自定义mybatis持久层框架
1.1 分析JDBC操作问题
public static void main(String[] args) { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { // 加载数据库驱动 Class.forName("com.mysql.jdbc.Driver"); // 通过驱动管理类获取数据库链接 connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis? characterEncoding=utf-8", "root", "root"); // 定义sql语句？表示占位符 String sql = "select * from user where username = ?"; // 获取预处理statement preparedStatement = connection.prepareStatement(sql); // 设置参数，第⼀个参数为sql语句中参数的序号(从1开始)，第⼆个参数为设置的参数值 preparedStatement.setString(1, "tom"); // 向数据库发出sql执⾏查询，查询出结果集 resultSet = preparedStatement.executeQuery(); // 遍历查询结果集 while (resultSet.next()) { int id = resultSet.getInt("id"); String username = resultSet.getString("username"); // 封装User user.setId(id); user.setUsername(username); } System.out.println(user); } } catch (Exception e) { e.printStackTrace(); } finally { // 释放资源 if (resultSet != null) { try { resultSet.close(); } catch (SQLException e) { e.printStackTrace(); if (preparedStatement != null) { try { preparedStatement.close(); } catch (SQLException e) { e.printStackTrace(); } } if (connection != null) { try { connection.close(); } catch (SQLException e) { e.printStackTrace(); } } }
JDBC问题总结：
原始jdbc开发存在的问题如下：
1、 数据库连接创建、释放频繁造成系统资源浪费，从⽽影响系统性能。
2、 Sql语句在代码中硬编码，造成代码不易维护，实际应⽤中sql变化的可能较⼤，sql变动需要改变
java代码。
3、 使⽤preparedStatement向占有位符号传参数存在硬编码，因为sql语句的where条件不⼀定，可能
多也可能少，修改sql还要修改代码，系统不易维护。
4、 对结果集解析存在硬编码(查询列名)，sql变化导致解析代码变化，系统不易维护，如果能将数据 库
记录封装成pojo对象解析⽐较⽅便
1.2 问题解决思路
①使⽤数据库连接池初始化连接资源
②将sql语句抽取到xml配置⽂件中
③使⽤反射、内省等底层技术，⾃动将实体与表进⾏属性与字段的⾃动映射
1.3 ⾃定义框架设计
使⽤端：
提供核⼼配置⽂件：
sqlMapConfig.xml : 存放数据源信息，引⼊mapper.xml
Mapper.xml : sql语句的配置⽂件信息
框架端：
1.读取配置⽂件
读取完成以后以流的形式存在，我们不能将读取到的配置信息以流的形式存放在内存中，不好操作，可
以创建javaBean来存储
（1）Configuration : 存放数据库基本信息、Map<唯⼀标识，Mapper> 唯⼀标识：namespace + "."
+ id
（2）MappedStatement：sql语句、statement类型、输⼊参数java类型、输出参数java类型
2.解析配置⽂件
创建sqlSessionFactoryBuilder类：
⽅法：sqlSessionFactory build()：
第⼀：使⽤dom4j解析配置⽂件，将解析出来的内容封装到Configuration和MappedStatement中
第⼆：创建SqlSessionFactory的实现类DefaultSqlSession
3.创建SqlSessionFactory：
⽅法：openSession() : 获取sqlSession接⼝的实现类实例对象
4.创建sqlSession接⼝及实现类：主要封装crud⽅法
⽅法：selectList(String statementId,Object param)：查询所有
selectOne(String statementId,Object param)：查询单个
具体实现：封装JDBC完成对数据库表的查询操作
涉及到的设计模式：
Builder构建者设计模式、⼯⼚模式、代理模式
1.4 ⾃定义框架实现
在使⽤端项⽬中创建配置配置⽂件
创建 sqlMapConfig.xml〈configuration〉
<!--数据库连接信息--> <property name="driverClass" value="com.mysql.jdbc.Driver"></property> <property name="jdbcUrl" value="jdbc:mysql:///zdy_mybatis"></property> <property name="user" value="root"></property> <property name="password" value="root"></property> <! --引⼊sql配置信息--> <mapper resource="mapper.xml"></mapper> </configuration> mapper.xml <mapper namespace="User"> <select id="selectOne" paramterType="com.lagou.pojo.User" resultType="com.lagou.pojo.User"> select * from user where id = #{id} and username =#{username} </select> <select id="selectList" resultType="com.lagou.pojo.User"> select * from user </select> </mapper>
User实体
public class User { //主键标识 private Integer id; //⽤户名 private String username; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } @Override public String toString() { return "User{" + "id=" + id + ", username='" + username + '\'' + '}'; } }
再创建⼀个Maven⼦⼯程并且导⼊需要⽤到的依赖坐标
<properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.encoding>UTF-8</maven.compiler.encoding> <java.version>1.8</java.version> <maven.compiler.source>1.8</maven.compiler.source> <maven.compiler.target>1.8</maven.compiler.target> </properties> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.17</version> </dependency> <dependency> <groupId>c3p0</groupId> <artifactId>c3p0</artifactId> <version>0.9.1.2</version> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.12</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.10</version> </dependency> <dependency> <groupId>dom4j</groupId> <artifactId>dom4j</artifactId> <version>1.6.1</version> </dependency> <dependency> <groupId>jaxen</groupId> <artifactId>jaxen</artifactId> <version>1.1.6</version> </dependency> </dependencies>
