如何在Java中将方法或对象从客户端传递到服务器？

Question

I have multiple clients and one server. Each client has a few commands at their disposal, eg:

public interface Command {
    public int run();
}

public class CommandOne implements Command {
    // ...
}

public class CommandTwo implements Command {
    // ...
}

These commands can be executed within the client (on their machine) - or they can be "passed" to the server to be executed, and then a result will be returned.

What is the simplest way of implementing both the client and server within Java?

The following are what I've come up with:

• Serialize the command, pass it to the server, have the server deserialize it, run the command and return the result. (This won't work because methods cannot be serialized.)
• Pass a the command's name (as a String) to the server, have the server run a switch statement, instantiate a new command of the same type, run it, and return the result. This means if I ever add a new command class, I will have to update both the client and the server.
• Serialize the necessary method logic into some structure (JSON, XML, etc.), pass it to the server, have the server deserialize it into a custom class, run the method logic, and then return the result. This seems like overkill and requires writing a DSL.

Is there something I'm missing?

EDIT

Each request must be threaded in some way - because multiple clients could communicate with the server at the same time. This is probably not an issue with the above problem, though.

Answer 1

In an ugly world, the simple thing you could do is make your server expose an interface like

/commands?run=CommandOne

and pass some parameters (in body or query string) to hold command parameters.

Then use some HTTP client to submit an HTTP request to that URI. The server would instantiate and dispatch some command to execute what you wanted.

In a more structured world, you should look into RPC calls or the RESTful architectural style.

Answer 2

One solution I found really elegant and fun.

If you open a port and have a listener that is just waiting for a "Runnable" to come in, you can execute the run method. The variables will all be passed over and whatever the run method does will be done.

Even a little better have a "runOnServer()" and "runOnClient()" method. the client creates the object, passes it to the server and goes on it's way, the server executes the runOnServer() method (against the variables since they were serialized over) then the class is automatically serialized back to the client where the runOnClient() stuff is executed.

Makes it really slick to execute something on the server.

If you want to get more advanced, look into Hazlecast, it does this already.