Trong khi lang thang tìm kiếm giải pháp trên internet hoặc đọc linh ta linh tinh trên internet có khi ngẫu nhiên tìm thấy nhiều source hay, nhưng quay qua quay lại thì lại quên mất tiêu, vì vậy mình quyết định tạo một chuyên mục riêng về source code free.
Bài mở màn là source Java Download Manager, nó cũng khá hay chịu khó ngồi phân tích xíu sẽ có rất kinh nghiệm bổ ích.
Ví dụ này cho thấy làm thế nào để tạo ra một trình quản lý download đơn giản trong Java. Nó bao gồm bốn lớp học trong bốn tập tin nguồn Java:
- Download.java: Chứa Tải về lớp học mà tải về một tập tin từ một URL.
- DownloadManager.java: Chứa các lớp chính cho ứng dụng quản lý download.
- DownloadsTableModel.java: Chứa các lớp học mà quản lý dữ liệu bảng tải về của.
- ProgressRenderer.java: Chứa các lớp học mà là trách nhiệm để làm cho một JProgressBar trong một ô trong bảng.
Download.java
import java.io.*;
import java.net.*;
import java.util.*;
// This class downloads a file from a URL.
class Download extends Observable implements Runnable {
// Max size of download buffer.
private static final int MAX_BUFFER_SIZE = 1024;
// These are the status names.
public static final String STATUSES[] = {"Downloading",
"Paused", "Complete", "Cancelled", "Error"};
// These are the status codes.
public static final int DOWNLOADING = 0;
public static final int PAUSED = 1;
public static final int COMPLETE = 2;
public static final int CANCELLED = 3;
public static final int ERROR = 4;
private URL url; // download URL
private int size; // size of download in bytes
private int downloaded; // number of bytes downloaded
private int status; // current status of download
// Constructor for Download.
public Download(URL url) {
this.url = url;
size = -1;
downloaded = 0;
status = DOWNLOADING;
// Begin the download.
download();
}
// Get this download's URL.
public String getUrl() {
return url.toString();
}
// Get this download's size.
public int getSize() {
return size;
}
// Get this download's progress.
public float getProgress() {
return ((float) downloaded / size) * 100;
}
// Get this download's status.
public int getStatus() {
return status;
}
// Pause this download.
public void pause() {
status = PAUSED;
stateChanged();
}
// Resume this download.
public void resume() {
status = DOWNLOADING;
stateChanged();
download();
}
// Cancel this download.
public void cancel() {
status = CANCELLED;
stateChanged();
}
// Mark this download as having an error.
private void error() {
status = ERROR;
stateChanged();
}
// Start or resume downloading.
private void download() {
Thread thread = new Thread(this);
thread.start();
}
// Get file name portion of URL.
private String getFileName(URL url) {
String fileName = url.getFile();
return fileName.substring(fileName.lastIndexOf('/') + 1);
}
// Download file.
public void run() {
RandomAccessFile file = null;
InputStream stream = null;
try {
// Open connection to URL.
HttpURLConnection connection =
(HttpURLConnection) url.openConnection();
// Specify what portion of file to download.
connection.setRequestProperty("Range",
"bytes=" + downloaded + "-");
// Connect to server.
connection.connect();
// Make sure response code is in the 200 range.
if (connection.getResponseCode() / 100 != 2) {
error();
}
// Check for valid content length.
int contentLength = connection.getContentLength();
if (contentLength < 1) {
error();
}
/* Set the size for this download if it
hasn't been already set. */
if (size == -1) {
size = contentLength;
stateChanged();
}
// Open file and seek to the end of it.
file = new RandomAccessFile(getFileName(url), "rw");
file.seek(downloaded);
stream = connection.getInputStream();
while (status == DOWNLOADING) {
/* Size buffer according to how much of the
file is left to download. */
byte buffer[];
if (size - downloaded > MAX_BUFFER_SIZE) {
buffer = new byte[MAX_BUFFER_SIZE];
} else {
buffer = new byte[size - downloaded];
}
// Read from server into buffer.
int read = stream.read(buffer);
if (read == -1)
break;
// Write buffer to file.
file.write(buffer, 0, read);
downloaded += read;
stateChanged();
}
/* Change status to complete if this point was
reached because downloading has finished. */
if (status == DOWNLOADING) {
status = COMPLETE;
stateChanged();
}
} catch (Exception e) {
error();
} finally {
// Close file.
if (file != null) {
try {
file.close();
} catch (Exception e) {}
}
// Close connection to server.
if (stream != null) {
try {
stream.close();
} catch (Exception e) {}
}
}
}
// Notify observers that this download's status has changed.
