[Cassandra教程] （六）Java API 简单例子

本文将简单介绍一些在Cassandra之中如何使用Java对数据进行操作的简单例子。包括了简单的CRUD。更深入一些的内容，将在后面逐个进行讲解。

本文代码源自：https://github.com/datastax/java-driver/blob/3.0/driver-examples/src/main/java/com/datastax/driver/examples/basic/CreateAndPopulateKeyspace.java

后来根据官方的例子做了一些说明，同时对其进行了一些补完。主要内容还请参考代码之中的注释。原文是英文注释，对重要内容进行了翻译，其他新增的注释，个人觉得也比较有帮助。

PS: 这真是极有态度的贴代码了！(修改之后的链接)

/*
 *      Copyright (C) 2012-2015 DataStax Inc.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */
package demo;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.Session;

/**
 * Creates a keyspace and tables, and loads some data into them.<br>
 * 创建Keyspace与table，并插入一些数据
 * <p/>
 * Preconditions:
 * - a Cassandra cluster is running and accessible through the contacts points identified by CONTACT_POINTS and PORT.
 * <p/>
 * Side effects:
 * - creates a new keyspace "simplex" in the cluster. If a keyspace with this name already exists, it will be reused;
 * - creates two tables "simplex.songs" and "simplex.playlists". If they exist already, they will be reused;
 * - inserts a row in each table.
 *
 * @see <a href="http://datastax.github.io/java-driver/manual/">Java driver online manual</a>
 */
public class CassandraUsageDemo {

    static String[] CONTACT_POINTS = {"127.0.0.1"};
    static int PORT = 9042;
    
    
    private Cluster cluster;
    private Session session;
    
    public static void main(String[] args) {

        CassandraUsageDemo client = new CassandraUsageDemo();

        try {

            client.connect(CONTACT_POINTS, PORT);
            client.createSchema();
            client.loadData();
            client.querySchema();
            client.deleteData();
        } finally {
            client.close();
        }
    }

	

    /**
     * Initiates a connection to the cluster
     * specified by the given contact point. <br>
     * 连接到指定的Cassandra节点。 该节点最好是Seeds server
     *
     * @param contactPoints the contact points to use. 连接点
     * @param port          the port to use. 端口，默认9042
     */
    public void connect(String[] contactPoints, int port) {

        cluster = Cluster.builder()
                .addContactPoints(contactPoints).withPort(port)
                .build();

        System.out.printf("Connected to cluster: %s%n", cluster.getMetadata().getClusterName());

        session = cluster.connect();
    }

    /**
     * Creates the schema (keyspace) and tables
     * for this example.
     */
    public void createSchema() {
    	// 创建Keyspace simplex, 如果之前已经创建了就直接复用
    	// 使用SimpleStrategy， 复制因子=1 （数据没有备份，只存放1份）
        session.execute("CREATE KEYSPACE IF NOT EXISTS simplex WITH replication " +
                "= {'class':'SimpleStrategy', 'replication_factor':1};");
        
        // 创建Table simplex.songs
        session.execute(
                "CREATE TABLE IF NOT EXISTS simplex.songs (" +
                        "id uuid PRIMARY KEY," +
                        "title text," +
                        "album text," +
                        "artist varchar," +	// Cassandra 之中varchar == text
                        "tags set<text>," +		// 这里用了set的数据类型
                        "data blob" +			// 二进制类型
                        ");");
        
        // 创建表simplex.playlists
        // 注意：playlists 跟 songs的数据是重复的， 
        // 只是primary key 不太一样。 
        // 这就是NoSQL跟RDBMS的不一样： 反范式
        session.execute(
                "CREATE TABLE IF NOT EXISTS simplex.playlists (" +
                        "id uuid," +
                        "title text," +
                        "album text, " +
                        "artist text," +
                        "song_id uuid," +
                        "PRIMARY KEY (id, title, album, artist)" +
                        ");");
    }

    /**
     * Inserts data into the tables.<br>
     * 插入数据
     */
    public void loadData() {

        session.execute(
                "INSERT INTO simplex.songs (id, title, album, artist, tags) " +
                        "VALUES (" +
                        "756716f7-2e54-4715-9f00-91dcbea6cf50," +
                        "'La Petite Tonkinoise'," +
                        "'Bye Bye Blackbird'," +
                        "'Joséphine Baker'," +
                        "{'jazz', '2013'})" +
                        ";");

        session.execute(
                "INSERT INTO simplex.playlists (id, song_id, title, album, artist) " +
                        "VALUES (" +
                        "2cc9ccb7-6221-4ccb-8387-f22b6a1b354d," +
                        "756716f7-2e54-4715-9f00-91dcbea6cf50," +
                        "'La Petite Tonkinoise'," +
                        "'Bye Bye Blackbird'," +
                        "'Joséphine Baker'" +
                        ");");
    }

    /**
     * Queries and displays data.<br>
     * 查询数据
     */
    public void querySchema() {

        ResultSet results = session.execute(
                "SELECT * FROM simplex.playlists " +
                        "WHERE id = 2cc9ccb7-6221-4ccb-8387-f22b6a1b354d;");

        System.out.printf("%-30s\t%-20s\t%-20s%n", "title", "album", "artist");
        System.out.println("-------------------------------+-----------------------+--------------------");

        for (Row row : results) {

            System.out.printf("%-30s\t%-20s\t%-20s%n",
                    row.getString("title"),
                    row.getString("album"),
                    row.getString("artist"));

        }

    }
    
    /**
     * Delete data <br>
     * 删除数据
     */
    private void deleteData() {
    	ResultSet results = session.execute(
                "delete from simplex.playlists " +
                        "WHERE id = 2cc9ccb7-6221-4ccb-8387-f22b6a1b354d;");
    	// 删除之后再次进行查询
		querySchema();
	}

    /**
     * Closes the session and the cluster.<br>
     * 最后一定要记得关闭！
     */
    public void close() {
        session.close();
        cluster.close();
    }

}

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* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

package demo;

import com.datastax.driver.core.Cluster;

import com.datastax.driver.core.ResultSet;

import com.datastax.driver.core.Row;

import com.datastax.driver.core.Session;

/**

* Creates a keyspace and tables, and loads some data into them.

