Singleton in J2ME

Hi,
I wonder if using the Singleton Design Pattern in J2ME will bring along some problems or not.
Generally i want to use a Singleton class as a sort of a datastore during the lifetime of my midlet. I want to create an instance in the midlet class, and whenever needed i want to get the Instance back with somethingh like Singleton.getInstance() in my Canvas-Classes and so on.
Will that cause any problems concerning Persitence, GarbageCollection problems or Memory issues?
Thansk for your help
Mik

Does that mean No?
If not i thought about it because J2ME has a much smaller footprint then J2SE. Maybe it has an other Garbage Collector behavior or holding the class up in memory the whole time can cause problems. E.g. what happens when the midlet is paused? That's why i asked this question.
Thanks anyway
Mik

Similar Messages

Design Patterns and J2mE

Hey,
I do wanna know if is recommendable to use a Java Design Pattern (like Singleton, Fa�ade, etc)... in a J2ME application. I mean, a colleague of mine made a j2me application using these kind of technologies, but, when he installed in his cell phone, the application occuppied much memory. So, another guy told me that due to the limited memory space we find on these devices it's better for us to use only the MVC idea. So, is it recommendable for me to use this kind of resources???
Thanks!

Hi,
it is a good programming practice to use Design patterns. But too much of design patterns results in more classes which will be a problem in j2me sometimes.
Most of the MIDP classes uses Singleton and abstract design patterns

Can not access the Instance Data of a Singleton class from MBean

I am working against the deadline and i am sweating now. From past few days i have been working on a problem and now its the time to shout out.
I have an application (let's call it "APP") and i have a "PerformanceStatistics" MBean written for APP. I also have a Singleton Data class (let's call it "SDATA") which provides some data for the MBean to access and calculate some application runtime stuff. Thus during the application startup and then in the application lifecysle, i will be adding data to the SDATA instance.So, this SDATA instance always has the data.
Now, the problem is that i am not able to access any of the data or data structures from the PerformanceStatistics MBean. if i check the data structures when i am adding the data, all the structures contains data. But when i call this singleton instance from the MBean, am kind of having the empty data.
Can anyone explain or have hints on what's happening ? Any help will be appreciated.
I tried all sorts of DATA class being final and all methods being synchronized, static, ect.,, just to make sure. But no luck till now.
Another unfortunate thing is that, i some times get different "ServicePerformanceData " instances (i.e. when i print the ServicePerformanceData.getInstance() they are different at different times). Not sure whats happening. I am running this application in WebLogic server and using the JConsole.
Please see the detailed problem at @ http://stackoverflow.com/questions/1151117/can-not-access-the-instance-data-of-a-singleton-class-from-mbean
I see related problems but no real solutions. Appreciate if anyone can throw in ideas.
http://www.velocityreviews.com/forums/t135852-rmi-singletons-and-multiple-classloaders-in-weblogic.html
http://www.theserverside.com/discussions/thread.tss?thread_id=12194
http://www.jguru.com/faq/view.jsp?EID=1051835
Thanks,
Krishna

I am working against the deadline and i am sweating now. From past few days i have been working on a problem and now its the time to shout out.
I have an application (let's call it "APP") and i have a "PerformanceStatistics" MBean written for APP. I also have a Singleton Data class (let's call it "SDATA") which provides some data for the MBean to access and calculate some application runtime stuff. Thus during the application startup and then in the application lifecysle, i will be adding data to the SDATA instance.So, this SDATA instance always has the data.
Now, the problem is that i am not able to access any of the data or data structures from the PerformanceStatistics MBean. if i check the data structures when i am adding the data, all the structures contains data. But when i call this singleton instance from the MBean, am kind of having the empty data.
Can anyone explain or have hints on what's happening ? Any help will be appreciated.
I tried all sorts of DATA class being final and all methods being synchronized, static, ect.,, just to make sure. But no luck till now.
Another unfortunate thing is that, i some times get different "ServicePerformanceData " instances (i.e. when i print the ServicePerformanceData.getInstance() they are different at different times). Not sure whats happening. I am running this application in WebLogic server and using the JConsole.
Please see the detailed problem at @ http://stackoverflow.com/questions/1151117/can-not-access-the-instance-data-of-a-singleton-class-from-mbean
I see related problems but no real solutions. Appreciate if anyone can throw in ideas.
http://www.velocityreviews.com/forums/t135852-rmi-singletons-and-multiple-classloaders-in-weblogic.html
http://www.theserverside.com/discussions/thread.tss?thread_id=12194
http://www.jguru.com/faq/view.jsp?EID=1051835
Thanks,
Krishna

Send email from j2me through servlet

Hi people,
i hope you can help me because i am new in network programming.
I am trying to send email from j2me to googlemail account I have 2 classes EmailMidlet (which has been tested with wireless Toolkit 2.5.2 and it works) and the second class is the servlet-class named EmailServlet:
when i call the EmailServlet, i get on the console:
Server: 220 mx.google.com ESMTP g28sm19313024fkg.21
Server: 250 mx.google.com at your service
this is the code of my EmailServlet
import java.io.*;
import java.net.Socket;
import java.net.UnknownHostException;
import java.text.*;
import java.util.Date;
import javax.servlet.*;
import javax.servlet.http.*;
public class EmailServlet extends HttpServlet {
   public void doPost(HttpServletRequest request, HttpServletResponse response)
         throws IOException, ServletException {
      System.out.println("____emailservlet.doPost");
      response.setContentType("text/plain");
      PrintWriter out = response.getWriter();
      System.out.println("______________________________");
      out.println();
      String to = request.getParameter("to");
      System.out.println("____________________________to" + to);
      String subject = request.getParameter("subject");
      String msg = request.getParameter("msg");
      // construct an instance of EmailSender
      System.out.println("servlet_to" + to);
      send("[email protected]", to, subject, msg);
      out.println("mail sent....");
   public void send(String from, String to, String subject, String msg) {
      Socket smtpSocket = null;
      DataOutputStream os = null;
      DataInputStream is = null;
      try {
         smtpSocket = new Socket("smtp.googlemail.com", 25);
         os = new DataOutputStream(smtpSocket.getOutputStream());
         is = new DataInputStream(smtpSocket.getInputStream());
      } catch (UnknownHostException e) {
         System.err.println("Don't know about host: hostname");
      } catch (IOException e) {
         System.err
               .println("Couldn't get I/O for the connection to: hostname");
      if (smtpSocket != null && os != null && is != null) {
         try {
            os.writeBytes("HELO there" + "\r\n");
            os.writeBytes("MAIL FROM: " + from + "\r\n");
            os.writeBytes("RCPT TO: " + to + "\r\n");
            os.writeBytes("DATA\r\n");
            os.writeBytes("Date: " + new Date() + "\r\n"); // stamp the msg
                                                // with date
            os.writeBytes("From: " + from + "\r\n");
            os.writeBytes("To: " + to + "\r\n");
            os.writeBytes("Subject: " + subject + "\r\n");
            os.writeBytes(msg + "\r\n"); // message body
            os.writeBytes(".\r\n");
            os.writeBytes("QUIT\r\n");
            // debugging
            String responseLine;
            while ((responseLine = is.readLine()) != null) {
               System.out.println("Server: " + responseLine);
               if (responseLine.indexOf("delivery") != -1) {
                  break;
            os.close();
            is.close();
            smtpSocket.close();
         } catch (UnknownHostException e) {
            System.err.println("Trying to connect to unknown host: " + e);
         } catch (IOException e) {
            System.err.println("IOException: " + e);
   } 1.when i print "to" in EmailServlet also:
String to = request.getParameter("to");
      System.out.println("____________________________to" + to); it show null on the console :confused:
2. ist this right in case of googlemail.com?
smtpSocket = new Socket("smtp.googlemail.com", 25); I would be very grateful if somebody can help me.

jackofall
Please don't post in old threads that are long dead. When you have a question, please start a topic of your own. Feel free to provide a link to an old thread if relevant.
I'm locking this thread now.
db

