1. Client command line operation

1.1 basic grammar

command	explain
help	Display all operation commands
ls path	View the child nodes of the current node (can listen) -w listen for changes in child nodes -s additional secondary information
create	Create normal node -s contains sequences -e temporary (restart or timeout disappears)
get path	Obtain the value of the node under the specified path (listening) -w listen for changes in node content -s additional secondary information
set	Set node details
stat	View node status
delete	Delete node
deleteall	Recursively delete nodes

1.2 node type

Persistent node: after the client and server are disconnected, the created node will not be deleted

• Persistent directory node: the node still exists after the client is disconnected from Zookeeper
• Persistent sequential numbering directory node: after the client is disconnected from Zookeeper, the node still exists, but Zookeeper sequentially numbers the section name

Ephemeral node: after the client and server are disconnected, the created node will be deleted

• Temporary directory node: the node is deleted after the client is disconnected from Zookeeper
• Temporary sequence number directory node: after the client is disconnected from Zookeeper, the node is deleted, but Zookeeper gives the sequence number to the node name

When creating a node, the sequence ID is set. A value is appended to the node name. The sequence number is a monotonically increasing counter maintained by the parent node.

1.3 node data details

details	describe
czxid	Create a transaction zxid for the node
ctime	Number of milliseconds a node was created (since 1970)
mzxid	The node follows the new transaction zxid
mtime	Number of milliseconds the node was last modified (since 1970)
pzxid	Node last updated child node zxid
cversion	Change number of child nodes, modification times of child nodes
dataversion	Node data change number
aclVersion	Change number of node access control list
ephemeralOwner	If it is a temporary node, this is the session id of the node owner. If it is not a temporary node, it is 0
dataLength	Data length of node
numChildren	Number of child nodes of node

2. Client API operation

2.1 project preparation

one ️⃣ Create Maven project

two ️⃣ Import dependency

<!--unit testing -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.1</version>
    <scope>test</scope>
</dependency>

<!--zookeeper rely on-->
<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.5.7</version>
</dependency>

<!--journal-->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.6.2</version>
</dependency>

2.2 create client

private String connectString = "node1:2181,node2:2181,node3:2181";
private int sessionTimeOut = 2000;
private ZooKeeper zooKeeper;


/**
 * Initialize connection
 * @throws IOException
 */
@Before
public void init() throws IOException {

    // connectString: connected host and port number
    // sessionTimeOut: timeout (in seconds)
    // Watcher: node listener
    zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
        @Override
        public void process(WatchedEvent watchedEvent) {

        }
    });
}

2.3 creating nodes

@Test
public void create() throws InterruptedException, KeeperException, IOException {

    // Create the address of the node
    // Data content of node
    // Node level
    // Node type
    String nodeCreated = zooKeeper.create("/mouse",
            "Jack".getBytes(),
            ZooDefs.Ids.OPEN_ACL_UNSAFE,
            CreateMode.PERSISTENT);
}

Test using the command line:

2.4 determining whether a node exists

@Test
public void exist() throws IOException, InterruptedException, KeeperException {
    if(zooKeeper == null){
        System.out.println("zooKeeper Null, creating new connection!----------------");
        zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }
    Stat stat = zooKeeper.exists("/mouse", false);
    System.out.println(stat==null ? "The node does not exist" : "The node does not exist");
}

IDEA output test:

2.5 listening node

@Test
public void getChildren() throws IOException, InterruptedException, KeeperException {
    if(zooKeeper == null){
        System.out.println("zooKeeper Null, creating new connection!----------------");
        zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                System.out.println("---------------------");
                List<String> childrens = null;
                try {
                    childrens = zooKeeper.getChildren("/", true);

                    for (String children : childrens) {
                        System.out.println(children);
                    }
                    System.out.println("---------------------");
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
    Thread.sleep(Long.MAX_VALUE);
}

Test: