Java InstantCode. Developing Applications Using Java NIO

Creating the User Interface for the File Download Application

The FileClient.java file helps create a user interface that contains a set of labels and buttons . This interface also has an empty tabular space where the file lists are displayed. End users can select a file from the list and download it.

Listing 3-5 shows the contents of the FileClient.java file:

Listing 3-5: The FileClient.java File

/* Imports java.io package class. */ import java.io.*; import java.io.File; /* Imports java.rmi package class. */ import java.rmi.*; /* Imports java.nio package class. */ import java.nio.*; import java.nio.charset.*; import java.nio.channels.*; /* Imports java.util package class. */ import java.util.Vector; import java.util.StringTokenizer; /* Imports java.awt package classes. */ import java.awt.BorderLayout; import java.awt.FlowLayout; import java.awt.GridLayout; import java.awt.Font; import java.awt.Color; import java.awt.*; /* Imports java.awt.event package classes. */ import java.awt.event.*; /* Imports javax.swing package classes. */ import javax.swing.*; import javax.swing.JButton; import javax.swing.JDialog; import javax.swing.JFileChooser; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTable; import javax.swing.JTextField; import javax.swing.LookAndFeel; import javax.swing.UIManager; /* Imports javax.swing.table package classes. */ import javax.swing.table.*; import javax.swing.table.AbstractTableModel; import javax.swing.table.DefaultTableModel; import javax.swing.table.DefaultTableColumnModel; /* Class FileClient - Initializes the interface and loads all components like table, label and button on the main window. This class is the main class of the application. Fields: title - Contains the content of the title label. panel - Contains the swing components. scrollpane - Contains the table component. table - Contains the list of files. model - Represents the default table model. listButton - Creates the Get File List button. downloadButton - Creates the Download File button. fileName - Stores the file name. filePath - Stores the file path. thread - Creates a progress bar thread. th - Creates a downloading thread. fName - Stores the file name. fExt - Stores the file extension. fout - Contains the file output stream. fchan - Contains the file channel. Methods: addWindowListener() - This method is called when an end user clicks the window close button to close the window. actionPerformed() - This method is invoked when an end user selects any command from the menu bar. display() - This method is called when an end user clicks the Get File List button to display the file list. download() - This method is called when an end user clicks the Download File button to download the specific file. main() - This method creates the main window of the application and displays it. */ public class FileClient extends JFrame implements ActionListener , Runnable { /* Declares the object of the JLabel class. */ JLabel title; /* Declares the object of the JPanel class. */ JPanel panel; JPanel pan1; JPanel pan2; JPanel pan3; /* Declares the object of the JScrollPane class. */ JScrollPane scrollpane; /* Declares the object of the JTable class. */ JTable table; /* Create and initialize the object of the Vector class. */ Vector vRow = new Vector(); Vector vCol = new Vector(); /* Declares the object of the DefaultTableModel class. */ DefaultTableModel model; /* Declare the objects of the JButton class. */ JButton listButton; JButton downloadButton; /* Declares the object of the GridBagLayout class. */ GridBagLayout gbl; /* Declares the object of the GridBagConstraints class. */ GridBagConstraints gbc; static String str1, str2; /* Declares the objects of the String class. */ String fileName; String filePath; Thread thread; Thread th; String fName; String fExt; String fname = null; String fpath = null; String path = null; static String ipAdd; /* Declares the object of the ProgressTest class. */ public ProgressTest pt; /* Declares the object of the FileOutputStream class. */ FileOutputStream fout; /* Declares the object of the FileChannel class. */ FileChannel fchan; int count = 0; int filesize, fs; int value; /* Declares the default constructor of the FileClient class. */ public FileClient() { try { /* Sets windows look and feel to the application. */ UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch(Exception e){} /* Sets the size of the window. */ setSize(470, 515); /* Sets the reliability of the progress dialog box to false. */ setResizable(false); /* Sets