我正在使用一个片段来理解 cassandra 和语法:
import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.Session;
public class App {
public static void main(String[] args) {
Cluster cluster;
Session session;
// Connect to the cluster and key space "demo"
cluster = Cluster.builder().addContactPoint("127.0.0.1").build();
session = cluster.connect("demo");
// Insert one record into the users table
session.execute("INSERT INTO users (lastname, age, city, email, firstname) VALUES ('Jones', 35, 'Austin', '[email protected]', 'Bob')");
// Use select to get the user we just entered
ResultSet results = session.execute("SELECT * FROM users WHERE lastname='Jones'");
for (Row row : results) {
System.out.format("%s %d\n", row.getString("firstname"), row.getInt("age"));
}
// Update the same user with a new age
session.execute("update users set age = 36 where lastname = 'Jones'");
// Select and show the change
results = session.execute("select * from users where lastname='Jones'");
for (Row row : results) {
System.out.format("%s %d\n", row.getString("firstname"), row.getInt("age"));
}
// Delete the user from the users table
session.execute("DELETE FROM users WHERE lastname = 'Jones'");
// Show that the user is gone
results = session.execute("SELECT * FROM users");
for (Row row : results) {
System.out.format("%s %d %s %s %s\n", row.getString("lastname"), row.getInt("age"), row.getString("city"),
row.getString("email"), row.getString("firstname"));
}
// Clean up the connection by closing it
cluster.close();
}
}
在执行时，我收到此错误:
log4j:WARN No appenders could be found for logger (com.datastax.driver.core.SystemProperties).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" com.datastax.driver.core.exceptions.InvalidQueryException: Keyspace 'demo' does not exist
at com.datastax.driver.core.exceptions.InvalidQueryException.copy(InvalidQueryException.java:35)
at com.datastax.driver.core.DefaultResultSetFuture.extractCauseFromExecutionException(DefaultResultSetFuture.java:289)
at com.datastax.driver.core.Cluster.connect(Cluster.java:287)
at org.sparkexamples.cassandraExample.main.App.main(App.java:17)
Caused by: com.datastax.driver.core.exceptions.InvalidQueryException: Keyspace 'demo' does not exist
at com.datastax.driver.core.Responses$Error.asException(Responses.java:103)
at com.datastax.driver.core.DefaultResultSetFuture.onSet(DefaultResultSetFuture.java:140)
at com.datastax.driver.core.RequestHandler.setFinalResult(RequestHandler.java:293)
at com.datastax.driver.core.RequestHandler.onSet(RequestHandler.java:455)
at com.datastax.driver.core.Connection$Dispatcher.messageReceived(Connection.java:734)
at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
at org.jboss.netty.handler.timeout.IdleStateAwareChannelUpstreamHandler.handleUpstream(IdleStateAwareChannelUpstreamHandler.java:36)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
at org.jboss.netty.handler.timeout.IdleStateHandler.messageReceived(IdleStateHandler.java:294)
at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
at org.jboss.netty.handler.codec.oneone.OneToOneDecoder.handleUpstream(OneToOneDecoder.java:70)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
at org.jboss.netty.handler.codec.frame.FrameDecoder.unfoldAndFireMessageReceived(FrameDecoder.java:462)
at org.jboss.netty.handler.codec.frame.FrameDecoder.callDecode(FrameDecoder.java:443)
at org.jboss.netty.handler.codec.frame.FrameDecoder.messageReceived(FrameDecoder.java:303)
at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:559)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)
at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88)
at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108)
at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89)
at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)
at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
上瘾，我用spark(maven/libs)配置了所有东西，但我不知道如何使用java代码创建一个键空间？
提前致谢。
最佳答案
您已经有一个 session 实例。使用它来发出一个 create keyspace 命令:
session.execute("CREATE KEYSPACE IF NOT EXISTS test WITH replication = {"
+ " 'class': 'SimpleStrategy', "
+ " 'replication_factor': '3' "
+ "};" );
IF NOT EXISTS 部分将防止语句在键空间已经存在的情况下抛出错误。关于java - 如何在 cassandra 中创建键空间？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/30703678/