Implementing the invocation classes

TextViewer class

The TextViewer class displays the invoked text content in a Form. It establishes a HTTP connection with the invocation URL to get the content. In this example, the URL for the text content is located in the res/links.txt file that is defined in the JAD file

1. Create the TextViewer class file.

2. Import the required classes and assign this class to the com.nokia.midp.example.jsr211.texthandler package.

   package com.nokia.midp.example.jsr211.texthandler;
   
   import java.io.InputStream;
   
   import javax.microedition.content.Invocation;
   import javax.microedition.io.HttpConnection;
   import javax.microedition.lcdui.Alert;
   import javax.microedition.lcdui.AlertType;
   import javax.microedition.lcdui.Command;
   import javax.microedition.lcdui.CommandListener;
   import javax.microedition.lcdui.Displayable;
   import javax.microedition.lcdui.Form;
   import javax.microedition.lcdui.Item;
   import javax.microedition.lcdui.StringItem;
   

3. Create the main class and the objects to be used in this application:

   public class TextViewer extends Form implements CommandListener{
   
   	/** Intial title of the text display form*/
   	private static final String DEFAULT_TITLE = "Text Viewer";
   	
   	/** Message saying.. No content to display*/
   	private static final String NO_CONTENT = "";
   
   	/** Instance of TextHandler used to display form*/
   	private TextHandler textHandler = null;
   	
   	/** Instance of invocation. Get value from the constructor*/
   	private Invocation invoc = null;
   	
   	Command detailCommand = new Command("Details",Command.OK,1);
   	
   	/** Go back to the choice list window*/
   	Command backCommand = new Command("Back", Command.OK, 2);
   

   Create the constructor for TextViewer instances.

   	/**
   	 * @param _invoc Text Invocation instance.
   	 * @param _textHandler Instance of TextHandler
   	 */
   	TextViewer(Invocation _invoc, TextHandler _textHandler){
   		super(TextViewer.DEFAULT_TITLE);
   		
   		invoc = _invoc;
   		textHandler = _textHandler;
   		
   		this.addCommand(detailCommand);
   		this.addCommand(backCommand);
   		setCommandListener(this);
   		displayContent(invoc);
   	}
   

4. Before the invocation, the invoc object and URL need to be validated.

   	/**
   	 * @param invoc Text Invocation instance.
   	 */
   	private void displayContent(Invocation invoc) {
   		
           String url = null;
           if ((invoc == null)) {
               this.append(TextViewer.NO_CONTENT);
               return;
           }
           
           if ((url = invoc.getURL()) == null){
           	this.append(TextViewer.NO_CONTENT);
               return;
           }
           
           // Set file name as a form title
           String title = url.substring(url.lastIndexOf('/')+1);
           this.setTitle(TextViewer.DEFAULT_TITLE+" - "+title);
   
           HttpConnection conn = null;
           InputStream input = null;
           StringBuffer txtContentBuff;
   

5. Next you need to create a HTTP connection to get the text content and then append the content to the Form on the Display. The code below creates a StringBuffer for the text and then enters it into the Form.

   try {
           	//Open connection using invocation
               conn = (HttpConnection)invoc.open(false);
               conn.setRequestMethod(HttpConnection.GET);
   
               // If not successful, Display response code with response message.
               if (conn.getResponseCode() != HttpConnection.HTTP_OK) {
                   this.append(conn.getResponseMessage() + " (" + conn.getResponseCode() + ")");
                   return;
               }
   
               // Create StringBuffer with the size of response length
               txtContentBuff = new StringBuffer((int)conn.getLength());
   
               // Max size supported is char 4096;
               int maxLen = 4096;
               input = conn.openInputStream();
               // Read char and store it to the StringBuffer
               int ch = 0;
               while ((ch = input.read()) != -1) {
                   txtContentBuff.append((char)ch);
   
                   if (txtContentBuff.length() >= maxLen) {
                       break;
                   }
               }
   
               // Process the buffer and append text to the form
               this.append(new StringItem(null, txtContentBuff.toString(), Item.PLAIN));
               
           } catch (Throwable th) {
           	
               txtContentBuff = null;
               th.printStackTrace();
           } finally {
               try {
                   if (input != null) {
                       input.close();
                   }
   
                   if (conn != null) {
                       conn.close();
                   }
               } catch (Exception e) {}
           }
   	}
   

6. Add Command handling functions for the choices.

   	public void commandAction(Command command, Displayable disp) {
   		if (command == detailCommand){
   			try {
   				String details = "";
   				details = "Invocation Type: "+invoc.findType()+ "\n";
   				details += "Action: "+invoc.getAction()+ "\n";
   				details += "ID: "+invoc.getID()+ "\n";
   				details += "Invoking App Name: "+invoc.getInvokingAppName()+ "\n";
   				details += "Invoking Authority: "+invoc.getInvokingAuthority()+ "\n";
   				details += "Invoking ID: "+ invoc.getInvokingID() +"\n";
   				
   				Alert alert = new Alert("Details",details,null,AlertType.INFO);
   				alert.setTimeout(Alert.FOREVER);
   				textHandler.display.setCurrent(alert);
   			} catch (Exception e) {
   				e.printStackTrace();
   			}	
   		} else if (command == backCommand) {
   			
   			textHandler.doFinish(Invocation.OK);
   			textHandler.display.setCurrent(textHandler.choices);
   		}
   	}
   }