the title of the progress dialog box. */ setTitle("File Download Application"); /* Initializes the object of the GridBagLayout class. */ gbl = new GridBagLayout(); /* Sets the Layout */ getContentPane().setLayout(gbl); /* Creates an object of the GridBagConstraints class. */ gbc = new GridBagConstraints(); /* Initializes the title label object and adds it to the 1,1,1,1 position with CENTER alignment. */ gbc.gridx = 1; gbc.gridy = 1; gbc.gridwidth = 1; gbc.gridheight = 1; gbc.anchor = GridBagConstraints.CENTER; pan1 = new JPanel(); pan1.setLayout(new BorderLayout()); title = new JLabel(" File Download Application "); title.setFont(new Font("Verdana",Font.BOLD,20)); pan1.add(title, BorderLayout.CENTER); getContentPane().add(pan1, gbc); /* Initializes listButton and downloadButton, adds these buttons to the panel. Next, adds it to the 1,2,1,1 position with CENTER alignment. */ gbc.gridx = 1; gbc.gridy = 2; gbc.gridwidth = 1; gbc.gridheight = 1; gbc.anchor = GridBagConstraints.CENTER; pan2 = new JPanel(); pan2.setLayout(new FlowLayout()); listButton = new JButton("Get File List"); listButton.addActionListener(this); pan2.add(listButton); downloadButton = new JButton("Download the File"); downloadButton.setEnabled(false); downloadButton.addActionListener(this); pan2.add(downloadButton); getContentPane().add(pan2, gbc); /* Initializes the table label object and adds it to the 1,3,1,1 position with CENTER alignment. */ gbc.gridx = 1; gbc.gridy = 3; gbc.gridwidth = 1; gbc.gridheight = 1; gbc.anchor = GridBagConstraints.CENTER; pan3 = new JPanel(); pan3.setLayout(new BorderLayout()); /* Adds the elements at the end of the column vector. */ vCol.addElement("S. No."); vCol.addElement("File Name"); vCol.addElement("Size (Bytes)"); /* Initializes the object of the DefaultTableModel class to create a table model. */ model = new DefaultTableModel(vRow, vCol); /* Initializes the object of JTable */ table = new JTable(model); /* Sets single selection on the table */ table.setSelectionMode(0); /* Creates instance of TableColumn class and set the width of the 0th column. */ int vColIndex = 0; TableColumn col = table.getColumnModel().getColumn(vColIndex); int width = 50; col.setPreferredWidth(width); /* Creates instance of TableColumn class and set the width of the 1st column. */ vColIndex = 1; col = table.getColumnModel().getColumn(vColIndex); width = 300; col.setPreferredWidth(width); /* Creates instance of TableColumn class and sets the width of the 2nd column. */ vColIndex = 2; col = table.getColumnModel().getColumn(vColIndex); width = 100; col.setPreferredWidth(width); scrollpane = new JScrollPane(table); pan3.add(scrollpane, BorderLayout.CENTER); getContentPane().add(pan3, gbc); /* addWindowListener - Contains a windowClosing() method. windowClosing: Closes the main window It is called when the end user clicks the cancel button of the Window. Parameter: we- Object of the WindowEvent class. Return Value: NA */ addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent we) { System.exit(0); } }); } /* actionPerformed() - This method is called when the end user selects any menu item from the menu bar. Parameters: ae - An ActionEvent object containing the details of the event. Return Value: NA */ public void actionPerformed(ActionEvent ae) { /* This is executed when end user clicks the Get File List button. */ if(ae.getSource() == listButton) { /* Calls the display method. */ display(); /* Sets the caption of the listButton to "Refresh". */ listButton.setText("Refresh"); /* Enables the download button. */ downloadButton.setEnabled(true); } /* This is executed when end user clicks the Download File button. */ else if(ae.getSource() == downloadButton) { int n = table.getSelectedRow(); if ( n != -1) { /* Retrieves the value of specified column. */ Object obj1 = table.getValueAt(n, 1); Object obj2 = table.getValueAt(n, 2); fname = (obj1).toString(); fs = Integer.parseInt(obj2.toString()); filesize = fs; /* Opens a Confirm dialog box. */ value = JOptionPane.showConfirmDialog(null, "Are you sure you want to download the file?", "Confirm", JOptionPane.YES_NO_OPTION); if(value == 0) { count = 1; /* Initializes a new thread. */ th = new Thread(this); /* Starts the thread. */ th.start(); } else if(value == 1) { } } else { /* Opens the error messages. */ JOptionPane.showMessageDialog(null, "You must select a file before downloading!", "Message", JOptionPane.ERROR_MESSAGE); } } } /* display() - This method is called when the end user clicks the List the File button of the File Download Application window. Parameters: NA Return Value: NA */ public void display() { /* Creates and initialize the object of the vector class. */ Vector vec = new Vector(); /* Sets the number of rows in a table model to ZERO. */ model.setRowCount(0); /* Creates the object of the FileInfo class. */ FileInfo obj; try { String str = "rmi://"+ipAdd+"/FServer"; /* Creates an instance of the FileRemote interface that looks up the remote object from the specified location. */ FileRemote f = (FileRemote)Naming.lookup(str); /* Calls the displayList() method that returns the list of files stored in the File server. */ vec = f.displayList(); if((vec!