聊聊feign的Contract

序

本文主要研究一下feign的Contract

Contract

feign-core-10.2.3-sources.jar!/feign/Contract.java

public interface Contract {

  /**
   * Called to parse the methods in the class that are linked to HTTP requests.
   *
   * @param targetType {@link feign.Target#type() type} of the Feign interface.
   */
  // TODO: break this and correct spelling at some point
  List<MethodMetadata> parseAndValidatateMetadata(Class<?> targetType);

  //......

}

• Contract定义了parseAndValidatateMetadata方法，该方法返回List形式的MethodMetadata

Contract.BaseContract

feign-core-10.2.3-sources.jar!/feign/Contract.java

abstract class BaseContract implements Contract {

    @Override
    public List<MethodMetadata> parseAndValidatateMetadata(Class<?> targetType) {
      checkState(targetType.getTypeParameters().length == 0, "Parameterized types unsupported: %s",
          targetType.getSimpleName());
      checkState(targetType.getInterfaces().length <= 1, "Only single inheritance supported: %s",
          targetType.getSimpleName());
      if (targetType.getInterfaces().length == 1) {
        checkState(targetType.getInterfaces()[0].getInterfaces().length == 0,
            "Only single-level inheritance supported: %s",
            targetType.getSimpleName());
      }
      Map<String, MethodMetadata> result = new LinkedHashMap<String, MethodMetadata>();
      for (Method method : targetType.getMethods()) {
        if (method.getDeclaringClass() == Object.class ||
            (method.getModifiers() & Modifier.STATIC) != 0 ||
            Util.isDefault(method)) {
          continue;
        }
        MethodMetadata metadata = parseAndValidateMetadata(targetType, method);
        checkState(!result.containsKey(metadata.configKey()), "Overrides unsupported: %s",
            metadata.configKey());
        result.put(metadata.configKey(), metadata);
      }
      return new ArrayList<>(result.values());
    }

    /**
     * @deprecated use {@link #parseAndValidateMetadata(Class, Method)} instead.
     */
    @Deprecated
    public MethodMetadata parseAndValidatateMetadata(Method method) {
      return parseAndValidateMetadata(method.getDeclaringClass(), method);
    }

    /**
     * Called indirectly by {@link #parseAndValidatateMetadata(Class)}.
     */
    protected MethodMetadata parseAndValidateMetadata(Class<?> targetType, Method method) {
      MethodMetadata data = new MethodMetadata();
      data.returnType(Types.resolve(targetType, targetType, method.getGenericReturnType()));
      data.configKey(Feign.configKey(targetType, method));

      if (targetType.getInterfaces().length == 1) {
        processAnnotationOnClass(data, targetType.getInterfaces()[0]);
      }
      processAnnotationOnClass(data, targetType);


      for (Annotation methodAnnotation : method.getAnnotations()) {
        processAnnotationOnMethod(data, methodAnnotation, method);
      }
      checkState(data.template().method() != null,
          "Method %s not annotated with HTTP method type (ex. GET, POST)",
          method.getName());
      Class<?>[] parameterTypes = method.getParameterTypes();
      Type[] genericParameterTypes = method.getGenericParameterTypes();

      Annotation[][] parameterAnnotations = method.getParameterAnnotations();
      int count = parameterAnnotations.length;
      for (int i = 0; i < count; i++) {
        boolean isHttpAnnotation = false;
        if (parameterAnnotations[i] != null) {
          isHttpAnnotation = processAnnotationsOnParameter(data, parameterAnnotations[i], i);
        }
        if (parameterTypes[i] == URI.class) {
          data.urlIndex(i);
        } else if (!isHttpAnnotation) {
          checkState(data.formParams().isEmpty(),
              "Body parameters cannot be used with form parameters.");
          checkState(data.bodyIndex() == null, "Method has too many Body parameters: %s", method);
          data.bodyIndex(i);
          data.bodyType(Types.resolve(targetType, targetType, genericParameterTypes[i]));
        }
      }

      if (data.headerMapIndex() != null) {
        checkMapString("HeaderMap", parameterTypes[data.headerMapIndex()],
            genericParameterTypes[data.headerMapIndex()]);
      }

      if (data.queryMapIndex() != null) {
        if (Map.class.isAssignableFrom(parameterTypes[data.queryMapIndex()])) {
          checkMapKeys("QueryMap", genericParameterTypes[data.queryMapIndex()]);
        }
      }

      return data;
    }

    private static void checkMapString(String name, Class<?> type, Type genericType) {
      checkState(Map.class.isAssignableFrom(type),
          "%s parameter must be a Map: %s", name, type);
      checkMapKeys(name, genericType);
    }

    private static void checkMapKeys(String name, Type genericType) {
      Class<?> keyClass = null;

