Zookeeper学习---2、客户端API操作、客户端向服务端写数据流程

1、客户端API操作

1.1 IDEA 环境搭建

前提：保证 hadoop102、hadoop103、hadoop104 服务器上 Zookeeper 集群服务端启动。
1、创建一个工程：Zookeeper
2、添加pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>Zookeeper</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.8.2</version>
        </dependency>

        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.5.7</version>
        </dependency>
        <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-framework</artifactId>
        <version>4.3.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-recipes</artifactId>
        <version>4.3.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-client</artifactId>
        <version>4.3.0</version>
    </dependency>
    </dependencies>
</project>

3、拷贝log4j.properties文件到项目根目录
需要在项目的 src/main/resources 目录下，新建一个文件，命名为“log4j.properties”，在文件中填入。

log4j.rootLogger=INFO, stdout 
log4j.appender.stdout=org.apache.log4j.ConsoleAppender 
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout 
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] 
- %m%n 
log4j.appender.logfile=org.apache.log4j.FileAppender 
log4j.appender.logfile.File=target/spring.log 
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout 
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] 
- %m%n

4、创建包名com.example.zk
5、创建类名称zkClient

1.2 创建Zookeeper客户端

// 注意：逗号前后不能有空格
private static String connectString =
"hadoop102:2181,hadoop103:2181,hadoop104:2181";
private static int sessionTimeout = 2000;
private ZooKeeper zkClient = null;
@Before
public void init() throws Exception {
zkClient = new ZooKeeper(connectString, sessionTimeout, new 
Watcher() {
@Override
public void process(WatchedEvent watchedEvent) {
// 收到事件通知后的回调函数（用户的业务逻辑）
System.out.println(watchedEvent.getType() + "--" 
+ watchedEvent.getPath());
// 再次启动监听
try {
List<String> children = zkClient.getChildren("/", 
true);
 for (String child : children) {
 System.out.println(child);
 }
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}

1.3 创建子节点

// 创建子节点
@Test
public void create() throws Exception {
// 参数 1：要创建的节点的路径； 参数 2：节点数据 ； 参数 3：节点权限 ；
参数 4：节点的类型
String nodeCreated = zkClient.create("/atguigu", 
"shuaige".getBytes(), Ids.OPEN_ACL_UNSAFE,
CreateMode.PERSISTENT);
}

1.4 获取子节点并监听节点变化

// 获取子节点
@Test
public void getChildren() throws Exception {
List<String> children = zkClient.getChildren("/", true);
for (String child : children) {
System.out.println(child);
}
// 延时阻塞
Thread.sleep(Long.MAX_VALUE);
}

1.5 判断 Znode 是否存在

// 判断 znode 是否存在
@Test
public void exist() throws Exception {
Stat stat = zkClient.exists("/atguigu", false);
System.out.println(stat == null ? "not exist" : "exist");
}

2、客户端向服务端写数据流程

1、写流程之写入请求直接发送给Leader节点

2、写流程之写入请求发送给follower节点