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12.1.1 Rhino Example

12.1.1 Rhino Example


Example 12-1 is a simple Rhino application that demonstrates many of the features and techniques described above. The example uses the javax.swing GUI package, the java.net networking package, the java.io streaming I/O package, and Java’s multithreading capabilities to implement a simple download manager application that downloads URLs to local files and displays download progress while it does so. Fig ure 12-1 shows what the application looks like when two downloads are pending.

Figure 12-1. A GUI created with Rhino

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Example 12-1. A download manager application with Rhino

/*

* 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

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