Configuration
public class Configuration { //数据源 private DataSource dataSource; //map集合： key:statementId value:MappedStatement private Map<String,MappedStatement> mappedStatementMap = new HashMap<String, MappedStatement>(); public DataSource getDataSource() { return dataSource; } public void setDataSource(DataSource dataSource) { this.dataSource = dataSource; } public Map<String, MappedStatement> getMappedStatementMap() { return mappedStatementMap; } public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) { this.mappedStatementMap = mappedStatementMap; } }
MappedStatement
public class MappedStatement { //id private Integer id; //sql语句 private String sql; //输⼊参数 private Class<?> paramterType; //输出参数 private Class<?> resultType; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getSql() { return sql; } public void setSql(String sql) { this.sql = sql; } public Class<?> getParamterType() { return paramterType; } public void setParamterType(Class<?> paramterType) { this.paramterType = paramterType; } public Class<?> getResultType() { return resultType; } public void setResultType(Class<?> resultType) { this.resultType = resultType; } }
Resources
public class Resources { public static InputStream getResourceAsSteam(String path){
InputStream resourceAsStream = Resources.class.getClassLoader.getResourceAsStream(path); return resourceAsStream; } }
SqlSessionFactoryBuilder
public class SqlSessionFactoryBuilder { private Configuration configuration; public SqlSessionFactoryBuilder() { this.configuration = new Configuration(); } public SqlSessionFactory build(InputStream inputStream) throws DocumentException, PropertyVetoException, ClassNotFoundException { //1.解析配置⽂件，封装Configuration XMLConfigerBuilder xmlConfigerBuilder = new XMLConfigerBuilder(configuration); Configuration configuration = xmlConfigerBuilder.parseConfiguration(inputStream); //2.创建 sqlSessionFactory SqlSessionFactory sqlSessionFactory = new DefaultSqlSessionFactory(configuration); return sqlSessionFactory; } XMLConfigerBuilder public class XMLConfigerBuilder { private Configuration configuration; public XMLConfigerBuilder(Configuration configuration) { this.configuration = new Configuration(); } public Configuration parseConfiguration(InputStream inputStream) throws DocumentException, PropertyVetoException, ClassNotFoundException { Document document = new SAXReader().read(inputStream); //<configuation> Element rootElement = document.getRootElement(); List<Element> propertyElements = rootElement.selectNodes("//property"); Properties properties = new Properties(); for (Element propertyElement : propertyElements) { String name = propertyElement.attributeValue("name"); String value = propertyElement.attributeValue("value"); properties.setProperty(name,value); } //连接池 ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource(); comboPooledDataSource.setDriverClass(properties.getProperty("driverClass")); comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl")); comboPooledDataSource.setUser(properties.getProperty("username")); comboPooledDataSource.setPassword(properties.getProperty("password")); //填充 configuration configuration.setDataSource(comboPooledDataSource); //mapper 部分 List<Element> mapperElements = rootElement.selectNodes("//mapper"); XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configuration); for (Element mapperElement : mapperElements) { String mapperPath = mapperElement.attributeValue("resource"); InputStream resourceAsSteam = Resources.getResourceAsSteam(mapperPath); xmlMapperBuilder.parse(resourceAsSteam); } return configuration; } XMLMapperBuilder public class XMLMapperBuilder { private Configuration configuration; public XMLMapperBuilder(Configuration configuration) { this.configuration = configuration; } public void parse(InputStream inputStream) throws DocumentException, ClassNotFoundException { Document document = new SAXReader().read(inputStream); Element rootElement = document.getRootElement(); String namespace = rootElement.attributeValue("namespace"); List<Element> select = rootElement.selectNodes("select"); for (Element element : select) { //id的值 String id = element.attributeValue("id"); String paramterType = element.attributeValue("paramterType"); String resultType = element.attributeValue("resultType"); //输⼊参 数class Class<?