Java RMI - 如何从客户端发送一个回调对象

Question

我正在使用 RMI，我有服务器客户端程序。

客户端从服务器访问一些方法。

但是在其中一种方法中，我想传递一个客户端本地对象，使用其引用服务器将执行回调（这将反过来在客户端上执行），至少这是我想要的，但可能是我正在这样做错误的。

在客户端

---------------------------------------------------------------------------------
   server.setLock("/hello.txt", 99, 125,Locker.Lock_type.WRITE,"Shubham Verma",true, new CallBackProcess());
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CallBackProcess implements an interface which is presented on both the ends. 

But I get this error    

Exception in thread "main" java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: scality.CallBackProcess (no security manager: RMI class loader disabled)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:353)
    at sun.rmi.transport.Transport$1.run(Transport.java:177)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:701)
    at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:273)
    at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:251)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:160)
    at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194)
    at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148)
    at com.sun.proxy.$Proxy1.setLock(Unknown Source)
    at scality.Client.main(Client.java:31)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: scality.CallBackProcess (no security manager: RMI class loader disabled)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:313)
    at sun.rmi.transport.Transport$1.run(Transport.java:177)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:701)
Caused by: java.lang.ClassNotFoundException: scality.CallBackProcess (no security manager: RMI class loader disabled)
    at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:393)
    at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:183)
    at java.rmi.server.RMIClassLoader$2.loadClass(RMIClassLoader.java:637)
    at java.rmi.server.RMIClassLoader.loadClass(RMIClassLoader.java:264)
    at sun.rmi.server.MarshalInputStream.resolveClass(MarshalInputStream.java:220)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1611)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1516)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1349)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
    at sun.rmi.server.UnicastRef.unmarshalValue(UnicastRef.java:324)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:307)
    ... 9 more

---

public interface Callback extends Remote{
    void execute() throws RemoteException;
}


public class CallBackProcess implements Callback, Serializable{
    public static int test = 0;
    @Override
    public void execute() {
        // need to do something here
    }
}

---

Answer 1

基本上，它试图告诉您它无法访问远程代码。它试图反序列化一个没有定义的类。这些类由客户端从“代码库”加载。它们不是由客户端通过 RMI 连接加载的，因此它们无法序列化这个它一无所知的类。

当您在命令行上启动 JVM 时，服务器应该指定系统属性“java.rmi.server.codebase”，或者在尝试运行 RMI 客户端之前在代码中设置它。该值必须是客户端可以访问的 URL，并且它应该指向要加载的必要类。通常我使用“file://”协议处理程序指定一个 .jar 文件。

反之亦然：如果客户端返回服务器必须反序列化的类，服务器必须将代码库属性设置为包含返回的类的服务器可访问的 URL。通常最好有一个 DAO 对象及其接口的 .jar 文件，由客户端和服务器共享，以避免混淆哪些类需要放在哪里。

Answer 2

你还没有导出回调对象，所以它被序列化而不是作为远程引用传递，并且对等体没有实现类，所以它得到这个错误。使其扩展 UnicastRemoteObject。