      // assume our type parameterized
      if (ParameterizedType.class.isAssignableFrom(genericType.getClass())) {
        Type[] parameterTypes = ((ParameterizedType) genericType).getActualTypeArguments();
        keyClass = (Class<?>) parameterTypes[0];
      } else if (genericType instanceof Class<?>) {
        // raw class, type parameters cannot be inferred directly, but we can scan any extended
        // interfaces looking for any explict types
        Type[] interfaces = ((Class) genericType).getGenericInterfaces();
        if (interfaces != null) {
          for (Type extended : interfaces) {
            if (ParameterizedType.class.isAssignableFrom(extended.getClass())) {
              // use the first extended interface we find.
              Type[] parameterTypes = ((ParameterizedType) extended).getActualTypeArguments();
              keyClass = (Class<?>) parameterTypes[0];
              break;
            }
          }
        }
      }

      if (keyClass != null) {
        checkState(String.class.equals(keyClass),
            "%s key must be a String: %s", name, keyClass.getSimpleName());
      }
    }


    /**
     * Called by parseAndValidateMetadata twice, first on the declaring class, then on the target
     * type (unless they are the same).
     *
     * @param data metadata collected so far relating to the current java method.
     * @param clz the class to process
     */
    protected abstract void processAnnotationOnClass(MethodMetadata data, Class<?> clz);

    /**
     * @param data metadata collected so far relating to the current java method.
     * @param annotation annotations present on the current method annotation.
     * @param method method currently being processed.
     */
    protected abstract void processAnnotationOnMethod(MethodMetadata data,
                                                      Annotation annotation,
                                                      Method method);

    /**
     * @param data metadata collected so far relating to the current java method.
     * @param annotations annotations present on the current parameter annotation.
     * @param paramIndex if you find a name in {@code annotations}, call
     *        {@link #nameParam(MethodMetadata, String, int)} with this as the last parameter.
     * @return true if you called {@link #nameParam(MethodMetadata, String, int)} after finding an
     *         http-relevant annotation.
     */
    protected abstract boolean processAnnotationsOnParameter(MethodMetadata data,
                                                             Annotation[] annotations,
                                                             int paramIndex);

    /**
     * links a parameter name to its index in the method signature.
     */
    protected void nameParam(MethodMetadata data, String name, int i) {
      Collection<String> names =
          data.indexToName().containsKey(i) ? data.indexToName().get(i) : new ArrayList<String>();
      names.add(name);
      data.indexToName().put(i, names);
    }
  }

• Contract.BaseContract是个抽象类，它processAnnotationOnClass、processAnnotationOnMethod、processAnnotationsOnParameter的抽象方法需要子类去实现；它的parseAndValidatateMetadata方法的实现主要是调用了parseAndValidateMetadata方法，而该方法会调用processAnnotationOnClass、processAnnotationOnMethod、processAnnotationsOnParameter这些方法

Contract.Default

feign-core-10.2.3-sources.jar!/feign/Contract.java

class Default extends BaseContract {

    static final Pattern REQUEST_LINE_PATTERN = Pattern.compile("^([A-Z]+)[ ]*(.*)$");

    @Override
    protected void processAnnotationOnClass(MethodMetadata data, Class<?> targetType) {
      if (targetType.isAnnotationPresent(Headers.class)) {
        String[] headersOnType = targetType.getAnnotation(Headers.class).value();
        checkState(headersOnType.length > 0, "Headers annotation was empty on type %s.",
            targetType.getName());
        Map<String, Collection<String>> headers = toMap(headersOnType);
        headers.putAll(data.template().headers());
        data.template().headers(null); // to clear
        data.template().headers(headers);
      }
    }

