Java RMI远程调用踩坑

Java RMI的原理就不多说了，可以在其他地方看到，这里记录主要是在尝试一个小的rmi示例的时候遇到的坑

1

示例里使用了jndi.properties来配置java的命名空间，所以要把这个文件跟编译生成的class文件放在一起(项目中就是out文件夹下那些class文件一起的位置)，并且在idea里设置项目的CLASSPATH为编译生成的文件位置

2

一开始使用的是Java13进行编译的，但是我的电脑上原来装的运行环境是Java8，这样就会报错说是版本有问题之类的，可以设置项目jdk为1.8

3

一定要在server启动之前，启动rmiregistery，在classpath下启动（也就是jndi配置文件所在的位置）

code

server

Warehouse.java

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

public interface Warehouse  extends Remote {
    double getPrice(String description) throws RemoteException;
}

WarehouseImpl.java

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
import java.util.HashMap;
import java.util.Map;

public class WarehouseImpl extends UnicastRemoteObject implements Warehouse {
    private Map<String, Double> prices;

    public WarehouseImpl() throws RemoteException
    {
        prices = new HashMap<String, Double>();
        prices.put("Blackwell Toaster", 24.95);
        prices.put("ZapXpress Microwave Oven", 49.95);
    }

    public double getPrice(String description) throws RemoteException
    {
        Double price = prices.get(description);
        return price == null ? 0 : price;
    }
}

WarehouseServer.java

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.rmi.RemoteException;

public class WarehouseServer {
    public static void main(String[] args) throws
            RemoteException, NamingException {
        System.out.println("Constructing server implementation...");
        WarehouseImpl centralWarehouse = new WarehouseImpl();

        System.out.println("Binding server implementation to registry...");
        Context namingContext = new InitialContext();
        namingContext.bind("rmi:central_warehouse", centralWarehouse);

        System.out.println("Waiting for invocations from clients...");
    }
}

client

Warehouse.java

这个文件与server端Warehouse相同

WarehouseClient.java

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.rmi.RemoteException;

public class WarehouseClient {
    public static void main(String[] args) throws NamingException, RemoteException {
        Context namingContext = new InitialContext();

        String url = "rmi://localhost/central_warehouse";
        Warehouse centralWarehouse = (Warehouse) namingContext.lookup(url);

        String descr = "Blackwell Toaster";
        double price = centralWarehouse.getPrice(descr);
        System.out.println(descr + ": " + price);
    }

}

jndi.properities

java.naming.factory.initial=com.sun.jndi.rmi.registry.RegistryContextFactory
java.naming.provider.url=rmi://localhost:1099