Feign的调用是对接口代理实现的调用，根据上文知道Feign的Bean注册是通过FactoryBean的方式实现FeignClientFactoryBean，其实现方式和mybatis的mapper接口代理实现完全一样。
该代理对象在Feign中得以创建
public class ReflectiveFeign extends Feign {private final ParseHandlersByName targetToHandlersByName;private final InvocationHandlerFactory factory;ReflectiveFeign(ParseHandlersByName targetToHandlersByName, InvocationHandlerFactory factory) {this.targetToHandlersByName = targetToHandlersByName;this.factory = factory;}@Overridepublic <T> T newInstance(Target<T> target) {Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();for (Method method : target.type().getMethods()) {if (method.getDeclaringClass() == Object.class) {continue;} else if(Util.isDefault(method)) {// defaultl方法封装为DefaultMethodHandler去处理DefaultMethodHandler handler = new DefaultMethodHandler(method);defaultMethodHandlers.add(handler);methodToHandler.put(method, handler);} else {// 接口方法封装为methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));}}// 代理对象的创建// 1.invocationHandler对象InvocationHandler handler = factory.create(target, methodToHandler);// 代理对象T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);for(DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {defaultMethodHandler.bindTo(proxy);}return proxy;}}
InvocationHandler的实现是
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();
}
// 最终执行的方法MethodHandler#invoke(args)
return dispatch.get(method).invoke(args);
}
}
MethodHandler的实现如下图
一般情况，非default方法是封装为SynchronousMethodHandler
final class SynchronousMethodHandler implements MethodHandler {
private static final long MAX_RESPONSE_BUFFER_SIZE = 8192L;
// feign配置信息
private final MethodMetadata metadata;
private final Target<?> target;
private final Client client;// http客户端实现
private final Retryer retryer;// 重试机制
private final List<RequestInterceptor> requestInterceptors;// 拦截器
private final Logger logger;// 日志
private final Logger.Level logLevel;// 日志级别
private final RequestTemplate.Factory buildTemplateFromArgs;
private final Options options;// 超时选项配置等
private final Decoder decoder;// 解码
private final ErrorDecoder errorDecoder;
private final boolean decode404;
@Override
public Object invoke(Object[] argv) throws Throwable {
// 编码等操作
RequestTemplate template = buildTemplateFromArgs.create(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
// 执行
return executeAndDecode(template);
} catch (RetryableException e) {
// 异常重试
retryer.continueOrPropagate(e);
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}
// do执行
Object executeAndDecode(RequestTemplate template) throws Throwable {
Request request = targetRequest(template);
// 日志的打印
if (logLevel != Logger.Level.NONE) {
logger.logRequest(metadata.configKey(), logLevel, request);
}
Response response;
long start = System.nanoTime();
try {
// 执行请求，可能是httpClient或okhttp之类，亦或者是ribbon封装的负载均衡客户端等等
response = client.execute(request, options);
// ensure the request is set. TODO: remove in Feign 10
response.toBuilder().request(request).build();
} catch (IOException e) {
if (logLevel != Logger.Level.NONE) {
logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
}
throw errorExecuting(request, e);
}
long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
boolean shouldClose = true;
try {
if (logLevel != Logger.Level.NONE) {
response =
logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime);
// ensure the request is set. TODO: remove in Feign 10
response.toBuilder().request(request).build();
}
if (Response.class == metadata.returnType()) {
if (response.body() == null) {
return response;
}
if (response.body().length() == null ||
response.body().length() > MAX_RESPONSE_BUFFER_SIZE) {
shouldClose = false;
return response;
}
// Ensure the response body is disconnected
// 响应字节流
byte[] bodyData = Util.toByteArray(response.body().asInputStream());
return response.toBuilder().body(bodyData).build();
}
if (response.status() >= 200 && response.status() < 300) {
if (void.class == metadata.returnType()) {
return null;
} else {
// 解码
return decode(response);
}
} else if (decode404 && response.status() == 404) {
return decode(response);
} else {
throw errorDecoder.decode(metadata.configKey(), response);
}
} catch (IOException e) {
if (logLevel != Logger.Level.NONE) {
logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);
}
throw errorReading(request, response, e);
} finally {
if (shouldClose) {
ensureClosed(response.body());
}
}
}
// 调用解码工具解码
Object decode(Response response) throws Throwable {
try {
return decoder.decode(response, metadata.returnType());
} catch (FeignException e) {
throw e;
} catch (RuntimeException e) {
throw new DecodeException(e.getMessage(), e);
}
}
}
SynchronousMethodHandler的主要功能就是执行Feign定义的流程，对请求编码，使用配置的http客户端发起请求，对响应进行解码，以及失败重试等等操作。
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