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zookeeper典型应用场景总结

分布式一致性配置

　　在集群环境下，挨个更改配置是比较繁琐的，使用zookeeper可以实现同步配置。

1、配置信息

 1 package com.zk;
 2 
 3 import java.io.Serializable;
 4 
 5 /**
 6  * 模拟公共配置类
 7  * 
 8  * @author Zomi
 9  */
10 public class DbConfig implements Serializable{
11     private static final long serialVersionUID = -4483388642208582886L;
12     
13     // 数据库配置,有默认值
14     private String url = "jdbc:mysql://127.0.0.1:3306/mydata?useUnicode=true&characterEncoding=utf-8";
15     private String username = "root";
16     private String password = "root";
17     private String driverClass = "com.mysql.jdbc.Driver";
18 
19 
20     public DbConfig(String url, String username, String password, String driverClass) {
21         this.url = url;
22         this.username = username;
23         this.password = password;
24         this.driverClass = driverClass;
25     }
26 
27     public DbConfig() {}
28     
29     public String getUrl() {
30         return url;
31     }
32 
33     public void setUrl(String url) {
34         this.url = url;
35     }
36 
37     public String getUsername() {
38         return username;
39     }
40 
41     public void setUsername(String username) {
42         this.username = username;
43     }
44 
45     public String getPassword() {
46         return password;
47     }
48 
49     public void setPassword(String password) {
50         this.password = password;
51     }
52 
53     public String getDriverClass() {
54         return driverClass;
55     }
56 
57     public void setDriverClass(String driverClass) {
58         this.driverClass = driverClass;
59     }
60 
61     @Override
62     public String toString() {
63         return "CommConfig [url=" + url + ", username=" + username + ", password=" + password + ", driverClass="
64                 + driverClass + "]";
65     }
66 
67 }

View Code

2、配置管理服务

 1 package com.zk;
 2 
 3 import org.I0Itec.zkclient.ZkClient;
 4 
 5 /**
 6  * zk配置管理服务器，用于将配置信息的修改同步到zk上
 7  * @author Zomi
 8  */
 9 public class ZkConfigMng {
10     private String nodePath = "/dbConfig";
11     private DbConfig dbConfig;
12     private ZkClient zkClient;
13     
14     public ZkConfigMng() {
15         this.zkClient = new ZkClient("192.168.31.130:2181");
16     }
17     //更新配置
18     public DbConfig update(DbConfig dbConfig) {
19         this.dbConfig = dbConfig;
20         syncConfigToZookeeper();//将配置变更同步给zk
21         return dbConfig;
22     }
23     private void syncConfigToZookeeper() {
24         if(!zkClient.exists(nodePath)) {
25             zkClient.createPersistent(nodePath);
26         }
27         zkClient.writeData(nodePath, dbConfig);
28     }
29 }

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3、模拟应用服务集群，具备监听配置变更的功能

 1 package com.zk;
 2 
 3 import java.util.concurrent.TimeUnit;
 4 
 5 import org.I0Itec.zkclient.IZkDataListener;
 6 import org.I0Itec.zkclient.ZkClient;
 7 import org.I0Itec.zkclient.ZkConnection;
 8 
 9 /**
10  * 模拟多服务器
11  * 
12  * @author Zomi
13  */
14 public class ZkConfigClient implements Runnable {
15 
16     private String nodePath = "/dbConfig";
17     private DbConfig dbConfig;
18     
19     @Override
20     public void run() {
21         ZkClient zkClient = new ZkClient(new ZkConnection("192.168.31.130:2181", 5000));
22         while (!zkClient.exists(nodePath)) {
23             System.out.println("配置节点不存在!");
24             try {
25                 TimeUnit.SECONDS.sleep(1);
26             } catch (InterruptedException e) {
27                 e.printStackTrace();
28             }
29         }
30         dbConfig = (DbConfig)zkClient.readData(nodePath);
31         System.out.println(Thread.currentThread().toString() +"原数据为=="+ dbConfig);
32         
33         //监听配置数据的改变
34         zkClient.subscribeDataChanges(nodePath, new IZkDataListener() {
35             @Override
36             public void handleDataDeleted(String dataPath) throws Exception {
37                 System.out.println(Thread.currentThread().toString() + "监听到节点：" + dataPath + "被删除了！");
38             }
39             @Override
40             public void handleDataChange(String dataPath, Object data) throws Exception {
41                 System.out.println(Thread.currentThread().toString() + "监听到节点：" + dataPath + ", 数据：" + data + " - 更新");
42                 dbConfig = (DbConfig) data;
43             }
44         });
45     }
46 }

View Code

 1 package com.zk;
 2 
 3 import java.util.concurrent.ExecutorService;
 4 import java.util.concurrent.Executors;
 5 
 6 public class BusinessServers {
 7     public static void main(String[] args) {
 8         ExecutorService executorService = Executors.newFixedThreadPool(3);
 9         // 模拟多个服务器获取配置
10         executorService.submit(new ZkConfigClient());
11         executorService.submit(new ZkConfigClient());
12         executorService.submit(new ZkConfigClient());
13     }
14 }

