RMI 双向通信，无需 2 个 RMI 服务器

发布于 2024-11-29 19:59:24 字数 1663 浏览 0 评论 0原文

我之前曾在许多项目中成功使用过 RMI（在 Java 6 中），其中存在明确定义的客户端/服务器关系。当我在以前的项目中使用它时，我创建了一个定义良好的接口 JAR，将其部署到客户端和服务器，并使用“-Djava.rmi.server.codebase=... -Djava”启动 RMI 服务器.rmi.server.hostname=localhost -Djava.security.policy=...\server.policy"

我现在尝试使用 RMI 执行双向通信，以构建基本集群。具体来说，我希望 B（工作人员“客户端”）向 A（中央“服务器”）注册。但是，我希望 B 实现 java.rmi.Remote 接口并将自己的引用传递回 A。这样做的主要动机是： * A 不需要知道 B 的所有实例驻留在哪里（如果需要，它们可以位于互联网上的任何位置！） * 一旦B的实例向A注册，那么A就可以控制B（即，根据A的判断对B执行任务）。

我的问题是，每当我尝试将此远程接口 (B) 作为参数传递回 A 时，我都会在 B 上收到以下异常（但如果我传递 null，则远程调用将成功发生，这使得这种解释不太可能：< a href="http://download.oracle.com/javase/1.4.2/docs/guide/rmi/codebase.html#section6" rel="nofollow">http://download.oracle.com/javase/1.4.2/docs/guide/rmi/codebase.html#section6 ）：

ERROR com.mycompany.server.dao.ServerInterfaceImpl - RMI registerWorker() failed: java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: com.mycompany.worker.MyWorker (no security manager: RMI class loader disabled)

其中： * A（实现）= com.mycompany.server.dao.ServerInterfaceImpl * B = com.mycompany.worker.MyWorker

(Q1) 是否可以执行我所描述的操作？有人能够编写我所描述的超级基本版本（即客户端 B 向服务器 A 注册，然后将对 B 的远程接口的引用传递给 A，以便 A 可以控制 B）？我最初假设我有一些模糊的拼写错误/配置问题，但我开始认为这个任务是不可能的...

（Q2）如果我想做的事情不可能，另一个想法是将 B 的每个实例变成一个 RMI 服务器，并在 B 连接到 A 后让 A 连接到 B。我不想这样做的主要原因是我希望 A 和 B（的每个实例）将被互联网分开，并且只有 A 拥有公共互联网地址（每个实例B 没有公共 IP 地址，并且可能被困在各种防火墙后面，这样 B 更容易连接到 A，反之亦然）...最终，一旦 B 有连接到A，我只是想方便双向通信！

（Q3）我正在考虑在 A 和 B 之间建立心跳。一种可能性是使用每个 B 的这些心跳来轮询 A 是否有任何未完成的工作...我更喜欢 A 异步控制 B，但是...

原文

I have used RMI (in Java 6) successfully before in a number of projects, where there was a well-defined client/server relationship. When I have been using it in previous projects, I have created a well-defined interface JAR which is deployed to both client and server, and start the RMI Server with the "-Djava.rmi.server.codebase=... -Djava.rmi.server.hostname=localhost -Djava.security.policy=...\server.policy"

I am trying to now use RMI to perform bi-directional communication, in order to build a basic cluster. Specifically, I want B (worker "client") to register with A (central "server"). However, I want B to implement the java.rmi.Remote interface and pass a reference of himself back to A. The main motivations of this are:
* A doesn't need to know where all the instances of B reside (they can be anywhere on the internet, if need be!)
* Once an instance of B has registered with A, then A can control B (ie, perform tasks on B at A's discression).

My issue is that whenever I try to pass this Remote interface (B) as a parameter back to A, I get the following exception on B (but the remote call will occur successfully if I pass null instead, which makes this explanation unlikely: http://download.oracle.com/javase/1.4.2/docs/guide/rmi/codebase.html#section6 ):

ERROR com.mycompany.server.dao.ServerInterfaceImpl - RMI registerWorker() failed: java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: com.mycompany.worker.MyWorker (no security manager: RMI class loader disabled)

Where:
* A (implementation) = com.mycompany.server.dao.ServerInterfaceImpl
* B = com.mycompany.worker.MyWorker

(Q1) Is it possible to do what I am describing? Would someone be able to write a super-basic version of what I am describing (ie, client B registers with server A, and then passes a reference to B's Remote interface to A so that A can control B)? I originally assumed I had some obscure typo/config issue, but I am starting to this this task is not possible...

(Q2) If what I am trying to do is not possible, another idea is to turn each instance of B into an RMI Server, and to get A to connect to B after B has connected to A. The main reason I do not want to do this is that I would expect A and (each instance of) B will separated by the internet, and only A would have a public internet address (each instance of B would not have a public IP address, and could be stuck behind various firewall(s), such that it is easier for B to connect to A than vice-versa) ... at the end of the day, once B has connected to A, I just want to facilitate bi-directional communication!

(Q3) I was considering having heartbeating between A and B. One possibility could be to use these heartbeats for each B to poll A with any outstanding work... I would prefer for A to asynchronously control B, however...

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