Question

在我的应用中，我有这段代码：

valueChanges

我有这个错误：

        SamplePoolableObjectFactory factory = new SamplePoolableObjectFactory();
        this.pool = new SampleObjectPool(factory);
.....

    SocketChannel channel = null;
            try {
    channel = (SocketChannel) this.pool.borrowObject();
....
}

我的演员出了什么问题？

Unable to borrow socket from pool java.lang.ClassCastException: java.lang.Object cannot be cast to java.nio.channels.SocketChannel

和

public class SamplePoolableObjectFactory implements PoolableObjectFactory{
    private final static Log log = LogFactory.getLog(SamplePoolableObjectFactory.class);

    /* (non-Javadoc)
     * @see org.apache.commons.pool.PoolableObjectFactory#activateObject(java.lang.Object)
     */
    public void activateObject(Object obj) throws Exception {
        log.debug("Activate object ..." + obj.hashCode());
    }
    /* (non-Javadoc)
     * @see org.apache.commons.pool.PoolableObjectFactory#destroyObject(java.lang.Object)
     */
    public void destroyObject(Object obj) throws Exception {
        log.debug("Destroy object ..." + obj.hashCode());
        obj = null;
    }
    /* (non-Javadoc)
     * @see org.apache.commons.pool.PoolableObjectFactory#makeObject()
     */
    public Object makeObject() throws Exception {
        Object obj = new Object();
        log.debug("Make object ..." + obj.hashCode());
        return obj;
    }
    /* (non-Javadoc)
     * @see org.apache.commons.pool.PoolableObjectFactory#passivateObject(java.lang.Object)
     */
    public void passivateObject(Object obj) throws Exception {
        log.debug("Passivate object ..." + obj.hashCode());

    }
    /* (non-Javadoc)
     * @see org.apache.commons.pool.PoolableObjectFactory#validateObject(java.lang.Object)
     */
    public boolean validateObject(Object obj) {
        log.debug("Validate object ..." + obj.hashCode());
        return false;
    }
}

Answer 1

您的response = emr.run_job_flow( Name="start-my-cluster", ReleaseLabel="emr-5.3.1", LogUri='s3://logs', Instances={ 'InstanceGroups': [ {'Name': 'EmrMaster', 'InstanceRole': 'MASTER', 'InstanceType': 'm3.xlarge', 'InstanceCount': 1}, {'Name': 'EmrCore', 'InstanceRole': 'CORE', 'InstanceType': 'm3.xlarge', 'InstanceCount': 2} ], 'Ec2KeyName': 'my-key-name', 'KeepJobFlowAliveWhenNoSteps' : True, }, Applications=[{'Name': 'Hadoop'}, {'Name': 'Spark'}, {'Name': 'Hive'}], JobFlowRole='EMR_EC2_DefaultRole', ServiceRole='EMR_DefaultRole', VisibleToAllUsers=True, Steps=[ # steps go here... ] )创建了public Object makeObject()。您正试图将其转换为Object。

就像猫不是狗一样，SocketChannel不是Objects，无论你多少尝试投射它们。

Answer 2

以下摘自GenericObjectPool.borrowObject()。

836             // create new object when needed
837             boolean newlyCreated = false;
838             if(null == pair) {
839                 try {
840                     Object obj = _factory.makeObject();
841                     pair = new ObjectTimestampPair(obj);
842                     newlyCreated = true;
843                 } finally {
844                     if (!newlyCreated) {
845                         // object cannot be created
846                         _numActive--;
847                         notifyAll();
848                     }
849                 }
850             }

正如您所看到的，在makeObject()的提供实例上调用了PoolableObjectFactory，因此您应该相应地实现此方法。

现在您只返回Object的实例，当然 - 无法将其转换为SocketChannel。

public Object makeObject() throws Exception {
    SocketChannel  obj = ... // create channel here
    log.debug("Make object ..." + obj.hashCode());
    return obj;
}

java.lang.Object无法强制转换为java.nio.channels.SocketChannel

2 个答案: