【OpenFeign】【源码+图解】【五】创建FeignClient接口的代理（上）

6.2 RequestTemplate.Factory

先看下类图

从类图中可以看出RequestTemplate.Factory的作用主要是创建RequestTemplate的，再看看源码如何创建RequestTemplate.Factory

static final class ParseHandlersByName {
    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;
            // 2、创建RequestTemplate.Factory
            if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
                // 没有@PathVariable、@RequestPart且非DeclarativeContract
                buildTemplate =
                    new BuildFormEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
            } else if (md.bodyIndex() != null || md.alwaysEncodeBody()) {
                // 满足以下情况：
                //  1、 参数类型不是URI, Request.Options类型
                //  2、 没有@RequestHeader, @RequestParam, @RequestPart, @SpringQueryMap, @CookieValue, @MatrixVariable, @PathVariable
                //  3、 使用的Contract不是AlwaysEncodeBodyContract类
                buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
            } else {
                // 默认
                buildTemplate = new BuildTemplateByResolvingArgs(md, queryMapEncoder, target);
            }
            ......
        }
        return result;
    }
}

6.3 创建SynchronousMethodHandler

static final class ParseHandlersByName {
    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) {
            // ......
                result.put(md.configKey(),
                           // 创建SynchronousMethodHandler
                           factory.create(target, md(6.1), buildTemplate(6.2), options, decoder, errorDecoder));
        }
        return result;
    }
}

static class Factory {
    public MethodHandler create(Target<?> target,
                                MethodMetadata md,
                                RequestTemplate.Factory buildTemplateFromArgs,
                                Options options,
                                Decoder decoder,
                                ErrorDecoder errorDecoder) {
        // 只是简单赋值，不再详细探究。其作用见后文
        return new SynchronousMethodHandler(target, client, retryer, requestInterceptors,
                                            responseInterceptor, logger, logLevel, md, buildTemplateFromArgs, options, decoder,
                                            errorDecoder, dismiss404, closeAfterDecode, propagationPolicy, forceDecoding);
    }
}

6.4 创建FeignInvocationHandler

public class ReflectiveFeign extends Feign {
    @Override
  public <T> T newInstance(Target<T> target) {
    ......
    // factory为InvocationHandlerFactory.Default
    InvocationHandler handler = factory.create(target, methodToHandler);
    ......
    return proxy;
  }
}

static final class Default implements InvocationHandlerFactory {

    @Override
    public InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch) {
        // 创建类型为FeignInvocationHandler的InvocationHandler
        return new ReflectiveFeign.FeignInvocationHandler(target, dispatch);
    }
}

FeignInvocationHandler创建好后，当http请求进来时会由其invoke方法处理。

7. FeignInvocationHandler处理HTTP请求

前面四个步骤都是创建FeignClient的代理，代理创建好后就可以使用了，当发起请求时代理接受到请求并交由FeignInvocationHandler处理

FeignInvocationHandler.invoke(…)

static class FeignInvocationHandler implements InvocationHandler {
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
          ......
          // dispatch.get(method)获取method对应的处理器SynchronousMethodHandler
          // invoke(args)：调用SynchronousMethodHandler.invoke(args)
          return dispatch.get(method).invoke(args);
      }
}

下一节再讲SynchronousMethodHandler是如何处理请求的。