Spring Remoting: Remote Method Invocation (RMI)

Concept Overview

Spring provides four ways to develop remote services. Remote services are services hosted on remote servers and accessed by clients over the network. For example, lets say you are developing a desktop application that needs to connect to a central server. The desktop application can be on various machines. you can use spring remoting to connect the clients on the desktop to the server. Web services developed using JAX-WS can also be developed and integrated using Spring. Here are the four remoting ways supported by spring-

  1. RMI – Remote Method Invocation – Use RMI to invoke a remote method. The java objects are serialized
  2. Hessian – Transfer binary data between the client and the server.
  3. Burlap – Transfer XML data between the client and the server. It is the XML alternative to Hessian
  4. JAX-WS – Java XML API for Web Services.

In this first tutorial we look at Spring remoting using RMI. This is how it works – Spring creates a proxy that represents the actual remote bean. The proxy is created using RmiProxyFactoryBean. The proxy can be used as a normal Spring bean and the client code does not need to know that it is actually calling a remote method. Lets look at the important classes :
org.springframework.aop.framework.ProxyFactory.RmiProxyFactoryBean
– This class will be used by the client to create a proxy to connect to the remote service. This is a spring FactoryBean for creating RMI proxies. The proxied service is use a spring bean using the interface specified in the
ServiceInterface
property. The Remote service URL can be specified by the
serviceUrl
property.
org.springframework.remoting.rmi.RmiServiceExporter –
This class will be used by the server to create a remote service. The service can be accessed by plain RMI or spring proxy class created using RmiProxyFactoryBean as explain above. This class also supports exposing non-RMI services via RMI Invoker. Any Serializable java object can be transported between the client and the server.

Sample Program Overview

The sample program below develops a simple greeting service. The example demonstrates Spring remoting using RMI

Required Libraries
  • aopalliance.jar
  • commons-logging.jar
  • log4j.jar
  • org.springframework.aop.jar
  • org.springframework.asm.jar
  • org.springframework.beans.jar
  • org.springframework.context.jar
  • org.springframework.context.support.jar
  • org.springframework.core.jar
  • org.springframework.expression.jar

Interaction Flow


  • Client sends a message call
  • This message call is handled by an RMI Proxy created by RmiProxyFactoryBean
  • The RMI Proxy converts the call into a remote call over JRMP (Java Remote Method Protocol)
  • The RMI Service Adapter created by RmiServiceExporter intercepts the remote call over JRMP
  • It forwards the method call to Service



RMI Server Code Package Structure

RMI Server Source Code



Create the GreetingService interface as shown below.

Create a method named getGreeting() that takes a name as a parameter and returns the greeting message (see line 5 below).



Create a class GreetingServiceImpl as shown below.

It implements the GreetingService interface
(described earlier)

Implement the getGreeting() method by sending a greeting message (see lines 6-8 below).



Create the StartRmiServer class as shown below.

It loads spring-config.xml
(described later)
(see line 10 below) .

Note that loading of spring-config.xml automatically starts the RMI server.



Create the spring-config-server.xml file (see below).

Declare the ‘greetingService’ (see lines 13-14 below).

Export the ‘greetingService’ using Spring’s
RmiServiceExporter
class (see lines 16-21 below).

Note the following properties of
RmiServiceExporter
class:

  • serviceName : refers the name of the server as used by the RMI Client (described later) (see line 17 below)
  • service: the service class bean which shall handle the RMI call (see line 18 below)
  • serviceInterface: The interface to be used by Spring to create proxies for RMI (see line 19 below)
  • registryPort: the default port on which the RMI service is exposed

RMI Client Code Package Structure

RMI Client Source Code

Create the GreetingService interface as shown below.

Copy the GreetingService interface created for RMI Server
(described above)
and paste it in RMI Client source code while retaining the java package structure.

Note: For reference, the source code is shown below.



Create a class TestSpringRemotingRmi shown below to test Spring RMI Remoting.

Load spring configuration file (see line 11 below)

Get a reference to GreetingService using the bean name ‘greetingService’ (see line 12 below)

Call the GreetingService.getGreting() method by passing the name ‘Alpha’ (see line 13 below)

Print the greeting message (see line 14 below).





Create the spring-config-client.xml file (see below).

Declare the ‘greetingService’ using Spring’s
RmiProxyFactoryBean
class (see lines 13-16 below).

Note the following properties of
RmiProxyFactoryBean
class:

  • serviceUrl : refers the URL of the remote service (see line 14 below).
    Note URL part ‘greetingService’ corresponds to ‘serviceName’ property of RmiServiceExporter bean defined in spring-config-server.xml (defined earlier)
  • serviceInterface: The interface to be used by Spring to create proxies for RMI (see line 15 below)


Running Sample Program
RMI Server Sample Program

This sample program has been packaged as a jar installer which will copy the source code (along with all necessary dependencies)on your machine and automatically run the program for you as shown in the steps below. To run the sampleprogram, you only need Java Runtime Environment (JRE) on your machine and nothing else.

Download And Automatically Run RMI Server Sample Program
  • Save the springremotingrmiserver-installer.jar on your machine
  • Execute/Run the jar using Java Runtime Environment


  • (Alternatively you can go the folder containing the springremotingrmiserver-installer.jar and execute the jar using
    java -jar springremotingrmiserver-installer.jar
    command)

  • You will see a wizard page as shown below
  • Enter the location of the directory where you want the program to install and run (say, C:\Temp)
  • The installer will copy the program on your machine and automatically execute it. The expected output indicating that the program has run successfully on your machine is shown in the image below.
    This shows that the RMI Server program has run successfully on your machine
  • RMI Client Sample Program

    This sample program has been packaged as a jar installer which will copy the source code (along with all necessary dependencies)on your machine and automatically run the program for you as shown in the steps below. To run the sampleprogram, you only need Java Runtime Environment (JRE) on your machine and nothing else.

    Download And Automatically Run RMI Client Sample Program
  • Save the springremotingrmiserver-installer.jar on your machine
  • Execute/Run the jar using Java Runtime Environment


  • (Alternatively you can go the folder containing the springremotingrmiserver-installer.jar and execute the jar using
    java -jar springremotingrmiclient-installer.jar
    command)

  • You will see a wizard page as shown below
  • Enter the location of the directory where you want the program to install and run (say, C:\Temp)
  • The installer will copy the program on your machine and automatically execute it. The expected output indicating that the program has run successfully on your machine is shown in the image below.
    This shows that the RMI Client program has run successfully on your machine
  • Browsing the Program
    RMI Server Sample Code

    This source code for this program is downloaded in the folder specified by you (say, C:\Temp) as an eclipse project called
    springremotingrmiserver
    . All the required libraries have also been downloaded and placed in the same location. You can open this project from Eclipe IDE and directly browse the source code. See below for details of the project structure.

    RMI Client Sample Code

    This source code for this program is downloaded in the folder specified by you (say, C:\Temp) as an eclipse project called
    springremotingrmiclient
    . All the required libraries have also been downloaded and placed in the same location. You can open this project from Eclipe IDE and directly browse the source code. See below for details of the project structure.

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