Retrofit2 注解如何处理

近年来,Retrofit非常火,配合Rxjava简直就是Android开发神器,今天谈谈它到底是如何处理注解的。

Retrofit注解分为方法注解和参数注解,具体就不多说。

Retrofit:compile 'com.squareup.retrofit2:retrofit:2.2.0'

直接进源码

  • Retrofit.create
public <T> T create(final Class<T> service) {
    Utils.validateServiceInterface(service);
    if (validateEagerly) {
      eagerlyValidateMethods(service);
    }
    return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },
        new InvocationHandler() {
          private final Platform platform = Platform.get();

          @Override public Object invoke(Object proxy, Method method, Object[] args)
              throws Throwable {
            // If the method is a method from Object then defer to normal invocation.
            if (method.getDeclaringClass() == Object.class) {
              return method.invoke(this, args);
            }
            if (platform.isDefaultMethod(method)) {
              return platform.invokeDefaultMethod(method, service, proxy, args);
            }
//此处是重点
            ServiceMethod<Object, Object> serviceMethod =
                (ServiceMethod<Object, Object>) loadServiceMethod(method);
            OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
            return serviceMethod.callAdapter.adapt(okHttpCall);
          }
        });
  }

首先看Proxy.newProxyInstance:

try {
            return getProxyClass(loader, interfaces)
                    .getConstructor(InvocationHandler.class)
                    .newInstance(invocationHandler);
        } catch (NoSuchMethodException e) {
            cause = e;
        } catch (IllegalAccessException e) {
            cause = e;
        } catch (InstantiationException e) {
            cause = e;
        } catch (InvocationTargetException e) {
            cause = e;
        }

Proxy实例化就是返回一个InvocationHandler的示例,类似代理模式;

回到上面的代码,Retrofit.create就是创建了一个InvocationHandler,InvocationHandler执行invoke返回ServiceMethod,

注解就是在ServiceMethod中处理的

  • ServiceMethod
    ServiceMethod是Builder模式,靠内部类Builder实例化
  1. Builder初始化方法注解、参数注解数组
Builder(Retrofit retrofit, Method method) {
      this.retrofit = retrofit;
      this.method = method;
      this.methodAnnotations = method.getAnnotations();
      this.parameterTypes = method.getGenericParameterTypes();
      this.parameterAnnotationsArray = method.getParameterAnnotations();
    }
  1. ServiceMethod.Builder.build()
public ServiceMethod build() {
      callAdapter = createCallAdapter();
      responseType = callAdapter.responseType();
     ...
      responseConverter = createResponseConverter();

      for (Annotation annotation : methodAnnotations) {
        parseMethodAnnotation(annotation);//方法注解处理
      }

     ....

      int parameterCount = parameterAnnotationsArray.length;
      parameterHandlers = new ParameterHandler<?>[parameterCount];
      for (int p = 0; p < parameterCount; p++) {
        Type parameterType = parameterTypes[p];
        if (Utils.hasUnresolvableType(parameterType)) {
          throw parameterError(p, "Parameter type must not include a type variable or wildcard: %s",
              parameterType);
        }

        Annotation[] parameterAnnotations = parameterAnnotationsArray[p];
   ......

        parameterHandlers[p] = parseParameter(p, parameterType, parameterAnnotations);//参数注解处理
      }
.....

      return new ServiceMethod<>(this);
    }

只看两个方法, parseMethodAnnotation(annotation)和parseParameter,分别处理方法和参数注解

  • parseMethodAnnotation方法注解处理
private void parseMethodAnnotation(Annotation annotation) {
      if (annotation instanceof DELETE) {
        parseHttpMethodAndPath("DELETE", ((DELETE) annotation).value(), false);
      } else if (annotation instanceof GET) {
        parseHttpMethodAndPath("GET", ((GET) annotation).value(), false);
      } else if (annotation instanceof HEAD) {
        parseHttpMethodAndPath("HEAD", ((HEAD) annotation).value(), false);
        if (!Void.class.equals(responseType)) {
          throw methodError("HEAD method must use Void as response type.");
        }
      } else if (annotation instanceof PATCH) {
        parseHttpMethodAndPath("PATCH", ((PATCH) annotation).value(), true);
      } else if (annotation instanceof POST) {
        parseHttpMethodAndPath("POST", ((POST) annotation).value(), true);
      } else if (annotation instanceof PUT) {
        parseHttpMethodAndPath("PUT", ((PUT) annotation).value(), true);
      } else if (annotation instanceof OPTIONS) {
        parseHttpMethodAndPath("OPTIONS", ((OPTIONS) annotation).value(), false);
      } else if (annotation instanceof HTTP) {
        HTTP http = (HTTP) annotation;
        parseHttpMethodAndPath(http.method(), http.path(), http.hasBody());
      } else if (annotation instanceof retrofit2.http.Headers) {
        String[] headersToParse = ((retrofit2.http.Headers) annotation).value();
        if (headersToParse.length == 0) {
          throw methodError("@Headers annotation is empty.");
        }
        headers = parseHeaders(headersToParse);
      } 
    }

方法注解实现 parseHttpMethodAndPath:

赋值httpMethod和relativeUrl,请求方法和url:
private void parseHttpMethodAndPath(String httpMethod, String value, boolean hasBody) {
    ...
      this.httpMethod = httpMethod;
      this.hasBody = hasBody;
  ....
      this.relativeUrl = value;
      this.relativeUrlParamNames = parsePathParameters(value);
    }

看parsePathParameters:

