Back | Tutorial Home | Next

There are various IPC(Inter Process Communications) approaches used in the desktop environment like

• Signals along with shared memory and pipes
  
• File writing by one application and polling/retrieval by another application.
  
• Database insert by one application and retrieval by another application.
  
• Server and client sockets
  
• In Java you can use the Classes - Process and ProcessBuilder to do IPC

Here each application runs as a separate process and can interact with the other processes. With introduction of MIDlet concurrency in MIDP 3.0, the MIDlet to MIDlet communication seems to be an important fallout. Now Two MIDlets can communicate with each other using IMC(Inter MIDlet Communication). This protocol is similar to Socket communication protocol. There are two parties here

• IMC server: MIDlet can initialize an IMC server connection
  
• IMC client: MIDlet can initialize an IMC client connection

IMC client

javax.microedition.io.IMCConnection is used for creating IMC client connection

Example : (IMCConnection)Connector.open("imc://*com.j2mesalsa.MyServer:1.0 ; false”);

Parameter definitions of the connection string is given below

MIDlet UID: This is a unique identifier of a MIDlet suite containing MIDlet name, vendor name and version. If the client want to connect to any MIDlet then * is used.
Server name: The class name of the Server.
Server version: MIDlet-Version attribute of the server. Backward compatibility is supported.
Authmode: Define whether the client is authorized to access IMC server

Code to create a IMC client connection

void imcClientRequest() throws IOException {

IMCConnection con  = null;
DataInputStream is = null;
DataOutputStream os = null;

try {

// Create connection to IMC server Class
(com.j2mesalsa.MyServer) defined in another MIDlet
con = (IMCConnection)Connector.open(
"imc://*:com.j2mesalsa.MyServer:1.0;authmode=false");


// Open outbound connection
os = con.openDataOutputStream();

// write data to output stream
String sentData = “I am J2ME=ED, Are You?”;
os.write(sentData.getBytes());
os.flush();

// Get response from IMC server
is = con.openDataInputStream();

} catch (ClassCastException e) {
		// Do your exception handling here
	} finally {
		if (is != null)
			is.close();
		if (os != null)
			os.close();
		if (con != null)
			con.close();
	}
}

As you should have already guessed from the above code. The code is similar to other Network client connections like HTTP and UDP.

Class IMCConnection has the following getter methods

• getRemoteIdentity(): Identity of the IMC server this client connects to. This method returns an object called javax.microedition.midlet.MIDletIdentity which is a new class in MIDP 3.0. This class contains information like MIDlet Name, MIDlet Version and MIDlet Vendor.
  
• getRequestedServerVersion(): Version of the IMC Server MIDlet
  
• getServerName(): Class name of the IMC Server.

IMC Server

javax.microedition.io.IMCServerConnection is used to create an IMC Server connection

(IMCServerConnection)Connector.open("imc://:<Server 
  name> :<Server version>; [<Authmode>]);

Example: (IMCServerConnection)Connector.open(
"imc://:com.j2mesalsa.MyServer:1.0;authmode=true);

Parameter definitions of the connection string is given below

Server name: The class name of the Server.
Server version: MIDlet-Version attribute of the server. Backward compatibility is supported.
Authmode: Define whether the client is authorized to access IMC server

Code to create IMC Server connection

void imcServerConnection() throws IOException {

IMCServerConnection serverCon = null;
IMCConnection con = null;
DataInputStream is = null;
DataOutputStream os = null;

try {

// Create connection to IMC server Class(com.j2mesalsa.MyServer) 
// defined in another MIDlet
IMCServerConnection serverCon = (IMCServerConnection)Connector.
open("imc://: com.j2mesalsa.MyServer:1.0;authmode=true);

while(true) {
con = (IMCConnection) serverCon.acceptAndOpen();

// Open outbound connection
os = con.openDataOutputStream();

// Open Inbound Connection
is = con.openDataInputStream();

// read data sent by the IMC client
String stringFromIMCClient = is.readString();

// write data to output stream
String sentData = “Yes, I am J2ME-ED”;
os.write(sentData.getBytes());
}

} catch (ClassCastException e) {
		// Do your exception handling here
	} finally {
		if (is != null)
			is.close();
		if (os != null)
			os.close();
		if (con != null)
			con.close();
		if (serverCon!= null)
			serverCon.close();
	}
}

Configure the server for auto launch

You will have to configure the server to push registry so that the server can auto launch whenever the request comes from the IMC client.

MIDlet-Push-1:imc://:com.j2mesalsa.MyServer:1.0;authmode=true, com.j2mesalsa.MyServer, *

MIDlet_UID is set to “*” here to allow any IMC client to connect to this IMC server, Alternatively this registration can be done in the code using PushRegistry.registerConnection().

Class IMCServerConnection has the following getter methods

• getVersion(): Version of the IMC Server MIDlet
  
• getName(): Class name of the IMC Server.

• IMC server can run in the background or can have a GUI.
• MIDlet can start the IMC server at device startup.

Interface MIDletIdentity

As discussed in the earlier section this interface has been added to MIDP 3.0 to facilitate the identification of the MIDlet during IMC. If a MIDlet-A is communicating with another MIDlet-B then MIDlet-A can query for the following parameters of MIDlet-B.

• MIDlet's suite name
  
• Version
  
• Vendor
  
• Authorization

IMCConnection con = (IMCConnection)Connector.open(
  "imc://*:com.j2mesalsa.MyServer:1.0;authmode=false");
  MIDletIdentity identity = con.getRemoteIdentity();
// MIDletIdentity gives 
// four methods to query parameters of the remote MIDlet
  String midletSuiteName = identity.getName();
  String midletVersion = identity.getVersion();
  String midletVendor = identity.getVendor();
  boolean authorization = identity.isAuthorized() 

Back | Tutorial Home | Next

More Tutorials

MIDP for Beginners
MIDP Gaming
JSR 179: Location Based Services

This page is a part of a frames based web site. If you have landed on this page from a search engine click here to view the complete page.