    @Override
    protected void processAnnotationOnMethod(MethodMetadata data,
                                             Annotation methodAnnotation,
                                             Method method) {
      Class<? extends Annotation> annotationType = methodAnnotation.annotationType();
      if (annotationType == RequestLine.class) {
        String requestLine = RequestLine.class.cast(methodAnnotation).value();
        checkState(emptyToNull(requestLine) != null,
            "RequestLine annotation was empty on method %s.", method.getName());

        Matcher requestLineMatcher = REQUEST_LINE_PATTERN.matcher(requestLine);
        if (!requestLineMatcher.find()) {
          throw new IllegalStateException(String.format(
              "RequestLine annotation didn't start with an HTTP verb on method %s",
              method.getName()));
        } else {
          data.template().method(HttpMethod.valueOf(requestLineMatcher.group(1)));
          data.template().uri(requestLineMatcher.group(2));
        }
        data.template().decodeSlash(RequestLine.class.cast(methodAnnotation).decodeSlash());
        data.template()
            .collectionFormat(RequestLine.class.cast(methodAnnotation).collectionFormat());

      } else if (annotationType == Body.class) {
        String body = Body.class.cast(methodAnnotation).value();
        checkState(emptyToNull(body) != null, "Body annotation was empty on method %s.",
            method.getName());
        if (body.indexOf('{') == -1) {
          data.template().body(body);
        } else {
          data.template().bodyTemplate(body);
        }
      } else if (annotationType == Headers.class) {
        String[] headersOnMethod = Headers.class.cast(methodAnnotation).value();
        checkState(headersOnMethod.length > 0, "Headers annotation was empty on method %s.",
            method.getName());
        data.template().headers(toMap(headersOnMethod));
      }
    }

    @Override
    protected boolean processAnnotationsOnParameter(MethodMetadata data,
                                                    Annotation[] annotations,
                                                    int paramIndex) {
      boolean isHttpAnnotation = false;
      for (Annotation annotation : annotations) {
        Class<? extends Annotation> annotationType = annotation.annotationType();
        if (annotationType == Param.class) {
          Param paramAnnotation = (Param) annotation;
          String name = paramAnnotation.value();
          checkState(emptyToNull(name) != null, "Param annotation was empty on param %s.",
              paramIndex);
          nameParam(data, name, paramIndex);
          Class<? extends Param.Expander> expander = paramAnnotation.expander();
          if (expander != Param.ToStringExpander.class) {
            data.indexToExpanderClass().put(paramIndex, expander);
          }
          data.indexToEncoded().put(paramIndex, paramAnnotation.encoded());
          isHttpAnnotation = true;
          if (!data.template().hasRequestVariable(name)) {
            data.formParams().add(name);
          }
        } else if (annotationType == QueryMap.class) {
          checkState(data.queryMapIndex() == null,
              "QueryMap annotation was present on multiple parameters.");
          data.queryMapIndex(paramIndex);
          data.queryMapEncoded(QueryMap.class.cast(annotation).encoded());
          isHttpAnnotation = true;
        } else if (annotationType == HeaderMap.class) {
          checkState(data.headerMapIndex() == null,
              "HeaderMap annotation was present on multiple parameters.");
          data.headerMapIndex(paramIndex);
          isHttpAnnotation = true;
        }
      }
      return isHttpAnnotation;
    }

    private static Map<String, Collection<String>> toMap(String[] input) {
      Map<String, Collection<String>> result =
          new LinkedHashMap<String, Collection<String>>(input.length);
      for (String header : input) {
        int colon = header.indexOf(':');
        String name = header.substring(0, colon);
        if (!result.containsKey(name)) {
          result.put(name, new ArrayList<String>(1));
        }
        result.get(name).add(header.substring(colon + 1).trim());
      }
      return result;
    }
  }

• Contract.Default继承了BaseContract，其processAnnotationOnClass方法处理feign.Headers注解；其processAnnotationOnMethod方法处理feign.RequestLine、feign.Body注解；其processAnnotationsOnParameter方法处理feign.Param、feign.QueryMap、feign.HeaderMap注解

SpringMvcContract

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/support/SpringMvcContract.java

public class SpringMvcContract extends Contract.BaseContract
        implements ResourceLoaderAware {

    private static final String ACCEPT = "Accept";

    private static final String CONTENT_TYPE = "Content-Type";

    private static final TypeDescriptor STRING_TYPE_DESCRIPTOR = TypeDescriptor
            .valueOf(String.class);

    private static final TypeDescriptor ITERABLE_TYPE_DESCRIPTOR = TypeDescriptor
            .valueOf(Iterable.class);

    private static final ParameterNameDiscoverer PARAMETER_NAME_DISCOVERER = new DefaultParameterNameDiscoverer();

    private final Map<Class<? extends Annotation>, AnnotatedParameterProcessor> annotatedArgumentProcessors;

    private final Map<String, Method> processedMethods = new HashMap<>();

    private final ConversionService conversionService;

    private final ConvertingExpanderFactory convertingExpanderFactory;

    private ResourceLoader resourceLoader = new DefaultResourceLoader();

    public SpringMvcContract() {
        this(Collections.emptyList());
    }

    public SpringMvcContract(
            List<AnnotatedParameterProcessor> annotatedParameterProcessors) {
        this(annotatedParameterProcessors, new DefaultConversionService());
    }

    public SpringMvcContract(
            List<AnnotatedParameterProcessor> annotatedParameterProcessors,
            ConversionService conversionService) {
        Assert.notNull(annotatedParameterProcessors,
                "Parameter processors can not be null.");
        Assert.notNull(conversionService, "ConversionService can not be null.");

        List<AnnotatedParameterProcessor> processors;
        if (!annotatedParameterProcessors.isEmpty()) {
            processors = new ArrayList<>(annotatedParameterProcessors);
        }
        else {
            processors = getDefaultAnnotatedArgumentsProcessors();
        }
        this.annotatedArgumentProcessors = toAnnotatedArgumentProcessorMap(processors);
        this.conversionService = conversionService;
        this.convertingExpanderFactory = new ConvertingExpanderFactory(conversionService);
    }

    //......

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    @Override
    public MethodMetadata parseAndValidateMetadata(Class<?> targetType, Method method) {
        this.processedMethods.put(Feign.configKey(targetType, method), method);
        MethodMetadata md = super.parseAndValidateMetadata(targetType, method);

        RequestMapping classAnnotation = findMergedAnnotation(targetType,
                RequestMapping.class);
        if (classAnnotation != null) {
            // produces - use from class annotation only if method has not specified this
            if (!md.template().headers().containsKey(ACCEPT)) {
                parseProduces(md, method, classAnnotation);
            }

            // consumes -- use from class annotation only if method has not specified this
            if (!md.template().headers().containsKey(CONTENT_TYPE)) {
                parseConsumes(md, method, classAnnotation);
            }

            // headers -- class annotation is inherited to methods, always write these if
            // present
            parseHeaders(md, method, classAnnotation);
        }
        return md;
    }

    @Override
    protected void processAnnotationOnClass(MethodMetadata data, Class<?> clz) {
        if (clz.getInterfaces().length == 0) {
            RequestMapping classAnnotation = findMergedAnnotation(clz,
                    RequestMapping.class);
            if (classAnnotation != null) {
                // Prepend path from class annotation if specified
                if (classAnnotation.value().length > 0) {
                    String pathValue = emptyToNull(classAnnotation.value()[0]);
                    pathValue = resolve(pathValue);
                    if (!pathValue.startsWith("/")) {
                        pathValue = "/" + pathValue;
                    }
                    data.template().uri(pathValue);
                }
            }
        }
    }

    @Override
    protected void processAnnotationOnMethod(MethodMetadata data,
            Annotation methodAnnotation, Method method) {
        if (!RequestMapping.class.isInstance(methodAnnotation) && !methodAnnotation
                .annotationType().isAnnotationPresent(RequestMapping.class)) {
            return;
        }

        RequestMapping methodMapping = findMergedAnnotation(method, RequestMapping.class);
        // HTTP Method
        RequestMethod[] methods = methodMapping.method();
        if (methods.length == 0) {
            methods = new RequestMethod[] { RequestMethod.GET };
        }
        checkOne(method, methods, "method");
        data.template().method(Request.HttpMethod.valueOf(methods[0].name()));