J2me and java card, need help to communicate

we are trying to put together a reader to read smartcards using j2me and we figure that it would be easiest if we could develop it to work with java cards rather than standard smart cards, the problem is we get garbage when we communicate to it, the chip sends us crap, any suggestions what might be wrong, any calls we might be missing, has anyone worked with j2me and java cards or smart cards, any help would be appreciated.
einar

.... reader app and the ME behind it .... smells like mobile ....
First of all - if you want to have one mobile application running on this just make sure that whatever is written in ME can use drivers from the reader chip ....
Workin on the PC is something completely different. There was one good example how to develop one host application in Java provided with the JCOP tools long ago ... I don't know if this is now in the new Eclipse tools.
But - there was a small API provided that can give you good hints what to do - and - once you have it on the reader side - you can easily integrate ME methods with this ...

Image Processing in j2me

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I want to do image processing in mobile application(j2me).
But there are not enough java packages in mobile environment.
How to do it please let me know if any body knows.
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brightness: convert every RGB pixel to HSB -> increase luminance by constant value -> convert back to RGB
contrast: convert every RGB pixel to HSB -> multiply luminance by constant value-> convert back to RGB
You can also do both in one go.

UTF-8 encoding in J2ME

Hello,
I'm currently developing J2ME application for downloading bus schedules.
The data that I download is in polish language (eg. bus directions, stop names etc). These are xml files generated by a php script encoded in UTF-8.
The problem is that I don't know how to display that properly, so that all the polish characters are what they're supposed to be.
Some of my code for downloading content:
String getXML(String url)
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        InputStream str = null;
        //DataInputStream strd = null;
        StringBuffer sb = null;
        try
            int code;
            cn = (HttpConnection) Connector.open(url);
            code = cn.getResponseCode();
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                int read = 0;
                while ((read = r.read()) >= 0)
                    total++;
                    sb.append((char) read);
                return sb.toString();
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                throw new Exception("Nie udało się połączyć z serwerem");
        catch (Exception e)
            return null;
        finally
            try
                if (str != null)
                    str.close();
                if (cn != null)
                    cn.close();
            catch (Exception e)
    }And parsing it:
InputStreamReader reader = null;
                String xml = getScheduleXML(getSel_Line(), null, null);
                ByteArrayInputStream stream = new ByteArrayInputStream(xml.getBytes());
                reader = new InputStreamReader(stream, "UTF-8");
                parser.setInput(reader);
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                            String d2 = (String) parser.getAttributeValue(1);
                            v2.addElement(d2);
                }What do I do wrong? What is missing?

Problem solved. I had to add "UTF-8" parameter to getBytes method.

How to send sms from gsm modem(AT commands) to j2me application(not inbox)

hi
i want to send sms from gsm modem to a j2me application, for this to happen i have to send sms to a specific port in which j2me application is running.when i m trying to send sms from modem it doesnt go to application it goes to inbox.
is it related to udh settings if yes then how do i set port no in settings?if no what are the other ways.

Hi Vignesh,
Might be you can call ActiveX or DLL objects of the software installed for modem from LabVIEW, if it is unblocked.
Have a look on the link > http://zone.ni.com/devzone/cda/tut/p/id/2983
CLA 2014
CCVID 2014

Problem with Display.setCurrentItem() using J2ME-Polish

Hi,
I am fairly new to J2ME-polish and have encountered a situation that I am having a problem with. I am loading a form with a number of String Items. When I display the form I would like to focus to the last String Item that has been placed on the form. I have been using Display.setCurrentItem() in J2ME but when I try using it in J2ME-Polish I receive this message :"de.enough.polish.ui.Screen (3022): Screen: unable to focus item (did not find it in the container or is not activatable ) "
Below is a snippet of my code.
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http://forums.sun.com/thread.jspa?threadID=686256&messageID=10864566

