【发布时间】：2012-07-01 16:01:48
【问题描述】：
我刚刚开始学习如何使用 RMI，我有一个问题。我有以下目录结构：
compute.jar
client
|
org\examples\rmi\client
|--> ComputePi // client main
|--> Pi // implements Task
org\examples\rmi\compute
|--> Compute // interface
|--> Task // interface
server
|
org\examples\rmi\engine
|--> ComputeEngine // server main, implements Compute
org\examples\rmi\compute
|--> Compute // interface
|--> Task // interface
这是 ComputePi 类中的main 方法：
if (System.getSecurityManager() == null) {
System.setSecurityManager(new SecurityManager());
}
try {
String name = "Compute";
// args[0] = 127.0.0.1, args[1] is irrelevant
Registry registry = LocateRegistry.getRegistry(args[0], 0);
Compute comp = (Compute) registry.lookup(name);
Pi task = new Pi(Integer.parseInt(args[1]));
BigDecimal pi = comp.executeTask(task);
System.out.println(pi);
}
catch (Exception e) {
System.err.println("ComputePi exception:");
e.printStackTrace();
}
这是 ComputeEngine 类中的 main 方法：
if (System.getSecurityManager() == null) {
System.setSecurityManager(new SecurityManager());
}
try {
String name = "Compute";
Compute engine = new ComputeEngine();
Compute stub = (Compute) UnicastRemoteObject.exportObject(engine, 0);
Registry registry = LocateRegistry.getRegistry();
registry.rebind(name, stub);
System.out.println("ComputeEngine bound.");
}
catch (Exception e) {
System.err.println("ComputeEngine exception: ");
e.printStackTrace();
}
这是 executeTask 方法，也在 ComputeEngine 类中：
public <T> T executeTask(Task<T> task) throws RemoteException {
if (task == null) {
throw new IllegalArgumentException("task is null");
}
return task.execute();
}
RMI 注册表和服务器启动正常。以下是服务器的参数：
C:\Users\Public\RMI\server>set CLASSPATH=
C:\Users\Public\RMI\server>start rmiregistry
C:\Users\Public\RMI\server>java -Djava.rmi.server.codebase="file:/C:/Users/Public/RMI/compute.jar" -Djava.rmi.server.hostname=127.0.0.1 -Djava.security.policy=server.policy org.examples.rmi.engine.ComputeEngine
这是客户端的参数：
C:\Users\Public\RMI\client>java -Djava.rmi.server.codebase="file:/C:/Users/Public/RMI/compute.jar" -Djava.security.policy=client.policy org.examples.rmi.client.ComputePi 127.0.0.1 45
但是，当我尝试运行客户端时，出现以下异常：
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is:
java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
java.lang.ClassNotFoundException: org.examples.rmi.client.Pi
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
at sun.rmi.server.UnicastRef.invoke(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invoke(Unknown Source)
at $Proxy0.executeTask(Unknown Source)
at org.examples.rmi.client.ComputePi.main(ComputePi.java:38)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
java.lang.ClassNotFoundException: org.examples.rmi.client.Pi
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.examples.rmi.client.Pi
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
at java.rmi.server.RMIClassLoader$2.loadClass(Unknown Source)
at java.rmi.server.RMIClassLoader.loadClass(Unknown Source)
at sun.rmi.server.MarshalInputStream.resolveClass(Unknown Source)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at sun.rmi.server.UnicastRef.unmarshalValue(Unknown Source)
... 11 more
但是如果我将 Pi.class 文件添加到服务器目录：
server
|
org\examples\rmi\engine
|--> ComputeEngine // server main, implements Compute
org\examples\rmi\compute
|--> Compute // interface
|--> Task // interface
org\examples\rmi\client
|--> Pi // same as Pi for client
该程序有效。我的问题是，Pi.class 真的需要在服务器上才能让我的程序运行吗？我的理解是（如果我错了，请纠正我）我将该类的一个实例发送到服务器，服务器会知道如何处理它，即它不关心实现。有人可以解释 RMI 在我的情况下是如何工作的吗？对此，我真的非常感激。谢谢！
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