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Mobility-RPC is a Java library to bring seamless Code Mobility to any application.

Move objects or tasks, execution state, and the underlying code, seamlessly between JVMs or machines at runtime.

Overview of Mobility-RPC

Trivially easy to use

  • Move regular, unmodified Java code and objects between machines as easily as moving them around within a single application - without deploying code to the remote machines in advance
  • Write objects which can move themselves around the network seamlessly, and statefully
  • Invoke arbitrary methods or third-party libraries remotely, even if they were never designed for RPC

Powerful Design Patterns

  • Take advantage of application architectures which are not possible with conventional RPC
  • As well as the classic code mobility paradigms: remote evaluation, code on demand, mobile agents (see Wikipedia)

High performance

Read more: What is Code Mobility? and How does Mobility-RPC differ from conventional RPC?

Example Usage

These examples send objects to fictitious machines named alice and bob. In practice replace these with the name or ip address of an actual machine to which you want to send an object.

Hello World

Print "Hello World" to the console on a remote machine called "bob".

The line of code System.out.println("Hello World") is actually moved to the remote machine and executed there automatically, even though it was not deployed there in advance.

public class HelloWorld {

    public static void main(String[] args) {
        QuickTask.execute("bob", new Runnable() { public void run() {
                System.out.println("Hello World");

Retrieve Data

Retrieve system properties from the remote machine and print to the console on the local machine.

public class RetrieveData {

    public static void main(String[] args) {
        Properties data = QuickTask.execute("bob", new Callable<Properties>() {
            public Properties call() throws Exception {
                return System.getProperties();

Here a serialized Callable object, and its underlying bytecode, is sent to and executed on the remote machine, and the value it produced (a Properties object) is transported back to the local machine seamlessly.

Boomerang Pattern

The Boomerang Pattern - a Callable object which returns itself.

Send a Callable object to a remote machine, where it gathers some data, and then returns itself back to the local machine. The data is printed to the console on the local machine.

public class BoomerangPattern {

    static class BoomerangObject implements Callable<BoomerangObject> {

        private Properties someData;
        private InetAddress someOtherData;

        public BoomerangObject call() throws Exception {
            someData = System.getProperties();
            someOtherData = InetAddress.getLocalHost();
            return this;

    public static void main(String[] args) {
        BoomerangObject boomerangObject = QuickTask.execute("bob", new BoomerangObject());

Regular Object Migration

Transfer a regular object to a remote machine. The object is not special in any way and does not implement any particular interfaces.

Send the object, and call its printDetails() method on the remote machine.

public class RegularObjectMigration {

    static class RegularObject {

        private String name = "Joe Bloggs";
        private String address = "Sesame Street";

        public void printDetails() {

    public static void main(String[] args) {
        final RegularObject regularObject = new RegularObject();
        QuickTask.execute("bob", new Runnable() { public void run() {

Mobile Agent

An object which autonomously migrates itself around the network.

The main method transfers the object to machine bob, where the run() method is called. It prints "Hello World" and its hop number, 1, to the console on bob.

From bob the object transfers itself to alice, which is the next machine on its list of machines to visit. It prints "Hello World" and its incremented hop number, 2, to the console on alice.

From alice the object transfers itself back to bob again, where it prints "Hello World" and an incremented hop number, 3, but then it finds that it has run out of machines to visit, so it prints "Ran out of machines to visit".

public class MobileAgentPattern {

    static class MobileAgent implements Runnable {
        private List<String> machinesToVisit = new ArrayList<String>(Arrays.asList("alice", "bob"));
        private int hopNumber = 0;

        public void run() {
            MobilitySession session = MobilityContext.getCurrentSession();
            System.out.println("Hello World, this is hop number: " + (++hopNumber) + " in " + session);
            if (machinesToVisit.isEmpty()) {
                System.out.println("Ran out of machines to visit");
            } else {
                // Migrate to next machine and remove from the list...
                session.execute(machinesToVisit.remove(0), this);
    // Agent visits bob, then alice, then bob again...
    public static void main(String[] args) {
        QuickTask.execute("bob", new MobileAgent());

Output on bob

Hello World, this is hop number: 1 in MobilitySession{sessionId=836d7e5f-42ca-445f-acf0-4db525dcd6ab}
Hello World, this is hop number: 3 in MobilitySession{sessionId=836d7e5f-42ca-445f-acf0-4db525dcd6ab}
Ran out of machines to visit

Output on alice

Hello World, this is hop number: 2 in MobilitySession{sessionId=836d7e5f-42ca-445f-acf0-4db525dcd6ab}

Getting Started

Usage in Maven and Non-Maven Projects

Mobility-RPC is in Maven Central, and can be added to a Maven project as follows. See ReleaseNotes for the latest version number.


