MyBatis源码分析：SqlSessionFactory
MyBatis源码分析：SqlSessionFactory
- 1.SqlSessionFactory
- 1.1 DefaultSqlSessionFactory
- 1.2 SqlSessionManager
1.SqlSessionFactory
功能：生产SqlSession对象的工厂，是一个接口；
源码：
/**
* Copyright 2009-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.ibatis.session;
import java.sql.Connection;
/**
* Creates an {@link SqlSession} out of a connection or a DataSource
*
* @author Clinton Begin
*/
public interface SqlSessionFactory {
SqlSession openSession();
SqlSession openSession(boolean autoCommit);
SqlSession openSession(Connection connection);
SqlSession openSession(TransactionIsolationLevel level);
SqlSession openSession(ExecutorType execType);
SqlSession openSession(ExecutorType execType, boolean autoCommit);
SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);
SqlSession openSession(ExecutorType execType, Connection connection);
Configuration getConfiguration();
}
接口中定义了许多获取SqlSession的方法，我们暂时略过此部分，先看一下接口的具体实现；
MyBatis中包含了SqlSessionFactory接口的两个实现类：分别为DefaultSqlSessionFactory和SqlSessionManager。
1.1 DefaultSqlSessionFactory
源码：
* Copyright 2009-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.ibatis.session.defaults;
import java.sql.Connection;
import java.sql.SQLException;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.managed.ManagedTransactionFactory;
/**
* @author Clinton Begin
*/
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private final Configuration configuration;
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
@Override
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
@Override
public SqlSession openSession(boolean autoCommit) {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
}
@Override
public SqlSession openSession(ExecutorType execType) {
return openSessionFromDataSource(execType, null, false);
}
@Override
public SqlSession openSession(TransactionIsolationLevel level) {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), level, false);
}
@Override
public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
return openSessionFromDataSource(execType, level, false);
}
@Override
public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
return openSessionFromDataSource(execType, null, autoCommit);
}
@Override
public SqlSession openSession(Connection connection) {
return openSessionFromConnection(configuration.getDefaultExecutorType(), connection);
}
@Override
public SqlSession openSession(ExecutorType execType, Connection connection) {
return openSessionFromConnection(execType, connection);
}
@Override
public Configuration getConfiguration() {
return configuration;
}
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
final Executor executor = configuration.newExecutor(tx, execType);
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
try {
boolean autoCommit;
try {
autoCommit = connection.getAutoCommit();
} catch (SQLException e) {
// Failover to true, as most poor drivers
// or databases won't support transactions
autoCommit = true;
}
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
final Transaction tx = transactionFactory.newTransaction(connection);
final Executor executor = configuration.newExecutor(tx, execType);
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
if (environment == null || environment.getTransactionFactory() == null) {
return new ManagedTransactionFactory();
}
return environment.getTransactionFactory();
}
private void closeTransaction(Transaction tx) {
if (tx != null) {
try {
tx.close();
} catch (SQLException ignore) {
// Intentionally ignore. Prefer previous error.
}
}
}
}
从源码中可以看出，DefaultSqlSessionFactory 只包含一个属性和一个构造方法，属性为Configuration；构造方法为：
public DefaultSqlSessionFactory(Configuration configuration);
SqlSessionFactoryBuilder中便是使用此构造方法来构造SqlSessionFactory。
从源码中可以看出，DefaultSqlSessionFactory最终会调用SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit)方法或SqlSession openSessionFromConnection(ExecutorType execType, Connection connection)方法来返回一个SqlSession对象。
openSessionFromDataSource方法的执行步骤如下：
1.首先使用configuration中的environment对象构造一个事物工厂（TransactionFactory）；
2.用这个工厂得到一个Transaction对象（使用dataSource，TransactionFactory和TransactionLevel作为参数）；
3.用Transaction对象和execType对象一起构造了一个Executor对象；
4.用Executor对象，autoCommit和Configuration一起构造了一个DefaultSqlSessionFactory;
流程图如下：
openSessionFromConnection方法的流程和openSessionFromDataSource类似，具体流程如下：
- 从
connection中获取autoCommit: - 使用
configuration中的environment对象构造一个事物工厂（TransactionFactory）； - 用这个工厂得到一个
Transaction对象，和openSessionFromDataSource方法不同的是，这个环节中仅使用connection作为参数； - 用
Transaction对象和execType对象一起构造了一个Executor对象； - 用
Executor对象，autoCommit和Configuration一起构造了一个DefaultSqlSessionFactory;
流程图如下：
在openSessionFromDataSource和openSessionFromConnection方法中，涉及到了如下几个对象：
- org.apache.ibatis.session.ExecutorType
- org.apache.ibatis.session.TransactionIsolationLevel
- org.apache.ibatis.transaction.Transaction
- org.apache.ibatis.mapping.Environment
- org.apache.ibatis.transaction.TransactionFactory
- org.apache.ibatis.executor.Executor
1.2 SqlSessionManager
源码：
/**
* Copyright 2009-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.ibatis.session;
import java.io.InputStream;
import java.io.Reader;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import org.apache.ibatis.cursor.Cursor;
