【Spring Cloud】--声明式服务调用Feign

Feign 就是整合了spring cloud的Ribbon和Hystrix两个组件的更高一级封装的组件

快速入门：

使用http://blog.csdn.net/wangpengzhi19891223/article/details/78840646中的基础工程。

第一步： 在consumer中引入feign 组件

<!-- 声明式服务调用-->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
</dependency>
</dependencies>

整个项目结构：



pom文件：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>

<groupId>spring-eureka-client</groupId>
<artifactId>spring-eureka-client</artifactId>
<version>1.0-SNAPSHOT</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.9.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>

<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<!-- 加入监控开始 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<!-- 加入监控结束 -->

<!-- 增加Eureka开始 -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka-server</artifactId>
</dependency>
<!-- 增加Eureka结束 -->

<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-ribbon</artifactId>
</dependency>

<!-- 容错保护机制 -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>

<!-- 声明式服务调用-->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Camden.SR6</version>
<!-- Dalston.SR1 -->
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>

</project>

ConsumerApplication.java

@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class ConsumerApplication {

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

ConsumerController.java

@RestController
public class ConsumerController {
@Autowired
private HelloService helloService;

@RequestMapping(value = "/consumer", method = RequestMethod.GET)
public String helloConsumer(){
String str1 = helloService.hello("wpz");
User user1 = helloService.hello("wpz", 18);
User user = new User();
user.setAge(20);
user.setName("yx");
String str2 = helloService.hello(user);
return  helloService.hello()+str1+","+user1.getName()+user1.getAge()+","+str2;
}
}

HelloService.java

@FeignClient("hello-service")
public interface HelloService {

@RequestMapping("/hello")
String hello();

@RequestMapping(value = "/hello1", method = RequestMethod.GET)
String hello(@RequestParam("name") String name);

@RequestMapping(value = "/hello2", method = RequestMethod.GET)
User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age);

@RequestMapping(value = "/hello3", method = RequestMethod.POST)
String hello(@RequestBody User user);
}

User.java

public class User {
private String name;

private Integer age;

public User(){}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Integer getAge() {
return age;
}

public void setAge(Integer age) {
this.age = age;
}
}

服务端：

项目结构：



User对象和上面的一样，值需要修改Controller.java就可以了。

@RestController
public class HelloController {

private final Logger logger = Logger.getLogger(HelloController.class);
@Autowired
private DiscoveryClient client;

@RequestMapping(value = "/hello", method = RequestMethod.GET)
public String index() throws Exception{
ServiceInstance instance = client.getLocalServiceInstance();
int sleepTime = new Random().nextInt(3000);
logger.info("sleeptime"+sleepTime);
Thread.sleep(sleepTime);
logger.info("host:"+instance.getHost()+instance.getServiceId()+":"+instance.getPort());
return "New Hello world server!";
}

@RequestMapping(value = "/hello1", method = RequestMethod.GET)
public String hello(@RequestParam("name") String name){
return "hello"+name;
}

@RequestMapping(value = "/hello2", method = RequestMethod.GET)
public User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age){
User user = new User();
user.setAge(age);
user.setName(name);
return user;
}

@RequestMapping(value = "/hello3", method = RequestMethod.POST)
public String hello(@RequestBody User user){
return "hello" +user.getName()+"年龄："+user.getAge();
}
}

测试：

访问http://localhost:9000/consumer 会得到如下输出：

New Hello world server!hellowpz,wpz18,helloyx年龄：20

通过继承减少代码：

上面的例子中User对象明显是重复的，HelloService中也有很多的重复，我们可以抽取出一个单独的工程api, 两个项目中引用这个工程即可。



HelloService.java

@RequestMapping("/refactor")
public interface HelloService {

@RequestMapping(value = "/hello4", method = RequestMethod.GET)
String hello(@RequestParam("name") String name);

@RequestMapping(value = "/hello5", method = RequestMethod.GET)
User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age);

@RequestMapping(value = "/hello6", method = RequestMethod.POST)
String hello(@RequestBody User user);
}

改造service中的HelloService 重命名为RefactorHelloService

RefactorHelloService.java

@RestController
public class RefactorHelloService implements HelloService{

@Override
public String hello(@RequestParam("name") String name){
return "hello"+name;
}
@Override
public User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age){
User user = new User();
user.setAge(age);
user.setName(name);
return user;
}
@Override
public String hello(@RequestBody User user){
return "hello" +user.getName()+"年龄："+user.getAge();
}
}

可以看见没有RequestMapping的声明，不仅仅减少了代码，也减少了出错的概率。

consumer中新建RefactorHelloService.java

@FeignClient("hello-service")
public interface RefactorHelloService extends HelloService{
}

可以看的出来，除了继承接口之外，没有任何代码。

优点显而易见，缺点是两面工程都依赖api,api产生变动，回对项目产生影响。

增加断路器功能实现自动降级：

需要改造两个类：

consumer中新增RefactorHelloFalBackService.java

@Component
public class RefactorHelloFalBackService implements RefactorHelloService{

public String hello(@RequestParam("name") String name){
return "error";
}

public User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age){
User user = new User();
user.setName("error");
user.setAge(0);
return user;
}

public String hello(@RequestBody User user){
return "error";
}
}

consumer中RefactorHelloService.java

@FeignClient(value = "hello-service", fallback = RefactorHelloFalBackService.class)
public interface RefactorHelloService{

@RequestMapping(value = "/hello1", method = RequestMethod.GET)
String hello(@RequestParam("name") String name);

@RequestMapping(value = "/hello2", method = RequestMethod.GET)
User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age);

@RequestMapping(value = "/hello3", method = RequestMethod.POST)
String hello(@RequestBody User user);
}