For non-Maven projects, and for running Mobility-RPC as a standalone server, a version built with maven-shade-plugin is also provided. It contains Mobility-RPC and all of its own dependencies packaged in a single jar file (ending "-all"). It can be downloaded from Maven central as "-all.jar" here.

Receive Incoming Objects

You can run Mobility-RPC as a library inside your application on remote machine(s), or you can run Mobility-RPC as a standalone server in its own right on remote machine(s).

Run as a library: receive incoming objects in your application

Add the Maven dependency to your application, and have your application call the following method.


Your application can then receive objects from client machines and those objects can interact with your application.

Note if your application will both send and receive objects, it is recommended that you use the same MobilityController for both, as provided by EmbeddedMobilityServer.

Run as a standalone server: send objects to arbitrary machines

Download the standalone Mobility-RPC "-all.jar" from maven central as discussed above, and then there are two ways to launch it as follows.

Method 1: Run in Graphical Mode


  • Double-click the jar on the machine on which you want to run the server. This will start Mobility-RPC as a standalone server, and it will add an icon to the system tray on Windows, the menu bar on Mac, or the notification area on Linux automatically.
  • The icon displays the IP address on which the server is running, which you can use that to send objects to the machine. The icon also allows you to shut down the mobility-rpc server when you have finished.

Method 2: Run from the command line

  • The standalone server can be launched from the command line as follows: java -jar mobility-rpc-x.x.x-all.jar
  • If a GUI is available, this will also start mobility-rpc standalone server in the system tray. If you wish to force the library not to use the GUI, supply "-Dcom.googlecode.mobilityrpc.headless=true" as a command line parameter. If no GUI is available in the first place (for example on a headless Linux server), the library will run "headless" automatically.


Note: if you have a firewall on the remote machine, choose to allow incoming connections to port 5739 on that machine.

See StandaloneMobilityServer for more details.

Running the Examples

Once you have launched Mobility-RPC as a server on a remote machine, take note of the IP address on which it is listening.

The best way to get started with Mobility-RPC, is then to add the library as a dependency to a Maven project, and try running a few of the examples above in your IDE, to send objects to the remote machine.

Copy & paste the examples into your IDE, and replace "alice" or "bob" in the examples with the ip address on which the server is running. You can then start sending objects to the remote machine.

You can launch the server on multiple remote machines, to build more sophisticated applications or to send Mobile Agents around the network.


The examples above mostly use the QuickTask class, in the quickstart package - a simplified API to the library, wrapping the main APIs, tailored for specific use cases and for getting started with the library quickly.

The main APIs of the library are marked [public api] in the API JavaDocs, but essentially the main API is as follows:

  • MobilityRPC - A static factory, to get an instance of MobilityController
  • MobilityController - Manages an instance of the library
  • MobilitySession - The gateway through which the application can send objects to remote machines

Compiling from source

If you want to compile from source and tinker with the internals of the library itself, you will need Protobuf on your machine. That's command sudo port install protobuf-java if you're on Mac, sudo apt-get install protobuf-java (or similar) if you're on Linux, or download the binaries manually from the Protobuf website if you're on Windows.

Note that Mobility-RPC was compiled with Protobuf 2.4.1. If you will compile it with a newer version of Protobuf, remember to update the version of protobuf-java in the pom.xml file to match the version of Protobuf installed on your system.


For more documentation, see the documentation directory.

Project Status

Mobility-RPC is in Maven Central (see above), and is largely feature-complete. See ReleaseNotes for version details.

Report any bugs/feature requests in the Issues tab.

For support please use the Discussion Group, not direct email to the developers.

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