SpringCloud-service 服务提供

微服务架构中，一般存在2种服务，一种是消费服务，一种是提供服务，消费服务在 SpringCloud-feign 声明式服务调用这一篇文章中已讲过，本章我们主要讲解提供服务

不论是什么服务，都需要注册中心，可以参考 SpringCloud-eureka构建简单注册中心或SpringCloud-eureka高可用注册中心，启动注册中心后，消费服务和提供服务才能注册。

下面创建一个Gradle工程，工程依赖如下(这里使用boot1.5.x)：

dependencyManagement {
    imports {
        mavenBom 'org.springframework.cloud:spring-cloud-dependencies:Edgware.SR4'
    }
}

dependencies {
    compile('org.springframework.boot:spring-boot-starter')
    compile('org.springframework.boot:spring-boot-starter-web')
    compile 'org.slf4j:slf4j-api:1.7.14'
    compile('org.springframework.cloud:spring-cloud-starter-eureka')
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

配置文件application.properties如下：

spring.application.name=hello-service
# 单机
eureka.client.serviceUrl.defaultZone=http://localhost:1111/eureka/
server.port=8081

配置启动类，将启动服务配置为可发现的服务，如下：

@EnableDiscoveryClient
@SpringBootApplication
public class CloudApplication {
    public static void main(String[] args) {
        SpringApplication.run(CloudApplication.class, args);
    }
}

接着，创建controller，定义相应在的服务接口，如下：

@RestController
public class HelloController {
    private final Logger logger = LoggerFactory.getLogger(HelloController.class);

    @Autowired
    private DiscoveryClient client;

    @RequestMapping(value = "/hello", method = RequestMethod.GET)
    public String hello() throws Exception {
        ServiceInstance instance = client.getLocalServiceInstance();

        logger.info("/hello, host:" + instance.getHost() + ", service_id:" + instance.getServiceId());
        return "Hello World";
    }

    @RequestMapping(value = "/hello1", method = RequestMethod.GET)
    public String hello(@RequestParam String name) {
        ServiceInstance instance = client.getLocalServiceInstance();
        logger.info("/hello1, host:" + instance.getHost() + ", service_id:" + instance.getServiceId());
        return "Hello " + name;
    }

    @RequestMapping(value = "/hello2", method = RequestMethod.GET)
    public User hello(@RequestHeader String name, @RequestHeader Integer age) {
        ServiceInstance instance = client.getLocalServiceInstance();
        logger.info("/hello2, host:" + instance.getHost() + ", service_id:" + instance.getServiceId());
        return new User(name, age);
    }

    @RequestMapping(value = "/hello3", method = RequestMethod.POST)
    public String hello(@RequestBody User user) {
        ServiceInstance instance = client.getLocalServiceInstance();
        logger.info("/hello3, host:" + instance.getHost() + ", service_id:" + instance.getServiceId());
        return "Hello "+ user.getName() + ", " + user.getAge();
    }

这样就可以被消费服务消费了，如restTemplate.getForEntity("http://HELLO-SERVICE/hello", String.class).getBody()
虽然实现了service的服务接口，但却有个问题，提供服务的接口不容易被消费服务知道，如何解决这个问题呢？

我们可以抽取一个通用的服务，将url写在这个服务上，如下：

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

    @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);

}

这个服务可以放在一个单独的工程内，受maven/gradle管理，这样就可以在消费端和提供端共享，下面看下新的controller如下：

@RestController
public class RefactorHelloController 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) {
        return new User(name, age);
    }

    @Override
    public String hello(@RequestBody User user) {
        return "Hello "+ user.getName() + ", " + user.getAge();
    }

}

新的controller只需实现这个接口服务就可以了。
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