feign的代理调用invoker源码解析

从feign的动态代理开始分析 ReflectiveFeign.newInstance()

    InvocationHandler handler = factory.create(target, methodToHandler);
    T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
        new Class<?>[] {target.type()}, handler);

根据jdk动态调用原理，字节码编译后，feign调用最终是调用hander里面的invoker方法。 再看factory.create方法里面内容

    public InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch) {
      return new ReflectiveFeign.FeignInvocationHandler(target, dispatch);
    }

进一步再分析ReflectiveFeign.FeignInvocationHandler

    static class FeignInvocationHandler implements InvocationHandler {

    private final Target target;
    private final Map<Method, MethodHandler> dispatch;

    FeignInvocationHandler(Target target, Map<Method, MethodHandler> dispatch) {
      this.target = checkNotNull(target, "target");
      this.dispatch = checkNotNull(dispatch, "dispatch for %s", target);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      if ("equals".equals(method.getName())) {
        try {
          Object otherHandler =
              args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
          return equals(otherHandler);
        } catch (IllegalArgumentException e) {
          return false;
        }
      } else if ("hashCode".equals(method.getName())) {
        return hashCode();
      } else if ("toString".equals(method.getName())) {
        return toString();
      }

      return dispatch.get(method).invoke(args);
    }

看代码里面最终是dispatch.get(method).invoke(args)，其中args,是动态代理最终方法调用传入的参数，dispatch单看这个单词有些迷惑性 其实是一个map，map中取对应的方法。最终是Map<Method, MethodHandler> dispatch，那么最终是MethodHandler里面的invoker方法。

代码再往上翻，ReflectiveFeign.newInstance。里面可以看到 Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);

MethodHandler里面的内容有apply生成

   public Map<String, MethodHandler> apply(Target target) {
    List<MethodMetadata> metadata = contract.parseAndValidateMetadata(target.type());
      Map<String, MethodHandler> result = new LinkedHashMap<String, MethodHandler>();
      for (MethodMetadata md : metadata) {
        BuildTemplateByResolvingArgs buildTemplate;
        if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
          buildTemplate =
              new BuildFormEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
        } else if (md.bodyIndex() != null) {
          buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
        } else {
          buildTemplate = new BuildTemplateByResolvingArgs(md, queryMapEncoder, target);
        }
        if (md.isIgnored()) {
          result.put(md.configKey(), args -> {
            throw new IllegalStateException(md.configKey() + " is not a method handled by feign");
          });
        } else {
          result.put(md.configKey(),
              factory.create(target, md, buildTemplate, options, decoder, errorDecoder));
        }
      }
      return result;
    }

最终是SynchronousMethodHandler.create方法生成MethodHandler内容。 构造方法生成实例

private SynchronousMethodHandler(Target<?> target, Client client, Retryer retryer,
      List<RequestInterceptor> requestInterceptors, Logger logger,
      Logger.Level logLevel, MethodMetadata metadata,
      RequestTemplate.Factory buildTemplateFromArgs, Options options,
      Decoder decoder, ErrorDecoder errorDecoder, boolean decode404,
      boolean closeAfterDecode, ExceptionPropagationPolicy propagationPolicy,
      boolean forceDecoding) {

    this.target = checkNotNull(target, "target");
    this.client = checkNotNull(client, "client for %s", target);
    this.retryer = checkNotNull(retryer, "retryer for %s", target);
    this.requestInterceptors =
        checkNotNull(requestInterceptors, "requestInterceptors for %s", target);
    this.logger = checkNotNull(logger, "logger for %s", target);
    this.logLevel = checkNotNull(logLevel, "logLevel for %s", target);
    this.metadata = checkNotNull(metadata, "metadata for %s", target);
    this.buildTemplateFromArgs = checkNotNull(buildTemplateFromArgs, "metadata for %s", target);
    this.options = checkNotNull(options, "options for %s", target);
    this.propagationPolicy = propagationPolicy;

    if (forceDecoding) {
      // internal only: usual handling will be short-circuited, and all responses will be passed to
      // decoder directly!
      this.decoder = decoder;
      this.asyncResponseHandler = null;
    } else {
      this.decoder = null;
      this.asyncResponseHandler = new AsyncResponseHandler(logLevel, logger, decoder, errorDecoder,
          decode404, closeAfterDecode);
    }
  }

最核心的是SynchronousMethodHandler类里面的invoke方法。feign的远程调用最终是这个invoker方法。

public Object invoke(Object[] argv) throws Throwable {
    RequestTemplate template = buildTemplateFromArgs.create(argv);
    Options options = findOptions(argv);
    Retryer retryer = this.retryer.clone();
    while (true) {
      try {
        return executeAndDecode(template, options);
      } catch (RetryableException e) {
        try {
          retryer.continueOrPropagate(e);
        } catch (RetryableException th) {
          Throwable cause = th.getCause();
          if (propagationPolicy == UNWRAP && cause != null) {
            throw cause;
          } else {
            throw th;
          }
        }
        if (logLevel != Logger.Level.NONE) {
          logger.logRetry(metadata.configKey(), logLevel);
        }
        continue;
      }
    }
  }