如何使用Java类连接Cassandra

Question

我这样做是为了连接cassandra.But，我的代码正在返回一个错误。这是我的密码

public class CassandraConnection {

public static void main(String[] args) {
    String serverIp = "166.78.10.41";
    String keyspace = "gamma";
    CassandraConnection connection;

    Cluster cluster = Cluster.builder()
            .addContactPoints(serverIp)
            .build();

    Session session = cluster.connect(keyspace);


    String cqlStatement = "SELECT * FROM TestCF";
    for (Row row : session.execute(cqlStatement)) {
        System.out.println(row.toString());
    }

}
}

这是错误日志。

未能对项目com.mycompany:CassandraConnection:jar:1.0-SNAPSHOT:执行目标:无法解决项目CassandraConnection的依赖关系，无法解决下列工件: org.specs2:scalaz-effect_2.11.0-SNAPSHOT:jar:7.0.1-SNAPSHOT，org.scalaz:scalaz-effect_2.9.3:jar:7.1.0-SNAPSHOT:找不到工件org.specs2:scalaz-effect_2.11.0-SNAPSHOT:jar:7.0.1-SNAPSHOT -> Help 1 要查看错误的完整堆栈跟踪，请使用-e开关重新运行Maven。使用-X开关重新运行Maven以启用完全调试日志记录。 有关错误和可能的解决方案的更多信息，请阅读以下文章：帮助1

Answer 1

你对这件事做过调查吗？

挑选司机

您需要一种与cassandra通信的方法，最好的选择是使用高级API。你在这里有很多选择，但是当我们从高水平的预感来看它时，实际上有两种选择。

1. 基于CQL的驱动程序-更高层次的抽象什么节俭。同样更新的工具，为cassandra提供支持/文档的公司建议，新的cassandra应用程序基于CQL。
2. 基于的驱动程序--能够访问低级别的存储，因此更容易出错。

我要用datastax的CQL驱动程序。

从datastax的github repo 或下载并构建驱动程序，使用maven并添加以下依赖项：

<dependency>
  <groupId>com.datastax.cassandra</groupId>
  <artifactId>cassandra-driver-core</artifactId>
  <version>2.1.3</version>
</dependency>

<dependency>
  <groupId>com.datastax.cassandra</groupId>
  <artifactId>cassandra-driver-mapping</artifactId>
  <version>2.1.2</version>
</dependency>

选择maven是个好主意，因为它将为您管理所有的依赖项，但是如果您不使用maven，至少您将了解如何管理jars和读取堆栈跟踪。

​

代码

司机文件进展得很好。如果您被卡住了，请阅读它，文档中包含许多示例。

我将在整个示例中使用以下两个变量。

String serverIP = "127.0.0.1";
String keyspace = "system";

Cluster cluster = Cluster.builder()
  .addContactPoints(serverIP)
  .build();

Session session = cluster.connect(keyspace);

// you are now connected to the cluster, congrats!

读

String cqlStatement = "SELECT * FROM local";
for (Row row : session.execute(cqlStatement)) {
  System.out.println(row.toString());
}

Create/Update/Delete

// for all three it works the same way (as a note the 'system' keyspace cant 
// be modified by users so below im using a keyspace name 'exampkeyspace' and
// a table (or columnfamily) called users

String cqlStatementC = "INSERT INTO exampkeyspace.users (username, password) " + 
                      "VALUES ('Serenity', 'fa3dfQefx')";

String cqlStatementU = "UPDATE exampkeyspace.users " +
                      "SET password = 'zzaEcvAf32hla'," +
                      "WHERE username = 'Serenity';";

String cqlStatementD = "DELETE FROM exampkeyspace.users " + 
                      "WHERE username = 'Serenity';";

session.execute(cqlStatementC); // interchangeable, put any of the statements u wish.

​

其他有用代码

创建密钥空间

String cqlStatement = "CREATE KEYSPACE exampkeyspace WITH " + 
  "replication = {'class':'SimpleStrategy','replication_factor':1}";

session.execute(cqlStatement);

创建ColumnFamily (又名表)

// based on the above keyspace, we would change the cluster and session as follows:
Cluster cluster = Cluster.builder()
  .addContactPoints(serverIP)
  .build();
Session session = cluster.connect("exampkeyspace");

String cqlStatement = "CREATE TABLE users (" + 
                      " username varchar PRIMARY KEY," + 
                      " password varchar " + 
                      ");";

session.execute(cqlStatement);

Answer 2

要从java程序连接cassandra，您需要向程序添加一些基本的依赖项。将下列依赖项添加到程序。Maven依赖项列表：

<dependency>
    <groupId>com.datastax.cassandra</groupId>
    <artifactId>cassandra-driver-core</artifactId>
    <version>3.6.0</version>
</dependency>

<dependency>
  <groupId>com.datastax.cassandra</groupId>
  <artifactId>cassandra-driver-mapping</artifactId>
  <version>3.6.0</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.25</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>1.7.25</version>
    <scope>test</scope>
</dependency>

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>21.0</version>
</dependency>

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.20.Final</version>
</dependency>

<dependency>
    <groupId>com.codahale.metrics</groupId>
    <artifactId>metrics-core</artifactId>
    <version>3.0.2</version>
</dependency>

与cassandra连接到键空间并检索表值的简单java程序

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

public class Test {

    public static void main(String[] args) {
        String serverIp = "127.0.0.1";
        String keyspace = "test";

        Cluster cluster = Cluster.builder()
                .addContactPoints(serverIp)
                .build();

        Session session = cluster.connect(keyspace);


        String cqlStatement = "SELECT * FROM emp";
        for (Row row : session.execute(cqlStatement)) {
            System.out.println(row.toString());
        }

        session.close();
    }
}

作为maven项目的程序的Git集线器回购：GitURL