Why does java rmi keep connecting to 127.0.1.1. When ip is 192.168.X.X?

问题

I have a java rmi application i simply do:

Client:

Registry registry = LocateRegistry.getRegistry("localhost");
costApi = (CostApi) registry.lookup("server.CostApi");

Everything works fine when I host the server at localhost. When I start the same program at another machine withing the local network, at 192.168.x.x and change to:

Client:

Registry registry = LocateRegistry.getRegistry("192.168.x.x");
costApi = (CostApi) registry.lookup("server.CostApi");

it does not work anymore and it fails with a very strange error:

java.rmi.ConnectException: Connection refused to host: 127.0.1.1; nested exception is: 
    java.net.ConnectException: Connection refused
    at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:619)
    at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216)
    at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:129)
    at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194)
    at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148)
    at com.sun.proxy.$Proxy0.dataCost(Unknown Source)
    at billing.data.DataBiller.performBilling(DataBiller.java:57)
    at billing.data.DataBiller.consumeMessage(DataBiller.java:46)
    at general.templates.RabbitWorker.run(RabbitWorker.java:124)
    at java.lang.Thread.run(Thread.java:744)
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)

I'm not even trying to connect to 127.0.1.1 but to 192.168.x.x, how do I solve this? I prefer to use java code only and not modify my machine with config files. I'm using linux

回答1:

This is usually caused by a misconfiguration. Check your /etc/hosts file to ensure that:

localhost maps to 127.0.0.1
your real hostname maps to your real host address

Some Linux distributions are known to have this back to front.

If the problem persists, try setting java.rmi.server.hostname at the server to the IP address the client should use when executing remote method calls. It needs to be set before you export any remote objects, including the Registry.

The problem is caused by the IP address embedded in the stub, which ultimately comes from something like InetAddress.getLocalAddress(), which is fallible as above. It is overridden by java.rmi.server.hostname.

This is item A.1 in the FMI FAQ, but note that the item is mistitled. It doesn't happen during lookup(), it happens when you call a remote method on the resulting stub.

回答2:

I just ran into the same issue. I'm doing something very similar to what you are doing. What I noticed was that the first time I ran the client program, and it failed ( by design of the firewall test ) - that it failed with an error message showing the actual ip address of the host that I originally specified ( the 192.168.x.x address ), but all subsequent failures show that it is failing to make a connection to 127.0.0.1. Currently I'm suspecting some kind of caching on the client - has the JVM marked that ip address as never accessible again and it's refusing to ever try to connect to it again?

UPDATE: In my case, the JVM on the RMI Server side was not able to properly set the java.rmi.server.hostname property at JVM startup. This property was being left as null. When clients connect to a specific RMI Registry and ask for a stub to a particular named object, they receive a stub containing the ip address of the remote machine where the actual object can be found. The RMI server copies the contents of the java.rmi.server.hostname property into the stubs it returns to clients, so if the java.rmi.server.hostname property is "" and it copies that to each stub it creates, each stub contains a reference to remote server with an IP address of "". By default the client jvm reacts to this by attempting to connect to the server object on the localhost, 127.0.0.1. To work around the problem, try this line of code before exporting any remote objects on the server side:

System.setProperty( "java.rmi.server.hostname", "192.168.RMIServer.IP" ) ;

This property will be automatically copied to all remote stubs exported on that server, and clients who receive that stub should then be able to reach the remote server ( assuming any firewalls are configured correctly ).

来源：https://stackoverflow.com/questions/23478649/why-does-java-rmi-keep-connecting-to-127-0-1-1-when-ip-is-192-168-x-x

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java

Linux

rmi