1 SQL语句的执行过程介绍
MyBatis核心执行组件：
2 SQL执行的入口分析
2.1 为Mapper接口创建代理对象
// 方式1： User user = session.selectOne("com.oldlu.dao.UserMapper.findUserById", 101); // 方式2： UserMapper mapper = session.getMapper(UserMapper.class); List<User> userList = mapper.findAll();
2.2 执行代理逻辑
方式1入口分析：
session是DefaultSqlSession类型的，因为sqlSessionFactory默认生成的SqlSession是
DefaultSqlSession类型。
selectOne()会调用selectList()。
// DefaultSqlSession类 public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); // CURD操作是交给Excetor去处理的 return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
方式2入口分析：
获取代理对象：
//DefaultSqlSession类 ====================> @Override public <T> T getMapper(Class<T> type) { return configuration.getMapper(type, this); } // Configuration类 ====================> public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return mapperRegistry.getMapper(type, sqlSession); } //MapperRegistry ----> apperProxyFactory.newInstance ====================> public <T> T getMapper(Class<T> type, SqlSession sqlSession) { //从缓存中获取该Mapper接口的代理工厂对象 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); //如果该Mapper接口没有注册过，则抛异常 if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { //【使用代理工厂创建Mapper接口的代理对象】 return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } } //MapperProxyFactory --->此时生成代理对象 ====================> protected T newInstance(MapperProxy<T> mapperProxy) { //Mybatis底层是调用JDK的Proxy类来创建代理实例 return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
代理对象执行逻辑：
//MapperProxy ====================> /**代理对象执行的方法，代理以后，所有Mapper的方法调用时，都会调用这个invoke方法*/ public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { if (Object.class.equals(method.getDeclaringClass())) { //如果是Object方法，则调用方法本身 return method.invoke(this, args); } else { //调用接口方法：根据被调用接口的Method对象，从缓存中获取MapperMethodInvoker对象 //apper接口中的每一个方法都对应一个MapperMethodInvoker对象，而MapperMethodInvoker 对象里面的MapperMethod保存着对应的SQL信息和返回类型以完成SQL调用 ... return cachedInvoker(method).invoke(proxy, method, args, sqlSession); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } /** 获取缓存中MapperMethodInvoker，如果没有则创建一个，而MapperMethodInvoker内部封装这一 个MethodHandler */ private MapperMethodInvoker cachedInvoker(Method method) throws Throwable { try { return methodCache.computeIfAbsent(method, m -> { if (m.isDefault()) { //如果调用接口的是默认方法（default方法） try { if (privateLookupInMethod == null) { return new DefaultMethodInvoker(getMethodHandleJava8(method)); } else { return new DefaultMethodInvoker(getMethodHandleJava9(method)); } } catch (IllegalAccessException | InstantiationException | InvocationTargetException | NoSuchMethodException e) { throw new RuntimeException(e); } } else { //如果调用的普通方法（非default方法），则创建一个PlainMethodInvoker并放 入缓存，其中MapperMethod保存对应接口方法的SQL以及入参和出参的数据类型等信息 return new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration())); } }); } catch (RuntimeException re) { Throwable cause = re.getCause(); throw cause == null ? re : cause; } } // MapperProxy内部类： PainMethodInvoker ====================> // 当cacheInvoker返回了PalinMethodInvoker实例之后，紧接着调用了这个实例的 PlainMethodInvoker:invoke方法 @Override public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable { //Mybatis实现接口方法的核心: MapperMethod::execute方法： return mapperMethod.execute(sqlSession, args); } // MapperMethod ====================> public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { case INSERT: { // 将args进行解析，如果是多个参数则，则根据@Param注解指定名称将参数转换为Map， 如果是封装实体则不转换 Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.insert(command.getName(), param)); break; } case UPDATE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); break; } case DELETE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); break; } case SELECT: //查询操作 if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else { //解析参数，因为SqlSession::selectOne方法参数只能传入一个，但是我们 Mapper中可能传入多个参数， //有可能是通过@Param注解指定参数名，所以这里需要将Mapper接口方法中的多个参 数转化为一个ParamMap, //也就是说如果是传入的单个封装实体，那么直接返回出来；如果传入的是多个参数， 实际上都转换成了Map Object param = method.convertArgsToSqlCommandParam(args); //可以看到动态代理最后还是使用SqlSession操作数据库的 result = sqlSession.selectOne(command.getName(), param); if (method.returnsOptional() && (result == null || !method.getReturnType().equals(result.getClass()))) { result = Optional.ofNullable(result); } } break; case FLUSH: result = sqlSession.flushStatements(); break; default: throw new BindingException("Unknown execution method for: " + command.getName()); } if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; } // 此时我们发现： 回到了sqlsession中 private <E> Object executeForMany(SqlSession sqlSession, Object[] args) { List<E> result; Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.selectList(command.getName(), param, rowBounds); } else { result = sqlSession.selectList(command.getName(), param); } // ... return result; }
3 查询语句的执行过程分析
3.1 selectOne方法分析
// DefaultSqlSession类 ===============> // selectOne @Override public <T> T selectOne(String statement, Object parameter) { // //selectOne()会调用selectList()。 List<T> list = this.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; } } // selectList public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); // CURD操作是交给Excetor去处理的 return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
3.2 sql获取
// CachingExecutor ===============> public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { // 获取绑定的sql命令，比如"SELECT * FROM xxx" BoundSql boundSql = ms.getBoundSql(parameterObject); CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql); return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } @Override public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { Cache cache = ms.getCache(); if (cache != null) { flushCacheIfRequired(ms); if (ms.isUseCache() && resultHandler == null) { ensureNoOutParams(ms, boundSql); @SuppressWarnings("unchecked") List<E> list = (List<E>) tcm.getObject(cache, key); if (list == null) { list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); tcm.putObject(cache, key, list); // issue #578 and #116 } return list; } } return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } //真正执行query操作的是SimplyExecutor代理来完成的，SimplyExecutor的父类BaseExecutor的 query方法中: // BaseExecutor类:SimplyExecutor的父类 =================> @Override public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId()); if (closed) { throw new ExecutorException("Executor was closed."); } if (queryStack == 0 && ms.isFlushCacheRequired()) { clearLocalCache(); } List<E> list; try { queryStack++; //localCache是一级缓存，如果找不到就调用queryFromDatabase从数据库中查找 list = resultHandler == null ? (List<E>) localCache.getObject(key) : null; if (list != null) { handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); } else { list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); } } finally { queryStack--; } if (queryStack == 0) { for (DeferredLoad deferredLoad : deferredLoads) { deferredLoad.load(); } deferredLoads.clear(); if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { clearLocalCache(); } } return list; } //第一次，没有缓存，所以会调用queryFromDatabase方法来执行查询。 private <E> List<E> queryFromDatabase(...) throws SQLException { List<E> list; localCache.putObject(key, EXECUTION_PLACEHOLDER); try { // 查询 list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql); } finally { localCache.removeObject(key); } localCache.putObject(key, list); if (ms.getStatementType() == StatementType.CALLABLE) { localOutputParameterCache.putObject(key, parameter); } return list; } // SimpleExecutor类 ============================> public <E> List<E> doQuery(...) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); StatementHandler handler = configuration.newStatementHandler(....); // 1：SQL查询参数的设置 stmt = prepareStatement(handler, ms.getStatementLog()); // StatementHandler封装了Statement // 2：SQL查询操作和结果集的封装 return handler.<E>query(stmt); } finally { closeStatement(stmt); } }
3.3 参数设置
// SimplyExecutor类 ============================> // 【1】 参数设置： prepareStatement private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Statement stmt; // 通过getConnection方法来获取一个Connection， Connection connection = getConnection(statementLog); // 调用prepare方法来获取一个Statement stmt = handler.prepare(connection, transaction.getTimeout()); // 设置SQL查询中的参数值 *** handler.parameterize(stmt); return stmt; } // RoutingStatementHandler ============================> // PreparedStatementHandler ============================> @Override public void parameterize(Statement statement) throws SQLException { parameterHandler.setParameters((PreparedStatement) statement); } // DefaultParameterHandler ============================> 此时参数设置成功 @Override public void setParameters(PreparedStatement ps) { ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId()); List<ParameterMapping> parameterMappings = boundSql.getParameterMappings(); if (parameterMappings != null) { for (int i = 0; i < parameterMappings.size(); i++) { ParameterMapping parameterMapping = parameterMappings.get(i); if (parameterMapping.getMode() != ParameterMode.OUT) { Object value; String propertyName = parameterMapping.getProperty(); if (boundSql.hasAdditionalParameter(propertyName)) { value = boundSql.getAdditionalParameter(propertyName); } else if (parameterObject == null) { value = null; } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) { value = parameterObject; } else { MetaObject metaObject = configuration.newMetaObject(parameterObject); value = metaObject.getValue(propertyName); } TypeHandler typeHandler = parameterMapping.getTypeHandler(); JdbcType jdbcType = parameterMapping.getJdbcType(); if (value == null && jdbcType == null) { jdbcType = configuration.getJdbcTypeForNull(); } try { typeHandler.setParameter(ps, i + 1, value, jdbcType); } catch (TypeException | SQLException e) { throw new TypeException("Could not set parameters for mapping....."); } } } } }
3.4 SQL执行和结果集的封装
// RoutingStatementHandler ============================> @Override public <E> List<E> query(Statement statement) throws SQLException { return delegate.<E>query(statement); } // PreparedStatementHandler ============================> @Override public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { // 这里就到了熟悉的PreparedStatement了 PreparedStatement ps = (PreparedStatement) statement; // 执行SQL查询操作 ps.execute(); // 结果交给ResultHandler来处理 return resultSetHandler.<E> handleResultSets(ps); } // DefaultResultSetHandler类（封装返回值，将查询结果封装成Object对象） @Override public List<Object> handleResultSets(Statement stmt) throws SQLException { ErrorContext.instance().activity("handling results").object(mappedStatement.getId()); final List<Object> multipleResults = new ArrayList<Object>(); int resultSetCount = 0; ResultSetWrapper rsw = getFirstResultSet(stmt); List<ResultMap> resultMaps = mappedStatement.getResultMaps(); int resultMapCount = resultMaps.size(); validateResultMapsCount(rsw, resultMapCount); while (rsw != null && resultMapCount > resultSetCount) { ResultMap resultMap = resultMaps.get(resultSetCount); handleResultSet(rsw, resultMap, multipleResults, null); rsw = getNextResultSet(stmt); cleanUpAfterHandlingResultSet(); resultSetCount++; } String[] resultSets = mappedStatement.getResultSets(); if (resultSets != null) { while (rsw != null && resultSetCount < resultSets.length) { ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]); if (parentMapping != null) { String nestedResultMapId = parentMapping.getNestedResultMapId(); ResultMap resultMap = configuration.getResultMap(nestedResultMapId); handleResultSet(rsw, resultMap, null, parentMapping); } rsw = getNextResultSet(stmt); cleanUpAfterHandlingResultSet(); resultSetCount++; } } return collapseSingleResultList(multipleResults); }
4 更新语句的执行过程分析
- Executor 的 update 方法分析
insert、update 和 delete 操作都会清空一二级缓存 - doUpdate 方法
- PreparedStatementHandler 的 update 方法
默认是创建PreparedStatementHandler，然后执行prepareStatement方法。
执行结果为受影响行数
执行更新语句的SQL
4.1 sqlsession增删改方法分析
// DefaultSqlSession ===============> @Override public int insert(...) { return update(statement, parameter); } @Override public int update(String statement) { return update(statement, null); } @Override public int delete(...) { return update(....); } // insert 、delete操作是通过调用update语句进行的相关逻辑 @Override public int update(String statement, Object parameter) { try { dirty = true; MappedStatement ms = configuration.getMappedStatement(statement); // 增删改 最终底层都是 update return executor.update(ms, wrapCollection(parameter)); } catch (Exception e) { throw ExceptionFactory.wrapException("Error updating database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
