我们如何在代码中实现主从的选择-Java

问题描述：我们在分布式任务系统之中，会经常遇见一种情况，比如：定时的对任务进行刷新，然后进行一些操作。通常我们会将这个定时任我Job单独部署成一个服务，这个服务如果我们不进行主选择，便会出现多个服务同时进行刷新，造成业务的紊乱。

解决方案：使用Zookeeper来进行主的选择

1、添加对应的依赖

<!-- zookeeper 客户端 -->
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>2.13.0</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-recipes</artifactId>
    <version>2.13.0</version>
</dependency>

code

package com.lee.schedule;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.leader.LeaderSelector;import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;import org.apache.curator.retry.ExponentialBackoffRetry;import java.util.HashMap;import java.util.Map;import java.util.concurrent.TimeUnit;/**
 * @author Lee
 * @date 2022-05-18 17:02
 */publicclassSelectMasterTest{//自己的zookeeper地址private String selectMasterZookeeper="localhost:2181";//可以放很多节点
    Map<String, Boolean> masterMap =newHashMap<String, Boolean>();/**
     * 选主
     * @param leaderPath  zookeeper目录节点
     */publicvoid selectMaster (String leaderPath){
        CuratorFramework client = CuratorFrameworkFactory.builder().connectString(selectMasterZookeeper).sessionTimeoutMs(5000)//超时时间.retryPolicy(newExponentialBackoffRetry(1000,3))//连接不上重试三次.build();
        client.start();//争抢注册节点@SuppressWarnings("resource")
        LeaderSelector selector =newLeaderSelector(client, leaderPath,newLeaderSelectorListenerAdapter(){@OverridepublicvoidtakeLeadership(CuratorFramework client)throws Exception {//如果争抢到当前注册节点
                        masterMap.put(leaderPath,true);while(true){//抢占当前节点
                            TimeUnit.SECONDS.sleep(3);}}});
        masterMap.put(leaderPath,false);
        selector.autoRequeue();
        selector.start();}publicboolean checkMaster (String leaderPath){
        Boolean isMaster = masterMap.get(leaderPath);return isMaster == null ?false: isMaster;}publicstaticvoidmain(String[] args)throws InterruptedException {//leaderPath 可以根据我们的业务情况，设置对应的业务path
        String leaderPath ="/master";
        SelectMasterTest selectMaster =newSelectMasterTest();
        selectMaster.selectMaster(leaderPath);

        TimeUnit.SECONDS.sleep(1);while(true){if(selectMaster.checkMaster(leaderPath)){
                System.out.println(" 节点1 主节点 ");}else{
                System.out.println(" 节点1 从节点 ");}
            TimeUnit.SECONDS.sleep(6);}}}