        // path
        checkAtMostOne(method, methodMapping.value(), "value");
        if (methodMapping.value().length > 0) {
            String pathValue = emptyToNull(methodMapping.value()[0]);
            if (pathValue != null) {
                pathValue = resolve(pathValue);
                // Append path from @RequestMapping if value is present on method
                if (!pathValue.startsWith("/") && !data.template().path().endsWith("/")) {
                    pathValue = "/" + pathValue;
                }
                data.template().uri(pathValue, true);
            }
        }

        // produces
        parseProduces(data, method, methodMapping);

        // consumes
        parseConsumes(data, method, methodMapping);

        // headers
        parseHeaders(data, method, methodMapping);

        data.indexToExpander(new LinkedHashMap<Integer, Param.Expander>());
    }

    @Override
    protected boolean processAnnotationsOnParameter(MethodMetadata data,
            Annotation[] annotations, int paramIndex) {
        boolean isHttpAnnotation = false;

        AnnotatedParameterProcessor.AnnotatedParameterContext context = new SimpleAnnotatedParameterContext(
                data, paramIndex);
        Method method = this.processedMethods.get(data.configKey());
        for (Annotation parameterAnnotation : annotations) {
            AnnotatedParameterProcessor processor = this.annotatedArgumentProcessors
                    .get(parameterAnnotation.annotationType());
            if (processor != null) {
                Annotation processParameterAnnotation;
                // synthesize, handling @AliasFor, while falling back to parameter name on
                // missing String #value():
                processParameterAnnotation = synthesizeWithMethodParameterNameAsFallbackValue(
                        parameterAnnotation, method, paramIndex);
                isHttpAnnotation |= processor.processArgument(context,
                        processParameterAnnotation, method);
            }
        }

        if (isHttpAnnotation && data.indexToExpander().get(paramIndex) == null) {
            TypeDescriptor typeDescriptor = createTypeDescriptor(method, paramIndex);
            if (this.conversionService.canConvert(typeDescriptor,
                    STRING_TYPE_DESCRIPTOR)) {
                Param.Expander expander = this.convertingExpanderFactory
                        .getExpander(typeDescriptor);
                if (expander != null) {
                    data.indexToExpander().put(paramIndex, expander);
                }
            }
        }
        return isHttpAnnotation;
    }
    //......

}

• SpringMvcContract继承了Contract.BaseContract并实现了ResourceLoaderAware接口；其setResourceLoader存储了resourceLoader
• 其覆盖了父类的parseAndValidateMetadata方法，它首先调用父类的parseAndValidateMetadata方法，然后对org.springframework.web.bind.annotation.RequestMapping注解进行进一步解析
• processAnnotationOnClass方法处理了RequestMapping注解；processAnnotationOnMethod方法处理了RequestMapping注解；processAnnotationsOnParameter方法处理了RequestParam、RequestHeader等注解

小结

• Contract定义了parseAndValidatateMetadata方法，该方法返回List形式的MethodMetadata；它有一个抽象类为Contract.BaseContract，它processAnnotationOnClass、processAnnotationOnMethod、processAnnotationsOnParameter的抽象方法需要子类去实现；它的parseAndValidatateMetadata方法的实现主要是调用了parseAndValidateMetadata方法，而该方法会调用processAnnotationOnClass、processAnnotationOnMethod、processAnnotationsOnParameter这些方法
• Contract.Default继承了BaseContract，其processAnnotationOnClass方法处理feign.Headers注解；其processAnnotationOnMethod方法处理feign.RequestLine、feign.Body注解；其processAnnotationsOnParameter方法处理feign.Param、feign.QueryMap、feign.HeaderMap注解
• SpringMvcContract继承了Contract.BaseContract并实现了ResourceLoaderAware接口；其setResourceLoader存储了resourceLoader；其覆盖了父类的parseAndValidateMetadata方法，它首先调用父类的parseAndValidateMetadata方法，然后对org.springframework.web.bind.annotation.RequestMapping注解进行进一步解析；processAnnotationOnClass方法处理了RequestMapping注解；processAnnotationOnMethod方法处理了RequestMapping注解；processAnnotationsOnParameter方法处理了RequestParam、RequestHeader等注解

doc

• Contract