cassandra java 例子_Cassandra教程：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。

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！

/*

*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.

* 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 Java driver online manual

*/

public class CassandraUsageDemo {

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

static int PORT = 9042;

private Clustercluster;

private Sessionsession;

public static void main(String[] args) {

CassandraUsageDemoclient = 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 portthe 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 varchart," + // Cassandra 之中varchar == text

"tags set," + // 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() {

ResultSetresults = 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 (Rowrow : 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() {

ResultSetresults = 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();

}

}