mybatis-plugin插件执行原理解析

public class InterceptorChain {

  private final List<Interceptor> interceptors = new ArrayList<>();

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

  public void addInterceptor(Interceptor interceptor) {
    interceptors.add(interceptor);
  }

  public List<Interceptor> getInterceptors() {
    return Collections.unmodifiableList(interceptors);
  }

}

@Intercepts({@Signature( type= Executor.class,  method = "query", args ={
        MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class
})})
    public class ExamplePlugin implements Interceptor {

    //  分页   读写分离    Select  增删改

        public Object intercept(Invocation invocation) throws Throwable {
            System.out.println("代理");
        Object[] args = invocation.getArgs();
        MappedStatement ms= (MappedStatement) args[0];
        // 执行下一个拦截器、直到尽头
        return invocation.proceed();
    }
}

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    /**
     * 判断执行器的类型
     * 批量的执行器
     */
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      //可重复使用的执行器
      executor = new ReuseExecutor(this, transaction);
    } else {
      //简单的sql执行器对象
      executor = new SimpleExecutor(this, transaction);
    }
    //判断mybatis的全局配置文件是否开启缓存
    if (cacheEnabled) {
      //把当前的简单的执行器包装成一个CachingExecutor
      executor = new CachingExecutor(executor);
    }
    /**
     * TODO:调用所有的拦截器对象plugin方法
     * 插件： 责任链+ 装饰器模式（动态代理）
     */
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

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

public interface Interceptor {

  Object intercept(Invocation invocation) throws Throwable;

  default Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }
  default void setProperties(Properties properties) {
    // NOP
  }
}

  public static Object wrap(Object target, Interceptor interceptor) {
    // 获得interceptor配置的@Signature的type
    Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
    // 当前代理类型
    Class<?> type = target.getClass();
    // 根据当前代理类型 和 @signature指定的type进行配对， 配对成功则可以代理
    Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
    if (interfaces.length > 0) {
      return Proxy.newProxyInstance(
          type.getClassLoader(),
          interfaces,
          new Plugin(target, interceptor, signatureMap));
    }
    return target;
  }

@Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      Set<Method> methods = signatureMap.get(method.getDeclaringClass());
      if (methods != null && methods.contains(method)) {
        return interceptor.intercept(new Invocation(target, method, args));
      }
      return method.invoke(target, args);
    } catch (Exception e) {
      throw ExceptionUtil.unwrapThrowable(e);
    }
  }