Question

I am new to J2ME and am building a mobile application where users can register, login and be presented with some member only screen where they can perform some operations.

(I am into web development, hence kindly correct me where I use a web approach. Also, I clearly understand basic java concepts but have not built a mobile app before)

So far, I have created the first screen with a login form containing a username and password textbox, and Login and Exit buttons.

The problems I am currently facing are:

1. How can I provide access to Register, Login and Exit at the same time (it seems the phone can only have two buttons at a time). Do I provide them as command buttons or normal ‘web like buttons that appear on page’? Kindly tell me how for any of the options that seems appropriate.

2. How do I send and receive data over http in the mobile application? Sample code will be appreciated.

3. How do I manage the different screens? In web development, I simply create pages and link them up. In this case, how can I display a register screen when the register button is pressed? The home screen when login is successful? or an error message when unsuccessful?

Do I have different functions that dynamically generates the screens? and I call them each time when the screens are requested?

Simple samples will be highly appreciated.

Answer 1

In J2ME,

You have the display object which determines what is shown on the screen. There are something which can be displayed. For example a Form, List, Textbox etc. Therefore what you can do is you can create the following displays

public class IndexScreen extends List implements CommandListener {

    //This will contain the options 
    //1. Register
    //2. Login
    //3. Exit
}


public class RegsterScreen extends Form implements CommandListener {

    //This will contain register fields and submit cancel command buttons

}

public class LoginScreen extends Form implements CommandListener {

   //This will contain Login specific controls
}

Now once these displayable objects are ready you can keep changing the display on some events like click of a command button.

public void commandAction(Command c, Displayable d) {

    if (c == OK) {
        nextScreen = new RegisterScreen();
        display.setCurrent(nextScreen);
    }
    if (c == BACK) {
        display.setCurrent(prevScreen);
    }

For sending and receiving data the following may help….

package madmin.client;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Display;
import madmin.res.Globals;


public class ClientRequest {

private Client client;
private Display display;
private String requestServlet;
private String requestCode;
private String requestId;
private String userId;
private String url;
private String response;
private String parameterOne;



public ClientRequest() {

}

 public boolean sendRequest() {

      boolean result = false;
      userId = Globals.getUserId();
      url = Globals.getURL() + requestServlet + "?requestCode=" + requestCode + "&requestId=" + requestId + "&userId=" + userId + "&clientIP=" + client.getIpAddress() + "&clientHostName=" + client.getHostname() + "&parameterOne=" + parameterOne;

      System.out.println("User Id value in ClientRequest " + userId);


      System.out.println("Start HTTP Connection");
      HttpConnection connection = null;
      InputStream inputstream = null;

       try {
            connection = (HttpConnection) Connector.open(url);
            connection.setRequestMethod(HttpConnection.GET);
            connection.setRequestProperty("Content-Type", "//text plain");
            connection.setRequestProperty("Connection", "close");

            System.out.println("Status Line COde: "+ connection.getResponseCode());
            System.out.println("Status Line Message: "+ connection.getResponseMessage());


            if(connection.getResponseCode()==HttpConnection.HTTP_OK){
                inputstream = connection.openInputStream();
                int length = (int) connection.getLength();
                if(length!=-1){
                    byte incomingData[] = new byte[length];
                    inputstream.read(incomingData);
                    response = new String(incomingData);
                }
                else {
                    ByteArrayOutputStream bytestream = new ByteArrayOutputStream();
                    int ch;
                    while((ch = inputstream.read())!=-1){
                        bytestream.write(ch);
                    }
                    response = new String(bytestream.toByteArray());
                    bytestream.close();
                }

               System.out.println("Response:" + response.trim());

               if(response.trim().equals("Request Submitted Successfully")){
                       result = true;
               }
               else{
                    result = false;
               }
            }
            connection.close();
            if(inputstream!=null)inputstream.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
        finally {
            if(inputstream!=null){
                try{
                    inputstream.close();
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }
        }
     return result;
 }

public Client getClient() {
    return client;
}

public void setClient(Client client) {
    this.client = client;
}

public Display getDisplay() {
    return display;
}

public void setDisplay(Display display) {
    this.display = display;
}

public String getRequestCode() {
    return requestCode;
}

public void setRequestCode(String requestCode) {
    this.requestCode = requestCode;
}

public String getRequestId() {
    return requestId;
}

public void setRequestId(String requestId) {
    this.requestId = requestId;
}

public String getRequestServlet() {
    return requestServlet;
}

public void setRequestServlet(String requestServlet) {
    this.requestServlet = requestServlet;
}

public String getResponse() {
    return response;
}

public void setResponse(String response) {
    this.response = response;
}

public String getUrl() {
    return url;
}

public void setUrl(String url) {
    this.url = url;
}

public String getUserId() {
    return userId;
}

public void setUserId(String userId) {
    this.userId = userId;
}

public String getParameterOne() {
    return parameterOne;
}

public void setParameterOne(String parameterOne) {
    this.parameterOne = parameterOne;
}

}

and….

package madmin.client;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import madmin.res.Globals;


public class ClientResponse {

private String response;


public String getResponse(String requestId) {

         System.out.println("Start HTTP Connection");
         HttpConnection connection = null;
         InputStream inputstream = null;
         response = "";

          try{

            connection = (HttpConnection) Connector.open( Globals.getURL() + "ResponseServlet?requestId=" + requestId);
            connection.setRequestMethod(HttpConnection.GET);
            connection.setRequestProperty("Content-Type", "//text plain");
            connection.setRequestProperty("Connection", "close");

            System.out.println("Status Line COde: "+ connection.getResponseCode());
            System.out.println("Status Line Message: "+ connection.getResponseMessage());

            if(connection.getResponseCode()==HttpConnection.HTTP_OK){
                inputstream = connection.openInputStream();
                int length = (int) connection.getLength();
                if(length!=-1){
                    byte incomingData[] = new byte[length];
                    inputstream.read(incomingData);
                    response = new String(incomingData);
                }
                else {
                    ByteArrayOutputStream bytestream = new ByteArrayOutputStream();
                    int ch;
                    while((ch = inputstream.read())!=-1){
                        bytestream.write(ch);
                    }
                    response = new String(bytestream.toByteArray());
                    bytestream.close();
                }

               System.out.println("Response:" + response.trim());

              connection.close();
              if(inputstream!=null)inputstream.close();
            }
            }
            catch(Exception e){

                e.printStackTrace();
            }

    return response;
}
}

edited:
something like this

     public class MenuScreen extends List implements CommandListener{

     public MenuScreen() {
 append("Register", null);
     append("Login", null);
     append("Forgot password", null);


     select = new Command("Select", Command.OK, 1);
     addCommand(select);
     setCommandListener(this);

}

}

     public void commandAction(Command command, Displayable display) {

      if(command==List.SELECT_COMMAND){                 
        String menuItem = this.getString(menuIndex);
      }

      if(command==select){       
        if( menuItem.equals("Register"))
     display.setCurrent(new RegisterScreen())
 }
      }