如何使用Java类连接Cassandra

Question

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());
    }

}
}

有关错误和可能的解决方案的更多信息，请阅读以下文章:[Help 1]http://cwiki.apache.org/confluence/display/maven/dependencyresolutionException

Answer 1

你对这件事做过调查吗？

您需要一种与cassandra通信的方法，最好的选择是使用高级API。这里你有很多选择，但是当我们从一个高水平的prespective来看，实际上有两个选择。

1. 基于CQL的驱动程序-节俭功能的更高级别的抽象。同样是较新的工具，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. 基于节俭的驱动器-可以访问低级别存储，因此更容易出错。

<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>

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!

阅读

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.

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

session.execute(cqlStatement);

// 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);