445 lines
16 KiB
Markdown
445 lines
16 KiB
Markdown
# 精尽 MyBatis 源码解析 —— Spring 集成（三）之 SqlSession
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# 1. 概述
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本文我们就来看看，Spring 和 MyBatis 的 SqlSession 是如何集成。
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# 2. SqlSessionTemplate
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`org.mybatis.spring.SqlSessionTemplate` ，实现 SqlSession、DisposableBean 接口，SqlSession 操作模板实现类。实际上，代码实现和 `org.apache.ibatis.session.SqlSessionManager` 超级相似。或者说，这是 `mybatis-spring` 项目实现的 “SqlSessionManager” 类。
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## 2.1 构造方法
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```
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// SqlSessionTemplate.java
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private final SqlSessionFactory sqlSessionFactory;
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/**
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* 执行器类型
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*/
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private final ExecutorType executorType;
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/**
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* SqlSession 代理对象
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*/
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private final SqlSession sqlSessionProxy;
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/**
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* 异常转换器
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*/
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private final PersistenceExceptionTranslator exceptionTranslator;
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public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
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this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
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}
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public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
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this(sqlSessionFactory, executorType,
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new MyBatisExceptionTranslator(
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sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));
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}
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public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
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PersistenceExceptionTranslator exceptionTranslator) {
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notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
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notNull(executorType, "Property 'executorType' is required");
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this.sqlSessionFactory = sqlSessionFactory;
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this.executorType = executorType;
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this.exceptionTranslator = exceptionTranslator;
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// <1> 创建 sqlSessionProxy 对象
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this.sqlSessionProxy = (SqlSession) newProxyInstance(
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SqlSessionFactory.class.getClassLoader(),
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new Class[]{SqlSession.class},
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new SqlSessionInterceptor());
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}
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// ... 省略 setting 方法
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```
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- `executorType` 属性，执行器类型。后续，根据它来创建对应类型的执行器。
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- `sqlSessionProxy` 属性，SqlSession 代理对象。在 `<1>` 处，进行创建 `sqlSessionProxy` 对象，使用的方法拦截器是 SqlSessionInterceptor 类。😈 是不是发现和 SqlSessionManager 灰常像。
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- `exceptionTranslator` 属性，异常转换器。
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## 2.2 对 SqlSession 的实现方法
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① 如下是直接调用 `sqlSessionProxy` 对应的方法。代码如下：
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```
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// SqlSessionTemplate.java
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@Override
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public <T> T selectOne(String statement) {
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return this.sqlSessionProxy.selectOne(statement);
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}
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@Override
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public <T> T selectOne(String statement, Object parameter) {
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return this.sqlSessionProxy.selectOne(statement, parameter);
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}
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@Override
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public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
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return this.sqlSessionProxy.selectMap(statement, mapKey);
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}
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@Override
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public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
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return this.sqlSessionProxy.selectMap(statement, parameter, mapKey);
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}
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@Override
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public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) {
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return this.sqlSessionProxy.selectMap(statement, parameter, mapKey, rowBounds);
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}
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@Override
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public <T> Cursor<T> selectCursor(String statement) {
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return this.sqlSessionProxy.selectCursor(statement);
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}
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@Override
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public <T> Cursor<T> selectCursor(String statement, Object parameter) {
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return this.sqlSessionProxy.selectCursor(statement, parameter);
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}
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@Override
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public <T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds) {
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return this.sqlSessionProxy.selectCursor(statement, parameter, rowBounds);
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}
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@Override
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public <E> List<E> selectList(String statement) {
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return this.sqlSessionProxy.selectList(statement);
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}
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@Override
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public <E> List<E> selectList(String statement, Object parameter) {
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return this.sqlSessionProxy.selectList(statement, parameter);
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}
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@Override
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public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
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return this.sqlSessionProxy.selectList(statement, parameter, rowBounds);
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}
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@Override
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public void select(String statement, ResultHandler handler) {
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this.sqlSessionProxy.select(statement, handler);
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}
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@Override
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public void select(String statement, Object parameter, ResultHandler handler) {
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this.sqlSessionProxy.select(statement, parameter, handler);
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}
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@Override
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public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
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this.sqlSessionProxy.select(statement, parameter, rowBounds, handler);
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}
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@Override
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public int insert(String statement) {
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return this.sqlSessionProxy.insert(statement);
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}
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@Override
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public int insert(String statement, Object parameter) {
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return this.sqlSessionProxy.insert(statement, parameter);
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}
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@Override
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public int update(String statement) {
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return this.sqlSessionProxy.update(statement);
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}
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@Override
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public int update(String statement, Object parameter) {
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return this.sqlSessionProxy.update(statement, parameter);
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}
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@Override
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public int delete(String statement) {
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return this.sqlSessionProxy.delete(statement);
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}
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@Override
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public int delete(String statement, Object parameter) {
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return this.sqlSessionProxy.delete(statement, parameter);
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}
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@Override
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public <T> T getMapper(Class<T> type) {
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return getConfiguration().getMapper(type, this);
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}
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@Override