将方法注解值放入Set中
static Set<String> parsePathParameters(String path) {
    Matcher m = PARAM_URL_REGEX.matcher(path);
    Set<String> patterns = new LinkedHashSet<>();
    while (m.find()) {
      patterns.add(m.group(1));
    }
    return patterns;
  }
  • parseParameter-参数注解处理
循环处理每个注解
private ParameterHandler<?> parseParameter(
        int p, Type parameterType, Annotation[] annotations) {
      ParameterHandler<?> result = null;
      for (Annotation annotation : annotations) {
       //处理单个注解
        ParameterHandler<?> annotationAction = parseParameterAnnotation(
            p, parameterType, annotations, annotation);
        ...
        if (result != null) {
          throw parameterError(p, "Multiple Retrofit annotations found, only one allowed.");
        }

        result = annotationAction;
      }

...
      return result;
    }

处理单个注解:

这里我保留了Query,Path,Filed,Body注解的处理,其他注解类似;

private ParameterHandler<?> parseParameterAnnotation(
        int p, Type type, Annotation[] annotations, Annotation annotation) {
     ...
        gotUrl = true;

        if (type == HttpUrl.class
            || type == String.class
            || type == URI.class
            || (type instanceof Class && "android.net.Uri".equals(((Class<?>) type).getName()))) {
          return new ParameterHandler.RelativeUrl();
        } else {
          throw parameterError(p,
              "@Url must be okhttp3.HttpUrl, String, java.net.URI, or android.net.Uri type.");
        }

      } else if (annotation instanceof Path) {
        if (gotQuery) {
    ...
        gotPath = true;

        Path path = (Path) annotation;
        String name = path.value();
        validatePathName(p, name);

        Converter<?, String> converter = retrofit.stringConverter(type, annotations);
        return new ParameterHandler.Path<>(name, converter, path.encoded());

      } else if (annotation instanceof Query) {
        Query query = (Query) annotation;
        String name = query.value();
        boolean encoded = query.encoded();

        Class<?> rawParameterType = Utils.getRawType(type);
        gotQuery = true;
        if (Iterable.class.isAssignableFrom(rawParameterType)) {
          if (!(type instanceof ParameterizedType)) {
            throw parameterError(p, rawParameterType.getSimpleName()
                + " must include generic type (e.g., "
                + rawParameterType.getSimpleName()
                + "<String>)");
          }
          ParameterizedType parameterizedType = (ParameterizedType) type;
          Type iterableType = Utils.getParameterUpperBound(0, parameterizedType);
          Converter<?, String> converter =
              retrofit.stringConverter(iterableType, annotations);
          return new ParameterHandler.Query<>(name, converter, encoded).iterable();
        } else if (rawParameterType.isArray()) {
          Class<?> arrayComponentType = boxIfPrimitive(rawParameterType.getComponentType());
          Converter<?, String> converter =
              retrofit.stringConverter(arrayComponentType, annotations);
          return new ParameterHandler.Query<>(name, converter, encoded).array();
        } else {
          Converter<?, String> converter =
              retrofit.stringConverter(type, annotations);
          return new ParameterHandler.Query<>(name, converter, encoded);
        }

      } 
       ...
       else if (annotation instanceof Field) {
        if (!isFormEncoded) {
          throw parameterError(p, "@Field parameters can only be used with form encoding.");
        }
        Field field = (Field) annotation;
        String name = field.value();
        boolean encoded = field.encoded();

        gotField = true;

        Class<?> rawParameterType = Utils.getRawType(type);
        if (Iterable.class.isAssignableFrom(rawParameterType)) {
          if (!(type instanceof ParameterizedType)) {
            throw parameterError(p, rawParameterType.getSimpleName()
                + " must include generic type (e.g., "
                + rawParameterType.getSimpleName()
                + "<String>)");
          }
          ParameterizedType parameterizedType = (ParameterizedType) type;
          Type iterableType = Utils.getParameterUpperBound(0, parameterizedType);
          Converter<?, String> converter =
              retrofit.stringConverter(iterableType, annotations);
          return new ParameterHandler.Field<>(name, converter, encoded).iterable();
        } else if (rawParameterType.isArray()) {
          Class<?> arrayComponentType = boxIfPrimitive(rawParameterType.getComponentType());
          Converter<?, String> converter =
              retrofit.stringConverter(arrayComponentType, annotations);
          return new ParameterHandler.Field<>(name, converter, encoded).array();
        } else {
          Converter<?, String> converter =
              retrofit.stringConverter(type, annotations);
          return new ParameterHandler.Field<>(name, converter, encoded);
        }

      } ...
       ...
else if (annotation instanceof Body) {
        if (isFormEncoded || isMultipart) {
          throw parameterError(p,
              "@Body parameters cannot be used with form or multi-part encoding.");
        }
        if (gotBody) {
          throw parameterError(p, "Multiple @Body method annotations found.");
        }

        Converter<?, RequestBody> converter;
        try {
          converter = retrofit.requestBodyConverter(type, annotations, methodAnnotations);
        } catch (RuntimeException e) {
          // Wide exception range because factories are user code.
          throw parameterError(e, p, "Unable to create @Body converter for %s", type);
        }
        gotBody = true;
        return new ParameterHandler.Body<>(converter);
      }

      return null; // Not a Retrofit annotation.
    }

该方法针对注解类型,返回不同的ParameterHandler内部类实例,比如ParameterHandler.Body,ParameterHandler.Query。

就说这么多,注解处理流程大概就是这么多。

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