Cassandra-参考的API

简介

Apache Cassandra是一个开源的分布式NoSQL数据库，可以实现高可用性和可扩展性，常用于处理大数据、高并发场景下的存储和查询。在Cassandra中，数据以列式方式存储，每行数据可以有千兆字节的列。本文将介绍Cassandra参考的API，帮助开发者更好地了解Cassandra的使用方式。

安装

Cassandra的安装可以通过官方网站下载安装包或者通过源代码编译安装。安装完成后，可以使用以下命令启动Cassandra：

$ bin/cassandra

使用

连接到Cassandra集群

在Java应用程序中使用Cassandra，我们需要使用Cassandra Java驱动程序。首先需要导入Cassandra Java驱动程序的依赖：

<dependency>
    <groupId>com.datastax.cassandra</groupId>
    <artifactId>cassandra-driver-core</artifactId>
    <version>3.3.0</version>
</dependency>

连接到Cassandra集群的主要步骤如下：

import com.datastax.driver.core.*;

public class CassandraConnector {

    public Cluster cluster;
    public Session session;

    public void connect(String node, Integer port, String keyspace) {
        this.cluster = Cluster.builder().addContactPoint(node).withPort(port).build();
        Metadata metadata = cluster.getMetadata();
        System.out.printf("Connected to cluster: %s\n", metadata.getClusterName());
        for ( Host host : metadata.getAllHosts() ) {
            System.out.printf("Datacenter: %s; Host: %s; Rack: %s\n",
                    host.getDatacenter(), host.getAddress(), host.getRack());
        }
        this.session = cluster.connect(keyspace);
    }

    public void close() {
        this.session.close();
        this.cluster.close();
    }

}

创建keyspace

public class CreateKeySpace {

    public static void createKeySpace(String keyspaceName, String replicationStrategy, int replicationFactor) {
        StringBuilder sb = new StringBuilder("CREATE KEYSPACE IF NOT EXISTS ")
                .append(keyspaceName).append(" WITH replication = {")
                .append("'class':'").append(replicationStrategy)
                .append("','replication_factor':").append(replicationFactor)
                .append("};");

        String query = sb.toString();
        CassandraConnector connector = new CassandraConnector();
        connector.connect("127.0.0.1", 9042, "");
        Session session = connector.getSession();
        session.execute(query);
        session.close();
        connector.close();
    }
}

创建table

public class CreateTable {

    public static void createTable(String keyspaceName, String tableName) {
        StringBuilder sb = new StringBuilder("CREATE TABLE IF NOT EXISTS ")
                .append(keyspaceName).append(".")
                .append(tableName).append("(")
                .append("id uuid PRIMARY KEY, ")
                .append("name text,")
                .append("email text);");

        String query = sb.toString();
        CassandraConnector connector = new CassandraConnector();
        connector.connect("127.0.0.1", 9042, keyspaceName);
        Session session = connector.getSession();
        session.execute(query);
        session.close();
        connector.close();
    }
}

插入数据

public class InsertData {

    public static void insertData(String keyspaceName, String tableName) {
        CassandraConnector connector = new CassandraConnector();
        connector.connect("127.0.0.1", 9042, keyspaceName);
        Session session = connector.getSession();
        UUID uuid = UUID.randomUUID();
        String name = "Alan";
        String email = "alan@test.com";
        String query = "INSERT INTO " + keyspaceName + "." + tableName + "(id, name, email) VALUES(" + uuid + ", '" + name + "', '" + email + "');";
        session.execute(query);
        session.close();
        connector.close();
    }
}

查询数据

public class ReadData {

    public static void readData(String keyspaceName, String tableName) {
        CassandraConnector connector = new CassandraConnector();
        connector.connect("127.0.0.1", 9042, keyspaceName);
        Session session = connector.getSession();
        String query = "SELECT * FROM " + keyspaceName + "." + tableName + ";";
        ResultSet result = session.execute(query);
        for (Row row : result) {
            System.out.println(String.format("%s %s %s\n", row.getUUID("id"), row.getString("name"), row.getString("email")));
        }
        session.close();
        connector.close();
    }
}

结论

本文介绍了Cassandra参考的API，包括连接到Cassandra集群，创建keyspace，创建table，插入数据，查询数据等。希望这篇文章能够帮助读者更好地了解Cassandra的使用方法。