4.2 sql获取
// CachingExecutor ===============> @Override public int update(MappedStatement ms, Object parameterObject) throws SQLException { // 执行增删改，清除缓存 flushCacheIfRequired(ms); // 跳转BaseExecutor return delegate.update(ms, parameterObject); } // BaseExecutor ===============> @Override public int update(MappedStatement ms, Object parameter) throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId()); if (closed) { throw new ExecutorException("Executor was closed."); } // 清除 LocalCache 一级缓存 clearLocalCache(); //执行 doUpdate return doUpdate(ms, parameter); } // SimpleExecutor ===============> // doUpdate @Override public int doUpdate(MappedStatement ms, Object parameter) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); StatementHandler handler = configuration.newStatementHandler(...); // 【1】.获取statement,并进行参数映射 stmt = prepareStatement(handler, ms.getStatementLog()); // 【2】.handler.update()方法执行具体sql指令 return handler.update(stmt); } finally { closeStatement(stmt); } }
4.3 参数设置
// SimplyExecutor类 ============================> //【1】 prepareStatement private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Statement stmt; Connection connection = getConnection(statementLog); // 使用connection对象信息创建statement，并将超时时间绑定 stmt = handler.prepare(connection, transaction.getTimeout()); // parameterize方法设置sql执行时候需要的参数 handler.parameterize(stmt); return stmt; } // RoutingStatementHandler ============================> // PreparedStatementHandler ============================> @Override public void parameterize(Statement statement) throws SQLException { parameterHandler.setParameters((PreparedStatement) statement); } // DefaultParameterHandler ============================> 此时参数设置成功 @Override public void setParameters(PreparedStatement ps) { ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId()); List<ParameterMapping> parameterMappings = boundSql.getParameterMappings(); if (parameterMappings != null) { for (int i = 0; i < parameterMappings.size(); i++) { ParameterMapping parameterMapping = parameterMappings.get(i); if (parameterMapping.getMode() != ParameterMode.OUT) { Object value; String propertyName = parameterMapping.getProperty(); if (boundSql.hasAdditionalParameter(propertyName)) { value = boundSql.getAdditionalParameter(propertyName); } else if (parameterObject == null) { value = null; } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) { value = parameterObject; } else { MetaObject metaObject = configuration.newMetaObject(parameterObject); value = metaObject.getValue(propertyName); } TypeHandler typeHandler = parameterMapping.getTypeHandler(); JdbcType jdbcType = parameterMapping.getJdbcType(); if (value == null && jdbcType == null) { jdbcType = configuration.getJdbcTypeForNull(); } try { typeHandler.setParameter(ps, i + 1, value, jdbcType); } catch (TypeException | SQLException e) { throw new TypeException("Could not set parameters for mapping....."); } } } } }
4.4 SQL执行
// RoutingStatementHandler ============================> @Override public int update(Statement statement) throws SQLException { return delegate.update(statement); } // PreparedStatementHandler ============================> @Override public int update(Statement statement) throws SQLException { // 这里就是底层JDBC的PreparedStatement 操作了 PreparedStatement ps = (PreparedStatement) statement; // 执行SQL增删改操作 ps.execute(); // 获取影响的行数 int rows = ps.getUpdateCount(); Object parameterObject = boundSql.getParameterObject(); KeyGenerator keyGenerator = mappedStatement.getKeyGenerator(); keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject); // 返回影响的行数 return rows; }
5 小结
mybatis执行SQL的流程都是：
1.根据statement字符串从configuration中获取对应的mappedStatement；
2.根据获取的mappedStatement创建相应的Statement实例；
3.根据传入的参数对statement实例进行参数设置；
4.执行statement并执行后置操作；
