MyBatis运行原理(二) : 获取SqlSession的流程、getMapper获取接口代理对象流程 (源码分析)

浅浅的花香味﹌ 2023-01-15 10:23 215阅读 0赞

# 二、获取SqlSession的流程 #

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1、进入到openSession()方法, 因为sqlSessionFactory在运行时的对象为DefaultSqlSessionFactory, 所以通过动态绑定机制调用的openSession为DefaultSqlSessionFactory的

@Override
      public SqlSession openSession(boolean autoCommit) { 
      	// configuration.getDefaultExecutorType() 为默认的SIMPLE类型的执行器
        return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
      }

2、进入到DefaultSqlSessionFactory类的openSessionFromDataSource方法中

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { 
        Transaction tx = null;
        try { 
          // 获取环境信息
          final Environment environment = configuration.getEnvironment();
          final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
          // 创建事务
          tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
          // 创建Executor执行器对象
          final Executor executor = configuration.newExecutor(tx, execType);
          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();
        }
      }

3、进入Configuration类的newExecutor(tx, execType)方法

public Executor newExecutor(Transaction transaction, ExecutorType executorType) { 
        executorType = executorType == null ? defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
        // 此处根据全局配置文件中配置的ExecutorType的类型, 来创建不同的XxxExecutor
        if (ExecutorType.BATCH == executorType) { 
          executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) { 
          executor = new ReuseExecutor(this, transaction);
        } else { 
          // 默认是SIMPLE类型, 所以创建SimpleExecutor对象
          executor = new SimpleExecutor(this, transaction);
        }
        // 如果有二级缓存, 就会创建CachingExecutor对象
        /* 该对象内部调用的查询方法对象, 实际还是传进去的executor */
        if (cacheEnabled) { 
          executor = new CachingExecutor(executor);
        }
        
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }
    
    public enum ExecutorType { 
      // BATCH为批量执行器
      SIMPLE, REUSE, BATCH
    }

Executor : **每一个SqlSession都会拥有一个Executor对象，这个对象负责增删改查的具体操作，我们可以简单的将它理解为JDBC中Statement的封装版。**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 2]

4、进入CachingExecutor看一下

public class CachingExecutor implements Executor { 
    
      private final Executor delegate;
      private final TransactionalCacheManager tcm = new TransactionalCacheManager();
    
      public CachingExecutor(Executor delegate) { 
        this.delegate = delegate;
        delegate.setExecutorWrapper(this);
      }
      
      // 省略...
      
      @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, boundSql);
            @SuppressWarnings("unchecked")
            List<E> list = (List<E>) tcm.getObject(cache, key);
            if (list == null) { 
              // 使用的仍然是传进来的executor
              list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
              tcm.putObject(cache, key, list); // issue #578 and #116
            }
            return list;
          }
        }
    	// 使用的仍然是通过构造器传进来的executor
        return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
      }

5、newExecutor方法最终返回的executor对象都要走InterceptorChain类的pluginAll方法, 来将executor对象通过每个拦截器包装一下, 并返回最终的executor

executor = (Executor) interceptorChain.pluginAll(executor);

public Object pluginAll(Object target) { 
      for (Interceptor interceptor : interceptors) { 
        target = interceptor.plugin(target);
      }
      return target;
    }

6、最终将这个包装好的executor对象, 传入到DefaultSqlSession中  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 3]  
7、最终调用的openSession()方法, 会返回一个DefaultSqlSession对象  
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**1-7时序图如下:**

总结: **返回的SqlSession的实现类DefaultSqlSession对象, 它包含了Executor和Configuration。**`Executor`**会在这一步被创建**  
![在这里插入图片描述][20210421221638538.png]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 5]

# 三、getMapper获取接口的代理对象 #

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1、进入DefaultSqlSession类的getMapper(Class class)方法

// 进入到DefaultSqlSession的getMapper方法
      @Override
      public <T> T getMapper(Class<T> type) { 
      	// 调用configuration的getMapper
        return configuration.getMapper(type, this);
      }
    
    // 进入到Configuration的getMapper方法
      public <T> T getMapper(Class<T> type, SqlSession sqlSession) { 
        return mapperRegistry.getMapper(type, sqlSession);
      }

2、进入到MapperRegistry类的getMapper方法

public <T> T getMapper(Class<T> type, SqlSession sqlSession) { 
      	// 直接从knownMappers拿到type的MapperProxy对象
        final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
        if (mapperProxyFactory == null) { 
          throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        }
        try { 
          return mapperProxyFactory.newInstance(sqlSession);
        } catch (Exception e) { 
          throw new BindingException("Error getting mapper instance. Cause: " + e, e);
        }
      }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 7]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 8]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 9]  
3、进入mapperProxyFactory.newInstance(sqlSession)方法

// MapperProxyFactory类的方法
      public T newInstance(SqlSession sqlSession) { 
        // 创建了MapperProxy对象
        // public class MapperProxy<T> implements InvocationHandler, Serializable {}
        // 所以MapperProxy
        final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
        return newInstance(mapperProxy);
      }
    
    // 进入newInstance(MapperProxy proxy)方法
      // 创建MapperProxy代理对象
      protected T newInstance(MapperProxy<T> mapperProxy) { 
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {  mapperInterface }, mapperProxy);
      }

4、最终就创建了UserMapper接口的代理对象  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 10]

**时序图如下:**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 11]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L20wXzM3OTg5OTgw_size_16_color_FFFFFF_t_70 1]: /images/20221022/933bcc2460834dee84954255a16eb84e.png
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[20210421221638538.png]: /images/20221022/f9e2785521314a8d8d1c716237c4f0c8.png
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