IBatis入门
iBatis 简介：
iBatis 是apache 的一个开源项目，一个O/R Mapping 解决方案，iBatis 最大的特点就是小巧，上手很快。如果不需要太多复杂的功能，iBatis 是能够满足你的要求又足够灵活的最简单的解决方案，现在的iBatis 已经改名为Mybatis 了。
官网为：http://www.mybatis.org/
二、iBatis的工作原理与流程
iBatis使用简单的xml描述文件将JavaBean，Map实现和基本数据类型的包装类（String，Integer等）映射成JDBC的PreparedStatement的输入参数和ResultSet结果集，流程如下：
1、在sqlMapConfig的XML配置文件中进行数据库连接的配置，XML配置文件名称任意，比如SqlMapConfig.xml
2、在sqlMapConfig的XML配置文件中引用sqlMap的XML配置文件
<sqlMap resource="User.xml"/>
<sqlMap url="file://User.xml"/>
3、在sqlMap的XML配置文件中进行SQL的配置，文件名称任意
4、通过SqlMapClientBuilder生成具体的操作sqlMap配置文件中的SQL文的ibatis对象SqlMapClient
String resource="SqlMapConfig.xml"
Reader reader=Resources.getResourceAsReader(resource);
SqlMapClient sqlMap=SqlMapClientBuilder.buildSqlMapClient(reader);
5、SqlMapClient对象提供函数，函数的参数对应替换sqlMap配置文件中的id，parameter等属性，完成SQL文的执行。
public List queryForList(String statementName, Object parameterObject, int skipResults, int maxResults)
statement：SqlMap配置中id属性，parameterObject：sqlMap配置中parameter###属性
搭建iBatis 开发环境：
1 、创建工程，导入相关的jar 包，ibatis.jar 、mysql.jar
2 、编写配置文件：
总属性文件：application-global.properties
总配置文件：SqlMapConfig.xml
每个实体的映射文件（Map 文件）：User.xml
application-global.properties
driverClass=com.mysql.jdbc.Driver url=jdbc:mysql://localhost:3306/ibatis username=root password=123456
SqlMapConfig.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE sqlMapConfig PUBLIC "-//ibatis.apache.org//DTD SQL Map Config 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-config-2.dtd"> <sqlMapConfig> <!-- 引用JDBC属性的配置文件 --> <properties resource="application-global.properties" /> <!-- 默认配置 --> <settings cacheModelsEnabled="true" enhancementEnabled="true" lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32" maxSessions="10" maxTransactions="5" useStatementNamespaces="false" /> <!-- Configure a built-in transaction manager. If you're using an app server, you probably want to use its transaction manager and a managed datasource --> <transactionManager type="JDBC"> <dataSource type="SIMPLE"> <property name="JDBC.Driver" value="${driverClass}" /> <property name="JDBC.ConnectionURL" value="${url}" /> <property name="JDBC.Username" value="${username}" /> <property name="JDBC.Password" value="${password}" /> </dataSource> </transactionManager> <!-- 这里可以写多个实体的映射文件 --> <sqlMap resource="User.xml" /> </sqlMapConfig>
User.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE sqlMap PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-2.dtd"> <sqlMap namespace="user"> <typeAlias alias="User" type="org.apache.ibatis.bo.User" /> <insert id="insertUser" parameterClass="User"> insert into user values (#id#,#name#,#sex#) </insert> <delete id="deleteById" parameterClass="int"> delete from user where id=#id# </delete> <update id="updateUser" parameterClass="User"> update user set name=#name#,sex=#sex# where id=#id# </update> <select id="queryById" parameterClass="int" resultClass="User"> select * from user where id=#id# </select> <select id="queryAllUsers" resultClass="User"> select * from user </select> </sqlMap>
User.java
package org.apache.ibatis.bo; import java.io.Serializable; import java.util.List; public class User implements Serializable { /** * */ private static final long serialVersionUID = -5560728144383386239L; int id; String name; int sex; List<Role> roles; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getSex() { return sex; } public void setSex(int sex) { this.sex = sex; } public List<Role> getRoles() { return roles; } public void setRoles(List<Role> roles) { this.roles = roles; } @Override public String toString() { return "id=" + id + ",name=" + name + ",sex=" + sex; } }
IbatisUtils.java
