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婚恋网站开发平台代理招商,成都服装网站建设,百度seo关键词优化si,net 网站开发1 执行器的创建

1. SimpleExecutor 描述#xff1a;最基本的执行器#xff0c;每次查询都会创建新的语句对象#xff0c;并且不会缓存任何结果。 特点#xff1a; 每次查询都会创建新的 PreparedStatement 对象。 不支持一级缓存。 适用于简单的查询操作#xff0c;不…1 执行器的创建 1. SimpleExecutor 描述最基本的执行器每次查询都会创建新的语句对象并且不会缓存任何结果。 特点 每次查询都会创建新的 PreparedStatement 对象。 不支持一级缓存。 适用于简单的查询操作不需要缓存的情况。
   2. ReuseExecutor 描述复用型执行器会复用 PreparedStatements。 特点 通过缓存 PreparedStatement 对象来提高性能。 支持一级缓存。 适用于多次执行相同的 SQL 语句尤其是参数不同的情况。
   3. BatchExecutor 描述批量执行器用于批量执行 SQL 语句。 特点 支持批量插入和更新操作。 通过缓存 PreparedStatement 对象来提高性能。 将多个 SQL 语句打包在一起减少数据库通信次数提高性能。 适用于大数据量的批量操作。 需要手动调用 flushStatements 方法来提交批量操作。
   执行语句如下 SqlSession session sqlSessionFactory.openSession(); 核心类DefaultSqlSessionFactory 执行方法openSession public SqlSession openSession() {return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false); }private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx null;try {//1 获取环境变量final Environment environment configuration.getEnvironment();//2 获取事务工厂final TransactionFactory transactionFactory getTransactionFactoryFromEnvironment(environment);tx transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);//3 创建一个sql执行器对象 默认创建SimpleExecutorfinal Executor executor configuration.newExecutor(tx, execType);//4 创建返回一个DefaultSqlSession对象返回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();} } 2 代理对象的创建 语句如下 UserMapper mapper session.getMapper(UserMapper.class); 源码解析 核心类DefaultSqlSession 核心方法getMapper public T T getMapper(ClassT type) {return configuration.getMapper(type, this); }public T T getMapper(ClassT type, SqlSession sqlSession) {//1 直接去缓存knownMappers中通过Mapper的class类型去找我们的mapperProxyFactory//xml解析时 会把所有的mapper接口存放至这个map value是一个代理final MapperProxyFactoryT mapperProxyFactory (MapperProxyFactoryT) knownMappers.get(type);//2 缓存中没有获取到 直接抛出异常if (mapperProxyFactory null) {throw new BindingException(Type type is not known to the MapperRegistry.);}try {//3 通过MapperProxyFactory来创建我们的实例return mapperProxyFactory.newInstance(sqlSession);} catch (Exception e) {throw new BindingException(Error getting mapper instance. Cause: e, e);} }public T newInstance(SqlSession sqlSession) {//1 创建我们的代理对象final MapperProxyT mapperProxy new MapperProxy(sqlSession, mapperInterface, methodCache);//2 创建我们的Mapper代理对象返回return newInstance(mapperProxy); } //JDK代理生成对象 protected T newInstance(MapperProxyT mapperProxy) {return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } 3 sql的执行 执行语句 User user mapper.selectById(1); 执行这条语句时由于mapper是一个代理对象会自动执行创建代理对象中构造函数的InvocationHandler中invoke方法这里mybatis包装了InvocationHandler对象自定义了一个类继承InvocationHandler。 核心类MapperProxy 核心方法invoke public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {//1 判断我们的方法是不是我们的Object类定义的方法若是直接通过反射调用if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else if (method.isDefault()) { //是否接口的默认方法//2 调用我们的接口中的默认方法return invokeDefaultMethod(proxy, method, args);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}//3 真正的进行调用,做了二个事情//第一步:把我们的方法对象封装成一个MapperMethod对象(带有缓存作用的)final MapperMethod mapperMethod cachedMapperMethod(method);//4 通过sqlSessionTemplate来调用我们的目标方法return mapperMethod.execute(sqlSession, args); }public Object execute(SqlSession sqlSession, Object[] args) {Object result;//1 判断我们执行sql命令的类型switch (command.getType()) {//insert操作case INSERT: {Object param method.convertArgsToSqlCommandParam(args);result rowCountResult(sqlSession.insert(command.getName(), param));break;}//update操作case UPDATE: {Object param method.convertArgsToSqlCommandParam(args);result rowCountResult(sqlSession.update(command.getName(), param));break;}//delete操作case DELETE: {Object param method.convertArgsToSqlCommandParam(args);result