* 创建Keyspace与table，并插入一些数据

*

* Preconditions:

* - a Cassandra cluster is running and accessible through the contacts points identified by CONTACT_POINTS and PORT.

*

* Side effects:

* - creates a new keyspace "simplex" in the cluster. If a keyspace with this name already exists, it will be reused;

* - creates two tables "simplex.songs" and "simplex.playlists". If they exist already, they will be reused;

* - inserts a row in each table.

* @see <a href="http://datastax.github.io/java-driver/manual/">Java driver online manual</a>

public class CassandraUsageDemo {

static String[] CONTACT_POINTS = {"127.0.0.1"};

static int PORT = 9042;

private Cluster cluster;

private Session session;

public static void main(String[] args) {

CassandraUsageDemo client = new CassandraUsageDemo();

try {

client.connect(CONTACT_POINTS, PORT);

client.createSchema();

client.loadData();

client.querySchema();

client.deleteData();

} finally {

client.close();

}

/**

* Initiates a connection to the cluster

* specified by the given contact point.

* 连接到指定的Cassandra节点。该节点最好是Seeds server

* @param contactPoints the contact points to use. 连接点

* @param port the port to use. 端口，默认9042

public void connect(String[] contactPoints, int port) {

cluster = Cluster.builder()

.addContactPoints(contactPoints).withPort(port)

.build();

System.out.printf("Connected to cluster: %s%n", cluster.getMetadata().getClusterName());

session = cluster.connect();

}

/**

* Creates the schema (keyspace) and tables

* for this example.

public void createSchema() {

// 创建Keyspace simplex, 如果之前已经创建了就直接复用

// 使用SimpleStrategy，复制因子=1 （数据没有备份，只存放1份）

session.execute("CREATE KEYSPACE IF NOT EXISTS simplex WITH replication " +

"= {'class':'SimpleStrategy', 'replication_factor':1};");

// 创建Table simplex.songs

session.execute(

"CREATE TABLE IF NOT EXISTS simplex.songs (" +

"id uuid PRIMARY KEY," +

"title text," +

"album text," +

"artist varchar," + // Cassandra 之中varchar == text

"tags set<text>," + // 这里用了set的数据类型

"data blob" + // 二进制类型

");");

// 创建表simplex.playlists

// 注意：playlists 跟 songs的数据是重复的，

// 只是primary key 不太一样。

// 这就是NoSQL跟RDBMS的不一样：反范式

session.execute(

"CREATE TABLE IF NOT EXISTS simplex.playlists (" +

"id uuid," +

"title text," +

"album text, " +

"artist text," +

"song_id uuid," +

"PRIMARY KEY (id, title, album, artist)" +

");");

}

/**

* Inserts data into the tables.

* 插入数据

public void loadData() {

session.execute(

"INSERT INTO simplex.songs (id, title, album, artist, tags) " +

"VALUES (" +

"756716f7-2e54-4715-9f00-91dcbea6cf50," +

"'La Petite Tonkinoise'," +

"'Bye Bye Blackbird'," +

"'Joséphine Baker'," +

"{'jazz', '2013'})" +

";");

session.execute(

"INSERT INTO simplex.playlists (id, song_id, title, album, artist) " +

"VALUES (" +

"2cc9ccb7-6221-4ccb-8387-f22b6a1b354d," +

"756716f7-2e54-4715-9f00-91dcbea6cf50," +

"'La Petite Tonkinoise'," +

"'Bye Bye Blackbird'," +

"'Joséphine Baker'" +

");");

}

/**

* Queries and displays data.

* 查询数据

public void querySchema() {

ResultSet results = session.execute(

"SELECT * FROM simplex.playlists " +

"WHERE id = 2cc9ccb7-6221-4ccb-8387-f22b6a1b354d;");

System.out.printf("%-30s\t%-20s\t%-20s%n", "title", "album", "artist");

System.out.println("-------------------------------+-----------------------+--------------------");

for (Row row : results) {

System.out.printf("%-30s\t%-20s\t%-20s%n",

row.getString("title"),

row.getString("album"),

row.getString("artist"));

}

/**

* Delete data

* 删除数据

private void deleteData() {

ResultSet results = session.execute(

"delete from simplex.playlists " +

"WHERE id = 2cc9ccb7-6221-4ccb-8387-f22b6a1b354d;");

// 删除之后再次进行查询

querySchema();

}

/**

* Closes the session and the cluster.

* 最后一定要记得关闭！

public void close() {

session.close();

cluster.close();

}

更新：

2016-09-09 更新创建表的语句，之前将varchar 写成 varchart

本文为原创文章，转载请注明出处

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文章评论

焦志广

你好，，我的一个表插入100万条的时候，查询超时，

你教程5的配置超时我已经配置很大了，但还是超时，不知道你是否遇见过这种问题
read_request_timeout_in_ms: 1000000000000
下面那几个设置同上，我已经设置很大了，再大都无法启动了
select count(*) from table_name where type = '1';

2016年09月10日

rangerwolf

你好！
我感觉这还是Cassandra的原因呢。我猜想，还是因为select count(*) 操作会对全表进行扫描所致~

我后来类似的这些操作都是在Spark 上进行

感谢你的提问，我后面会更详细的研究。

请继续关注我的博客，感谢！

2016年09月11日

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