Java Tutorial/J2ME/HttpConnection

An example MIDlet to fetch a page using an HttpConnection

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 * 
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 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;
/**
 * An example MIDlet to fetch a page using an HttpConnection.
 */
public class J2MESecondExample extends MIDlet {
  private Display display;
  private String url = "http://www.y.ru/hello.txt";
  public J2MESecondExample() {
    display = Display.getDisplay(this);
  }
  /**
   * This will be invoked when we activate the MIDlet.
   */
  public void startApp() {
    // Use the specified URL is overriden in the descriptor
    try {
      downloadPage(url);
    } catch (IOException e) {
      // handle the exception
    }
  }
  private void downloadPage(String url) throws IOException {
    StringBuffer b = new StringBuffer();
    InputStream is = null;
    HttpConnection c = null;
    TextBox t = null;
    try {
      long len = 0;
      int ch = 0;
      c = (HttpConnection) Connector.open(url);
      is = c.openInputStream();
      len = c.getLength();
      if (len != -1) {
        // Read exactly Content-Length bytes
        for (int i = 0; i < len; i++)
          if ((ch = is.read()) != -1)
            b.append((char) ch);
      } else {
        // Read till the connection is closed.
        while ((ch = is.read()) != -1) {
          len = is.available();
          b.append((char) ch);
        }
      }
      t = new TextBox("hello again....", b.toString(), 1024, 0);
    } finally {
      is.close();
      c.close();
    }
    display.setCurrent(t);
  }
  /**
   * Pause, discontinue....
   */
  public void pauseApp() {
  }
  /**
   * Destroy must cleanup everything.
   */
  public void destroyApp(boolean unconditional) {
  }
}

An example MIDlet to invoke a CGI script (POST method is used).

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.TextBox;
import javax.microedition.midlet.MIDlet;
public class InvokeCgiMidlet2 extends MIDlet {
  private Display display;
  String url = "http://www.g.ru/get.cgi";
  public InvokeCgiMidlet2() {
    display = Display.getDisplay(this);
  }
  public void startApp() {
    try {
      getGrade(url);
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  void getGrade(String url) throws IOException {
    HttpConnection c = null;
    InputStream is = null;
    OutputStream os = null;
    StringBuffer b = new StringBuffer();
    TextBox t = null;
    try {
      c = (HttpConnection) Connector.open(url);
      c.setRequestMethod(HttpConnection.POST);
      c.setRequestProperty("CONTENT-TYPE", "application/x-www-form-urlencoded");
      c.setRequestProperty("User-Agent", "Profile/MIDP-1.0 Confirguration/CLDC-1.0");
      c.setRequestProperty("Content-Language", "en-CA");
      os = c.openOutputStream();
      String str = "name=1";
      byte postmsg[] = str.getBytes();
      for (int i = 0; i < postmsg.length; i++) {
        os.write(postmsg[i]);
      }
      os.flush();
      is = c.openDataInputStream();
      int ch;
      while ((ch = is.read()) != -1) {
        b.append((char) ch);
      }
      t = new TextBox("Final Grades", b.toString(), 1024, 0);
    } 
    display.setCurrent(t);
  }
}

Load Image with HttpConnection

import java.io.DataInputStream;
import java.io.IOException;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.ImageItem;
import javax.microedition.lcdui.Item;
import javax.microedition.lcdui.StringItem;
import javax.microedition.midlet.MIDlet;
public class ImageLoaderMIDlet extends MIDlet {
  private Item mItem;
  public void startApp() {
    final Display display = Display.getDisplay(this);
    Form mainForm = new Form("Loading...");
    display.setCurrent(mainForm);
    final Form imageForm = new Form("Image");
    imageForm.addCommand(new Command("Exit", Command.EXIT, 0));
    imageForm.setCommandListener(new CommandListener() {
      public void commandAction(Command c, Displayable s) {
        notifyDestroyed();
      }
    });
    Thread t = new Thread() {
      public void run() {
        try {
          String URL = "http://localhost/Duke.png";
          Image image = loadImage(URL);
          mItem = new ImageItem(null, image, 0, null);
        } catch (IOException ioe) {
          mItem = new StringItem(null, ioe.toString());
        }
        imageForm.append(mItem);
        display.setCurrent(imageForm);
      }
    };
    t.start();
  }
  public Image loadImage(String url) throws IOException {
    HttpConnection hpc = null;
    DataInputStream dis = null;
    try {
      hpc = (HttpConnection) Connector.open(url);
      int length = (int) hpc.getLength();
      byte[] data = new byte[length];
      dis = new DataInputStream(hpc.openInputStream());
      dis.readFully(data);
      return Image.createImage(data, 0, data.length);
    } finally {
      if (hpc != null)
        hpc.close();
      if (dis != null)
        dis.close();
    }
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
}

