源码实现@Testpublic void testSelect() throws IOException {SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH); // ExecutorType.BATCHtry {BlogMapper mapper = session.getMapper(BlogMapper.class);//走到代理类的invoke对象Blog blog = mapper.selectBlogById(1);System.out.println(blog);} finally {session.close();}}从knownMappers中拿到代理对象
public <T> T getMapper(Class<T> type) {return configuration.getMapper(type, this);}public <T> T getMapper(Class<T> type, SqlSession sqlSession) {return mapperRegistry.getMapper(type, sqlSession);}public <T> T getMapper(Class<T> type, SqlSession sqlSession) {final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);if (mapperProxyFactory == null) {throw new BindingException("Type " + type + " is not known to the MapperRegistry.");}try {//通过代理对象进行实例化return mapperProxyFactory.newInstance(sqlSession);} catch (Exception e) {throw new BindingException("Error getting mapper instance. Cause: " + e, e);}}public T newInstance(SqlSession sqlSession) {final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);return newInstance(mapperProxy);}protected T newInstance(MapperProxy<T> mapperProxy) {// 1：类加载器:2：被代理类实现的接口、3：实现了 InvocationHandler 的触发管理类return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);}执行该方法会走到代理类的invoke对象
Blog blog = mapper.selectBlogById(1);
@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {// toString hashCode equals getClass等方法 ， 无需走到执行SQL的流程if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else {// 提升获取 mapperMethod 的效率 ， 先到 MapperMethodInvoker（内部接口） 的 invoke// 普通方法会走到 PlainMethodInvoker（内部类） 的 invokereturn cachedInvoker(method).invoke(proxy, method, args, sqlSession);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}}interface MapperMethodInvoker {Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable;}private MapperMethodInvoker cachedInvoker(Method method) throws Throwable {try {// JAVA8 中 Map 的方法 ， 根据 key 获取值 ， 如果值是 null ， 则把后面Object 的值赋给 key// 如果获取不到 ， 就创建// 获取的是 MapperMethodInvoker（接口） 对象 ， 只有一个invoke方法return methodCache.computeIfAbsent(method, m -> {if (m.isDefault()) {// 接口的默认方法(Java8) ， 只要实现接口都会继承接口的默认方法 ， 例如 List.sort()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 {// 创建了一个 MapperMethodreturn new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));}});} catch (RuntimeException re) {Throwable cause = re.getCause();throw cause == null ? re : cause;}}public PlainMethodInvoker(MapperMethod mapperMethod) {super();this.mapperMethod = mapperMethod;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {// SQL执行的真正起点return mapperMethod.execute(sqlSession, args);}public Object execute(SqlSession sqlSession, Object[] args) {Object result;switch (command.getType()) {case INSERT: {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: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 {Object param = method.convertArgsToSqlCommandParam(args);// 普通 select 语句的执行入口 >>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;}//举个查询多条的例子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);}// issue #510 Collections & arrays supportif (!method.getReturnType().isAssignableFrom(result.getClass())) {if (method.getReturnType().isArray()) {return convertToArray(result);} else {return convertToDeclaredCollection(sqlSession.getConfiguration(), result);}}return result;}@Overridepublic <E> List<E> selectList(String statement, Object parameter) {// 为了提供多种重载（简化方法使用） ， 和默认值// 让参数少的调用参数多的方法 ， 只实现一次return this.selectList(statement, parameter, RowBounds.DEFAULT);}@Overridepublic <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {try {//从configuration中获取MappedStatement 这是在初始化的时候存进去的//这里是通过namespace+sqlId来进行获取的MappedStatement ms = configuration.getMappedStatement(statement);// 如果 cacheEnabled = true（默认） ， Executor会被 CachingExecutor装饰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();}}//我们在这里看的是走缓存的@Overridepublic <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {// 获取SQLBoundSql boundSql = ms.getBoundSql(parameterObject);// 创建CacheKey：什么样的SQL是同一条SQL？CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);}@Overridepublic <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)throws SQLException {Cache cache = ms.getCache();// cache 对象是在哪里创建的？XMLMapperBuilder类 xmlconfigurationElement()// 由 <cache> 标签决定if (cache != null) {// flushCache="true" 清空一级二级缓存 >>flushCacheIfRequired(ms);//是否使用缓存if (ms.isUseCache() && resultHandler == null) {ensureNoOutParams(ms, boundSql);// 获取二级缓存// 缓存通过 TransactionalCacheManager、TransactionalCache 管理@SuppressWarnings("unchecked")List<E> list = (List<E>) tcm.getObject(cache, key);if (list == null) {//如果二级缓存中没有就去查询数据库list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);// 写入二级缓存tcm.putObject(cache, key, list); // issue #578 and #116}return list;}}// 走到 SimpleExecutor | ReuseExecutor | BatchExecutorreturn delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);}//没有走缓存的  ， 是直接查询数据库的操作@Overridepublic <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {// 异常体系之 ErrorContextErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());if (closed) {throw new ExecutorException("Executor was closed.");}if (queryStack == 0 && ms.isFlushCacheRequired()) {// flushCache="true"时 ， 即使是查询 ， 也清空一级缓存clearLocalCache();}List<E> list;try {// 防止递归查询重复处理缓存queryStack++;// 查询一级缓存// ResultHandler 和 ResultSetHandler的区别list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;if (list != null) {handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);} else {// 真正的查询流程 查看下方代码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> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {List<E> list;// 先占位localCache.putObject(key, EXECUTION_PLACEHOLDER);try {// 三种 Executor 的区别 ， 看doUpdate// 默认Simplelist = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);} finally {// 移除占位符localCache.removeObject(key);}// 写入一级缓存localCache.putObject(key, list);if (ms.getStatementType() == StatementType.CALLABLE) {localOutputParameterCache.putObject(key, parameter);}return list;}@Overridepublic <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt = null;try {//拿到MappedStatement 中的所有信息Configuration configuration = ms.getConfiguration();// 注意 ， 已经来到SQL处理的关键对象 StatementHandlerStatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);// 获取一个 Statement对象 详情看下方代码stmt = prepareStatement(handler, ms.getStatementLog());// 执行查询return handler.query(stmt, resultHandler);} finally {// 用完就关闭closeStatement(stmt);}}public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {//这里进行的预编译 详情看下方代码StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);// 植入插件逻辑（返回代理对象）statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);return statementHandler;}public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {// StatementType 是怎么来的？ 增删改查标签中的 statementType="PREPARED" ， 默认值 PREPAREDswitch (ms.getStatementType()) {case STATEMENT:delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;case PREPARED:// 创建 StatementHandler 的时候做了什么？ >>delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;case CALLABLE:delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);break;default:throw new ExecutorException("Unknown statement type: " + ms.getStatementType());}}private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Statement stmt;Connection connection = getConnection(statementLog);// 获取 Statement 对象stmt = handler.prepare(connection, transaction.getTimeout());// 为 Statement 设置参数handler.parameterize(stmt);return stmt;}//执行查询 - 执行sqlhandler.query(stmt, resultHandler);@Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;// 到了JDBC的流程ps.execute();// 处理结果集 并返回return resultSetHandler.handleResultSets(ps);}@Overridepublic List<Object> handleResultSets(Statement stmt) throws SQLException {ErrorContext.instance().activity("handling results").object(mappedStatement.getId());final List<Object> multipleResults = new ArrayList<>();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);}