> paramterTypeClass = getClassType(paramterType); //返回结果class Class<?> resultTypeClass = getClassType(resultType); //statementId String key = namespace + "." + id; //sql语句 String textTrim = element.getTextTrim(); //封装 mappedStatement MappedStatement mappedStatement = new MappedStatement(); mappedStatement.setId(id); mappedStatement.setParamterType(paramterTypeClass); mappedStatement.setResultType(resultTypeClass); mappedStatement.setSql(textTrim); //填充 configuration configuration.getMappedStatementMap().put(key, mappedStatement); private Class<?> getClassType (String paramterType) throws ClassNotFoundException { Class<?> aClass = Class.forName(paramterType); return aClass; } } sqlSessionFactory 接⼝及D efaultSqlSessionFactory 实现类public interface SqlSessionFactory { public SqlSession openSession(); } public class DefaultSqlSessionFactory implements SqlSessionFactory { private Configuration configuration; public DefaultSqlSessionFactory(Configuration configuration) { this.configuration = configuration; } public SqlSession openSession(){ return new DefaultSqlSession(configuration); } } sqlSession 接⼝及 DefaultSqlSession 实现类 public interface SqlSession { public <E> List<E> selectList(String statementId, Object... param) Exception; public <T> T selectOne(String statementId,Object... params) throws Exception; public void close() throws SQLException; } public class DefaultSqlSession implements SqlSession { private Configuration configuration; public DefaultSqlSession(Configuration configuration) { this.configuration = configuration; //处理器对象 private Executor simpleExcutor = new SimpleExecutor(); public <E > List < E > selectList(String statementId, Object...param) throws Exception { MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId); List<E> query = simpleExcutor.query(configuration, mappedStatement, param); return query; } //selectOne 中调⽤ selectList public <T > T selectOne(String statementId, Object...params) throws Exception { List<Object> objects = selectList(statementId, params); if (objects.size() == 1) { return (T) objects.get(0); } else { throw new RuntimeException("返回结果过多"); } } public void close () throws SQLException { simpleExcutor.close(); } }
Executor
public interface Executor { <E> List<E> query(Configuration configuration, MappedStatement mappedStatement,Object[] param) throws Exception; void close() throws SQLException; }
SimpleExecutor
public class SimpleExecutor implements Executor { private Connection connection = null; public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object[] param) throws SQLException, NoSuchFieldException, IllegalAccessException, InstantiationException, IntrospectionException, InvocationTargetException { //获取连接 connection = configuration.getDataSource().getConnection(); // select * from user where id = #{id} and username = #{username} String sql = mappedStatement.getSql(); //对sql进⾏处理 BoundSql boundsql = getBoundSql(sql); // select * from where id = ? and username = ? String finalSql = boundsql.getSqlText(); //获取传⼊参数类型 Class<?