1、Executor

1.1 BaseExecutor

是SimpleExecutor，ReusedExecutor，BatchExecutor的基类，主要是处理一级缓存。当调用该类的查询方法时，先查看一级缓存中已经有数据，如果有则直接从缓存获取，如果没有调用子类的查询方法从数据库中获取。当调用该类的update方法时(包含添加和删除),将一级缓存清空，然后调用子类对应的增删改方法。调用执行commit/rollback时，该类清空一级缓存。

DeferredLoad：处理延时加载，在嵌套子查询中用到。如果一级缓存中缓存了嵌套查询的结果对象，则可以从一级缓存中直接加载该结果对象。如果一级缓存中记录的嵌套查询的结果并未完全加载(缓存中没有数据或者等于占位符认为是没有完全加载)，则可以通过DeferredLoad实现延迟加载的功能。

在从数据库中查询时，会在一级缓存中设置一个占位符，待查询结果返回后，将真实的值放入缓存。

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {List<E> 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;}

1.2 SimpleExecutor

创建SatementHandler，获取数据库连接，创建 PrepareStatement或者Statement对象，设置参数，执行sql语句，最后将数据库返回结果转化为设定的对象。

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();StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);stmt = prepareStatement(handler, ms.getStatementLog());return handler.query(stmt, resultHandler);} finally {closeStatement(stmt);}}

1.3 BatchExecutor

执行更新方法与SimpleExecutor不同，不是直接执行sql语句，而是将其放到批次里，等到提交的时候一起执行。当连接执行的sql语句相同时，会将其加入到同一个批次中，否则新建Statement或者PrepareStatement对象，将创建新批次。当提交事务时，执行doFlushStatements方法。在查询时也会执行doFlushStatements方法。

public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {final Configuration configuration = ms.getConfiguration();final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);final BoundSql boundSql = handler.getBoundSql();final String sql = boundSql.getSql();final Statement stmt;if (sql.equals(currentSql) && ms.equals(currentStatement)) {int last = statementList.size() - 1;stmt = statementList.get(last);applyTransactionTimeout(stmt);handler.parameterize(stmt);// fix Issues 322BatchResult batchResult = batchResultList.get(last);batchResult.addParameterObject(parameterObject);} else {Connection connection = getConnection(ms.getStatementLog());stmt = handler.prepare(connection, transaction.getTimeout());handler.parameterize(stmt);    // fix Issues 322currentSql = sql;currentStatement = ms;statementList.add(stmt);batchResultList.add(new BatchResult(ms, sql, parameterObject));}handler.batch(stmt);return BATCH_UPDATE_RETURN_VALUE;}public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {try {List<BatchResult> results = new ArrayList<>();if (isRollback) {return Collections.emptyList();}for (int i = 0, n = statementList.size(); i < n; i++) {Statement stmt = statementList.get(i);applyTransactionTimeout(stmt);BatchResult batchResult = batchResultList.get(i);try {batchResult.setUpdateCounts(stmt.executeBatch());MappedStatement ms = batchResult.getMappedStatement();List<Object> parameterObjects = batchResult.getParameterObjects();KeyGenerator keyGenerator = ms.getKeyGenerator();if (Jdbc3KeyGenerator.class.equals(keyGenerator.getClass())) {Jdbc3KeyGenerator jdbc3KeyGenerator = (Jdbc3KeyGenerator) keyGenerator;jdbc3KeyGenerator.processBatch(ms, stmt, parameterObjects);} else if (!NoKeyGenerator.class.equals(keyGenerator.getClass())) { //issue #141for (Object parameter : parameterObjects) {keyGenerator.processAfter(this, ms, stmt, parameter);}}// Close statement to close cursor #1109closeStatement(stmt);} catch (BatchUpdateException e) {StringBuilder message = new StringBuilder();message.append(batchResult.getMappedStatement().getId()).append(" (batch index #").append(i + 1).append(")").append(" failed.");if (i > 0) {message.append(" ").append(i).append(" prior sub executor(s) completed successfully, but will be rolled back.");}throw new BatchExecutorException(message.toString(), e, results, batchResult);}results.add(batchResult);}return results;} finally {for (Statement stmt : statementList) {closeStatement(stmt);}currentSql = null;statementList.clear();batchResultList.clear();}}

1.4 ReuseExecutor

复用Statement或者PrepareStatement对象，该类中有属性statementMap。key是sql语句，value是statement对象。每次执行首先根据sql语句查询statementMap，如果有对应的statement对象，则直接使用该statement对象，如果没有，则创建新的statement对象，然后将其和sql语句添加到statementMap中。

public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);Statement stmt = prepareStatement(handler, ms.getStatementLog());return handler.update(stmt);}public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);Statement stmt = prepareStatement(handler, ms.getStatementLog());return handler.query(stmt, resultHandler);}private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Statement stmt;BoundSql boundSql = handler.getBoundSql();String sql = boundSql.getSql();if (hasStatementFor(sql)) {stmt = getStatement(sql);applyTransactionTimeout(stmt);} else {Connection connection = getConnection(statementLog);stmt = handler.prepare(connection, transaction.getTimeout());putStatement(sql, stmt);}handler.parameterize(stmt);return stmt;}

1.5 CachingExecutor

用于处理二级缓存。

查询时，如果当前MappedStatement是使用缓存，并且resultHandler没有设置时，如果缓存中不存在要查询的数据，将查询请求委托给其他的Executor，查询到结果后放入二级缓存。

增删改时会清空二级缓存，委托给其他的Executor。

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);}public int update(MappedStatement ms, Object parameterObject) throws SQLException {flushCacheIfRequired(ms);return delegate.update(ms, parameterObject);}

2、sqlSource生成BoundSql

主要是基于参数对象来创建DynamicContext，对于非Map对象，基于参数对象创建MetaObject,然后传入创建ContextMap。map对象直接创建ContextMap。然后在ContextMap中绑定两个key:_parameter, _databaseId。通过ContextMap以及Ongl语法来针对SqlNode生成对应的sql语句。其结构图为

public DynamicContext(Configuration configuration, Object parameterObject) {if (parameterObject != null && !(parameterObject instanceof Map)) {MetaObject metaObject = configuration.newMetaObject(parameterObject);boolean existsTypeHandler = configuration.getTypeHandlerRegistry().hasTypeHandler(parameterObject.getClass());bindings = new ContextMap(metaObject, existsTypeHandler);} else {bindings = new ContextMap(null, false);}bindings.put(PARAMETER_OBJECT_KEY, parameterObject);bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId());}

2.1 解析#{}

将带有#{}的解析成带有?占位符的语句，即StaticSqlSource,会携带#{}对应的参数映射，最后生成BoundSql

支持的属性有

javaType

jdbcType

mode

numericScale

resultMap

typeHandler

jdbcTypeName

public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);String sql;if (configuration.isShrinkWhitespacesInSql()) {sql = parser.parse(removeExtraWhitespaces(originalSql));} else {sql = parser.parse(originalSql);}return new StaticSqlSource(configuration, sql, handler.getParameterMappings());}

3、参数填充

通过StatementHandler的prepare来创建Statement，同时设置超时数据库的一些参数，同时使用parameterize来绑定参数。

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Statement stmt;Connection connection = getConnection(statementLog);stmt = handler.prepare(connection, transaction.getTimeout());handler.parameterize(stmt);return stmt;}

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