=null) && (vec.size()>0)) { for(int i=0; i<vec.size(); i++) { /* Initializes the vRow object of the Vector class. */ vRow = new Vector(); /* Retrieves the value from the ith location. */ obj = (FileInfo)vec.elementAt(i); /* Adds the fileIndex at the end of the vector. */ vRow.addElement(obj.fileIndex); /* Adds the fileName at the end of the vector. */ vRow.addElement(obj.fileName); /* Adds the fileSize at the end of the vector. */ vRow.addElement(obj.fileSize); /* Adds the row in the table model. */ model.addRow(vRow); } } } catch(Exception e) { System.out.println("Vector Error:" + e); } } /* download() - This method is called when the end user clicks the Download File button of the File Download Application window. Parameters: fileName - Contains the name of the file. filePath - Contains the path of the file. Return Value: NA */ public void download(String fileName, String filePath) { /* Declares the object of the ByteBuffer class. */ ByteBuffer buff; long fsize; try { String str = "rmi://"+ipAdd+"/FServer"; /* Creates an instance of the FileRemote interface that looks up the remote object from the specified location. */ FileRemote f = (FileRemote)Naming.lookup(str); /* Creates and initialize the object of the StringTokenizer class. */ StringTokenizer st = new StringTokenizer(fileName, "."); /* Retrieves the value of the string before the delimiter "." */ fName = st.nextToken(); /* Retrieves the value of the string after the delimiter ".". */ fExt = st.nextToken(); path = filePath + "." + fExt; count = 2; /* Initializes the object of the Thread class. */ thread = new Thread(this); /* Starts the thread. */ thread.start(); /* Calls the downloadFile() method that returns the content of the file. */ byte[] data = f.downloadFile(fileName); try { /* Initializes the object of the FileOutputStream class. */ fout = new FileOutputStream(path); /* Gets the channel from the output stream. */ fchan = fout.getChannel(); /* Allocates the size of the buffer. */ buff = ByteBuffer.allocateDirect((int)(data.length)); for(int i=0; i<data.length; i++) /* Reads the data from the byte array to the buffer. */ buff.put(data[i]); /* Rewinds the buffer. */ buff.rewind(); /* Writes the buffer to the channel. */ fchan.write(buff); /* Closes the channel. */ fchan.close(); /* Closes the output stream. */ fout.close(); } catch(Exception e) { } } catch(Exception e) { e.printStackTrace(); System.out.println("Error: " + e); } } /* run() - This method is called when the thread is started. Parameters: NA Return Value: NA */ public void run() { if(count == 1) { try { /* Creates and initialize the object of the JFileChooser class. */ JFileChooser jfc = new JFileChooser(); /* Sets the selection mode of the file chooser. */ jfc.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES); /* Displays the Save dialog box. */ value = jfc.showSaveDialog(this); if(value == JFileChooser.APPROVE_OPTION) { try { /* Selects the file. */ File file = jfc.getSelectedFile(); /* Retrieves the file path. */ fpath = file.getAbsolutePath(); /* Calls the downlaod() method. */ download(fname, fpath); } catch(Exception e) { e.printStackTrace(); System.out.println("Error" + e); } } } catch(Exception e) { e.printStackTrace(); System.out.println("Error" + e); } } else if(count == 2) { /* Initializes the object of ProgressTest class. */ pt = new ProgressTest(filesize, path, th); /* Sets the title. */ pt.setTitle("Download Complete."); /* Sets the label text. */ pt.label.setText("Download Complete."); /* Sets the button caption. */ pt.ok.setText(" OK "); /* Hides the progress bar. */ pt.bar.setVisible(false); } } /* main() - This method creates the main window of the user interface and displays it. Parameters: args[] - Contains any command line arguments passed. Return Value: NA */ public static void main(String args[]) { ipAdd = args[0]; /* Creates and initializes the object of the FileClient class. */ FileClient fc = new FileClient(); fc.show(); } }

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In the above code, the main() method creates an instance of the FileClient class. This class generates the main window of the File Download application, as shown in Figure 3-2:

Figure 3-2: The File Download Application User Interface

The application interface contains a tabular space where the list of files is displayed. The various methods defined in the above listing are:

• actionPerformed() : Acts as an event listener and activates an appropriate method, based on the button the end user clicks. If the end user clicks the Get File List button, the actionPerformed() method calls a display() method to display the list of files stored in the server. The actionPerformed() method also changes the button caption to Get File List to Refresh and enables the Download the File button. If an end user clicks the Download the File button, the actionPerformed() method retrieves the file name and size from the selected row of the table and opens a Confirm dialog box. After the end user clicks OK in the Confirm dialog box, the actionPerformed() method sets the value of the count variable to 1 and starts the newly initialized thread.

• display() : Creates and initializes the object of the vector class. This method then sets the row count of the table model to 0 and creates an instance of the FileInfo object to retrieve the description of a file. The display() method looks up the remote object from the specified location and calls the displayList() method that returns the list of files stored in the file server. Next, the display() method retrieves the value from the file list vector and adds the element to the table row, vRow vector. Finally, the display() method adds the row vector to the table model.

• download() : Takes the file name and file path as input parameters to download the specified file and declares the object of the ByteBuffer class. Next, the download() method looks up the remote object from the specified location and creates and initializes the object of the StringTokenizer class to get the file name extension. This method then sets the counter value to 2 and starts another new thread. The download() method also calls the downloadFile() method that returns the file in the form of a byte array. The download() method then initializes the object of the FileOutputStream class to write a file at a specified location and calls the getChannel() method of the FileChannel class. Next, this method initializes the object of the ByteBuffer class, allocates the size of the byte buffer, reads the bytes from the byte array to the buffer, and rewinds the byte buffer. Finally, the download() method writes the byte buffer to the file channel and close the file channel and output stream.

• run() : Runs the threads that are started in the application and checks the count value. If the value is 1, the run() method creates and initializes the object of the JFileChooser class to open the Save dialog box. This method then initializes the File object and gets the file using the getSelectedFile() method and the path using the getAbsolutePath() method of the File class. Next, the run() method calls the download() method. If the count value is 2, the run() method initializes the object of the ProgressTest class and opens the Download Status dialog box. After downloading, the run() method changes the title, label caption, and button caption to indicate that the file has been downloaded.