获取datastax中的nullpointer异常

Question

我正在使用cassandra1.2和datastax java client 1.0.3使用来自datastax的java客户端的示例我已经创建了一个类，它将返回会话

public class DataStaxPlugin {

    public static final Logger LOGGER = Logger.getLogger(DataStaxPlugin.class.getName());
    private static Cluster cluster;
    private static Session session = null;
    private static String node;
    private static String port;
    private static DataStaxPlugin instance = null;

    protected DataStaxPlugin() {
        // Exists only to defeat instantiation.
    }

    public void connect() {
        node = ReadPropertiesFile.getProperty("db.server.name");
        port = ReadPropertiesFile.getProperty("db.server.port");

        LOGGER.debug("Connecting to DB server: " + node);
        LOGGER.debug("port: " + port);

        cluster = Cluster.builder().withPort(Integer.parseInt(port))
                .addContactPoint(node).build();

        Metadata metadata = cluster.getMetadata();
        System.out.printf("Connected to cluster: %s\n",
                metadata.getClusterName());
        for (Host host : metadata.getAllHosts()) {
            System.out.printf("Datatacenter: %s; Host: %s; Rack: %s\n",
                    host.getDatacenter(), host.getAddress(), host.getRack());
        }
        session = cluster.connect();

    }

    public void close() {
        cluster.shutdown();
    }

    public static Session getDataStaxSession() {
        synchronized (DataStaxPlugin.class) {
            try {
                if (instance == null) {
                    instance = new DataStaxPlugin();
                    instance.connect();
                }

                return session;
            } finally {
            }
        }
    }
}

我使用getDatastaxSession函数获取会话并在数据库中执行一次插入操作。最初的几个插入工作正常，但过了一段时间后，我得到了空指针异常，如下所示：

Exception in thread "Cassandra Java Driver worker-5" java.lang.NullPointerException
    at com.datastax.driver.core.Connection$Future.onException(Connection.java:602)
    at     com.datastax.driver.core.RequestHandler.setFinalException(RequestHandler.java:219)
    at com.datastax.driver.core.RequestHandler.sendRequest(RequestHandler.java:103)
    at com.datastax.driver.core.RequestHandler$1.run(RequestHandler.java:170)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:724)

此异常是由于会话为null/timedout所致吗？如果我以错误的方式创建或管理会话，请让我知道。或者，如果我的代码有任何问题，请告诉我。

Answer 1

我对获取会话的代码进行了更改

public void connect() {
    node = ReadPropertiesFile.getProperty("db.server.name");
    port = ReadPropertiesFile.getProperty("db.server.port");

    LOGGER.debug("Connecting to DB server: " + node);
    LOGGER.debug("port: " + port);

    cluster = Cluster.builder().withPort(Integer.parseInt(port))
    .addContactPoint(node).build();

    Metadata metadata = cluster.getMetadata();
    System.out.printf("Connected to cluster: %s\n", 
            metadata.getClusterName());
    for ( Host host : metadata.getAllHosts() ) {
        System.out.printf("Datatacenter: %s; Host: %s; Rack: %s\n",
                host.getDatacenter(), host.getAddress(), host.getRack());
    }


}

public void close() {
    cluster.shutdown();
}


public static Session getDataStaxSession() {
    synchronized (DataStaxPlugin.class) {
        try {
            if(instance == null)
            {
                instance = new DataStaxPlugin();
                instance.connect();
            } 
            session = cluster.connect();        
            return session;
        } finally {
        }
    }
}


public static void closeDataStaxSession() {
    synchronized (DataStaxPlugin.class) {
        try {
            if(session != null)
            {
                session.shutdown();
                session = null;
            }
        } finally {
        }
    }
}

现在，每次我为每个请求创建一个session=cluster.session，并在所有处理完成后关闭会话。

我想以前当我获取会话并试图再次使用它时，在一段时间后，当会话空闲了一段时间后导致异常，这是为Datastax java驱动程序实现会话的正确方式吗？感谢您的评论和反馈