Question

将py4J与多线程Java应用程序一起使用时遇到问题。

我已经用Python实现了一个Java接口

class PythonListener(object):
    def __init__(self):
        pass
    def onNewMessage(self, message):
        print(message)
    class Java:
        implements = ["com.myMessaging.IListener"]

我从Python启动JVM：

java_gateway = JavaGateway.launch_gateway(
                die_on_exit = True)

java_import(java_gateway.jvm, 'com.myMessaging.*')

// Start the multithread messaging server
myMessaging.Server.start()
// Register the listener
myMessaging.Server.registerListener(PythonListener())

myMessaging是一个Java多线程应用程序。当消息到达时，某个线程将接收它并将调用已注册监听器的onNewMessage方法

事实上，当消息到达时，我收到此错误

py4j.Py4JException: Error while obtaining a new communication channel
    at py4j.CallbackClient.getConnectionLock(CallbackClient.java:257)
    at py4j.CallbackClient.sendCommand(CallbackClient.java:377)
    at py4j.CallbackClient.sendCommand(CallbackClient.java:356)
    at py4j.reflection.PythonProxyHandler.invoke(PythonProxyHandler.java:106)
    at com.sun.proxy.$Proxy79.onNewMessage(Unknown Source)
    at com.myMessaging.Server.notifyMessage(Server.java:235)
       ...Some stuff...
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:218)
    at javax.net.DefaultSocketFactory.createSocket(SocketFactory.java:212)
    at py4j.CallbackConnection.start(CallbackConnection.java:226)
    at py4j.CallbackClient.getConnection(CallbackClient.java:238)
    at py4j.CallbackClient.getConnectionLock(CallbackClient.java:250)
    ... 32 more

我认为这是因为有多个Java线程试图在同一个端口上连接到同一个Python实例，但是如何修复它？我假设系统是多线程的，如here in the Py4J guide所述。

这可能是接口实现中的错误吗？谢谢你的帮助！

Answer 1

使用launch_gateway时，不会启动负责执行Python回调的回调服务器。你必须明确地启动它：

java_gateway = JavaGateway.launch_gateway(die_on_exit = True)
java_gateway.start_callback_server()
# Your code here

请注意，这将使用Python回调的默认端口，但您正在使用短暂的端口进行Java调用。如果您想为Java和Python使用临时端口the solution presented in the advanced topics section of Py4J is a bit more convoluted。

py4J在多线程java上获取新通信通道时出错

1 个答案: