先看示例代码
@RestController
@RequestMapping("/students")
public class StudentController {
@Autowired
private TeacherFeignClient teacherFeignClient;
@GetMapping("/{id}")
public ResponseEntity getTeacher(@PathVariable("id") int id) {
return ResponseEntity.ok(teacherFeignClient.findTeacher(5));
}
}
@FeignClient(name = "teacher-service",path = "/teachers")
public interface TeacherFeignClient {
@GetMapping("/{id}")
Teacher findTeacher(@PathVariable("id") int id);
}
- 首先我们肯定知道spring会基于TeacherFeignClient生成代理类Proxy,代理类的代码如下
public final Teacher findTeacher(int var1) throws {
try {
return (Teacher)super.h.invoke(this, m3, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
代理类中的invoke方法指向的是feign.ReflectiveFeign.FeignInvocationHandler.invoke方法,之后会走向调用SynchronousMethodHandler invoke方法,其中SynchronousMethodHandler中的target属性就是包装了feignclient的相关属性,比如service,url等; 在这个类里面还有一些很重要的属性,比如List
然后会调用executeAndDecode方法,该方法第一步就会根据target构造Request对象,这个方法最终会调用Cilent接口的实现类LoadBalancerFeignClient。
@Override
public Response execute(Request request, Request.Options options) throws IOException {
try {
URI asUri = URI.create(request.url());
String clientName = asUri.getHost();
URI uriWithoutHost = cleanUrl(request.url(), clientName);
FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
this.delegate, request, uriWithoutHost);
IClientConfig requestConfig = getClientConfig(options, clientName);
return lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
requestConfig).toResponse();
}
catch (ClientException e) {
IOException io = findIOException(e);
if (io != null) {
throw io;
}
throw new RuntimeException(e);
}
}
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- LoadBalancerFeignClient execute方法先构造RibbonRequest,然后会去获取IClientConfig,再去调用SpringClientFactory的getInstance方法,走到NamedContextFactory getInstance方法。
@Override
public C getInstance(String name, Class type) {
C instance = super.getInstance(name, type);
if (instance != null) {
return instance;
}
IClientConfig config = getInstance(name, IClientConfig.class);
return instantiateWithConfig(getContext(name), type, config);
}
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- 最终会通过AnnotationConfigApplicationContext getBean方法经过一些列流程走到 RibbonClientConfiguration 装载IClientConfig bean方法,最后就获得了当前service ribbon的相关配置
@Bean
@ConditionalOnMissingBean
public IClientConfig ribbonClientConfig() {
DefaultClientConfigImpl config = new DefaultClientConfigImpl();
config.loadProperties(this.name);
config.set(CommonClientConfigKey.ConnectTimeout, DEFAULT_CONNECT_TIMEOUT);
config.set(CommonClientConfigKey.ReadTimeout, DEFAULT_READ_TIMEOUT);
config.set(CommonClientConfigKey.GZipPayload, DEFAULT_GZIP_PAYLOAD);
return config;
}
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- 回到LoadBalancerFeignClient execute方法64行获取到IClientConfig后,此时有个核心步骤就是根据当前clientName获取到一个FeignLoadBalancer的实现,可以看到其中有一个cache属性,如果cache有的话就从cache返回,这也就feign第一次调用会慢的原因之一,因为首次需要去加载这个FeignLoadBalancer;首次加载的时候因为这里我们没有配置retryFactory,所以会返回一个 FeignLoadBalancer
public FeignLoadBalancer create(String clientName) {
FeignLoadBalancer client = this.cache.get(clientName);
if(client != null) {
return client;
}
IClientConfig config = this.factory.getClientConfig(clientName);
ILoadBalancer lb = this.factory.getLoadBalancer(clientName);
ServerIntrospector serverIntrospector = this.factory.getInstance(clientName, ServerIntrospector.class);
client = loadBalancedRetryFactory != null ? new RetryableFeignLoadBalancer(lb, config, serverIntrospector,
loadBalancedRetryFactory) : new FeignLoadBalancer(lb, config, serverIntrospector);
this.cache.put(clientName, client);
return client;
}
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- 获取到FeignLoadBalancer会执行它父类AbstractLoadBalancerAwareClient中的executeWithLoadBalancer(该方法中牵扯到负载均衡的逻辑,会在下一篇中说到),该方法最终还是会执行FeignLoadBalancer的execute方法,方法中会获取request的client,该client默认是feign.Client.Default,实现就是通过构造HttpURLConnection发起http请求
@Override
public RibbonResponse execute(RibbonRequest request, IClientConfig configOverride)
throws IOException {
Request.Options options;
if (configOverride != null) {
RibbonProperties override = RibbonProperties.from(configOverride);
options = new Request.Options(
override.connectTimeout(this.connectTimeout),
override.readTimeout(this.readTimeout));
}
else {
options = new Request.Options(this.connectTimeout, this.readTimeout);
}
Response response = request.client().execute(request.toRequest(), options);
return new RibbonResponse(request.getUri(), response);
}
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Original: https://www.cnblogs.com/minjay/p/15897845.html
Author: minjay26
Title: 从服务间的一次调用分析整个springcloud的调用过程(二)
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