problem with HTTP connection in J2ME

[Salman Faraz]

Respected Friends,
I am trying to establish HTTP connection through my J2ME application and trying to read the contents of a web page using this HTTP connection,but the code is throwing exceptions,I got this code from the book "Wireless Java Programming with Java 2 Micro Edition" by Yu Feng and Jun Zhu,according to the author the code is running fine and the author has also shown the results in his book,can any one please tellwhy is it throwing exceptions on my PC,the code is as follows:

/**
 * This J2ME program demonstrates how to establish a
 * HttpConnection and uses it to send a GET request
 * to web server.
 *
 * @author Yu Feng
 *
*/
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;
 
public class HttpGET extends MIDlet implements CommandListener  {
 
    /*
     * the default value for the url string is
     * <a href="http://64.28.105.110/servlets/webyu/Chapter7Servlet?request=gettimestamp" target="_blank" rel="nofollow">http://64.28.105.110/servlets/webyu/Chapter7Servlet?request=gettimestamp</a>
     *
     * user can change it to some other urls within the application
     *
    */
    private static String defaultURL =
        "http://64.28.105.110/servlets/webyu/Chapter7Servlet?request=gettimestamp";
 
    // GUI component for user to enter web url
    private Display myDisplay = null;
    private Form mainScreen;
    private TextField requestField;
 
    // GUI component for displaying web page content
    private Form resultScreen;
    private StringItem resultField;
 
    // the "send" button used on mainScreen
    Command sendCommand = new Command("SEND", Command.OK, 1);
    // the "back" button used on resultScreen
    Command backCommand = new Command("BACK", Command.OK, 1);
 
    public HttpGET(){
 
        // initializing the GUI components for entering web urls
        myDisplay = Display.getDisplay(this);
        mainScreen = new Form("Type in a URL:");
        requestField =
          new TextField(null, defaultURL,
          100, TextField.URL);
        mainScreen.append(requestField);
        mainScreen.addCommand(sendCommand);
        mainScreen.setCommandListener(this);
    }
 
    public void startApp() {
        myDisplay.setCurrent(mainScreen);
    }
 
    public void pauseApp() {
    }
 
    public void destroyApp(boolean unconditional) {
    }
 
    public void commandAction(Command c, Displayable s) {
 
        // when user clicks on "send" button on mainScreen
        if (c == sendCommand) {
 
            // retrieving the web url that user entered
            String urlstring = requestField.getString();
 
            // sending a GET request to web server
            String resultstring = sendGetRequest(urlstring);
 
            // displaying the page content retrieved from web server
            resultScreen = new Form("GET Result:");
            resultField  =
              new StringItem(null, resultstring);
            resultScreen.append(resultField);
            resultScreen.addCommand(backCommand);
            resultScreen.setCommandListener(this);
            myDisplay.setCurrent(resultScreen);
 
        } else if (c == backCommand) {
 
            // do it all over again
            requestField.setString(defaultURL);
            myDisplay.setCurrent(mainScreen);
        }
    }
 
    // send a GET request to web server
    public String sendGetRequest(String urlstring) {
 
        HttpConnection hc = null;
        DataInputStream dis = null;
 
        String message = "";
 
        try {
 
           /* openning up http connection with the web server
            * when the connection is opened, the default request
            * method is GET
           */
           hc = (HttpConnection)
              Connector.open(urlstring);
 
           // establishing input stream from the connection
           dis = new DataInputStream(hc.openInputStream());
 
           // reading the response from web server character by character
           int ch;
           while ((ch = dis.read()) != -1) {
               message = message + (char) ch;
           }
 
        } catch (IOException ioe) {
           message = "ERROR";
        } finally {
          try { if (hc != null) hc.close();} catch (IOException ignored) {}
          try { if (dis != null) dis.close();} catch (IOException ignored) {}
        }
        return message;
    }
}
 

Please reply as soon as possible.

Thanking You,
Salman Faraz.
[ July 17, 2005: Message edited by: Mark Spritzler ]

[Mark Spritzler]

The address is not found.

Just putting the address in a web browser comes back with a "404 Not FOund"

Mark

[Salman Faraz]

Respected Friend,
If I change the address to www.javaranch.com or www.yahoo.com than also the same exception is thrown,which means that either the toolkit fails to establish a connection or if it establishes a connection it fails to read the contents of the web page,can you please tell me thereason behind this?if there is some error in the code than please corrent it and inform me.

Thanking You,
Salman Faraz.

[Glenn Castro]

When I run your code, I encountered the following warning:

Running with storage root DefaultColorPhone
Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.

So I tried to change some code and make it run the connection in a separate thread. The address, http://64.28.105.110/servlets/webyu/Chapter7Servlet?request=gettimestamp, returns 404 Not Found. But if I tried to change the address into http://www.google.com it runs fine.

[lexander Bosco]

hi salman

i have used the same book too
though haven't tried out that particular example
but with some related experience i will advise u to use tomcat or any other servlet container on ur system or a system on ur local network to try it out
so u will just change the address to
.http://localhost:8080/app/mypage.html or whatever
try this i blieve it will work.

lets here what happens afterwards.
yeah castro the command handler() thing i get also
but i think it due t when u tryin to make a connection it cant establish from ur machine

[ July 28, 2005: Message edited by: lexander Bosco ]
[ July 28, 2005: Message edited by: lexander Bosco ]

[Mark Spritzler]

Originally posted by Glenn Castro:
When I run your code, I encountered the following warning:

Running with storage root DefaultColorPhone
Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.

So I tried to change some code and make it run the connection in a separate thread. The address, http://64.28.105.110/servlets/webyu/Chapter7Servlet?request=gettimestamp, returns 404 Not Found. But if I tried to change the address into http://www.google.com it runs fine.

Actually that statement is just a warning and not a problem, it is merely a suggestion to create a new thread. But in many applications you want it to block.

Mark

[Mark Spritzler]

Code works fine for me too. Using www.google.com

Mark

[pradeep u nair]

Warning: To avoid potential deadlock, operations that may block, such as
networking, should be performed in a different thread than the
commandAction() handler.

the problem is caused as you have performed an io or http action in the command handler. do as it says make it a different thread.try this code out

this code goes inside your command handler
new Thread(new Runnable()
{
public void run()
{
try{
//your desired action
}catch(Exception e){}
}
}
).start();

please verify it and inform me if it works