package org.apache.ibatis.util; import java.io.IOException; import java.io.Reader; import java.sql.SQLException; import java.util.List; import org.apache.ibatis.bo.User; import com.ibatis.common.resources.Resources; import com.ibatis.sqlmap.client.SqlMapClient; import com.ibatis.sqlmap.client.SqlMapClientBuilder; /** * This is not a best practices class. It's just an example to give you an idea * of how iBATIS works. For a more complete example, see JPetStore 5.0 at * http://www.ibatis.com. */ public class IBatisUtils { /** * SqlMapClient instances are thread safe, so you only need one. In this * case, we'll use a static singleton. So sue me. ;-) */ private static SqlMapClient sqlMapper; /** * It's not a good idea to put code that can fail in a class initializer, * but for sake of argument, here's how you configure an SQL Map. */ static { try { Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml"); sqlMapper = SqlMapClientBuilder.buildSqlMapClient(reader); reader.close(); } catch (IOException e) { // Fail fast. throw new RuntimeException( "Something bad happened while building the SqlMapClient instance." + e.getMessage(), e); } } public static void createUser(String paramString) throws SQLException { sqlMapper.update(paramString, null); } public static void dropUser(String paramString) throws SQLException { sqlMapper.update(paramString, null); } public static List<?> queryAllUsers(String paramString) throws SQLException { return sqlMapper.queryForList(paramString); } public static User selectUserById(String paramString, int id) throws SQLException { return (User) sqlMapper.queryForObject(paramString, id); } public static void insertUser(String paramString, User user) throws SQLException { sqlMapper.insert(paramString, user); } public static void updateUser(String paramString, User user) throws SQLException { sqlMapper.update(paramString, user); } public static void deleteUser(String paramString, int id) throws SQLException { sqlMapper.delete(paramString, id); } }
Main.java
package org.apache.ibatis.test; import java.sql.SQLException; import java.util.Arrays; import java.util.List; import org.apache.ibatis.bo.User; import org.apache.ibatis.util.IBatisUtils; public class Main { public void insertUser() throws SQLException { User user = new User(); user.setId(0); user.setName("张三"); user.setSex(1); IBatisUtils.insertUser("insertUser", user); System.out.println("insert success!, user = " + user); } private void queryAllUsers() throws SQLException { List<?> list = IBatisUtils.queryAllUsers("queryAllUsers"); for (int i = 0; i < list.size(); i++) { User user = (User) list.get(i); System.out.println(user); } System.out.println(Arrays.toString(list.toArray())); } public static void main(String[] args) { Main main = new Main(); try { main.queryAllUsers(); } catch (SQLException e) { e.printStackTrace(); } } }
至此，测试结束
FAQ:
1、com.ibatis.sqlmap.client.SqlMapException: There is already a statement named xxx in this SqlMap.
Exception in thread "main" java.lang.ExceptionInInitializerError at org.apache.ibatis.data.Main.selectAllAccounts(Main.java:23) at org.apache.ibatis.data.Main.main(Main.java:59) Caused by: java.lang.RuntimeException: Error occurred.
Cause: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMapConfig/sqlMap'. Cause: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMap/select'.
Cause: com.ibatis.sqlmap.client.SqlMapException: There is already a statement named selectById in this SqlMap. at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:89) at com.ibatis.sqlmap.client.SqlMapClientBuilder.buildSqlMapClient(SqlMapClientBuilder.java:63) at org.apache.ibatis.data.IBatisUtils.<clinit>(IBatisUtils.java:35) ... 2 more
这个是因为存在相同的SQL ID
解决方案如下：
<!-- 启用命名空间 -->
<settings useStatementNamespaces="true" />
useStatementNamespaces
如果启用本属性，必须使用全限定名来引用 mapped useStatementNamespaces statement。
Mapped statement 的全限定名由 sql-map 的名称和 mapped-statement 的名称合成。例如： queryForObject("sqlMapName.statementName");
缺省值：false（禁用）
2、org.xml.sax.SAXParseException: The content ofelement type “sqlMapConfig” must match“(properties?,settings?,resultObjectFactory?,ypeAlias*,typeHandler*,transactionManager?,sqlMap+)+”
