通过源码分析Mybatis运行原理

SqlSession类关系图

MapperFactoryBean 获取SqlSessionTemplate,SqlSessionTemplate的Configuration持有了mapper

 **************************MapperFactoryBean**********************************public T getObject() throws Exception {return this.getSqlSession().getMapper(this.mapperInterface);}**************************SqlSessionTemplate**********************************public <T> T getMapper(Class<T> type) {return this.getConfiguration().getMapper(type, this);}**************************Configuration***************************************public <T> T getMapper(Class<T> type, SqlSession sqlSession) {return this.mapperRegistry.getMapper(type, sqlSession);}

MapperRegistry 注册中心会根据mapper的接口生成代理类

 **************************MapperRegistry***************************************public <T> T getMapper(Class<T> type, SqlSession sqlSession) {MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);if (mapperProxyFactory == null) {throw new BindingException("Type " + type + " is not known to the MapperRegistry.");} else {try {return mapperProxyFactory.newInstance(sqlSession);} catch (Exception var5) {throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);}}}
**************************MapperProxyFactory***************************************protected T newInstance(MapperProxy<T> mapperProxy) {return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);}public T newInstance(SqlSession sqlSession) {MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);return this.newInstance(mapperProxy);

代理类的handler MapperProxy通过反射生成接口的实现方法

   public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);}if (this.isDefaultMethod(method)) {return this.invokeDefaultMethod(proxy, method, args);}} catch (Throwable var5) {throw ExceptionUtil.unwrapThrowable(var5);}MapperMethod mapperMethod = this.cachedMapperMethod(method);return mapperMethod.execute(this.sqlSession, args);}private MapperMethod cachedMapperMethod(Method method) {MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);if (mapperMethod == null) {mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());this.methodCache.put(method, mapperMethod);}return mapperMethod;}
**************************MapperMethod***************************************//根据查询类型诸如select、delete生成新的方法public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {this.command = new MapperMethod.SqlCommand(config, mapperInterface, method);this.method = new MapperMethod.MethodSignature(config, mapperInterface, method);}

根据命令模式进行解析执行

**************************MapperMethod***************************************
public Object execute(SqlSession sqlSession, Object[] args) {Object param;Object result;switch(this.command.getType()) {case INSERT:param = this.method.convertArgsToSqlCommandParam(args);result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));break;case UPDATE:param = this.method.convertArgsToSqlCommandParam(args);result = this.rowCountResult(sqlSession.update(this.command.getName(), param));break;case DELETE:param = this.method.convertArgsToSqlCommandParam(args);result = this.rowCountResult(sqlSession.delete(this.command.getName(), param));break;case SELECT:if (this.method.returnsVoid() && this.method.hasResultHandler()) {this.executeWithResultHandler(sqlSession, args);result = null;} else if (this.method.returnsMany()) {result = this.executeForMany(sqlSession, args);} else if (this.method.returnsMap()) {result = this.executeForMap(sqlSession, args);} else if (this.method.returnsCursor()) {result = this.executeForCursor(sqlSession, args);} else {param = this.method.convertArgsToSqlCommandParam(args);result = sqlSession.selectOne(this.command.getName(), param);}break;case FLUSH:result = sqlSession.flushStatements();break;default:throw new BindingException("Unknown execution method for: " + this.command.getName());}if (result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) {throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ").");} else {return result;}}

调用到sqlsession去执行命令，这里对应的是select

**************************MapperMethod***************************************private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {Object param = this.method.convertArgsToSqlCommandParam(args);List result;if (this.method.hasRowBounds()) {RowBounds rowBounds = this.method.extractRowBounds(args);result = sqlSession.selectList(this.command.getName(), param, rowBounds);} else {result = sqlSession.selectList(this.command.getName(), param);}if (!this.method.getReturnType().isAssignableFrom(result.getClass())) {return this.method.getReturnType().isArray() ? this.convertToArray(result) : this.convertToDeclaredCollection(sqlSession.getConfiguration(), result);} else {return result;}}
**************************SqlSessionTemplate**********************************public <E> List<E> selectList(String statement, Object parameter) {return this.selectList(statement, parameter, RowBounds.DEFAULT);}// SqlSessionTemplatede 的代理类(内部类)获取SqlSession的实体类(默认是DefaultSqlSession)了,在invoke SqlSession的接口过程中，会open和colsesession ，session的打开是放在
SqlSessionFactory中管理的private class SqlSessionInterceptor implements InvocationHandler {private SqlSessionInterceptor() {}public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {SqlSession sqlSession = SqlSessionUtils.getSqlSession(SqlSessionTemplate.this.sqlSessionFactory, SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);Object unwrapped;try {Object result = method.invoke(sqlSession, args);if (!SqlSessionUtils.isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {sqlSession.commit(true);}unwrapped = result;} catch (Throwable var11) {unwrapped = ExceptionUtil.unwrapThrowable(var11);if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {SqlSessionUtils.closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);sqlSession = null;Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException)unwrapped);if (translated != null) {unwrapped = translated;}}throw (Throwable)unwrapped;} finally {if (sqlSession != null) {SqlSessionUtils.closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);}}return unwrapped;}}

实现类DefaultSqlSession调用executor执行query

 **************************DefaultSqlSession**********************************public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {List var5;try {MappedStatement ms = this.configuration.getMappedStatement(statement);var5 = this.executor.query(ms, this.wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);} catch (Exception var9) {throw ExceptionFactory.wrapException("Error querying database.  Cause: " + var9, var9);} finally {ErrorContext.instance().reset();}return var5;}

最终会调到BaseExecutor的query方法去操作数据库

**************************BaseExecutor**********************************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 (this.closed) {throw new ExecutorException("Executor was closed.");} else {if (this.queryStack == 0 && ms.isFlushCacheRequired()) {this.clearLocalCache();}List list;try {++this.queryStack;list = resultHandler == null ? (List)this.localCache.getObject(key) : null;if (list != null) {this.handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);} else {list = this.queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);}} finally {--this.queryStack;}if (this.queryStack == 0) {Iterator var8 = this.deferredLoads.iterator();while(var8.hasNext()) {BaseExecutor.DeferredLoad deferredLoad = (BaseExecutor.DeferredLoad)var8.next();deferredLoad.load();}this.deferredLoads.clear();if (this.configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {this.clearLocalCache();}}return list;}}private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {this.localCache.putObject(key, ExecutionPlaceholder.EXECUTION_PLACEHOLDER);List list;try {list = this.doQuery(ms, parameter, rowBounds, resultHandler, boundSql);} finally {this.localCache.removeObject(key);}this.localCache.putObject(key, list);if (ms.getStatementType() == StatementType.CALLABLE) {this.localOutputParameterCache.putObject(key, parameter);}return list;}

在SimpleExecutor中最终会创建sql 的Statement 打开数据库的连接，调用MySQL的API去执行查询

    public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt = null;List var9;try {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql);stmt = this.prepareStatement(handler, ms.getStatementLog());var9 = handler.query(stmt, resultHandler);} finally {this.closeStatement(stmt);}return var9;}private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Connection connection = this.getConnection(statementLog);Statement stmt = handler.prepare(connection, this.transaction.getTimeout());handler.parameterize(stmt);return stmt;}

SQL执行器Executor的类关系图

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