Developing Web Applications With Ant by Richard Hightower - HTML preview

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Overview of the Applet Class

The meat of the applet implementation is in the init() method, as shown here:

public void init(){
URL uGreeting;
String sGreeting="Bye Bye";

getAppletContext()
.showStatus("Getting hello message from server.");

try{
uGreeting = new URL(
getDocumentBase(), "HelloWorldServlet");

sGreeting = getGreeting(uGreeting);
}
catch(Exception e){

getAppletContext()
.showStatus("Unable to communicate with server.");
e.printStackTrace();
}
text.setText(sGreeting);

}

The init() method gets the document base URL (the URL from which the applet's page was loaded) from the applet context. Then, the init() method uses the document base and the URI identifying HelloWorldServlet to create a URL that has the output of HelloWorldServlet:

uGreeting = new URL( getDocumentBase(), "HelloWorldServlet");

The init() method uses a helper method called getGreeting() to parse the output of HelloWorldServlet. It then displays the greeting in the applet's JLabel (text.setText(sGreeting);). The helper method looks like this:

private String getGreeting(URL uGreeting)throws Exception{ String line;
int endTagIndex;
BufferedReader reader=null;

. . .
reader = new BufferedReader(
new InputStreamReader (
uGreeting.openStream())); while((line=reader.readLine())!=null){ System.out.println(line);

if (line.startsWith("<h1>")){
getAppletContext().showStatus("Parsing message."); endTagIndex=line.indexOf("</h1>");
line=line.substring(4,endTagIndex);
break;

}
}
...
return line;
}

Basically, the method gets the output stream from the URL (uGreeting.openStream()) and goes through the stream line by line looking for a line that begins with <h1>. Then, it pulls the text out of the <h1> tag.

The output of HelloServlet looks like this:

<html>
<head>
<title>Hello World</title>
</head>
<body>
<h1>Hello World!</h1>
</body>

The code that the helper method retrieves appears in bold. Listing 20.20 shows the complete code for HelloWorldApplet.

package xptoolkit.applet;
import javax.swing.JApplet;
import javax.swing.JLabel;
import java.awt.Font;
import java.awt.BorderLayout;
import java.applet.AppletContext;
import java.net.URL;
import java.io.InputStreamReader;
import java.io.BufferedReader;

public class HelloWorldApplet extends javax.swing.JApplet {

JLabel text; public HelloWorldApplet() {
this.getContentPane().setLayout(new BorderLayout()); text = new JLabel("Bye Bye");
text.setAlignmentX(JLabel.CENTER_ALIGNMENT); text.setAlignmentY(JLabel.CENTER_ALIGNMENT); Font f = new Font("Arial", Font.BOLD, 20); text.setFont(f);
getContentPane().add(text,BorderLayout.CENTER);

}

public void init(){
URL uGreeting;
String sGreeting="Bye Bye";

this.doLayout();
getAppletContext()
.showStatus("Getting hello message from server.");

try{ uGreeting = new URL(
this.getDocumentBase(), "HelloWorldServlet");

sGreeting = getGreeting(uGreeting); }
catch(Exception e){

getAppletContext()
.showStatus("Unable to communicate with server.");
e.printStackTrace();
}
text.setText(sGreeting);

}

private String getGreeting(URL uGreeting)throws Exception{ String line;
int endTagIndex;
BufferedReader reader=null;

try{
reader = new BufferedReader(
new InputStreamReader (

uGreeting.openStream()));
while((line=reader.readLine())!=null){
System.out.println(line);
if (line.startsWith("<h1>")){

getAppletContext().showStatus("Parsing message."); endTagIndex=line.indexOf("</h1>");
line=line.substring(4,endTagIndex);
break;

}
}
}
finally{

if (reader!=null)reader.close(); }
return line;

}
} Listing 20.20