目录1 SQL语句的执行过程介绍2 SQL执行的入口分析2.1 为Mapper接口创建代理对象2.2 执行代理逻辑3 查询语句的执行过程分析3.1 selectOne方法分析3.2 sql获取3.3 参数设置3.4 SQL执行和结果集的封装4 更新语句的执行过程分析4.1 sqlsession增删改方法分析4.2 sql获取4.3 参数设置4.4 SQL执行5 小结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 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 List 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 getMapper(Class type) {return configuration.getMapper(type, this);}// Configuration类 ====================>public T getMapper(Class type, SqlSession sqlSession) {return mapperRegistry.getMapper(type, sqlSession);}//MapperRegistry ----> apperProxyFactory.newInstance ====================>public T getMapper(Class type, SqlSession sqlSession) {//从缓存中获取该Mapper接口的代理工厂对象final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) 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 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 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 Object executeForMany(SqlSession sqlSession, Object[] args) {List 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 selectOne(String statement, Object parameter) {// //selectOne()会调用selectList()。
List 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 List 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 List 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 List 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 list = (List) 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 List 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 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) 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 List queryFromDatabase(...) throws SQLException {List 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 List 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.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 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 List query(Statement statement) throws SQLException {return delegate.query(statement);}// PreparedStatementHandler ============================>@Override public List 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. handleResultSets(ps);}// DefaultResultSetHandler类（封装返回值，将查询结果封装成Object对象）
@Override public List handleResultSets(Statement stmt) throws SQLException {ErrorContext.instance().activity("handling results").object(mappedStatement.getId());final List multipleResults = new ArrayList();int resultSetCount = 0;ResultSetWrapper rsw = getFirstResultSet(stmt);List 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xecutor 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 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；
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