Java Rmi UnknownHostException
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Java Rmi UnknownHostException
提问by user1822343
I am trying to write a simple RMI file but for some reason it is giving me an unknown host nameexception. I have tried simply everything before actually asking a question. Here is the code for the project.
我正在尝试编写一个简单的 RMI 文件，但由于某种原因，它给了我一个未知的主机名异常。在实际提问之前，我已经尝试了一切。这是该项目的代码。
RMI interface class:
RMI接口类：
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface Hello extends Remote {
String sayHello() throws RemoteException;
}
Server Class:
服务器类：
import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class Server implements Hello {
public Server() {}
public String sayHello() {
return "Hello, world!";
}
public static void main(String args[]) {
try {
Server obj = new Server();
Hello stub = (Hello) UnicastRemoteObject.exportObject(obj, 0);
// Bind the remote object's stub in the registry
Registry registry = LocateRegistry.getRegistry();
registry.bind("Hello", stub);
System.err.println("Server ready");
} catch (Exception e) {
System.err.println("Server exception: " + e.toString());
e.printStackTrace();
}
}
}
Client class:
客户端类：
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class Client {
private Client() {}
public static void main(String[] args) {
String host = (args.length < 1) ? null : args[0];
try {
Registry registry = LocateRegistry.getRegistry(host);
Hello stub = (Hello) registry.lookup("Hello");
String response = stub.sayHello();
System.out.println("response: " + response);
} catch (Exception e) {
System.err.println("Client exception: " + e.toString());
e.printStackTrace();
}
}
}
When I run this over localhost this runs completely fine but for the life of me I cannot get this to run over the network across two machines. I've tried:
当我在本地主机上运行它时，它运行完全正常，但对于我的生活，我无法让它在两台机器上的网络上运行。我试过了：
- Connecting the machines over Wifi.
- Connecting over ethernet so they have addresses like
192.168.1.1and192.168.1.2respectively. Both machines can ping each other fine. If Inma -PNthe server from the client I can see that port1099is open and thermiregistryis running. But not matter what combination of hostnames I try it still doesn't connect the client to the server.
- 通过 Wifi 连接机器。
- 通过以太网连接，因此它们分别具有类似
192.168.1.1和 的地址192.168.1.2。两台机器可以互相ping通。如果我nma -PN从客户端访问服务器，我可以看到该端口1099已打开并且rmiregistry正在运行。但是无论我尝试什么主机名组合，它仍然无法将客户端连接到服务器。
Combinations I've tried for input as host name on client side:
我尝试在客户端作为主机名输入的组合：
rmi://192.168.1.1
rmi://192.168.1.1:1099
And maybe tens more with all possible slashes etc. still no clue why this isn't working (even though it works perfectly over localhost). Any ideas would be welcome.
并且可能还有数十个带有所有可能的斜杠等。仍然不知道为什么这不起作用（即使它在本地主机上运行良好）。欢迎任何想法。
For completeness here is the actualy error I get:
为了完整起见，这是我得到的实际错误：
java -classpath classes/ Client
Client exception: java.rmi.UnknownHostException: Unknown host: rmi://192.168.1.1; nested exception is:
java.net.UnknownHostException: rmi://192.168.1.1
java.rmi.UnknownHostException: Unknown host: rmi://192.168.1.1; nested exception is:
java.net.UnknownHostException: rmi://192.168.1.1
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:598)
at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:198)
at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:184)
at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:322)
at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
at Client.main(Client.java:14)
Caused by: java.net.UnknownHostException: rmi://192.168.1.1
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:195)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:529)
at java.net.Socket.connect(Socket.java:478)
at java.net.Socket.<init>(Socket.java:375)
at java.net.Socket.<init>(Socket.java:189)
at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:22)
at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:128)
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:595)
... 5 more
回答by user1822343
This was resolved. I'll just post my own solution. Apparently running the server like this works: java -Djava.rmi.server.hostname=192.168.1.1 Server.The problem was that when the client calls the server and gets back a stub, this stub contains this property and java sets this property to localhost by default, even if you bind the server to an ip when creating a registry. That is why it seems even though your client is connecting to a remote host, it crashes saying connection refused on localhost because the stub it has contains localhost.
这已解决。我只会发布我自己的解决方案。显然，像这样运行服务器是有效的：java -Djava.rmi.server.hostname=192.168.1.1 Server.The 问题是当客户端调用服务器并取回一个存根时，这个存根包含这个属性，java 将此属性设置为默认情况下为 localhost，即使您在创建注册表时将服务器绑定到 ip。这就是为什么即使您的客户端连接到远程主机，它也会崩溃，说 localhost 上的连接被拒绝，因为它的存根包含 localhost。
回答by George
Just a comment on the mapping between host name and IP: you can name you locator whatever you like but then you will have to insert an entry in your hosts file (C:\Windows\system32...\hosts), e.g.
只是对主机名和 IP 之间的映射的评论：您可以随意命名定位器，但随后您必须在主机文件（C:\Windows\system32...\hosts）中插入一个条目，例如
127.0.0.1 rmihost1
Then you can rmihost1 in the call:
然后你可以在调用 rmihost1 ：
LocateRegistry.getRegistry(host, port);
