etcd 和zookeeper 很像，都可以用来做配置管理。并且etcd可以在目前流行的Kubernetes中使用。

但是etcd 提供了v2版本合v3的版本的两种api。我们现在分别来介绍一下这两个版本api的使用。

一、Etcd V2版本API

1、java工程中使用maven引入 etcd v2的java api操作jar包

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.21.Final</version>
</dependency>

<dependency>
   <groupId>org.mousio</groupId>
   <artifactId>etcd4j</artifactId>
   <version>2.15.0</version>
</dependency>

2、etcd的链接

import mousio.etcd4j.EtcdClient;
import java.io.InputStream;
import java.net.URI;
import java.util.Properties;


public class EtcdUtil {
    //etcd客户端链接
    private static EtcdClient client = null;
    //链接初始化
    public static synchronized EtcdClient getClient(){
        if (null == client){
                client = new EtcdClient (URI.create(properties.getProperty("http://127.0.0.1:2379")));
        }
        return client;
    }
}
3、如何获取etcd的配置并且对配置进行监听
//初始化获取etcd配置并且进行配置监听

private void initEtcdConfig() {
    EtcdKeysResponse dataTree ;
    try {
        final EtcdClient etcdClient = EtcdUtil.getClient();
//获取etcd中名称叫ETCD文件夹下的配置
        EtcdKeyGetRequest etcdKeyGetRequest = etcdClient.getDir("ETCD").consistent();
        dataTree = etcdKeyGetRequest.send().get();
//获取etcd的版本
        System.out.println("ETCD's version:"+etcdClient.getVersion());
        getConfig("/ETCD/example.config",dataTree); //加载配置项
　　     //启动一个线程进行监听
        startListenerThread(etcdClient);
    } catch (Exception e) {
        System.out.println("EtcdClient init cause Exception:"+e.getMessage());
        e.printStackTrace();
    }
}

private String getConfig(String configFile,EtcdKeysResponse dataTree){
    if(null != dataTree && dataTree.getNode().getNodes().size()>0){
        for(EtcdKeysResponse.EtcdNode node:dataTree.getNode().getNodes()){
            if(node.getKey().equals(configFile)){
                return  node.getValue();
            }
        }
    }
    System.out.println("Etcd configFile"+ configFile+"is not exist,Please Check");
    return null;
}

public void startListenerThread(EtcdClient etcdClient){
    new Thread(()->{
        startListener(etcdClient);
    }).start();
}
public void startListener(EtcdClient etcdClient){
    ResponsePromise promise =null;
    try {
        promise = etcdClient.getDir(SYSTEM_NAME).recursive().waitForChange().consistent().send();
        promise.addListener(promisea -> {
            logger.info("found ETCD's config:{}cause change",ETCD_CONFIG_FILE_NAME);
            try {
                getConfig("/ETCD/example.config", etcdClient.getDir("ETCD").consistent().send().get()); //加载配置项
            } catch (Exception e) {
                e.printStackTrace();
                logger.info("listen etcd 's config change cause exception:{}",e.getMessage());
            }
            startListener(etcdClient);
        });
    } catch (Exception e) {
        startListener(etcdClient);
        System.out.println("listen etcd 's config change cause exception:"+e.getMessage());
        e.printStackTrace();

    }
}
4、使用dcmp管理 etcd的配置项

dcmp 是一个使用go语言开发的etcd配置界面，不足的时，这个只支持v2的API，项目的地址：

https://github.com/silenceper/dcmp

一、Etcd V3版本API

1、在工程引入如下依赖

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.15.Final</version>
</dependency>
<dependency>
    <groupId>com.coreos</groupId>
    <artifactId>jetcd-core</artifactId>
    <version>0.0.2</version>
</dependency>
2、v3 api操作工具类

public class EtcdUtil {
    //etcl客户端链接
    private static Client client = null;
    //链接初始化
    public static synchronized Client getEtclClient(){
        if(null == client){
            client = Client.builder().endpoints(props.getProperty("http://127.0.0.1:2379")).build();
        }
            return client;
    }

    /**
     * 根据指定的配置名称获取对应的value
     * @param key 配置项
     * @return
     * @throws Exception
     */
    public static String getEtcdValueByKey(String key) throws Exception {
        List<KeyValue> kvs = EtcdUtil.getEtclClient().getKVClient().get(ByteSequence.fromString(key)).get().getKvs();
        if(kvs.size()>0){
            String value = kvs.get(0).getValue().toStringUtf8();
            return value;
        }
        else {
            return null;
        }
    }

    /**
     * 新增或者修改指定的配置
     * @param key
     * @param value
     * @return
     */
    public static void putEtcdValueByKey(String key,String value) throws Exception{
        EtcdUtil.getEtclClient().getKVClient().put(ByteSequence.fromString(key),ByteSequence.fromBytes(value.getBytes("utf-8")));

    }

    /**
     * 删除指定的配置
     * @param key
     * @return
     */
    public static void deleteEtcdValueByKey(String key){
         EtcdUtil.getEtclClient().getKVClient().delete(ByteSequence.fromString(key));

    }
}
//V3 api配置初始化和监听
public void init(){

try {
    //加载配置
    getConfig(EtcdUtil.getEtclClient().getKVClient().get(ByteSequence.fromString(ETCD_CONFIG_FILE_NAME)).get().getKvs());
//启动监听线程
    new Thread(() -> {
//对某一个配置进行监听
        Watch.Watcher watcher = EtcdUtil.getEtclClient().getWatchClient().watch(ByteSequence.fromString("etcd_key"));
        try {
            while(true) {
                watcher.listen().getEvents().stream().forEach(watchEvent -> {
                    KeyValue kv = watchEvent.getKeyValue();
　　　　　　　　　　　　//获取事件变化类型
　　　　　　　　　　　　System.out.println(watchEvent.getEventType());
　　               //获取发生变化的key
                  System.out.println(kv.getKey().toStringUtf8());

　　　　　　　　　　//获取变化后的value
                    String afterChangeValue = kv.getValue().toStringUtf8();

                });
            }
        } catch (InterruptedException e) {
            e.printStackTrace();

        }
    }).start();
} catch (Exception e) {
    e.printStackTrace();

}

}

private String getConfig(List<KeyValue> kvs){
    if(kvs.size()>0){
        String config = kvs.get(0).getValue().toStringUtf8();
        logger.info("etcd 's config:{} 's configValue is :{}",ETCD_CONFIG_FILE_NAME,config);
        return config;
    }
    else {
        return null;
    }
}