
declareParameter(new SqlOutParameter("date", Types.DATE));
compile();
}
public Map execute() {
// the 'sysdate' sproc has no input parameters, so an empty Map is supplied...
return execute(new HashMap());
}
}
private static void printMap(Map results) {
for (Iterator it = results.entrySet().iterator(); it.hasNext(); ) {
System.out.println(it.next());
}
}
}
Find below an example of a StoredProcedure that has two output parameters (in this case Oracle REF cursors).
import oracle.jdbc.driver.OracleTypes;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;
public class TitlesAndGenresStoredProcedure extends StoredProcedure {
private static final String SPROC_NAME = "AllTitlesAndGenres";
public TitlesAndGenresStoredProcedure(DataSource dataSource) {
super(dataSource, SPROC_NAME);
declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));
declareParameter(new SqlOutParameter("genres", OracleTypes.CURSOR, new GenreMapper()));
compile();
}
public Map execute() {
// again, this sproc has no input parameters, so an empty Map is supplied...
return super.execute(new HashMap());
}
}
Notice how the overloaded variants of the declareParameter(..) method that have been used in the TitlesAndGenresStoredProcedure constructor are passed RowMapper implementation instances; this is a very convenient and powerful way to reuse existing functionality. (The code for the two RowMapper implementations is provided below in the interest of completeness.)
Firstly the TitleMapper class, which simply maps a ResultSet to a Title domain object for each row in the supplied ResultSet.
import com.foo.sprocs.domain.Title;
import org.springframework.jdbc.core.RowMapper;
import java.sql.ResultSet;
import java.sql.SQLException;
public final class TitleMapper implements RowMapper {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Title title = new Title();
title.setId(rs.getLong("id"));
title.setName(rs.getString("name"));
return title;
}
}
Secondly, the GenreMapper class, which again simply maps a ResultSet to a Genre domain object for each row in the supplied ResultSet.
import org.springframework.jdbc.core.RowMapper;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.foo.domain.Genre;
public final class GenreMapper implements RowMapper {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
return new Genre(rs.getString("name"));
}
}
If one needs to pass parameters to a stored procedure (that is the stored procedure has been declared as having one or more input parameters in its definition in the RDBMS), one would code a strongly typed execute(..) method which would delegate to the superclass' (untyped) execute(Map parameters) (which has protected access); for example:
import oracle.jdbc.driver.OracleTypes;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;
public class TitlesAfterDateStoredProcedure extends StoredProcedure {
private static final String SPROC_NAME = "TitlesAfterDate";
private static final String CUTOFF_DATE_PARAM = "cutoffDate";
public TitlesAfterDateStoredProcedure(DataSource dataSource) {
super(dataSource, SPROC_NAME);
declareParameter(new SqlParameter(CUTOFF_DATE_PARAM, Types.DATE);
declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));
compile();
}
public Map execute(Date cutoffDate) {
Map inputs = new HashMap();
inputs.put(CUTOFF_DATE_PARAM, cutoffDate);
return super.execute(inputs);
}
}
11.6.5. SqlFunction
The SqlFunction RDBMS operation class encapsulates an SQL "function" wrapper for a query that returns a single row of results. The default behavior is to return an int, but that can be overridden by using the methods with an extra return type parameter. This is similar to using the queryForXxx methods of the JdbcTemplate. The advantage with SqlFunction is that you don't have to create the JdbcTemplate, it is done behind the scenes.
This class is intended to use to call SQL functions that return a single result using a query like "select user()" or "select sysdate from dual". It is not intended for calling more complex stored functions or for using a CallableStatement to invoke a stored procedure or stored function. (Use the StoredProcedure or SqlCall classes for this type of processing).
SqlFunction is a concrete class, and there is typically no need to subclass it. Code using this package can create an object of this type, declaring SQL and parameters, and then invoke the appropriate run method repeatedly to execute the function. Here is an example of retrieving the count of rows from a table:
public int countRows() {
SqlFunction sf = new SqlFunction(dataSource, "select count(*) from mytable");
sf.compile();
return sf.run();
}
11.7. Common issues with parameter and data value handling
There are some issues involving parameters and data values that are common across all the different approaches provided by the Spring JDBC Framework.
11.7.1. Providing SQL type information for parameters
Most of the time Spring will assume the SQL type of the parameters based on the type of parameter passed in. It is possible to explicitly provide the SQL type to be used when setting parameter values. This is sometimes necessary to correctly set NULL values.
There are a few different ways this can be accomplished:
-
Many of the update and query methods of the JdbcTemplate take an additional parameter in the form of an int array. This array should contain the SQL type using constant values from the java.sql.Types class. There must be one entry for each parameter.
-
You can wrap the parameter value that needs this additional information using the SqlParameterValue class. Create a new instance for each value and pass in the SQL type and parameter value in the constructor. You can also provide an optional scale parameter for numeric values.
-
For methods working with named parameters, you can use the SqlParameterSource classes BeanPropertySqlParameterSource or MapSqlParameterSource. They both have methods for registering the SQL type for any of the named parameter values.
11.7.2. Handling BLOB and CLOB objects
You can store images and other binary objects as well and large chunks of text. These large object are called BLOB for binary data and CLOB for character data. Spring lets you handle these large objects using the JdbcTemplate directly and also when using the higher abstractions provided by RDBMS Objects and the SimpleJdbc classes. All of these approaches use an implementation of the LobHandler interface for the actual management of the LOB data. The LobHandler provides access to a LobCreator, via the getLobCreator method, for creating new LOB objects to be inserted.
