mybatis03-mybatis源码分析2

太过爱你忘了你带给我的痛 2023-06-17 14:58 21阅读 0赞

### 文章目录 ###

*  获取mapper接口实例源码
 *   *  jdk动态代理
     *  伪代码实现动态获取mapper接口实现类
 *  UserMapper.xml如何被加载到内存
 *  获取mapper代理源码
 *   *  执行方法分析
 *  SQLSession的作用
 *  build.openSession()源码分析
 *  执行器源码分析
 *   *  执行器分类

# 获取mapper接口实例源码 #

// 5.获取对应的mapper
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    // 6.执行方法
    UserEntity user = userMapper.getUser(1);

> 接口没有实例化怎么被调用的呢?使用jdk动态代理

## jdk动态代理 ##

*  略

## 伪代码实现动态获取mapper接口实现类 ##

public class JdkMapperProxy implements InvocationHandler {
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args){
            return new UserEntity(1L, "myx", 28);
        }
    }

public class TestMyBatisJdk {
        public static void main(String[] args) {
            // 代理模式 动态代理 不需要写代理类。  jdk和cglib mybatis jdk动态代理
            // jdk动态代理实现原理
            System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
            // 接口如果没有实例化，如何被调用呢？ 动态代理技术  走同一个invoke 方法
            UserMapper mapper = getMapper(UserMapper.class);
            UserEntity user = mapper.getUser(1);
            System.out.println(user.getName());
        }
    
        private static <T> T getMapper(Class<T> type) {
            //由于没有实现类只能写接口的类型
            //没有实现类对象 new JdkMapperProxy()无参数即可
            return (T) Proxy.newProxyInstance(type.getClassLoader(), new Class[]{type}, new JdkMapperProxy());
        }
    }

# UserMapper.xml如何被加载到内存 #

![在这里插入图片描述][20191129152058442.png]

# 获取mapper代理源码 #

// 5.获取对应的mapper
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    // 6.执行方法
    UserEntity user = userMapper.getUser(1);

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70]

> 由于MapperRegistry中存储MapperProxyFactory map的key是Class类型。  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 1]  
> 所以每执行一次sqlSession.getMapper()就会获取一个新的Mapper代理，但是我们平时开发过程中可能是通过spring管理bean所以只调用了一次获取Mapper代理方法。  
> mybatis基于多个不同接口生成代理类，不同接口肯定执行不同的invoke方法，相同接口，不同方法肯定走同一个invoke方法。

## 执行方法分析 ##

> 最终只执行的为MapperProxy.invoke()

*  org.apache.ibatis.binding.MapperProxy\#invoke

@Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (Object.class.equals(method.getDeclaringClass())) {
          try {
            return method.invoke(this, args);
          } catch (Throwable t) {
            throw ExceptionUtil.unwrapThrowable(t);
          }
        }
        //缓存提升速度
        final MapperMethod mapperMethod = cachedMapperMethod(method);
        return mapperMethod.execute(sqlSession, args);
      }

*  org.apache.ibatis.binding.MapperMethod\#execute

public Object execute(SqlSession sqlSession, Object[] args) {
        Object result;
        if (SqlCommandType.INSERT == command.getType()) {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.insert(command.getName(), param));
        } else if (SqlCommandType.UPDATE == command.getType()) {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.update(command.getName(), param));
        } else if (SqlCommandType.DELETE == command.getType()) {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.delete(command.getName(), param));
        } else if (SqlCommandType.SELECT == command.getType()) {
          //是否没有返回值
          if (method.returnsVoid() && method.hasResultHandler()) {
            executeWithResultHandler(sqlSession, args);
            result = null;
          } else if (method.returnsMany()) {//是否为多个结果
            result = executeForMany(sqlSession, args);
          } else if (method.returnsMap()) {//是否为resultmap
            result = executeForMap(sqlSession, args);
          } else {
            Object param = method.convertArgsToSqlCommandParam(args);
            //最终执行方法sqlSession.selectOne(com.grape.mapper.UserMapper.getUser,1)
            result = sqlSession.selectOne(command.getName(), param);
          }
        } else if (SqlCommandType.FLUSH == command.getType()) {
            result = sqlSession.flushStatements();
        } else {
          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;
      }

# SQLSession的作用 #

> SqlSession提供select/insert/update/delete方法，在旧版本中使用使用SqlSession接口的这些方法

每个线程都应该有它自己的 SqlSession 实例。SqlSession 的实例不是线程安全的，因此是不能被共享的。springboot集成mybatis每次都会创建新的sqlsession，操作完毕后回关闭sqlsession

# build.openSession()源码分析 #

*  org.apache.ibatis.session.defaults.DefaultSqlSessionFactory\#openSessionFromDataSource

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        Transaction tx = null;
        try {
          final Environment environment = configuration.getEnvironment();
          //创建事务管理器
          final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
          tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
          //创建执行器、默认是创建简单的执行器会变成缓存执行器呢
          final Executor executor = configuration.newExecutor(tx, execType);
          //最后交给DefaultSqlSession
          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();
        }
      }

*  configuration.newExecutor(tx, execType);

//创建执行器
    public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
        executorType = executorType == null ? defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
        if (ExecutorType.BATCH == executorType) {
          executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) {
          executor = new ReuseExecutor(this, transaction);
        } else {
          executor = new SimpleExecutor(this, transaction);
        }
        if (cacheEnabled) {
          //如果二级缓存开启(默认是开启的)最终都会创建成CachingExecutor
          //默认创建SimpleExecutor执行器，判断是否开启二级缓存，如果开启了二级缓存CachingExecutor执行器构造函数传递SimpleExecutor
          executor = new CachingExecutor(executor);
        }
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }

*  org.apache.ibatis.executor.CachingExecutor\#query()

> 应用责任链设计模式

@Override
    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, parameterObject, boundSql);
            @SuppressWarnings("unchecked")
            List<E> list = (List<E>) tcm.getObject(cache, key);
            if (list == null) { 
              list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
              tcm.putObject(cache, key, list); // issue #578 and #116
            }
            return list;
          }
        }
        //执行简单执行器查询
        return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

# 执行器源码分析 #

## 执行器分类 ##

*  SimpleExecutor: 默认的 Executor，每个 SQL 执行时都会创建新的 Statement
 *  ResuseExecutor: 相同的 SQL 会复用 Statement
 *  BatchExecutor: 用于批处理的 Executor
 *  CachingExecutor: 可缓存数据的 Executor，用代理模式包装了其它类型的 Executor

UserEntity user = userMapper.getUser(1);
    等同于
    UserEntity user1= sqlSession.selectOne("com.grape.demo.mybatis.hello.mapper.UserMapper.getUser", 1);

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 2]

底层还是调用selectList方法  
![在这里插入图片描述][20191129152151482.png]  
传入了默认分页参数，所以mybatis只能查询int最大值数量数据

@Override
    public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
        try {
          //获取具体sql
          MappedStatement ms = configuration.getMappedStatement(statement);
          //这里执行CachingExecutor里面的query方法
          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();
        }
      }

*  CachingExecutor\#query()

@Override
    public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
        BoundSql boundSql = ms.getBoundSql(parameterObject);
        //获取缓存key-参考以及缓存源码分析
        CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
        //查询
        return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

[20191129152058442.png]: https://img-blog.csdnimg.cn/20191129152058442.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191129152113392.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20191129152124139.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20191129152145550.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMxNDYzOTk5,size_16,color_FFFFFF,t_70
[20191129152151482.png]: https://img-blog.csdnimg.cn/20191129152151482.png