> paramterType = mappedStatement.getParamterType(); //获取预编译preparedStatement对象 PreparedStatement preparedStatement = connection.prepareStatement(finalSql); List<ParameterMapping> parameterMappingList = boundsql.getParameterMappingList(); for (int i = 0; i < parameterMappingList.size(); i++) { ParameterMapping parameterMapping = parameterMappingList.get(i); String name = parameterMapping.getName(); //反射 Field declaredField = paramterType.getDeclaredField(name); declaredField.setAccessible(true); //参数的值 Object o = declaredField.get(param[0]); //给占位符赋值 preparedStatement.setObject(i + 1, o); } ResultSet resultSet = preparedStatement.executeQuery(); Class<?> resultType = mappedStatement.getResultType(); ArrayList<E> results = new ArrayList<E>(); while (resultSet.next()) { ResultSetMetaData metaData = resultSet.getMetaData(); (E) resultType.newInstance(); int columnCount = metaData.getColumnCount(); for (int i = 1; i <= columnCount; i++) { //属性名 String columnName = metaData.getColumnName(i); //属性值 Object value = resultSet.getObject(columnName); //创建属性描述器，为属性⽣成读写⽅法 PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultType); //获取写⽅法 Method writeMethod = propertyDescriptor.getWriteMethod(); //向类中写⼊值 writeMethod.invoke(o, value); } results.add(o); } return results; } @Override public void close() throws SQLException { connection.close(); } private BoundSql getBoundSql(String sql) { //标记处理类：主要是配合通⽤标记解析器GenericTokenParser类完成对配置⽂件等的解 析⼯作，其中TokenHandler主要完成处理 ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler(); //GenericTokenParser :通⽤的标记解析器，完成了代码⽚段中的占位符的解析，然后再根 据给定的标记处理器(TokenHandler)来进⾏表达式的处理 //三个参数：分别为openToken (开始标记)、closeToken (结束标记)、handler (标记 处 理器) GenericTokenParser genericTokenParser = new GenericTokenParser("# {", "}", parameterMappingTokenHandler); String parse = genericTokenParser.parse(sql); List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings(); BoundSql boundSql = new BoundSql(parse, parameterMappings); return boundSql;BoundSql
1.5 ⾃定义框架优化
通过上述我们的⾃定义框架，我们解决了JDBC操作数据库带来的⼀些问题：例如频繁创建释放数据库连
接，硬编码，⼿动封装返回结果集等问题，但是现在我们继续来分析刚刚完成的⾃定义框架代码，有没
有什么问题？
问题如下：
dao的实现类中存在重复的代码，整个操作的过程模板重复(创建sqlsession,调⽤sqlsession⽅
法，关闭 sqlsession)
dao的实现类中存在硬编码，调⽤sqlsession的⽅法时，参数statement的id硬编码
}
}
public class BoundSql {
//解析过后的sql语句
private String sqlText;
//解析出来的参数
private List<ParameterMapping> parameterMappingList = new
ArrayList<ParameterMapping>();
public BoundSql(String sqlText, List<ParameterMapping>
parameterMappingList) {
this.sqlText = sqlText;
this.parameterMappingList = parameterMappingList;
}
public String getSqlText() {
return sqlText;
}
public void setSqlText(String sqlText) {
this.sqlText = sqlText;
}
public List<ParameterMapping> getParameterMappingList() {
return parameterMappingList;
}
public void setParameterMappingList(List<ParameterMapping>
parameterMappingList) {
this.parameterMappingList = parameterMappingList;
}
}解决：使⽤代理模式来创建接⼝的代理对象
@Test
public void test2() throws Exception {
InputStream resourceAsSteam = Resources.getResourceAsSteam(path：
"sqlMapConfig.xml")
SqlSessionFactory build = new
SqlSessionFactoryBuilder().build(resourceAsSteam);
SqlSession sqlSession = build.openSession();
User user = new User();
user.setld(l);
user.setUsername("tom");
//代理对象
UserMapper userMapper = sqlSession.getMappper(UserMapper.class);
User userl = userMapper.selectOne(user);
System・out.println(userl);
}
在sqlSession中添加⽅法
public interface SqlSession {
public <T> T getMappper(Class<?> mapperClass);
实现类
@Override
public <T> T getMappper(Class<?> mapperClass) {
T o = (T) Proxy.newProxyInstance(mapperClass.getClassLoader(), new
Class[] {mapperClass}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// selectOne
String methodName = method.getName();
// className:namespace
String className = method.getDeclaringClass().getName();
//statementid
String key = className+"."+methodName;
MappedStatement mappedStatement =
configuration.getMappedStatementMap().get(key);
Type genericReturnType = method.getGenericReturnType();
ArrayList arrayList = new ArrayList<> ();
//判断是否实现泛型类型参数化
if(genericReturnType instanceof ParameterizedType){
return selectList(key,args);
return selectOne(key,args);
}
});
