Send and receive data using a network connection

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The following task shows you how to send and receive data using an HTTP connection to a web site. The data that is returned from the web site is displayed on the screen. You can use a similar process to send and receive data using other network protocols. To make this task as general as possible, the following code sends an HTTP GET command manually to a server. Normally, you would use an HttpConnection interface, which constructs the HTTP command string according to the options that you configure.

CAUTION:

Network input and output operations are not thread-safe. Make sure that you create a separate thread when you use a Connection object.

Before you begin: Open a network connection and pass a Connection object to the constructor of the class that is developed in this task. For more information about opening network connections, see Open a network connection using the Network API or Open a network connection using the GCF.

Import the required classes and interfaces.

import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.component.RichTextField;
import net.rim.device.api.ui.UiApplication;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.microedition.io.*;

Create a class that extends the MainScreen class.

public class HTTPOutputScreen extends MainScreen 
{

Create an instance variable for a RichTextField object to display the results.
```
RichTextField _rtfOutput = new RichTextField();
```
Create a constructor that accepts a Connection object as an argument.
```
public HTTPOutputScreen(Connection conn)
{
```

Add the RichTextField to your screen, and start a thread to access the network connection.

_rtfOutput.setText("Retrieving data. Please wait...");
add(_rtfOutput);
ContentReaderThread t = new ContentReaderThread(conn);
t.start();

Create a method to populate your RichTextField with the data that is returned from the web site, after ContentReaderThread completes. You invoke this method in step 20.

public void showContents(final String result) 
{
    UiApplication.getUiApplication().invokeLater(new Runnable() {

        public void run() {
            _rtfOutput.setText(result);
        }
    });
}

In an inner class, create a thread to communicate with the web server. Accept a ConnectionDescriptor object as an argument.

private final class ContentReaderThread extends Thread
{
    private Connection _connection;

    ContentReaderThread(Connection conn)
    {
        _connection = conn;
    }
    public void run()
    {

Initialize an OutputStream object and an InputStream object to exchange data with the web site.
```
    OutputStream os = null;
    InputStream is = null;
```
Initialize a String object to store the response from the web site.
```
    String result = "";
```

Create an OutputConnection object to send data over your connection.

    try
    {
        OutputConnection outputConn = (OutputConnection) connection;

Retrieve an OutputStream from your OutputConnection.

        os = outputConn.openOutputStream();
        String getCommand = "GET " + "/" + " HTTP/1.0\r\n\r\n";
        os.write(getCommand.getBytes());
        os.flush();

Send an HTTP GET command to the web server over your OutputStream. Convert the GET command into a byte array.

        String getCommand = "GET " + "/" + " HTTP/1.0\r\n\r\n";
        os.write(getCommand.getBytes());
        os.flush();

Create an InputConnection object to receive data from your connection.

        InputConnection inputConn = (InputConnection) connection;

Retrieve an InputStream from your InputConnection.

        is = inputConn.openInputStream();

Retrieve the stream data and store it in a byte array.

        byte[] data = net.rim.device.api.io.IOUtilities.streamToBytes(is);
        result = new String(data);

Catch any errors that might be generated by your procedure.

    catch(Exception e)
    {
        result = "ERROR fetching content: " + e.toString();
    }

Close your OutputStream.

        if(os != null)
        {
            try
            {
                os.close();
            }
            catch(IOException e)
            {
                // process the error condition
            }
        }

Close your InputStream.

        if(is != null)
        {
            try
            {
                is.close();
            }
            catch(IOException e)
            {
            }
        }

Close your Connection.

        {
            connection.close();
        }
        catch(IOException ioe)
        {
        }
    }

Call showContents() that you created in step 6.
```
    showContents(result);
}
}
```

Next topic: Using the BlackBerry Enterprise Server as a network gateway

Previous topic: Open a network connection using the GCF

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