如何远程关闭 Java RMI 服务器
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How to remotely shutdown a Java RMI Server
提问by Clayton
I have a very simple Java RMI Server that looks like the following:
我有一个非常简单的 Java RMI 服务器，如下所示：
import java.rmi.*;
import java.rmi.server.*;
public class CalculatorImpl extends UnicastRemoteObject implements Calculator {
private String mServerName;
public CalculatorImpl(String serverName) throws RemoteException
{
super();
mServerName = serverName;
}
public int calculate(int op1, int op2) throws RemoteException
{
return op1 + op2;
}
public void exit() throws RemoteException
{
try{
Naming.unbind(mServerName);
System.out.println("CalculatorServer exiting.");
}
catch(Exception e){}
System.exit(1);
}
public static void main(String args[]) throws Exception
{
System.out.println("Initializing CalculatorServer.");
String serverObjName = "rmi://localhost/Calculator";
Calculator calc = new CalculatorImpl(serverObjName);
Naming.rebind(serverObjName, calc);
System.out.println("CalculatorServer running.");
}
}
When I call the exit method, System.exit(1) throws the following exception:
当我调用 exit 方法时，System.exit(1) 抛出以下异常：
CalculatorServer exiting.
java.rmi.UnmarshalException: Error unmarshaling return header; nested exception is:
java.io.EOFException
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:203)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:126)
at CalculatorImpl_Stub.exit(Unknown Source)
at CalculatorClient.<init>(CalculatorClient.java:17)
at CalculatorClient.main(CalculatorClient.java:29)
Caused by: java.io.EOFException
at java.io.DataInputStream.readByte(DataInputStream.java:243)
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:189)
... 4 more
[2]+ Exit 1 java CalculatorImpl
What am I doing wrong in this method?
我在这种方法中做错了什么？
回答by Clayton
In case anyone is having a similar problem, I figured out the answer myself. Here is my exit() method:
如果有人遇到类似的问题，我自己想出了答案。这是我的 exit() 方法：
public void exit() throws RemoteException
{
try{
// Unregister ourself
Naming.unbind(mServerName);
// Unexport; this will also remove us from the RMI runtime
UnicastRemoteObject.unexportObject(this, true);
System.out.println("CalculatorServer exiting.");
}
catch(Exception e){}
}
回答by Paul de Vrieze
Actually just unregistering and immediately calling System.exit doesn't shut down cleanly. It basically breaks the connection before informing the client that the message was completed. What works is to start a small thread that shuts down the system like:
实际上只是注销并立即调用 System.exit 并没有完全关闭。它基本上在通知客户端消息已完成之前断开连接。有效的是启动一个关闭系统的小线程，例如：
public void quit() throws RemoteException {
System.out.println("quit");
Registry registry = LocateRegistry.getRegistry();
try {
registry.unbind(_SERVICENAME);
UnicastRemoteObject.unexportObject(this, false);
} catch (NotBoundException e) {
throw new RemoteException("Could not unregister service, quiting anyway", e);
}
new Thread() {
@Override
public void run() {
System.out.print("Shutting down...");
try {
sleep(2000);
} catch (InterruptedException e) {
// I don't care
}
System.out.println("done");
System.exit(0);
}
}.start();
}
The thread is needed to be able to let something happen in the future while still returning from the quit method.
该线程需要能够让某些事情在未来发生，同时仍然从退出方法返回。
