Opening Files with JFileChooser
We conclude this chapter by introducing class JFileChooser. We use this class to display a dialog (known as the JFileChooser dialog) that enables users of our program to easily select files. To demonstrate the JFileChooser dialog, we enhance the example in Section 14.4, as shown in Fig. 14.37Fig. 14.38. The example now contains a graphical user interface, but still displays the same data as before. The constructor calls method analyzePath in line 34. This method then calls method getFile in line 68 to retrieve the File object.
Figure 14.37. Demonstrating JFileChooser.
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1 // Fig. 14.37: FileDemonstration.java 2 // Demonstrating the File class. 3 import java.awt.BorderLayout; 4 import java.awt.event.ActionEvent; 5 import java.awt.event.ActionListener; 6 import java.io.File; 7 import javax.swing.JFileChooser; 8 import javax.swing.JFrame; 9 import javax.swing.JOptionPane; 10 import javax.swing.JScrollPane; 11 import javax.swing.JTextArea; 12 import javax.swing.JTextField; 13 14 public class FileDemonstration extends JFrame 15 { 16 private JTextArea outputArea; // used for output 17 private JScrollPane scrollPane; // used to provide scrolling to output 18 19 // set up GUI 20 public FileDemonstration() 21 { 22 super( "Testing class File" ); 23 24 outputArea = new JTextArea(); 25 26 // add outputArea to scrollPane 27 scrollPane = new JScrollPane( outputArea ); 28 29 add( scrollPane, BorderLayout.CENTER ); // add scrollPane to GUI 30 31 setSize( 400, 400 ); // set GUI size 32 setVisible( true ); // display GUI 33 34 analyzePath(); // create and analyze File object 35 } // end FileDemonstration constructor 36 37 // allow user to specify file name 38 private File getFile() 39 { 40 // display file dialog, so user can choose file to open 41 JFileChooser fileChooser = new JFileChooser(); 42 fileChooser.setFileSelectionMode( 43 JFileChooser.FILES_AND_DIRECTORIES ); 44 45 int result = fileChooser.showOpenDialog( this ); 46 47 // if user clicked Cancel button on dialog, return 48 if ( result == JFileChooser.CANCEL_OPTION ) 49 System.exit( 1 ); 50 51 File fileName = fileChooser.getSelectedFile(); // get selected file 52 53 // display error if invalid 54 if ( ( fileName == null ) || ( fileName.getName().equals( "" ) ) ) 55 { 56 JOptionPane.showMessageDialog( this, "Invalid File Name", 57 "Invalid File Name", JOptionPane.ERROR_MESSAGE ); 58 System.exit( 1 ); 59 } // end if 60 61 return fileName; 62 } // end method getFile 63 64 // display information about file user specifies 65 public void analyzePath() 66 { 67 // create File object based on user input 68 File name = getFile(); 69 70 if ( name.exists() ) // if name exists, output information about it 71 { 72 // display file (or directory) information 73 outputArea.setText( String.format( 74 "%s%s %s %s %s %s%s %s%s %s%s %s%s %s%s", 75 name.getName(), " exists", 76 ( name.isFile() ? "is a file" : "is not a file" ), 77 ( name.isDirectory() ? "is a directory" : 78 "is not a directory" ), 79 ( name.isAbsolute() ? "is absolute path" : 80 "is not absolute path" ), "Last modified: ", 81 name.lastModified(), "Length: ", name.length(), 82 "Path: ", name.getPath(), "Absolute path: ", 83 name.getAbsolutePath(), "Parent: ", name.getParent() ) ); 84 85 if ( name.isDirectory() ) // output directory listing 86 { 87 String directory[] = name.list(); 88 outputArea.append( " Directory contents: " ); 89 90 for ( String directoryName : directory ) 91 outputArea.append( directoryName + " " ); 92 } // end else 93 } // end outer if 94 else // not file or directory, output error message 95 { 96 JOptionPane.showMessageDialog( this, name + 97 " does not exist.", "ERROR", JOptionPane.ERROR_MESSAGE ); 98 } // end else 99 } // end method analyzePath 100 } // end class FileDemonstration |
Figure 14.38. Testing class FileDemonstration.
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1 // Fig. 14.38: FileDemonstrationTest.java 2 // Testing the FileDmonstration class. 3 import javax.swing.JFrame; 4 5 public class FileDemonstrationTest 6 { 7 public static void main( String args[] ) 8 { 9 FileDemonstration application = new FileDemonstration(); 10 application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); 11 } // end main 12 } // end class FileDemonstrationTest
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Method getFile is defined in lines 3862 of Fig. 14.37. Line 41 creates a JFileChooser and assigns its reference to fileChooser. Lines 4243 call method setFileSelectionMode to specify what the user can select from the fileChooser. For this program, we use JFileChooser static constant FILES_AND_DIRECTORIES to indicate that files and directories can be selected. Other static constants include FILES_ONLY and DIRECTORIES_ONLY.
Line 45 calls method showOpenDialog to display the JFileChooser dialog titled Open. Argument this specifies the JFileChooser dialog's parent window, which determines the position of the dialog on the screen. If null is passed, the dialog is displayed in the center of the screenotherwise, the dialog is centered over the application window (specified by the argument this). A JFileChooser dialog is a modal dialog that does not allow the user to interact with any other window in the program until the user closes the JFileChooser by clicking the Open or Cancel button. The user selects the drive, directory or file name, then clicks Open. Method showOpenDialog returns an integer specifying which button ( Open or Cancel) the user clicked to close the dialog. Line 48 tests whether the user clicked Cancel by comparing the result with static constant CANCEL_OPTION. If they are equal, the program terminates. Line 51 retrieves the file the user selected by calling JFileChooser method getSelectedFile. The program then displays information about the selected file or directory.