在微服务架构中，服务注册中心是必不可少的组件，主要提供服务注册与管理的能力。目前使用ServiceComb服用中心的 java 微服务开发者，不仅需要写微服务业务代码，还要写客户端代码去调用 ServiceCenter 的 openAPI 。开发者首先需要熟悉 ServiceCenter 的 openAPI 文档，然后代码实现 http 客户端用于发起请求和接收响应，并绑定 ServiceCenter 配置参数，最后代码实现对服务中心 API 的调用，才能使用上 ServiceCenter 。为了简单化开发者使用 ServiceCenter ， ServiceCenter 客户端实现了上述步骤。开发者只需要添加客户端 jar 包调用 API 就能轻松使用 ServiceCenter ，不需要过多关注 openAPI 文档、不需要写 http 客户端层代码。使用 ServiceComb 客户端，开发者可以轻松调用 ServiceCenter ，更专注于写微服务业务代码。
了解更多ServiceComb-Service-Center： https://docs.servicecomb.io/service-center/zh_CN/index.html
了解更多ServiceCenter客户端： https://github.com/apache/s ervicecomb-java- chassis/tree/master/clients/service-center-client
客户端原理及关键代码解读
1
基于httpClient设计ServiceCenter客户端
客户端发起请求和接收响应
客户端选择httpclient作为底层组件，用于实际发起请求和接收响应，并对请求和响应类进行了封装。代码中get方法对应发起GET请求，调用doRequest方法首先添加服务注册中心信息到封装过的httpRequest请求头部，再基于httpclient组件发起实际的http请求，最后将请求响应结果转化为封装过的httpResponse对象返回。
//make GET request
@Override
public HttpResponse get(HttpRequest request) throws IOException {
request.setMethod(HttpRequest.GET);
return doRequest(request);
}
......
//make http request with httpClient component
public HttpResponse doRequest(HttpRequest httpRequest) throws IOException {
//add cse-serviceregistry-client header to identify client
httpRequest.addHeader(HEADER_CONTENT_TYPE, "application/json");
httpRequest.addHeader(HEADER_USER_AGENT, "cse-serviceregistry-client/1.0.0");
if (globalHeaders != null) {
globalHeaders.forEach(httpRequest::addHeader);
}
//make http request
org.apache.http.HttpResponse response = httpClient.execute(httpRequest.getRealRequest());
int statusCode = response.getStatusLine().getStatusCode();
String messgae = response.getStatusLine().getReasonPhrase();
String context = EntityUtils.toString(response.getEntity(), "UTF-8");
return new HttpResponse(statusCode, messgae, context);
}客户端支持定制化服务中心配置参数。
可以在代码中看到，客户端支持开发者定制服务中心IP、端口、项目名称、租户名称、导入TLSConfig和新增请求头，并通过客户端的Builder方法注入配置。TLSConfig为客户端TLS认证配置类，给客户端导入TLS证书配置，即可开启客户端双向认证模式。
/**
* Customized host, port, projectName, tenantName, TLSConf, headers and any one parameter can be null.
*/
public ServiceCenterClient(String host, int port, String projectName, String tenantName, TLSConfig tlsConfig,
Map<String, String> extraGlobalHeaders) {
HttpTransport httpTransport = HttpTransportFactory.getDefaultHttpTransport();
if (tlsConfig != null) {
httpTransport = new TLSHttpsTransport(tlsConfig);
}
httpTransport.addHeaders(extraGlobalHeaders);
//set configuration parameters
this.httpClient = new ServiceCenterRawClient.Builder()
.setHost(host)
.setPort(port)
.setProjectName(projectName)
.setTenantName(tenantName)
.setHttpTransport(httpTransport).build();
}2
ServiceCenter客户端核心API
服务注册与发现，注册服务和实例到服务注册中心，根据服务ID发现服务实例。registerMicroserviceInstance方法用于注册服务实例，发起httpPOST请求访问服务实例注册URL，并将实例注入到请求body中，返回服务ID字符串; getMicroserviceInstanceList方法用于发现服务的所有实例，根据服务ID，发起httpGET请求访问服务发现URL，返回MicroserviceInstancesResponse对象。
//service register
public String registerMicroserviceInstance(MicroserviceInstance instance, String serviceId) {
try {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
HttpResponse response = httpClient.postHttpRequest("/registry/microservices/" + serviceId + "/instances", null,
mapper.writeValueAsString(instance));
if (response.getStatusCode() == HttpStatus.SC_OK) {
return response.getContent();
} else {
throw new OperationException(
"register service instance fails, statusCode = " + response.getStatusCode() + "; message = " + response
.getMessage()
+ "; content = " + response.getContent());
}
} catch (IOException e) {
throw new OperationException(
"register service instance fails", e);
}
}
//service discovery
public MicroserviceInstancesResponse getMicroserviceInstanceList(String serviceId) {
try {
HttpResponse response = httpClient
.getHttpRequest("/registry/microservices/" + serviceId + "/instances", null, null);
if (response.getStatusCode() == HttpStatus.SC_OK) {
ObjectMapper mapper = new ObjectMapper();
return mapper.readValue(response.getContent(), MicroserviceInstancesResponse.class);
} else {
throw new OperationException(
"get service instances list fails, statusCode = " + response.getStatusCode() + "; message = " + response
.getMessage()
