我这样做是为了连接 cassandra。但我的代码返回错误。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..

Failed to execute goal on project CassandraConnection: Could not resolve dependencies for project com.mycompany:CassandraConnection:jar:1.0-SNAPSHOT: The following artifacts could not be resolved: 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: Could not find artifact org.specs2:scalaz-effect_2.11.0-SNAPSHOT:jar:7.0.1-SNAPSHOT -> [Help 1]

To see the full stack trace of the errors, re-run Maven with the -e switch. Re-run Maven using the -X switch to enable full debug logging.

For more information about the errors and possible solutions, please read the following articles: [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException

最佳答案

你对这件事做过任何研究吗？

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。您在这里有多种选择，但是当我们从高层次的角度来看它时，确实有两种选择。

1. 基于 CQL 的驱动程序 - thrift 所做的更高层次的抽象。同样是较新的工具，为 cassandra 提供支持/文档​​的公司建议新的 cassandra 应用程序基于 CQL。
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's CQL driver .

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>

选择 maven 是个好主意，因为它会为你管理所有依赖项，但如果你不使用 maven，至少你会学习管理 jar 和阅读堆栈跟踪。

代码

driver's documentation进展顺利。如果您无法通读它，该文档包含大量示例。

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!

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.

其他有用的代码

创建键空间

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);

关于java - 如何使用 Java 类连接 Cassandra，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16870502/