mybatis0120-mybatis拦截器执行流程-拦截器代理的实现

Dear 丶 2023-08-17 15:31 159阅读 0赞

mybatis的拦截是通过jdk的动态代理实现的，代理了Executor对象，下面先捋一下Executor代理的流程。

1. Executor对象初始化

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
      Transaction tx = null;
      try {
        final Environment environment = configuration.getEnvironment();
        final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
        tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
        // Executor对象是通过Configuration对象生成的
        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();
      }
    }

2. Configuration.newExecutor(tx, execType)

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) {
        executor = new CachingExecutor(executor);
      }
      // executor通过了层层代理，有多少个拦截器，就代理了多少次
      executor = (Executor) interceptorChain.pluginAll(executor);
      return executor;
    }

3. interceptorChain.pluginAll(executor)

public Object pluginAll(Object target) {
        // interceptors是通过xml解析时解析<plugins>标签得到的
      for (Interceptor interceptor : interceptors) {
          // 下面就是要生成代理对象， 不需要自己实现。调用Plugin.wrap()就可以了
        target = interceptor.plugin(target);
      }
      return target;
    }

4. 先来看看Plugin.wrap(Object target, Interceptor interceptor)方法

/**
    * @target 被代理对象，第一次是Executor对象
    * @interceptor 拦截器
    */
    public static Object wrap(Object target, Interceptor interceptor) {
        // 获取拦截上的签名
        /**
         @Intercepts({
                @Signature(type = Executor.class,
                        method = "update",
                        args = {MappedStatement.class, Object.class})
        })
        */
      Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
      Class<?> type = target.getClass();
      // 获取被代理对象的接口Executor
      Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
      // 如果有接口，创建代理对象，jdk的动态代理是基于接口实现的
      if (interfaces.length > 0) {
        return Proxy.newProxyInstance(
            type.getClassLoader(),
            interfaces,
            // InvocationHandler的实现类，后续会进入Plugin实现类的invoke方法
            new Plugin(target, interceptor, signatureMap));
      }
      return target;
    }

5. 最后再来看自己实现的拦截器

@Intercepts({
            @Signature(type = Executor.class,
                    method = "update",
                    args = {MappedStatement.class, Object.class})
    })
    public class BaseFieldInterceptor implements Interceptor {
    
        public Object intercept(Invocation invocation) throws Throwable {
            System.out.println("拦截器拦截");
            Object result = invocation.proceed();
            return result;
        }
    
        public Object plugin(Object target) {
            // 创建代理对象，直接调用方法即可，内部已经帮我门实现了
            return Plugin.wrap(target, this);
        }
    
        public void setProperties(Properties properties) {
    
        }
    }

6. 创建流程

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