How to get the Mobile information by using J2ME application

hi all,
I am lakshman.I am developing an application in j2me,I want my program compatible to all mobile devices.
I want to know properties and the device information with the help of a j2me application.I got the information with the help of System.getProperty(String).I found some of the information like sms,videocapture,and some of the values and the variables ... in the following
platform...null
encoding...ISO-8859-1
configuration...CLDC-1.0
profile...MIDP-2.0
locale...null
fileconnection...1.0
comport...null
hostname...iwmc-07
sms...null
smartcard...null
location version...null
sip version...null
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supmixing...false
mediaversion...1.1
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Now my question is I want to get the information of the service provider and also the present location that the mobile was present.I think there was some method to get that ...I want to get what firmware it was using .
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hi all,
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Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.
I am running the application from my Emulator(by using the default color phone).I have to check that in the device.
Can any body please give me the way to fix that,i want to test my application from my emulator is that is possible if possible ...how?.what is the procedure to implement..
thanks in advance

Sending an email through J2ME

What is the easiest way to send an email to an email account using J2ME?
I browsed google, and all of the results appeared very complex. Is there a simple way to do it (like you can with PHP)?
Thanks!

My phone doesn't have a mobile mailer.
I can't believe emailing is so difficult!
Would this solution work:
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
import javax.microedition.io.*;
import java.io.*;
import java.util.*;
public class Emailer
     String url;
     String to;
     String from;
     String subj;
     String msg;
     HttpConnection conn;
     OutputStream output;
     public Emailer(String url, String to, String from, String password,
                                            String subj)
          this.url = url;
          this.to = to;
          this.from = from+"/"+password;
          this.subj = subj;
     public boolean sendEmail(String msg)
          this.msg = msg;
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               StringBuffer buffer = new StringBuffer();
               buffer.append("To: " + to);
               buffer.append("From: " + from);
               buffer.append("Subject: " + subj);
               buffer.append("Message: " + msg);
               conn = (HttpConnection) Connector.open(url);
               conn.setRequestMethod(HttpConnection.POST);
               output = conn.openOutputStream();
               int i = 0;
               char c;
               while((c = buffer.charAt(i)) != 0)
                    output.write(c);
                    i++;
          catch (Exception e)
               return false;
          return true;
}I tried it, but I never got the email...
Also, is there a simple way to read from .txt files?
Thanks!

How to set up on device debuging with J2ME SDK 3.0 and window mobile 6.5?

I got some infomation about setting up on device debuging in J2ME SDK 3.0 with real device(e.g samsung windown mobile B7330). When I start debuging on device, I got exception when open RMS
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Hi dominikg,
At first, You can try to restart the device-manager from system tray.
If it doesn't help, then try the following:
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- Ran the device manager from <SDK>/bin directory
- try to debug again.
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BR,
Igor

How to print directly to printer using USB and Bluetooth from Java (J2ME) app.

I write mobile phone apps in Java (J2ME). I want to print directly to a printer via USB and via Bluetooth. I cannot use a print job with the Java available to me. Once upon a time you could just send text and print control characters to a printer. I would like to be able to do that again. Alternatively could you provide a 'skeleton' data stream into which I could insert my code to produce what is sent to the printer when a print job is used with Java on a laptop or PC. I just want to sent simple text with a little formatting.

Hi,
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I am an HP Employee.

MDB and Singleton

I have a MDB that receives data from a JSM queue in XML format. After converting the XML to proper Value Objects using JAXB, it calls a DAO.
We have configure the App server (WLS 8.1)to have 10 MDB in the pool.
The DAO is a singleton with a none static private data member that holds the DataSource.
The DAO.add() operation gets connection from the data source and performs the add.
When we put one msg on the JMS queue we see the transaction time in DAO.add() is an about 1 sec.
When we put 30 msgs on the JMS queue we see 10 threads accessing the singleton instance of the DAO.
I was hoping to see the DB transactions started by these 10 threads would be executed in parallel they way threaded operations should behave considering the context switching factor however what I am seeing from the log files is that the DB transactions are serialized meaning they get executed one at a time!!?? Therefore it takes 10 sec for the 10 threads to complete their work. I was expecting to see something like 3 to 4 sec for all 10 thread to complete the add operation.
Anyone has any ideas? Could it be that the Datasource is a private member of the Singleton DAO and each thread who calls the DAO.add() gets queued up to get access to the Data Source?
Any idea would be great.
Thanks.