rowCountResult(sqlSession.delete(command.getName(), param));break;}//select操作case SELECT://返回值为空if (method.returnsVoid() method.hasResultHandler()) {executeWithResultHandler(sqlSession, args);result null;} else if (method.returnsMany()) {//返回值是一个Listresult executeForMany(sqlSession, args);} else if (method.returnsMap()) {//返回值是一个mapresult executeForMap(sqlSession, args);} else if (method.returnsCursor()) {//返回游标result executeForCursor(sqlSession, args);} else {//查询返回单个// 解析我们的参数Object param method.convertArgsToSqlCommandParam(args);// 通过调用DefaultSqlSession来执行我们的sqlresult 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; }public T T selectOne(String statement, Object parameter) {// Popular vote was to return null on 0 results and throw exception on too many.//1 这里selectOne调用也是调用selectList方法ListT list this.selectList(statement, parameter);//2 若查询出来有且有一个一个对象直接返回要给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;} }public E ListE selectList(String statement, Object parameter, RowBounds rowBounds) {try {//1 第一步通过我们的statement去我们的全局配置类中获取MappedStatementMappedStatement ms configuration.getMappedStatement(statement);//2 通过执行器去执行我们的sql对象 默认实现CachingExecutorreturn 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();} }public E ListE query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)throws SQLException {/*** 判断我们我们的mapper中是否开启了二级缓存cache/cache/Cache cache ms.getCache();/** 判断是否配置了cache/cache/if (cache ! null) {//判断是否需要刷新缓存flushCacheIfRequired(ms);if (ms.isUseCache() resultHandler null) {ensureNoOutParams(ms, boundSql);/** 先去二级缓存中获取/SuppressWarnings(unchecked)ListE list (ListE) tcm.getObject(cache, key);/** 二级缓存中没有获取到*/if (list null) {//去一级缓存获取 实现类BaseExecutorlist delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);//加入到二级缓存中tcm.putObject(cache, key, list); // issue #578 and #116}return list;}}//没有整合二级缓存,直接去查询return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }public E ListE 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());//1 已经关闭则抛出 ExecutorException 异常if (closed) {throw new ExecutorException(Executor was closed.);}//2 清空本地缓存如果 queryStack 为零并且要求清空本地缓存。if (queryStack 0 ms.isFlushCacheRequired()) {clearLocalCache();}ListE list;try {//3 从一级缓存中获取查询结果queryStack;list resultHandler null ? (ListE) localCache.getObject(key) : null;//4 获取到则进行处理if (list ! null) {//5 处理存过的handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);} else {//6 获得不到则从数据库中查询list queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);}} finally {queryStack–;}if (queryStack 0) {for (DeferredLoad deferredLoad : deferredLoads) {deferredLoad.load();}// issue #601deferredLoads.clear();if (configuration.getLocalCacheScope() LocalCacheScope.STATEMENT) {// issue #482clearLocalCache();}}return list; }private E ListE queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {ListE list;localCache.putObject(key, EXECUTION_PLACEHOLDER);try {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; }private E ListE queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {ListE list;localCache.putObject(key, EXECUTION_PLACEHOLDER);try {//选择配置的执行器执行sql对象 默认是SimpleExecutorlist 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; }public E ListE doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt null;try {Configuration configuration ms.getConfiguration();StatementHandler handler configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);//1 拿到连接 预处理语句statement 默认实现PreparedStatementHandlerstmt prepareStatement(handler, ms.getStatementLog());return handler.query(stmt, resultHandler);} finally {closeStatement(stmt);} }public E ListE query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps (PreparedStatement) statement;//1 执行sql语句ps.execute();//2 处理返回结果return resultSetHandler.handleResultSets(ps); }