mybatis工作流程&源码详解
该篇主要讲解的是mybatis从seesion创建到执行sql语句的流程
流程主线:
1.创建SqlSessionFactoryBuilder
2.创建会话工厂SqlSessionFactory
3.创建执行实例Executor(实现类有BatchExecutor,ReuseExecutor,SimpleExecutor以及CachingExecutor)
4.创建会话SqlSession
5. 创建执行器StatementHandler(实现类有SimpleStatementHandler,CallableStatementHandler,PreparedStatementHandler以及RoutingStatementHandler)
6.执行JDBC操作
SqlSessionFactoryBuilder
public class SqlSessionFactoryBuilder { //创建SqlSessionFactory public SqlSessionFactory build(Reader reader) { return build(reader, null, null); } //创建SqlSessionFactory public SqlSessionFactory build(Reader reader, String environment) { return build(reader, environment, null); } //创建SqlSessionFactory public SqlSessionFactory build(Reader reader, Properties properties) { return build(reader, null, properties); } //创建SqlSessionFactory public SqlSessionFactory build(Reader reader, String environment, Properties properties) { try { //解析配置文件 XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties); return build(parser.parse()); } catch (Exception e) { throw ExceptionFactory.wrapException("Error building SqlSession.", e); } finally { ErrorContext.instance().reset(); try { reader.close(); } catch (IOException e) { // Intentionally ignore. Prefer previous error. } } } //创建SqlSessionFactory public SqlSessionFactory build(InputStream inputStream) { return build(inputStream, null, null); } //创建SqlSessionFactory public SqlSessionFactory build(InputStream inputStream, String environment) { return build(inputStream, environment, null); } //创建SqlSessionFactory public SqlSessionFactory build(InputStream inputStream, Properties properties) { return build(inputStream, null, properties); } //创建SqlSessionFactory public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { //解析配置文件 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); return build(parser.parse()); } catch (Exception e) { throw ExceptionFactory.wrapException("Error building SqlSession.", e); } finally { ErrorContext.instance().reset(); try { inputStream.close(); } catch (IOException e) { // Intentionally ignore. Prefer previous error. } } } //创建SqlSessionFactory public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); } }
DefaultSqlSessionFactory
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { Transaction tx = null; try { final Environment environment = configuration.getEnvironment(); final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); //创建事务 tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit); //创建执行实例 final Executor executor = configuration.newExecutor(tx, execType); //创建会话session 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); //创建事务 final Transaction tx = transactionFactory.newTransaction(connection); //创建执行实例 final Executor executor = configuration.newExecutor(tx, execType); //创建会话session return new DefaultSqlSession(configuration, executor, autoCommit); } catch (Exception e) { throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
创建执行实例 final Executor executor = configuration.newExecutor(tx, execType);
public Executor newExecutor(Transaction transaction, ExecutorType executorType) { executorType = executorType == null ? defaultExecutorType : executorType; executorType = executorType == null ? ExecutorType.SIMPLE : executorType; Executor executor; //生成不同的实现类 if (ExecutorType.BATCH == executorType) { executor = new BatchExecutor(this, transaction); } else if (ExecutorType.REUSE == executorType) { executor = new ReuseExecutor(this, transaction); } else { executor = new SimpleExecutor(this, transaction); } if (cacheEnabled) { executor = new CachingExecutor(executor); } executor = (Executor) interceptorChain.pluginAll(executor); return executor; }
创建会话session new DefaultSqlSession(configuration, executor, autoCommit);
// 这里是一部分源码public class DefaultSqlSession implements SqlSession { //持有配置对象(内部就包含了sql语句的元数据) private Configuration configuration; //持有执行实例 private Executor executor; private boolean autoCommit; private boolean dirty; public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) { this.configuration = configuration; this.executor = executor; this.dirty = false; this.autoCommit = autoCommit; } public DefaultSqlSession(Configuration configuration, Executor executor) { this(configuration, executor, false); } public <T> T selectOne(String statement) { return this.<T>selectOne(statement, null); } public <T> T selectOne(String statement, Object parameter) { // Popular vote was to return null on 0 results and throw exception on too many. List<T> list = this.<T>selectList(statement, parameter); if (list.size() == 1) { return list.get(0); } else if (list.size() > 1) { throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size()); } else { return null; } } //以下源码部分省略...... }
执行实例Executor持有执行器StatementHandler
以SimpleExecutor为例
public class SimpleExecutor extends BaseExecutor { public SimpleExecutor(Configuration configuration, Transaction transaction) { super(configuration, transaction); } public int doUpdate(MappedStatement ms, Object parameter) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); //根据对应场景生成不同的执行器 StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null); stmt = prepareStatement(handler, ms.getStatementLog()); return handler.update(stmt); } finally { closeStatement(stmt); } } public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); //根据不同的场景生成不同的执行器 StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql); stmt = prepareStatement(handler, ms.getStatementLog()); return handler.<E>query(stmt, resultHandler); } finally { closeStatement(stmt); } } public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException { return Collections.emptyList(); } //执行JDBC private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Statement stmt; Connection connection = getConnection(statementLog); stmt = handler.prepare(connection); handler.parameterize(stmt); return stmt; } }
备注:
如果自定义sql拦截器
当我们需要改变sql的时候,显然我们要在预编译SQL(prepare方法前加入修改的逻辑)。
当我们需要修改参数的时候我们可以在调用parameterize方法前修改逻辑。或者使用ParameterHandler来改造设置参数。
我们需要控制组装结果集的时候,也可以在query方法前后加入逻辑,或者使用ResultHandler来改造组装结果。
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