RMI示例

理论

学习笔记：JAVA RMI远程方法调用简单实例

实践

文件1
package DS.homework;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface Book extends Remote {
    String getDescription() throws RemoteException;
    Integer getNumberofStockpile() throws RemoteException;
}

文件2
package DS.homework;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class BookImpl extends UnicastRemoteObject implements Book {

    private static final long serialVersionUID = 1L;
    private String description;
    private Integer numberofStockpile;

    public BookImpl(String description, int numberofStockpile) throws RemoteException {
        super();
        this.description = description;
        this.numberofStockpile = numberofStockpile;
    }

    @Override
    public String getDescription() throws RemoteException {
        // TODO Auto-generated method stub
        return description;
    }

    @Override
    public Integer getNumberofStockpile() throws RemoteException {
        // TODO Auto-generated method stub
        return numberofStockpile;
    }

}

文件3
package DS.homework;

import java.rmi.Naming;
import java.rmi.registry.LocateRegistry;

public class Server {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try {
            BookImpl bookService1 = new BookImpl("Distributed System Concepts and Design", 1);
            BookImpl bookService2 = new BookImpl("Distributed Systems: Principles and Paradigms", 2);
            // 注册通讯端口
            LocateRegistry.createRegistry(6600);
            // 注册通讯路径
            Naming.rebind("rmi://127.0.0.1:6600/ReferenceBook1", bookService1);
            Naming.rebind("rmi://127.0.0.1:6600/ReferenceBook2", bookService2);
            System.out.println("Service Start!");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}
文件4
package DS.homework;

import java.rmi.Naming;

public class Client {
    public static void main(String[] args) {
        try {
            // 调用远程对象，注意RMI路径与接口必须与服务器配置一致
            System.out.println(Naming.lookup("rmi://127.0.0.1:6600/ReferenceBook1").getClass());
            Book book1 = (Book) Naming.lookup("rmi://127.0.0.1:6600/ReferenceBook1");
            Book book2 = (Book) Naming.lookup("rmi://127.0.0.1:6600/ReferenceBook2");
            System.out.println(book1.getDescription() + ":" + book1.getNumberofStockpile());
            System.out.println(book2.getDescription() + ":" + book2.getNumberofStockpile());
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

错误

1、java.lang.ClassCastException: $Proxy0 cannot be cast to DS.homework.BookImpl
at DS.homework.Client.main(Client.java:10)

Client中的类型应该是Book接口，而不是其实现类

2、java.rmi.server.ExportException: remote object implements illegal remote interface; nested exception is: java.lang.IllegalArgumentException: illegal remote method encountered: public abstract java.lang.String DS.homework.Book.getDescription()

remote接口应该抛出异常即

String getDescription() throws RemoteException

而不是

String getDescription()