springcloud(第八篇)springcloud feign

# spring cloud feign

introduction

netflix feign

是一个类似

retrofit

进行http调用框架，

Feign makes writing java http clients easier

使得编写

http client

代码更加简单

netflix feign

直接给出一段简单的案例

package com.lkl.netflix.feign;

import feign.*;
import feign.codec.ErrorDecoder;
import feign.codec.Decoder;
import feign.gson.GsonDecoder;

import java.io.IOException;
import java.util.List;

/**
* Created by liaokailin on 16/5/9.
*/
public class GitHubExample {

interface GitHub {  // 1
@RequestLine("GET /repos/{owner}/{repo}/contributors")
List<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);
}

public static void main(String... args) {
Decoder decoder = new GsonDecoder();  // 2
GitHub github = Feign.builder()
.decoder(decoder) // 3
.errorDecoder(new GitHubErrorDecoder(decoder))  // 4
.logger(new Logger.ErrorLogger())  // 5
.logLevel(Logger.Level.BASIC)  // 5
.target(GitHub.class, "https://api.github.com");  // 6

System.out.println("Let's fetch and print a list of the contributors to this library.");
List<Contributor> contributors = github.contributors("netflix", "feign");  // 7
for (Contributor contributor : contributors) {
System.out.println(contributor.login + " (" + contributor.contributions + ")");
}

System.out.println("Now, let's cause an error.");
try {
github.contributors("netflix", "some-unknown-project");  // 8
} catch (GitHubClientError e) {
System.out.println(e.getMessage());
}
}

static class Contributor {
String login;
int contributions;
}

static class GitHubClientError extends RuntimeException {  // 4
private String message; // parsed from json

@Override
public String getMessage() {
return message;
}
}

static class GitHubErrorDecoder implements ErrorDecoder {   // 4

final Decoder decoder;
final ErrorDecoder defaultDecoder = new ErrorDecoder.Default();

GitHubErrorDecoder(Decoder decoder) {
this.decoder = decoder;
}

@Override
public Exception decode(String methodKey, Response response) {
try {
return (Exception) decoder.decode(response, GitHubClientError.class);
} catch (IOException fallbackToDefault) {
return defaultDecoder.decode(methodKey, response);
}
}
}

}

1.首先定义接口

GitHub

,使用注解

RequestLine

表明

contributors()

方法为一个

get

请求，请求相对为

/repos/{owner}/{repo}/contributors

2.

Decoder decoder = new GsonDecoder();

创建一个

GsonDecoder

解码器，表明通过

Gson

解析返回数据

3.

decoder()

方法设置解码器

4.

errorDecoder()

指定发生异常时的解码器，需要实现

ErrorDecoder

接口，覆写

decode

方法，通过指定的

Decoder

解析错误信息，这里还是使用

GsonDecoder

5.logger 相关的表示配置日志系你系

6.

target()

方法指定访问url以及返回的类型

7.通过创建的

github

对象调用

contributors

获取结果

8.模拟异常情况

note:

feign

使用起来很简单，其原理和

retrofit

及其类似，通过接口定义访问访问，用jdk的动态代理创建接口的实现类，在类中解析方法上的注解信息用以识别用户配置的http请求信息，然后执行请求；

feign可以通过

ReflectiveFeign

下的

newInstance()

方法看到

return (T) Proxy
.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);

spring cloud feign

spring cloud feign

通过注解的封装使用起来更加简单

package com.lkl.springcloud.feign;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
* Created by liaokailin on 16/5/11.
*/
@Configuration
@EnableAutoConfiguration
@EnableFeignClients
@RestController
public class Application {

@Autowired
GitHub gitHub;
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}

@FeignClient(url = "https://api.github.com")
interface GitHub {
@RequestMapping(value = "/repos/{owner}/{repo}/contributors", method = RequestMethod.GET)
ResponseEntity<List<Contributor>> contributors(@PathVariable("owner") String owner, @PathVariable("repo") String repo);
}

@RequestMapping("/")
public void test(){
ResponseEntity< List<Contributor>>  responseEntity  =   gitHub.contributors("netflix", "feign");
List<Contributor> contributors = responseEntity.getBody();
for (Contributor contributor : contributors) {
System.out.println(contributor.login + " (" + contributor.contributions + ")");
}
}

static class Contributor {
String login;
int contributions;
}
}

注解

EnableFeignClients

表明需要扫描使用

FeignClient

注解的接口，在代码中定义了

@FeignClient(url = "https://api.github.com")

表明该接口为一个feign接口

通过

url

指定访问路径

RequestMapping

表明相对路径

在代码中注入bean

GitHub

，直接调用其中申明的方法即可。

重点说明下

FeignClient

注解

该注解表示申明创建一个rest client bean,可以直接通过

Autowired

注入使用，如果ribbon在工程中启用，则会使用

load balance

进行后端请求调用，可以为

FeignClient

指定value表明需要访问的serviceId

feign + ribbon + eureka

在springcloud(第七篇)springcloud ribbon with eureka中讲解了ribbon+eureka，其中使用

RestTemplate

进行调用，也可以通过

feign

调用

package com.lkl.springcloud.feign;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.cloud.netflix.ribbon.RibbonClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import static org.springframework.web.bind.annotation.RequestMethod.GET;

/**
* Created by liaokailin on 16/5/9.
*/
@SpringBootApplication
@EnableDiscoveryClient
@RestController
@RibbonClient("hello")
@EnableFeignClients
public class Application {

@Autowired
HelloClient client;

@RequestMapping("/")
public String hello() {
return client.hello();
}

public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}

@FeignClient("simple")
interface HelloClient {
@RequestMapping(value = "/", method = GET)
String hello();
}

}

使用

@FeignClient("simple")

指定要访问的

service id

由于

hello()

对应的mapping为

@RequestMapping(value = "/", method = GET)

那么该方法实际调用url为

http://simple/

，因此在执行

@RequestMapping("/")
public String hello() {
return client.hello();
}

调用的为

SimpleApplication.java

中

@RequestMapping("/")
public String hello() {
return "Hello";
}

ok ~ it’s work ! more about is here