Exception in thread "main" java.lang.ExceptionInInitializerError at org.apache.ibatis.data.Main.selectAllAccounts(Main.java:23) at org.apache.ibatis.data.Main.main(Main.java:59) Caused by: java.lang.RuntimeException: Error occurred. Cause: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+". at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:89) at com.ibatis.sqlmap.client.SqlMapClientBuilder.buildSqlMapClient(SqlMapClientBuilder.java:63) at org.apache.ibatis.data.IBatisUtils.<clinit>(IBatisUtils.java:35) ... 2 more Caused by: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+". at com.ibatis.common.xml.NodeletParser.parse(NodeletParser.java:53) at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:86) ... 4 more Caused by: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+". at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:195) at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:131) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:384) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:318) at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleEndElement(XMLDTDValidator.java:2017) at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.endElement(XMLDTDValidator.java:901) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2939) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:647) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119) at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:232) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:284) at com.ibatis.common.xml.NodeletParser.createDocument(NodeletParser.java:157) at com.ibatis.common.xml.NodeletParser.parse(NodeletParser.java:50) ... 5 more
这个是因为ibatis配置文件sqlMapConfig的属性是有顺序的，配置顺序properties,settings,resultObjectFactory,typeAlias*,typeHandler*,transactionManager,sqlMap 。
附录：
1、SqlMapConfig.xml中的setting属性
<settings
cacheModelsEnabled="true"
lazyLoadingEnabled="false"
enhancementEnabled="true"
maxSessions="64"
maxTransactions="8"
maxRequests="128"
useStatementNamespaces="false"
classInfoCacheEnabled="true"
errorTracingEnabled="true"
defaultStatementTimeout=""
statementCachingEnabled="true"
/>
<!--
maxRequests
同时执行 SQL 语句的最大线程数。大于这个值的线程将阻塞直到另一个线程执行完成。不同的 DBMS有不同的限制值，但任何数据库都有这些限制。通常这个值应该至少是maxTransactions（参见以下）的 10 倍，并且总是大于 maxSessions 和maxTranactions。减小这个参数值通常能提高性能。
例如：maxRequests=“256”
缺省值：512
maxSessions
同一时间内活动的最大 session 数。一个 session 可以maxSessions是代码请求的显式 session，也可以是当线程使用SqlMapClient 实例（即执行一条语句）自动获得的session。它应该总是大于或等于 maxTransactions 并小于 maxRequests。减小这个参数值通常能减少内存使用。
例如：maxSessions=“64”
缺省值：128
maxTransactions
同时进入 SqlMapClient.startTransaction()的最大线程maxTransactions 数。大于这个值的线程将阻塞直到另一个线程退出。不同的 DBMS 有不同的限制值，但任何数据库都有这些限制。这个参数值应该总是小于或等于maxSessions 并总是远远小于 maxRequests。减小这个参数值通常能提高性能。
例如：maxTransactions=“16”
缺省值：32
cacheModelsEnabled
全局性地启用或禁用 SqlMapClient 的所有缓存cacheModelsEnabled model。调试程序时使用。
例如：cacheModelsEnabled=“true”
缺省值：true（启用）
lazyLoadingEnabled
全局性地启用或禁用SqlMapClient的所有延迟加载。lazyLoadingEnabled 调试程序时使用。
例子：lazyLoadingEnabled=“true”
缺省值：true（启用）
enhancementEnabled
全局性地启用或禁用运行时字节码增强，以优化访enhancementEnabled
问Java Bean属性的性能，同时优化延迟加载的性能。
例子：enhancementEnabled=“true”
缺省值：false（禁用）
useStatementNamespaces
如果启用本属性，必须使用全限定名来引用 mapped useStatementNamespaces
statement。Mapped statement 的全限定名由 sql-map 的名称和 mapped-statement 的名称合成。例如： queryForObject("sqlMapName.statementName");
例如：useStatementNamespaces=“false”
缺省值：false（禁用）
defaultStatementTimeout
此设置值必须为一个整数，作为JDBC连接超时的时间，这个值可以被任意一个映射文件的statement属性来重新设置，
如果没有指明，查询将无超时时间限制除非在映射文件中设置statement属性值。被设置的值以秒为单位等待连接失效
classInfoCacheEnabled
With this setting enabled, iBATIS will maintain a cache of introspected
classes. This will lead to a significant reduction in startup time if many
classes are reused.
例如: classInfoCacheEnabled=“true”
缺省值: true (启用)
statementCachingEnabled (iBATIS 2.3.0以后版本中有)
With this setting enabled, iBATIS will maintain a local cache of
prepared statements. This can lead to significant performance
improvements.
例如: statementCachingEnabled=“true”
缺省值: true (启用)