import org.apache.ibatis.executor.BatchResult;
import org.apache.ibatis.reflection.ExceptionUtil;
/**
* @author Larry Meadors
*/
public class SqlSessionManager implements SqlSessionFactory, SqlSession {
private final SqlSessionFactory sqlSessionFactory;
private final SqlSession sqlSessionProxy;
private final ThreadLocal<SqlSession> localSqlSession = new ThreadLocal<>();
private SqlSessionManager(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
this.sqlSessionProxy = (SqlSession) Proxy.newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[]{SqlSession.class},
new SqlSessionInterceptor());
}
public static SqlSessionManager newInstance(Reader reader) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, null));
}
public static SqlSessionManager newInstance(Reader reader, String environment) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, environment, null));
}
public static SqlSessionManager newInstance(Reader reader, Properties properties) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, properties));
}
public static SqlSessionManager newInstance(InputStream inputStream) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, null));
}
public static SqlSessionManager newInstance(InputStream inputStream, String environment) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, environment, null));
}
public static SqlSessionManager newInstance(InputStream inputStream, Properties properties) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, properties));
}
public static SqlSessionManager newInstance(SqlSessionFactory sqlSessionFactory) {
return new SqlSessionManager(sqlSessionFactory);
}
public void startManagedSession() {
this.localSqlSession.set(openSession());
}
public void startManagedSession(boolean autoCommit) {
this.localSqlSession.set(openSession(autoCommit));
}
public void startManagedSession(Connection connection) {
this.localSqlSession.set(openSession(connection));
}
public void startManagedSession(TransactionIsolationLevel level) {
this.localSqlSession.set(openSession(level));
}
public void startManagedSession(ExecutorType execType) {
this.localSqlSession.set(openSession(execType));
}
public void startManagedSession(ExecutorType execType, boolean autoCommit) {
this.localSqlSession.set(openSession(execType, autoCommit));
}
public void startManagedSession(ExecutorType execType, TransactionIsolationLevel level) {
this.localSqlSession.set(openSession(execType, level));
}
public void startManagedSession(ExecutorType execType, Connection connection) {
this.localSqlSession.set(openSession(execType, connection));
}
public boolean isManagedSessionStarted() {
return this.localSqlSession.get() != null;
}
@Override
public SqlSession openSession() {
return sqlSessionFactory.openSession();
}
@Override
public SqlSession openSession(boolean autoCommit) {
return sqlSessionFactory.openSession(autoCommit);
}
@Override
public SqlSession openSession(Connection connection) {
return sqlSessionFactory.openSession(connection);
}
@Override
public SqlSession openSession(TransactionIsolationLevel level) {
return sqlSessionFactory.openSession(level);
}
@Override
public SqlSession openSession(ExecutorType execType) {
return sqlSessionFactory.openSession(execType);
}
@Override
public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
return sqlSessionFactory.openSession(execType, autoCommit);
}
@Override
public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
return sqlSessionFactory.openSession(execType, level);
}
@Override
public SqlSession openSession(ExecutorType execType, Connection connection) {
return sqlSessionFactory.openSession(execType, connection);
}
@Override
public Configuration getConfiguration() {
return sqlSessionFactory.getConfiguration();
}
@Override
public <T> T selectOne(String statement) {
return sqlSessionProxy.selectOne(statement);
}
@Override
public <T> T selectOne(String statement, Object parameter) {
return sqlSessionProxy.selectOne(statement, parameter);
}
@Override
public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
return sqlSessionProxy.selectMap(statement, mapKey);
}
@Override
public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
return sqlSessionProxy.selectMap(statement, parameter, mapKey);
}
@Override
public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) {
return sqlSessionProxy.selectMap(statement, parameter, mapKey, rowBounds);
}
@Override
public <T> Cursor<T> selectCursor(String statement) {
return sqlSessionProxy.selectCursor(statement);
}
@Override
public <T> Cursor<T> selectCursor(String statement, Object parameter) {
return sqlSessionProxy.selectCursor(statement, parameter);
}
@Override
public <T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds) {
return sqlSessionProxy.selectCursor(statement, parameter, rowBounds);
}
@Override
public <E> List<E> selectList(String statement) {
return sqlSessionProxy.selectList(statement);
}
@Override
public <E> List<E> selectList(String statement, Object parameter) {
return sqlSessionProxy.selectList(statement, parameter);
}
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
return sqlSessionProxy.selectList(statement, parameter, rowBounds);
}
@Override