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4、更新配置信息进行测试

 1 package com.zk;
 2 
 3 import java.util.concurrent.TimeUnit;
 4 
 5 public class MngServer {
 6 
 7     public static void main(String[] args) throws InterruptedException {
 8         
 9         DbConfig dbConfig = new DbConfig();
10         ZkConfigMng zkConfigMng = new ZkConfigMng();
11         DbConfig xx = zkConfigMng.update(dbConfig);//初始化节点及数据
12         System.out.println(xx);
13         
14         TimeUnit.SECONDS.sleep(10);
15         
16         // 修改值        
17         zkConfigMng.update(new DbConfig("jdbc:mysql://192.168.6.6:3306/mydata?"
18                 + "useUnicode=true&characterEncoding=utf-8","admin", "admin", "com.mysql.jdbc.Driver"));
19         
20     }
21 
22 }

View Code

5、测试结果

分布式锁

通常实现分布式锁有如下方式：

1、基于数据库锁。（for update悲观锁；或者版本号乐观锁）

2、基于redis方式。（可参考此文https://www.cnblogs.com/zomicc/p/12468324.html）

3、基于zookeeper方式。

Zookeeper中的节点分为四种类型：

持久节点（PERSISTENT）
持久顺序节点（PERSISTENT_SEQUENTIAL）
临时节点（EPHEMERAL）
临时顺序节点（EPHEMERAL_SEQUENTIAL）

zookeeper分布式锁基于第四种临时顺序节点实现分布式锁。原理图如下：

下面的代码是根据Zookeeper的开源客户端Curator实现分布式锁。采用zk的原生API实现会比较繁琐，所以这里就直接用Curator这个轮子，采用Curator的acquire和release两个方法就能实现分布式锁。

1、依赖包

 1 <dependency>
 2     <groupId>org.apache.curator</groupId>
 3     <artifactId>curator-framework</artifactId>
 4     <version>4.2.0</version>
 5 </dependency>
 6 <dependency>
 7     <groupId>org.apache.curator</groupId>
 8     <artifactId>curator-recipes</artifactId>
 9     <version>4.2.0</version>
10 </dependency>

View Code

2、测试代码

 1 package com.zk.distributeLock;
 2 
 3 import java.io.IOException;
 4 import java.util.concurrent.ExecutorService;
 5 import java.util.concurrent.Executors;
 6 import org.apache.curator.RetryPolicy;
 7 import org.apache.curator.framework.CuratorFramework;
 8 import org.apache.curator.framework.CuratorFrameworkFactory;
 9 import org.apache.curator.framework.recipes.locks.InterProcessMutex;
10 import org.apache.curator.retry.ExponentialBackoffRetry;
11 
12 public class CuratorDistributeLock {
13 
14     public static void main(String[] args) throws IOException {
15         //参数一：表示获取不到锁，则1000ms后重试 
16         //参数二：最多重试3次
17         RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
18         
19         ExecutorService excutor = Executors.newFixedThreadPool(5);
20         for(int i=0;i<5;i++) {//使用线程池模拟同时5个请求
21             excutor.submit(new Runnable() {
22                 InterProcessMutex mutex;
23                 CuratorFramework client;
24                 @Override
25                 public void run() {
26                     try {
27                         client = CuratorFrameworkFactory.newClient("192.168.31.130:2181", retryPolicy);
28                         client.start();
29                         mutex = new InterProcessMutex(client, "/curator/lock");
30                         try {
31                             mutex.acquire();
32                             System.out.println(Thread.currentThread().toString() + " 获取到了锁");
33                         } catch (Exception e) {
34                             e.printStackTrace();
35                         }
36                     } finally {
37                         System.out.println(Thread.currentThread().toString() + " 释放了锁");
38                         try {
39                             mutex.release();
40                             client.close();
41                         } catch (Exception e) {
42                             e.printStackTrace();
43                         }
44                     }
45                 }
46             });
47         }
48         excutor.shutdown();
49     }
50 }