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public void clearCache() {
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this.sqlSessionProxy.clearCache();
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}
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@Override
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public Configuration getConfiguration() {
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return this.sqlSessionFactory.getConfiguration();
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}
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@Override
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public Connection getConnection() {
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return this.sqlSessionProxy.getConnection();
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}
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@Override
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public List<BatchResult> flushStatements() {
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return this.sqlSessionProxy.flushStatements();
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}
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```
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② 如下是不支持的方法，直接抛出 UnsupportedOperationException 异常。代码如下：
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```
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// SqlSessionTemplate.java
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@Override
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public void commit() {
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throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
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}
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@Override
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public void commit(boolean force) {
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throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
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}
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@Override
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public void rollback() {
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throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
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}
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@Override
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public void rollback(boolean force) {
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throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
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}
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@Override
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public void close() {
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throw new UnsupportedOperationException("Manual close is not allowed over a Spring managed SqlSession");
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}
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```
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- 和事务相关的方法，不允许**手动**调用。
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## 2.3 destroy
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```
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// SqlSessionTemplate.java
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@Override
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public void destroy() throws Exception {
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//This method forces spring disposer to avoid call of SqlSessionTemplate.close() which gives UnsupportedOperationException
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}
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```
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## 2.4 SqlSessionInterceptor
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SqlSessionInterceptor ，是 SqlSessionTemplate 的内部类，实现 InvocationHandler 接口，将 SqlSession 的操作，路由到 Spring 托管的事务管理器中。代码如下：
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```
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// SqlSessionTemplate.java
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/**
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* Proxy needed to route MyBatis method calls to the proper SqlSession got
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* from Spring's Transaction Manager
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* It also unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to
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* pass a {@code PersistenceException} to the {@code PersistenceExceptionTranslator}.
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*/
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private class SqlSessionInterceptor implements InvocationHandler {
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@Override
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public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
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// <1> 获得 SqlSession 对象
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SqlSession sqlSession = getSqlSession(
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SqlSessionTemplate.this.sqlSessionFactory,
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SqlSessionTemplate.this.executorType,
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SqlSessionTemplate.this.exceptionTranslator);
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try {
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// 执行 SQL 操作
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Object result = method.invoke(sqlSession, args);
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// 如果非 Spring 托管的 SqlSession 对象，则提交事务
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if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
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// force commit even on non-dirty sessions because some databases require
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// a commit/rollback before calling close()
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sqlSession.commit(true);
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}
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// 返回结果
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return result;
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} catch (Throwable t) {
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// <4.1> 如果是 PersistenceException 异常，则进行转换
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Throwable unwrapped = unwrapThrowable(t);
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if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
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// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
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// <4.2> 根据情况，关闭 SqlSession 对象
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// 如果非 Spring 托管的 SqlSession 对象，则关闭 SqlSession 对象
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// 如果是 Spring 托管的 SqlSession 对象，则减少其 SqlSessionHolder 的计数
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closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
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// <4.3> 置空，避免下面 final 又做处理
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sqlSession = null;
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// <4.4> 进行转换
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Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
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if (translated != null) {
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unwrapped = translated;
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}
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}
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// <4.5> 抛出异常
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throw unwrapped;
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} finally {
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// <5> 根据情况，关闭 SqlSession 对象
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// 如果非 Spring 托管的 SqlSession 对象，则关闭 SqlSession 对象
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// 如果是 Spring 托管的 SqlSession 对象，则减少其 SqlSessionHolder 的计数
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if (sqlSession != null) {
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closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
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}
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}
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}
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}
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```
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- 类上的英文注释，胖友可以耐心看下。
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- `<1>` 处，调用 `SqlSessionUtils#getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator)` 方法，获得 SqlSession 对象。此处，和 Spring 事务托管的事务已经相关。详细的解析，见 [《精尽 MyBatis 源码解析 —— Spring 集成（四）之事务》](http://svip.iocoder.cn/MyBatis/Spring-Integration-4) 中。下面，和事务相关的，我们也统一放在该文中。
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- `<2>` 处，调用 `Method#invoke(sqlSession, args)` 方法，**反射执行 SQL 操作**。
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- `<3>` 处，调用 `SqlSessionUtils#isSqlSessionTransactional(SqlSession session, SqlSessionFactory sessionFactory)` 方法，判断是否为**非** Spring 托管的 SqlSession 对象，则调用 `SqlSession#commit(true)` 方法，提交事务。
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- ```
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<4.1>
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```
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处，如果是 PersistenceException 异常，则：
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- `<4.2>` 处，调用 `SqlSessionUtils#closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory)` 方法，根据情况，关闭 SqlSession 对象。1）如果非 Spring 托管的 SqlSession 对象，则关闭 SqlSession 对象。2）如果是 Spring 托管的 SqlSession 对象，则减少其 SqlSessionHolder 的计数。😈 也就是说，Spring 托管事务的情况下，最终是在“外部”执行最终的事务处理。
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- `<4.3>` 处，置空 `sqlSession` 属性，避免下面 `final` 又做关闭处理。
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- `<4.4>` 处，调用 `MyBatisExceptionTranslator#translateExceptionIfPossible(RuntimeException e)` 方法，转换异常。
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- `<4.5>` 处，抛出异常。
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- `<5>` 处，如果 `sqlSession` 非空，则调用 `SqlSessionUtils#closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory)` 方法，根据情况，关闭 SqlSession 对象。
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# 3. SqlSessionDaoSupport
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`org.mybatis.spring.support.SqlSessionDaoSupport` ，继承 DaoSupport 抽象类，SqlSession 的 DaoSupport 抽象类。代码如下：
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```
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// SqlSessionDaoSupport.java
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public abstract class SqlSessionDaoSupport extends DaoSupport {
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/**
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* SqlSessionTemplate 对象
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*/
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private SqlSessionTemplate sqlSessionTemplate;
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/**
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* Set MyBatis SqlSessionFactory to be used by this DAO.