The LobCreator/LobHandler provides the following support for LOB in- and output:
-
BLOB
-
byte[] – getBlobAsBytes and setBlobAsBytes
-
InputStream – getBlobAsBinaryStream and setBlobAsBinaryStream
-
-
CLOB
-
String – getClobAsString and setClobAsString
-
InputStream – getClobAsAsciiStream and setClobAsAsciiStream
-
Reader – getClobAsCharacterStream and setClobAsCharacterStream
-
We will now show an example of how to create and insert a BLOB. We will later see how to read it back from the database.
This example uses a JdbcTemplate and an implementation of the AbstractLobCreatingPreparedStatementCallback. There is one method that must be implemented and it is "setValues". In this method you will be provided with a LobCreator that can be used to set the values for the LOB columns in your SQL insert statement.
We are assuming that we have a variable named 'lobHandler' that already is set to an instance of a DefaultLobHandler. This is typically done using dependency injection.
final File blobIn = new File("spring2004.jpg");
final InputStream blobIs = new FileInputStream(blobIn);
final File clobIn = new File("large.txt");
final InputStream clobIs = new FileInputStream(clobIn);
final InputStreamReader clobReader = new InputStreamReader(clobIs);
jdbcTemplate.execute(
"INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)",
new AbstractLobCreatingPreparedStatementCallback(lobhandler) { 
protected void setValues(PreparedStatement ps, LobCreator lobCreator)
throws SQLException {
ps.setLong(1, 1L);
lobCreator.setClobAsCharacterStream(ps, 2, clobReader, (int)clobIn.length()); 
lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, (int)blobIn.length()); 
}
}
);
blobIs.close();
clobReader.close();
Here we use the lobHandler that in this example is a plain DefaultLobHandler
Using the method setClobAsCharacterStream we pass in the contents of the CLOB
Using the method setBlobAsBinartStream we pass in the contents of the BLOB
Now it's time to read the LOB data from the database. Again, we use a JdbcTempate and we have the same instance variable 'lobHandler' with a reference to a DefaultLobHandler.
List l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table",
new RowMapper() {
public Object mapRow(ResultSet rs, int i) throws SQLException {
Map results = new HashMap();
String clobText = lobHandler.getClobAsString(rs, "a_clob");
results.put("CLOB", clobText);
byte[] blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob");
results.put("BLOB", blobBytes);
return results;
}
});
Using the method getClobAsString we retrieve the contents of the CLOB
Using the method getBlobAsBytes we retrieve the contents of the BLOB
11.7.3. Passing in lists of values for IN clause
The SQL standard allows for selecting rows based on an expression that includes a variable list of values. A typical example would be "select * from T_ACTOR where id in (1, 2, 3)". This variable list is not directly supported for prepared statements by the JDBC standard - there is no way of declaring a variable number of place holders. You would have to either have a number of variations with the desired number of place holders prepared or you would have to dynamically generate the SQL string once you know how many place holders are required. The named parameter support provided in the NamedParameterJdbcTemplate and SimpleJdbcTemplate takes the latter approach. When you pass in the values you should pass them in as a java.util.List of primitive objects. This list will be used to insert the required place holders and pass in the values during the statement execution.
Note
You need to be careful when passing in a large number of values. The JDBC standard doesn't guarantee that you can use more than 100 values for an IN expression list. Various databases exceed this number, but they usually have a hard limit for how many values are allowed. Oracle's limit for instance is 1000.
In addition to the primitive values in the value list, you can create a java.util.List of object arrays. This would support a case where there are multiple expressions defined for the IN clause like "select * from T_ACTOR where (id, last_name) in ((1, 'Johnson'), (2, 'Harrop'))". This of course requires that your database supports this syntax.
11.7.4. Handling complex types for stored procedure calls
When calling stored procedures it's sometimes possible to use complex types specific to the database. To accommodate these types Spring provides a SqlReturnType for handling them when they are returned from the stored procedure call and SqlTypeValue when they are passed in as a parameter to the stored procedure.
Here is an example of returning the value of an Oracle STRUCT object of the user declared type "ITEM_TYPE". The SqlReturnType interface has a single method named "getTypeValue" that must be implemented. This interface is used as part of the declaration of an SqlOutParameter.
declareParameter(new SqlOutParameter("item", OracleTypes.STRUCT, "ITEM_TYPE",
new SqlReturnType() {
public Object getTypeValue(CallableStatement cs, int colIndx, int sqlType, String typeName)
throws SQLException {
STRUCT struct = (STRUCT)cs.getObject(colIndx);
Object[] attr = struct.getAttributes();
TestItem item = new TestItem();
item.setId(((Number) attr[0]).longValue());
item.setDescription((String)attr[1]);
item.setExpirationDate((java.util.Date)attr[2]);
return item;
}
}));
Going from Java to the database and passing in the value of a TestItem into a stored procedure is done using the SqlTypeValue. The SqlTypeValue interface has a single method named "createTypeValue" that must be implemented. The active connection is passed in and can be used to create database specific objects like StructDescriptors or ArrayDescriptors
SqlTypeValue value = new AbstractSqlTypeValue() {
protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException {
StructDescriptor itemDescriptor = new StructDescriptor(typeName, conn);
Struct item = new STRUCT(itemDescriptor, conn,
new Object[] {
testItem.getId(),
testItem.getDescription(),
new java.sql.Date(testItem.getExpirationDate().getTime())
});
return item;
}
};
This SqlTypeValue can now be added to the Map containing the input parameters for the execute call of the stored procedure.
Chapter 10. DAO support
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Chapter 12. Object Relational Mapping (ORM) data access
