1.说明

本文介绍SpringCloud发现服务代码的开发，
通过使用EurekaClient,DiscoveryClient来发现注册中心的服务等，
从而可以自定义客户端对注册中心的高级用法。

2.使用EurekaClient发现服务

通过Spring自动注入的EurekaClient，
不仅能发现服务实例，
还能查看客户端连接等各种配置。

2.1.代码

package com.yuwen.spring.config.client.controller;

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.netflix.eureka.EurekaClientConfigBean;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import com.netflix.appinfo.InstanceInfo;
import com.netflix.discovery.EurekaClient;
import com.netflix.discovery.EurekaClientConfig;
import com.netflix.discovery.shared.Application;
import com.netflix.discovery.shared.Applications;

@RestController
public class EurekaClientController {
    private static Logger logger = LoggerFactory.getLogger(DiscoveryClientController.class);

    @Autowired
    private EurekaClient eurekaClient;

    @GetMapping("/eureka")
    public String getEurekaClient() {
        EurekaClientConfig config = eurekaClient.getEurekaClientConfig();
        if (!(config instanceof EurekaClientConfigBean)) {
            return eurekaClient.toString();
        }
        EurekaClientConfigBean eurekaConfig = (EurekaClientConfigBean) config;
        logger.info("serviceUrl=" + eurekaConfig.getServiceUrl());
        Applications applications = eurekaClient.getApplications();
        List<Application> registeredApplications = applications.getRegisteredApplications();
        for (Application application : registeredApplications) {
            logger.info("Application Name=" + application.getName());
            List<InstanceInfo> instances = application.getInstances();
            for (InstanceInfo instance : instances) {
                StringBuilder sb = new StringBuilder();
                sb.append(instance.getAppName()).append("\t").append(instance.getHostName()).append("\t")
                        .append(instance.getPort()).append("\t").append(instance.getVIPAddress());
                logger.info("InstanceInfo=" + sb);
            }
        }

        return eurekaClient.toString();
    }
}

2.2.测试

使用浏览器访问：
http://localhost:8005/eureka
页面返回：

org.springframework.cloud.netflix.eureka.CloudEurekaClient@6715470c

控制台打印：

serviceUrl={fetch-registry=true, defaultZone=http://localhost:7007/eureka, register-with-eureka=true}
Application Name=CONFIG-CLIENT
InstanceInfo=CONFIG-CLIENT  192.168.171.1   8005    config-client

3.使用DiscoveryClient发现服务

使用DiscoveryClient可以发现注册中心上的服务，
注册中心可以是Eureka，也可以是Zookeeper等，
因为不使用原始Netflix EurekaClient，
所以在某种包装器后面的DiscoveryClient更易于使用。
它也能提供通过服务名称查询对应的所有服务实例等功能。

3.1.代码

package com.yuwen.spring.config.client.controller;

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class DiscoveryClientController {
    private static Logger logger = LoggerFactory.getLogger(DiscoveryClientController.class);

    @Autowired
    private DiscoveryClient discoveryClient;

    @GetMapping("/discovery")
    public Object getDiscoveryClient() {
        List<String> services = discoveryClient.getServices();
        for (String service : services) {
            logger.info("service=" + service);
        }

        String serviceId = "CONFIG-CLIENT";
        List<ServiceInstance> instances = discoveryClient.getInstances(serviceId);
        for (ServiceInstance instance : instances) {
            StringBuilder sb = new StringBuilder();
            sb.append(instance.getServiceId()).append("\t").append(instance.getHost()).append("\t")
                    .append(instance.getPort()).append("\t").append(instance.getUri());
            logger.info("instance=" + sb);
        }
        return discoveryClient;
    }
}

3.1.测试

使用浏览器访问：
http://localhost:8005/discovery

页面返回：

config-client00config-client0

控制台打印：

service=config-client
instance=CONFIG-CLIENT  192.168.171.1   8005    http://192.168.171.1:8005

可以看到Eureka上面只有一个服务CONFIG-CLIENT，
这个服务只有一个实例http://192.168.171.1:8005，
其实就是提供http://localhost:8005/discovery这个服务的实例。