Thanks for your answer,
So you never load classes then from configuration file? For example lets say you are processing xml message and for each xml message tag name you have in configuration file the appropriate class to handle such a message. Instead of configuration files would you then just store the values in a map of messageTagName to JNDI name?
Thanks
http://www.ellasweddingfavors.com
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Ellas Wedding Favors

How to connect the EJB webservices using kxmlrpc in J2ME

Hi all,
I am trying to develope a program in J2ME using kxmlrpc. I am having the EJB web serivce as server and its working fine , the webservice coding is as follows and i am using Sun application sever for web services
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import javax.ejb.EJBException;
import javax.ejb.Stateless;
import javax.jws.WebService;
import javax.jws.WebMethod;
import javax.jws.WebParam;
import javax.sql.*;
@Stateless()
@WebService()
public class test1 {
/* Sample Web Service Operation */
@WebMethod(operationName="sample_operation")
public String operation(@WebParam(name="param_name") String param) {
// implement the web service operation here
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param="helloworld";
return param;
Any body please help me how to call this web sevices method in J2ME client using kxmlrpc, i tried but it shows execption. And i want to know which url i want ot give inthe XmlRpcclient() and what are all the parameters to be given in xmlrpcclient.execute(). Anybody please help me on this and my kxml coding is as follows:
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;
import java.util.*;
import org.kxmlrpc.*;
public class kxmlrpc_demo extends MIDlet implements CommandListener {
private List list;
private Command exitCommand;
private String[] menuItems;
private Display display;
private Alert response;
private XmlRpcClient xmlrpc;
private Vector params, xmlArray;
public kxmlrpc_demo() {
//Initialize the User Interface
menuItems = new String[] {"Timestamp", "Randomizer", "AddressBook"};
list = new List( "Select a service", List.IMPLICIT, menuItems, null );
exitCommand = new Command( "Exit", Command.EXIT, 1 );
response = new Alert("Service Return", null, null, AlertType.INFO);
response.setTimeout( Alert.FOREVER );
//Add commands
list.addCommand( exitCommand );
list.setCommandListener( this );
//obtain a reference to the device's UI
display = Display.getDisplay( this );
}//end MyMidlet()
public void startApp() {
display.setCurrent( list );
}//end startApp()
public void pauseApp() {
}//end pauseApp()
public void destroyApp( boolean unconditional ) {
//clean up
list = null;
exitCommand = null;
display = null;
}//end destroyApp
public void commandAction( Command com, Displayable dis ) {
if ( dis == list && com == List.SELECT_COMMAND ) {
switch( list.getSelectedIndex() )
case 0:
try
xmlrpc = new XmlRpcClient( "http://localhost:4116/test1Service/test1?Tester" );
params = new Vector();
String serverTime = (String) xmlrpc.execute( "sysTime.getSystemTime", params );
response.setString( serverTime.toString() );
display.setCurrent( response );
catch ( Exception ex )
response.setString( ex.toString() );
ex.printStackTrace(); // DEBUG
display.setCurrent( response );
}//end try/catch
break;
case 1:
try
xmlrpc = new XmlRpcClient( "http://localhost:4116/test1Service/test1?Tester" );
System.out.println("url"+xmlrpc.getURL());
params = new Vector();
xmlArray = new Vector();
xmlArray.addElement( "param_name" );
// xmlArray.addElement( "5" );
// xmlArray.addElement( "12" );
params.addElement( xmlArray );
String serverTime = (String) xmlrpc.execute( "sample-operation", params);
System.out.println("servertime: "+serverTime);
response.setString( serverTime.toString() );
display.setCurrent( response );
catch ( Exception ex )
response.setString( ex.toString() );
ex.printStackTrace(); // DEBUG
display.setCurrent( response );
}//end try/catch
break;
case 2:
response.setString( "Not implemented yet." );
display.setCurrent( response );
break;
}//end switch( list.getSelectedIndex() )
else if ( com == exitCommand ) {
destroyApp( true );
notifyDestroyed();
}//end if ( dis == list && com == List.SELECT_COMMAND )
}//end CommandAction( Command, Displayable )
}//end MyMidlet
Thanks in advance.
regards
Senthil K

Any body please help me on this. I am really struggling on this

Singleton in J2ME

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