【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);
}