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* Will automatically create SqlSessionTemplate for the given SqlSessionFactory.
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*
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* @param sqlSessionFactory a factory of SqlSession
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*/
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public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
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if (this.sqlSessionTemplate == null || sqlSessionFactory != this.sqlSessionTemplate.getSqlSessionFactory()) {
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this.sqlSessionTemplate = createSqlSessionTemplate(sqlSessionFactory); // 使用 sqlSessionFactory 属性，创建 sqlSessionTemplate 对象
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}
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}
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/**
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* Create a SqlSessionTemplate for the given SqlSessionFactory.
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* Only invoked if populating the DAO with a SqlSessionFactory reference!
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* <p>Can be overridden in subclasses to provide a SqlSessionTemplate instance
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* with different configuration, or a custom SqlSessionTemplate subclass.
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* @param sqlSessionFactory the MyBatis SqlSessionFactory to create a SqlSessionTemplate for
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* @return the new SqlSessionTemplate instance
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* @see #setSqlSessionFactory
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*/
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@SuppressWarnings("WeakerAccess")
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protected SqlSessionTemplate createSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
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return new SqlSessionTemplate(sqlSessionFactory);
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}
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/**
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* Return the MyBatis SqlSessionFactory used by this DAO.
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*
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* @return a factory of SqlSession
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*/
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public final SqlSessionFactory getSqlSessionFactory() {
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return (this.sqlSessionTemplate != null ? this.sqlSessionTemplate.getSqlSessionFactory() : null);
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}
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/**
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* Set the SqlSessionTemplate for this DAO explicitly,
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* as an alternative to specifying a SqlSessionFactory.
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*
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* @param sqlSessionTemplate a template of SqlSession
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* @see #setSqlSessionFactory
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*/
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public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
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this.sqlSessionTemplate = sqlSessionTemplate;
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}
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/**
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* Users should use this method to get a SqlSession to call its statement methods
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* This is SqlSession is managed by spring. Users should not commit/rollback/close it
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* because it will be automatically done.
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*
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* @return Spring managed thread safe SqlSession
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*/
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public SqlSession getSqlSession() {
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return this.sqlSessionTemplate;
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}
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/**
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* Return the SqlSessionTemplate for this DAO,
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* pre-initialized with the SessionFactory or set explicitly.
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* <p><b>Note: The returned SqlSessionTemplate is a shared instance.</b>
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* You may introspect its configuration, but not modify the configuration
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* (other than from within an {@link #initDao} implementation).
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* Consider creating a custom SqlSessionTemplate instance via
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* {@code new SqlSessionTemplate(getSqlSessionFactory())}, in which case
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* you're allowed to customize the settings on the resulting instance.
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*
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* @return a template of SqlSession
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*/
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public SqlSessionTemplate getSqlSessionTemplate() {
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return this.sqlSessionTemplate;
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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protected void checkDaoConfig() {
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notNull(this.sqlSessionTemplate, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
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}
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}
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```
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- 主要用途是，`sqlSessionTemplate` 属性的初始化，或者注入。
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- 具体示例，可以看看 `org.mybatis.spring.sample.dao.UserDaoImpl` 类。
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# 4. 异常相关
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`mybatis-spring` 项目中，有两个异常相关的类：
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- `org.mybatis.spring.MyBatisExceptionTranslator` ，MyBatis 自定义的异常转换器。
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- `org.mybatis.spring.MyBatisSystemException` ，MyBatis 自定义的异常类。
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代码比较简单，胖友自己去看。
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# 666. 彩蛋
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简单水更，哈哈哈哈。
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参考和推荐如下文章：
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- 大新博客 [《Mybatis SqlSessionTemplate 源码解析》](https://www.cnblogs.com/daxin/p/3544188.html) |