如何使用Java类连接Cassandra

Question

我这样做是为了连接cassandra.But我的代码返回错误..这是我的代码

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..

无法在项目CassandraConnection上执行目标:无法解析项目com.mycompany的依赖项:CassandraConnection:jar:1.0-SNAPSHOT:无法解析以下工件: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以启用完整的调试日志记录.

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] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException

Answer 1

你有没有研究过这个问题？

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.你在这里有各种各样的选择,但是当我们从高层看时,有两种选择.

1. 基于CQL的驱动程序 - 对thrift执行的更高级别的抽象.另外,较新的工具,为cassandra提供支持/文档​​的公司建议新的cassandra应用程序是基于CQL的.
2. 基于Thrift的驱动器 - 可以访问低级存储,因此更容易出错.

我将使用datastax的CQL驱动程序.

从datastax的github repo下载并构建驱动程序或使用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>

挑选maven是一个好主意,因为它会为你管理所有依赖项,但如果你不使用maven,至少你将学习如何管理jar和阅读堆栈跟踪.

码

该驱动程序的文档是很好的磨磨蹭蹭.如果您遇到困难,请阅读该文档,其中包含大量示例.

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());
}

创建/更新/删除

// 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.

其他有用的代码

创造一个Keyspace

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

session.execute(cqlStatement);

创建ColumnFamily(aka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);