Response Header

import java.io.IOException;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.DateField;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
public class ResponseHeaderMIDlet extends MIDlet implements CommandListener {
  private Command exitCommand = new Command("Exit", Command.EXIT, 1);
  private Command sendCommand = new Command("Send", Command.OK, 1);
  private Command backCommand = new Command("Upload", Command.OK, 1);
  private Display display;
  private String defaultURL = "http://localhost/";
  private Form mainForm, resultForm;
  private TextField URL;
  private DateField DateField1 = new DateField("Date", DateField.DATE_TIME);
  private DateField DateField2 = new DateField("Expiration", DateField.DATE_TIME);
  private DateField DateField3 = new DateField("Last Modified", DateField.DATE_TIME);
  private StringItem resultItem;
  public ResponseHeaderMIDlet() {
    display = Display.getDisplay(this);
  }
  public void startApp() {
    URL = new TextField(null, defaultURL, 250, TextField.URL);
    mainForm = new Form("Test");
    mainForm.append(URL);
    mainForm.addCommand(sendCommand);
    mainForm.addCommand(exitCommand);
    mainForm.setCommandListener(this);
    display.setCurrent(mainForm);
  }
  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }
  public void commandAction(Command c, Displayable s) {
    if (c == sendCommand) {
      String result = "";
      resultItem = new StringItem(null, result);
      resultForm = new Form("");
      String URLString = URL.getString();
      try {
        result = requestUsingGET(URLString);
      } catch (IOException e) {
        result = "Falied";
      }
      resultItem.setText(result);
      resultForm.append(resultItem);
      resultForm.append(DateField1);
      resultForm.append(DateField2);
      resultForm.append(DateField3);
      resultForm.addCommand(backCommand);
      resultForm.setCommandListener(this);
      display.setCurrent(resultForm);
    } else if (c == backCommand) {
      URL.setString(defaultURL);
      display.setCurrent(mainForm);
    } else {
      destroyApp(false);
      notifyDestroyed();
    }
  }
  private String requestUsingGET(String URLString) throws IOException {
    HttpConnection hpc = null;
    String content = "";
    try {
      hpc = (HttpConnection) Connector.open(URLString);
      int status = hpc.getResponseCode();
      if (status != HttpConnection.HTTP_OK)
        content = "Falied";
      else {
        DateField1.setDate(new java.util.Date(hpc.getDate()));
        DateField2.setDate(new java.util.Date(hpc.getExpiration()));
        DateField3.setDate(new java.util.Date(hpc.getLastModified()));
        content += "Content Type: " + hpc.getType() + "\n";
        content += "Content Length: " + hpc.getLength() + "\n";
        content += "Contnet Encoding: " + hpc.getEncoding() + "\n";
      }
      if (hpc != null)
        hpc.close();
    } catch (IOException e2) {
    }
    return content;
  }
}

Use HttpConnection

import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Alert;
import javax.microedition.lcdui.AlertType;
import javax.microedition.lcdui.rumand;
import javax.microedition.lcdui.rumandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
public class HttpMIDlet extends MIDlet implements CommandListener, Runnable {
  private Display display;
  private Form addressForm = new Form("HTTP Client");
  private Form connectForm = new Form("Connecting");
  private Form displayForm = new Form("Server Reply");
  private TextField serverURL = new TextField("URL:", "", 256, TextField.ANY);
  private StringItem messageLabel = new StringItem(null, "Connecting...\nPlease wait.");
  private Command okCommand = new Command("OK", Command.OK, 0);
  private Command exitCommand = new Command("Exit", Command.EXIT, 0);
  private Command backCommand = new Command("Back", Command.BACK, 0);
  
  protected void startApp() throws MIDletStateChangeException {
    display = Display.getDisplay(this);
    addressForm.append(serverURL);
    addressForm.addCommand(okCommand);
    addressForm.addCommand(exitCommand);
    addressForm.setCommandListener(this);
    connectForm.append(messageLabel);
    connectForm.addCommand(backCommand);
    connectForm.setCommandListener(this);
    displayForm.append(messageLabel);
    displayForm.addCommand(backCommand);
    displayForm.setCommandListener(this);
    display.setCurrent(addressForm);
  }
  protected void pauseApp() {
  }
  protected void destroyApp(boolean unconditional)
      throws MIDletStateChangeException {
  }
  public void commandAction(Command cmd, Displayable d) {
    if (cmd == okCommand) {
      Thread t = new Thread(this);
      t.start();
      display.setCurrent(connectForm);
    } else if (cmd == backCommand) {
      display.setCurrent(addressForm);
    } else if (cmd == exitCommand) {
      try {
        destroyApp(true);
      } catch (MIDletStateChangeException ex) {
      }
      notifyDestroyed();
    }
  }
  public void run() {
    InputStream is = null;
    HttpConnection conn = null;
    try {
      String url = serverURL.getString();
      if (!url.startsWith("http://") && !url.startsWith("https://")) {
        url = "http://" + url;
      }
      conn = (HttpConnection) Connector.open(url, Connector.READ_WRITE);
      if (conn.getResponseCode() == HttpConnection.HTTP_OK) {
        is = conn.openInputStream();
        final int MAX_LENGTH = 128;
        byte[] buf = new byte[MAX_LENGTH];
        int total = 0;
        while (total < MAX_LENGTH) {
          int count = is.read(buf, total, MAX_LENGTH - total);
          if (count < 0) {
            break;
          }
          total += count;
        }
        is.close();
        String reply = new String(buf, 0, total);
        messageLabel.setText(reply);
      } else {
        messageLabel.setText("Failed: error " + conn.getResponseCode() + "\n"+ conn.getResponseMessage());
      }
      conn.close();
      display.setCurrent(displayForm);
    } catch (IOException ex) {
      System.out.println(ex);
      ex.printStackTrace();
      Alert alert = new Alert("I/O Error","An error occurred while communicating with the server.", null,AlertType.ERROR);
      alert.setTimeout(Alert.FOREVER);
      display.setCurrent(alert, addressForm);
      return;
    }
  }
}