public void select(String statement, ResultHandler handler) {
sqlSessionProxy.select(statement, handler);
}
@Override
public void select(String statement, Object parameter, ResultHandler handler) {
sqlSessionProxy.select(statement, parameter, handler);
}
@Override
public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
sqlSessionProxy.select(statement, parameter, rowBounds, handler);
}
@Override
public int insert(String statement) {
return sqlSessionProxy.insert(statement);
}
@Override
public int insert(String statement, Object parameter) {
return sqlSessionProxy.insert(statement, parameter);
}
@Override
public int update(String statement) {
return sqlSessionProxy.update(statement);
}
@Override
public int update(String statement, Object parameter) {
return sqlSessionProxy.update(statement, parameter);
}
@Override
public int delete(String statement) {
return sqlSessionProxy.delete(statement);
}
@Override
public int delete(String statement, Object parameter) {
return sqlSessionProxy.delete(statement, parameter);
}
@Override
public <T> T getMapper(Class<T> type) {
return getConfiguration().getMapper(type, this);
}
@Override
public Connection getConnection() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot get connection. No managed session is started.");
}
return sqlSession.getConnection();
}
@Override
public void clearCache() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot clear the cache. No managed session is started.");
}
sqlSession.clearCache();
}
@Override
public void commit() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot commit. No managed session is started.");
}
sqlSession.commit();
}
@Override
public void commit(boolean force) {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot commit. No managed session is started.");
}
sqlSession.commit(force);
}
@Override
public void rollback() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
}
sqlSession.rollback();
}
@Override
public void rollback(boolean force) {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
}
sqlSession.rollback(force);
}
@Override
public List<BatchResult> flushStatements() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
}
return sqlSession.flushStatements();
}
@Override
public void close() {
final SqlSession sqlSession = localSqlSession.get();
if (sqlSession == null) {
throw new SqlSessionException("Error: Cannot close. No managed session is started.");
}
try {
sqlSession.close();
} finally {
localSqlSession.set(null);
}
}
private class SqlSessionInterceptor implements InvocationHandler {
public SqlSessionInterceptor() {
// Prevent Synthetic Access
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
final SqlSession sqlSession = SqlSessionManager.this.localSqlSession.get();
if (sqlSession != null) {
try {
return method.invoke(sqlSession, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
} else {
try (SqlSession autoSqlSession = openSession()) {
try {
final Object result = method.invoke(autoSqlSession, args);
autoSqlSession.commit();
return result;
} catch (Throwable t) {
autoSqlSession.rollback();
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
}
}
}
SqlSessionManager实现了SqlSession和SqlSessionFactory接口中的方法，包含一个构造方法：
private SqlSessionManager(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
this.sqlSessionProxy = (SqlSession) Proxy.newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[]{SqlSession.class},
new SqlSessionInterceptor());
}
三个成员变量：
private final SqlSessionFactory sqlSessionFactory;
private final SqlSession sqlSessionProxy;
private final ThreadLocal<SqlSession> localSqlSession = new ThreadLocal<>();
以及一个内部类：
private class SqlSessionInterceptor implements InvocationHandler {
public SqlSessionInterceptor() {
// Prevent Synthetic Access
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
final SqlSession sqlSession = SqlSessionManager.this.localSqlSession.get();
if (sqlSession != null) {
try {
return method.invoke(sqlSession, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
} else {
try (SqlSession autoSqlSession = openSession()) {
try {
final Object result = method.invoke(autoSqlSession, args);
autoSqlSession.commit();
return result;
} catch (Throwable t) {
autoSqlSession.rollback();
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
}
}
构造方法以SqlSessionFactory作为参数，并使用动态代理模式生成了一个SqlSession对象的代理。这里涉及到了JDK的动态代理相关知识。
在构造方法中，构造SqlSession代理的代码如下：
this.sqlSessionProxy = (SqlSession) Proxy.newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[]{SqlSession.class},
new SqlSessionInterceptor());
其中，
SqlSessionFactory.class.getClassLoader()返回SqlSessionFactory的类加载器的实例；new Class[]{SqlSession.class}语句声明sqlSessionProxy对象实现了SqlSession接口；new SqlSessionInterceptor()为该代理对象的实际执行对象；
从内部类SqlSessionInterceptor的代码中可以看出，当代理对象执行方法时：
- 首先，会尝试从
localSqlSession中获取sqlSession对象，若成功获取，则执行invoke方法； - 否则，调用
openSession方法获取sqlSession对象；
通过观察openSession方法的代码：
@Override
public SqlSession openSession() {
return sqlSessionFactory.openSession();
}
可以发现，该方法返回的是属性sqlSessionFactory生成的sqlSession。
而localSqlSession是通过方法：
public void startManagedSession() {
this.localSqlSession.set(openSession());
}
来进行赋值。
由此可以得到结论：
- sqlSessionProxy代理对象实际上代理的是
sqlSessionFactory成员生成的sqlSession对象；
网络上一些关于SqlSessionManager的博客