Example 12-1. A download manager application with Rhino

Rhino.js

/*
 * A download manager application with a simple Java GUI
 */
// Import the Swing GUI components and a few other classes
importPackage(javax.swing); 
importClass(javax.swing.border.EmptyBorder);
importClass(java.awt.event.ActionListener);
importClass(java.net.URL);
importClass(java.io.FileOutputStream);
importClass(java.lang.Thread);
// Create some GUI widgets
var frame = new JFrame("Rhino URL Fetcher"); // The application window
var urlfield = new JTextField(30); // URL entry field
var button = new JButton("Download"); // Button to start download
var filechooser = new JFileChooser(); // A file selection dialog
var row = Box.createHorizontalBox(); // A box for field and button
var col = Box.createVerticalBox(); // For the row & progress bars
var padding = new EmptyBorder(3,3,3,3); // Padding for rows
// Put them all together and display the GUI
row.add(urlfield); // Input field goes in the row
row.add(button); // Button goes in the row
col.add(row); // Row goes in the column
frame.add(col); // Column goes in the frame
row.setBorder(padding); // Add some padding to the row
frame.pack(); // Set to minimum size
frame.visible = true; // Make the window visible
// When anything happens to the window, call this function.
frame.addWindowListener(function(e, name) {
 // If the user closes the window, exit the application.
 if (name === "windowClosing") // Rhino adds the name argument
 java.lang.System.exit(0);
});
// When the user clicks the button, call this function
button.addActionListener(function() {
 try {
 // Create a java.net.URL to represent the source URL.
 // (This will check that the user's input is well-formed)
 var url = new URL(urlfield.text);
 // Ask the user to select a file to save the URL contents to.
 var response = filechooser.showSaveDialog(frame);
 // Quit now if they clicked Cancel
 if (response != JFileChooser.APPROVE_OPTION) return;
 // Otherwise, get the java.io.File that represents the destination file
 var file = filechooser.getSelectedFile();
 // Now start a new thread to download the url
 new java.lang.Thread(function() { download(url,file); }).start();
 }
 catch(e) {
 // Display a dialog box if anything goes wrong
 JOptionPane.showMessageDialog(frame, e.message, "Exception",
 JOptionPane.ERROR_MESSAGE);
 }
});
// Use java.net.URL, etc. to download the content of the URL and use
// java.io.File, etc. to save that content to a file. Display download
// progress in a JProgressBar component. This will be invoked in a new thread.
function download(url, file) {
 try {
 // Each time we download a URL we add a new row to the window
 // to display the url, the filename, and the download progress
 var row = Box.createHorizontalBox(); // Create the row
 row.setBorder(padding); // Give it some padding
 var label = url.toString() + ": "; // Display the URL 
 row.add(new JLabel(label)); // in a JLabel
 var bar = new JProgressBar(0, 100); // Add a progress bar
 bar.stringPainted = true; // Display filename in
 bar.string = file.toString(); // the progress bar
 row.add(bar); // Add bar to this new row
 col.add(row); // Add row to the column
 frame.pack(); // Resize window
 // We don't yet know the URL size, so bar starts just animating
 bar.indeterminate = true; 
 // Now connect to the server and get the URL length if we can
 var conn = url.openConnection(); // Get java.net.URLConnection
 conn.connect(); // Connect and wait for headers
 var len = conn.contentLength; // See if we have URL length
 if (len) { // If length known, then 
 bar.maximum = len; // set the bar to display 
 bar.indeterminate = false; // the percent downloaded
 }
 // Get input and output streams
 var input = conn.inputStream; // To read bytes from server
 var output = new FileOutputStream(file); // To write bytes to file
 
 // Create an array of 4k bytes as an input buffer
 var buffer = java.lang.reflect.Array.newInstance(java.lang.Byte.TYPE,
 4096);
 var num;
 while((num=input.read(buffer)) != -1) { // Read and loop until EOF
 output.write(buffer, 0, num); // Write bytes to file
 bar.value += num; // Update progress bar
 }
 output.close(); // Close streams when done
 input.close();
 }
 catch(e) { // If anything goes wrong, display error in progress bar
 if (bar) {
 bar.indeterminate = false; // Stop animating
 bar.string = e.toString(); // Replace filename with error
 }
 }
 }