View Code

3、测试结果

发现不会如线程抢占式那样交替执行，而是顺序执行。只有获取锁的线程才会执行，其他线程等待。

集群负载均衡

　　概念这里不多讲，直接看代码。

1、服务提供者

 1 package com.zk.colony;
 2 
 3 import java.util.concurrent.TimeUnit;
 4 
 5 import org.I0Itec.zkclient.ZkClient;
 6 import org.I0Itec.zkclient.ZkConnection;
 7 import org.apache.zookeeper.CreateMode;
 8 
 9 /**
10    *      服务提供者
11  * @author Zomi
12  *
13  */
14 public class ServiceProvider {
15     static String ZOOKEEPER_STR = "192.168.31.130:2181";
16     static String NODE_PATH = "/service";
17     static String SERVICE_NAME = "/myService";
18     
19     private ZkClient zkClient;
20     
21     public ServiceProvider() {
22         zkClient = new ZkClient(new ZkConnection(ZOOKEEPER_STR));
23         System.out.println("provider sucess connected to zookeeper server!");
24         if(!zkClient.exists(NODE_PATH)) {
25             zkClient.create(NODE_PATH, "my test service", CreateMode.PERSISTENT);
26         }
27     }
28     
29     public void registryService(String serviceIp, Object obj) {
30         if(!zkClient.exists(NODE_PATH + SERVICE_NAME)) {            
31             zkClient.create(NODE_PATH + SERVICE_NAME, "provider services list", CreateMode.PERSISTENT);        
32         }
33         //对本机服务进行注册
34         zkClient.createEphemeral(NODE_PATH + SERVICE_NAME + "/" + serviceIp, obj);
35         System.out.println("注册成功！[" + serviceIp + "]");
36     }
37     /**
38      * 服务启动、注册服务
39      * @param args
40      * @throws InterruptedException 
41      */
42     public static void main(String[] args) throws InterruptedException {
43         System.out.println("服务器开始运行了.......");
44         ServiceProvider provider = new ServiceProvider();
45         provider.registryService("1.1.1.1", "1.1.1.1 data");
46         TimeUnit.SECONDS.sleep(20);
47         provider.registryService("2.2.2.2", "2.2.2.2 data");
48         TimeUnit.SECONDS.sleep(20);
49         provider.registryService("3.3.3.3", "3.3.3.3 data");
50         System.out.println("服务器异常宕机了.......");
51     }
52 }

View Code

2、服务消费者

 1 package com.zk.colony;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 import java.util.Random;
 6 import java.util.concurrent.TimeUnit;
 7 
 8 import org.I0Itec.zkclient.IZkChildListener;
 9 import org.I0Itec.zkclient.ZkClient;
10 import org.I0Itec.zkclient.ZkConnection;
11 import org.apache.zookeeper.CreateMode;
12 
13 /**
14  * 消费者，通过某种负载均衡算法选择一个提供者进行消费
15  * @author Zomi
16  *
17  */
18 public class ServiceConsumer {
19     static String ZOOKEEPER_STR = "192.168.31.130:2181";
20     static String NODE_PATH = "/service";
21     static String SERVICE_NAME = "/myService";
22     
23     private ZkClient zkClient;
24     
25     private List<String> serviceList = new ArrayList<String>();
26     
27     public ServiceConsumer() {
28         zkClient = new ZkClient(new ZkConnection(ZOOKEEPER_STR));
29         System.out.println("consumer sucess connected to zookeeper server!");
30         if(!zkClient.exists(NODE_PATH)) {
31             zkClient.create(NODE_PATH, "my test service", CreateMode.PERSISTENT);
32         }
33     }
34     
35     /**
36      * 订阅服务
37      */
38     public void subscribeSerivce() {
39         serviceList = zkClient.getChildren(NODE_PATH + SERVICE_NAME);//下载注册列表
40         zkClient.subscribeChildChanges(NODE_PATH + SERVICE_NAME, new IZkChildListener() {
41             @Override
42             public void handleChildChange(String parentPath, List<String> currentChilds) throws Exception {
43                 //注意：此处没有考虑空
44                 if(serviceList.size() != currentChilds.size() || !serviceList.containsAll(currentChilds)) {
45                     System.out.println("服务列表变化了，我要更新了:" + currentChilds);
46                     serviceList = currentChilds;
47                 }
48             }
49         });
50     }
51     /**
52      * 模拟调用服务
53      */
54     public void consume() {
55         if(serviceList!=null && serviceList.size()>0) {
56             //这里使用随机访问某台服务
57             int index = new Random().nextInt(serviceList.size());
58             System.out.println("调用[" + NODE_PATH + SERVICE_NAME + "]服务：" + serviceList.get(index));
59         }else {
60             System.out.println("没有服务提供者");
61         }
62     }
63     
64     /**
65      * 客户端调用启动
66      * @param args
67      */
68     public static void main(String[] args) {
69         ServiceConsumer consumer = new ServiceConsumer();
70         new Thread() {
71             public void run() {
72                 while(true) {
73                     try {
74                         consumer.subscribeSerivce();
75                         TimeUnit.SECONDS.sleep(5);
76                         consumer.consume();
77                     } catch (InterruptedException e) {
78                         e.printStackTrace();
79                     }
80                 }
81             };
82         }.start();
83         
84     }
85 }

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3、先启动消费者，再启动服务者。运行结果如下：

服务高可用

原理很简单，都是基于zk临时节点的特性，及监听机制。下面的图，一看就懂：

备服务监听到主服务挂掉了，立马当先，对外提供服务。

分布式协调

库存、订单的例子，保证库存先扣减成功，再订单处理成功（然后才能通知快递员过来揽件之类的，否则没有货订单却创建成功了，快递小哥就白跑了，整个工作就显得很不协调了）。

"我们所要追求的，永远不是绝对的正确，而是比过去的自己更好"

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原文地址：https://www.cnblogs.com/zomicc/p/12488758.html