+ "; content = " + response.getContent());
}
} catch (IOException e) {
throw new OperationException(
"get service instances list fails", e);
}
}心跳，服务实例发送心跳告知服务中心。代码中发起httpPUT请求中访问心跳URL，并导入HeartbeatsRequest （包含服务ID和实例ID）到请求body中，响应状态码为200表示心跳成功。
//heartBeats
public void sendHeartBeats(HeartbeatsRequest heartbeatsRequest) {
try {
ObjectMapper mapper = new ObjectMapper();
HttpResponse response = httpClient
.putHttpRequest("/registry/heartbeats", null, mapper.writeValueAsString(heartbeatsRequest));
if (response.getStatusCode() == HttpStatus.SC_OK) {
LOGGER.info("HEARTBEATS SUCCESS");
} else {
throw new OperationException(
"heartbeats fails, statusCode = " + response.getStatusCode() + "; message = " + response.getMessage()
+ "; content = " + response.getContent());
}
} catch (IOException e) {
throw new OperationException(
"heartbeats fails ", e);
}
}3
更多客户端API介绍
参考客户端说明文档 https://github.com/apache/servicecomb-java-chassis/tree/master/clients/service-center-client
ServiceCenter客户端实践
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实践准备
- 启动ServiceComb服务中心： http://servicecomb.apache.org/cn/docs/service-center/install/
- 下载演示代码： https://github.com/zaneChou1/spring-boot-servicecenter
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provider端启动服务，通过客户端注册到ServiceCenter
运行provider模块，启动helloServer服务，并调用客户端API创建客户端对象、创建helloServer服务和实例对象、注册服务和实例到servicecomb 服务中心，并保持30s一次心跳，代码实现如下。
public static void registerMicroservice(){ //new ServiceCenterClient object ServiceCenterClient sc = new ServiceCenterClient(); //new Microservice object and setting properties and serviceName is necessary Microservice microservice = new Microservice(); microservice.setServiceId("1111"); microservice.setServiceName("HelloServer"); //register microservice to service-center sc.registerMicroservice(microservice); //new MicroserviceInstance object and bind server IP and port MicroserviceInstance instance = new MicroserviceInstance(); List<String> endPoints = new ArrayList<String>(); endPoints.add("rest://127.0.0.1:8080/"); instance.setEndpoints(endPoints); //setting instance hostName, instanceId and hostName is necessary instance.setHostName("test"); instance.setInstanceId("2222"); //register microservice instance to service-center sc.registerMicroserviceInstance(instance,microservice.getServiceId()); //send a heartbeat every 30s HeartbeatsRequest heartbeatsRequest = new HeartbeatsRequest("1111","2222"); while(true){ sc.sendHeartBeats(heartbeatsRequest); try { Thread.sleep(30000); } catch (InterruptedException e) { e.printStackTrace(); } }}查看service-center的UI显示如下，helloServer服务注册到服务中心成功，且有一个服务实例test。
访问provider服务监听的8080端口，返回“Hello Spring-Boot-ServiceCenter !”。
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consumer端通过客户端发现服务实例，发起服务调用
运行 consumer模块，启动consumer服务，调用客户端API新建客户端对象、发现helloServer服务实例、获取服务监听的IP和端口，最后调用provider端helloServer服务返回结果。
public static void registerMicroservice(){
//new ServiceCenterClient object
ServiceCenterClient sc = new ServiceCenterClient();
//new Microservice object and setting properties and serviceName is necessary
Microservice microservice = new Microservice();
microservice.setServiceId("1111");
microservice.setServiceName("HelloServer");
//register microservice to service-center
sc.registerMicroservice(microservice);
//new MicroserviceInstance object and bind server IP and port
MicroserviceInstance instance = new MicroserviceInstance();
List<String> endPoints = new ArrayList<String>();
endPoints.add("rest://127.0.0.1:8080/");
instance.setEndpoints(endPoints);
//setting instance hostName, instanceId and hostName is necessary
instance.setHostName("test");
instance.setInstanceId("2222");
//register microservice instance to service-center
sc.registerMicroserviceInstance(instance,microservice.getServiceId());
//send a heartbeat every 30s
HeartbeatsRequest heartbeatsRequest = new HeartbeatsRequest("1111","2222");
while(true){
sc.sendHeartBeats(heartbeatsRequest);
try {
Thread.sleep(30000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}访问consumer端监听的8081端口，返回helloServer的响应结果“Hello Spring-Boot-ServiceCenter !”，consumer端通过ServiceComb服务注册中心调用provider端服务成功。
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