SpringCloud生产消费者

生产者与消费者

上一篇文章介绍了Euarka的搭建，SpringCloud服务注册中心 本篇文章，我们搭建俩个服务，生产者服务与消费者服务。

本文就以电商系统为例：服务生产者，订单查询服务order-server，服务消费者order-client

说明：order-server 服务提供查询订单信息的功能
order-client作为消费者服务，查询订单信息。

生产者服务搭建

选择我们需要的依赖,具体依赖如下

<dependency>
  <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

spring-cloud-starter-netflix-eureka-client 表示该服务是一个eureka的客户端 订单服务会注册到eureka服务端上

依赖添加完成后，我们需要在SpringBoot项目的入口类上加上 @EnableDiscoveryClient注解

表示开启服务注册到eureka服务上

@SpringBootApplication
@EnableDiscoveryClient
public class OrderServiceApplication {

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

}

接下来，需要我们对订单服务进行必要的配置

server:
  port: 8081

spring:
  application:
    name: order-service

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

说明：server.prot:订单服务的端口

spring.application.name:订单服务的名称，

这个名称会注册到eureka服务上

eureka.client.service-url.defaultZone:eureka服务的地址。

经过简单的配置以后，我们启动服务，访问eureka服务,http://localhost:8761，如下图：

我们将订单服务以及注册到eureka服务上了。此事， 我们提供一个订单查询的接口，模拟订单查询功能。

@RestController
@RequestMapping("query")
public class OrderQueryController {
    @Autowired
    OrderQueryService queryService;

    @RequestMapping("info")
    public String queryOrder(){
        return queryService.queryOrder();
    }
}


@Service
public class OrderQueryService {

    public String queryOrder(){
        return "订单信息查询成功";
    }
}

消费者服务搭建

只需要像搭建服务提供者一样搭建服务消费者就可以， 搭建完成以后，我们使用RestTemplate 来调用订单服务进行订单信息查询，具体配置及代码如下：

server:
  port: 8082

spring:
  application:
    name: order-client

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

//提供一个RestTemplate实例
@SpringBootApplication
@EnableDiscoveryClient
public class OrderClientApplication {

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

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

//编写测试接口
@RestController
public class ClientController {
    @Autowired
    ClientService clientService;

    @RequestMapping(value = "/info",method = RequestMethod.GET)
    public String queryOrderInfo(){
        return "restTemplate访问服务提供者返回的信息:"+clientService.queryOrderInfo();
    }
}

//模拟具体查询业务逻辑
@Service
public class ClientService {

    @Autowired
    RestTemplate restTemplate;

    public String queryOrderInfo(){
        System.out.println("通过restTemplate访问服务提供者");
        return restTemplate.getForEntity("http://ORDER-SERVER/query/info", 			  String.class).getBody();
    }

}

RestTemplate 介绍：
是spring框架提供的可用于在应用中调用rest服务，它简化了与http服务的通信方式，统一了RESTful的标准，封装了http链接， 我们只需要传入url及返回值类型即可。相较于之前常用的HttpClient，RestTemplate是一种更优雅的调用RESTful服务的方式。

源码分析

部分源码如下，可以看出，它包含了Get、Post、Put等请求，比如Get请求包含俩种方法getForObject、getForEntity,他们有什么区别呢？

• 从接口的签名上，可以看出一个是直接返回预期的对象，一个则是将对象包装到 ResponseEntity 封装类中
• 如果只关心返回结果，那么直接用 getForObject 即可
• 如果除了返回的实体内容之外，还需要获取返回的header等信息，则可以使用 getForEntity

@Override
	@Nullable
	public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException {
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T getForObject(URI url, Class<T> responseType) throws RestClientException {
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor);
	}

	@Override
	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables)
			throws RestClientException {

		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables)
			throws RestClientException {

		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException {
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor));
	}


	// HEAD

	@Override
	public HttpHeaders headForHeaders(String url, Object... uriVariables) throws RestClientException {
		return nonNull(execute(url, HttpMethod.HEAD, null, headersExtractor(), uriVariables));
	}

	@Override
	public HttpHeaders headForHeaders(String url, Map<String, ?> uriVariables) throws RestClientException {
		return nonNull(execute(url, HttpMethod.HEAD, null, headersExtractor(), uriVariables));
	}

	@Override
	public HttpHeaders headForHeaders(URI url) throws RestClientException {
		return nonNull(execute(url, HttpMethod.HEAD, null, headersExtractor()));
	}


	// POST

	@Override
	@Nullable
	public URI postForLocation(String url, @Nullable Object request, Object... uriVariables)
			throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor(), uriVariables);
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public URI postForLocation(String url, @Nullable Object request, Map<String, ?> uriVariables)
			throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor(), uriVariables);
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public URI postForLocation(URI url, @Nullable Object request) throws RestClientException {
		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor());
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType,
			Object... uriVariables) throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType,
			Map<String, ?> uriVariables) throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T postForObject(URI url, @Nullable Object request, Class<T> responseType)
			throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<>(responseType, getMessageConverters());
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor);
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request,
			Class<T> responseType, Object... uriVariables) throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request,
			Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(URI url, @Nullable Object request, Class<T> responseType)
			throws RestClientException {

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor));
	}

接下来，我们启动，服务消费者， 此时访问我们的eureka服务， 已经有俩个服务注册上来了，如下：

最后我们来验证一下，服务消费者是否能调用到服务提供者， 在浏览器输出http://localhost:8082/info

根据返回的信息，确认服务调用成功。

小结

以上就是我们基于eureka的服务注册发现机制，实现的服务之间的相互调用。 当然，这里边还有很多的细节需要讨论，后续的文章，继续和大家讨论。