private void stateChanged() {
setChanged();
notifyObservers();
}
}
import java.net.*;
import java.util.*;
// This class downloads a file from a URL.
class Download extends Observable implements Runnable {
// Max size of download buffer.
private static final int MAX_BUFFER_SIZE = 1024;
// These are the status names.
public static final String STATUSES[] = {"Downloading",
"Paused", "Complete", "Cancelled", "Error"};
// These are the status codes.
public static final int DOWNLOADING = 0;
public static final int PAUSED = 1;
public static final int COMPLETE = 2;
public static final int CANCELLED = 3;
public static final int ERROR = 4;
private URL url; // download URL
private int size; // size of download in bytes
private int downloaded; // number of bytes downloaded
private int status; // current status of download
// Constructor for Download.
public Download(URL url) {
this.url = url;
size = -1;
downloaded = 0;
status = DOWNLOADING;
// Begin the download.
download();
}
// Get this download's URL.
public String getUrl() {
return url.toString();
}
// Get this download's size.
public int getSize() {
return size;
}
// Get this download's progress.
public float getProgress() {
return ((float) downloaded / size) * 100;
}
// Get this download's status.
public int getStatus() {
return status;
}
// Pause this download.
public void pause() {
status = PAUSED;
stateChanged();
}
// Resume this download.
public void resume() {
status = DOWNLOADING;
stateChanged();
download();
}
// Cancel this download.
public void cancel() {
status = CANCELLED;
stateChanged();
}
// Mark this download as having an error.
private void error() {
status = ERROR;
stateChanged();
}
// Start or resume downloading.
private void download() {
Thread thread = new Thread(this);
thread.start();
}
// Get file name portion of URL.
private String getFileName(URL url) {
String fileName = url.getFile();
return fileName.substring(fileName.lastIndexOf('/') + 1);
}
// Download file.
public void run() {
RandomAccessFile file = null;
InputStream stream = null;
try {
// Open connection to URL.
HttpURLConnection connection =
(HttpURLConnection) url.openConnection();
// Specify what portion of file to download.
connection.setRequestProperty("Range",
"bytes=" + downloaded + "-");
// Connect to server.
connection.connect();
// Make sure response code is in the 200 range.
if (connection.getResponseCode() / 100 != 2) {
error();
}
// Check for valid content length.
int contentLength = connection.getContentLength();
if (contentLength < 1) {
error();
}
/* Set the size for this download if it
hasn't been already set. */
if (size == -1) {
size = contentLength;
stateChanged();
}
// Open file and seek to the end of it.
file = new RandomAccessFile(getFileName(url), "rw");
file.seek(downloaded);
stream = connection.getInputStream();
while (status == DOWNLOADING) {
/* Size buffer according to how much of the
file is left to download. */
byte buffer[];
if (size - downloaded > MAX_BUFFER_SIZE) {
buffer = new byte[MAX_BUFFER_SIZE];
} else {
buffer = new byte[size - downloaded];
}
// Read from server into buffer.
int read = stream.read(buffer);
if (read == -1)
break;
// Write buffer to file.
file.write(buffer, 0, read);
downloaded += read;
stateChanged();
}
/* Change status to complete if this point was
reached because downloading has finished. */
if (status == DOWNLOADING) {
status = COMPLETE;
stateChanged();
}
} catch (Exception e) {
error();
} finally {
// Close file.
if (file != null) {
try {
file.close();
} catch (Exception e) {}
}
// Close connection to server.
if (stream != null) {
try {
stream.close();
} catch (Exception e) {}
}
}
}
// Notify observers that this download's status has changed.
private void stateChanged() {
setChanged();
notifyObservers();
}
}
DownloadManager.java
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
// The Download Manager.
public class DownloadManager extends JFrame
implements Observer {
// Add download text field.
private JTextField addTextField;
// Download table's data model.
private DownloadsTableModel tableModel;
// Table listing downloads.
private JTable table;
// These are the buttons for managing the selected download.
private JButton pauseButton, resumeButton;
private JButton cancelButton, clearButton;
// Currently selected download.
private Download selectedDownload;
// Flag for whether or not table selection is being cleared.
private boolean clearing;
// Constructor for Download Manager.
public DownloadManager() {
// Set application title.
setTitle("Download Manager");
// Set window size.
setSize(640, 480);
// Handle window closing events.
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
actionExit();
}
});
// Set up file menu.
JMenuBar menuBar = new JMenuBar();
JMenu fileMenu = new JMenu("File");
fileMenu.setMnemonic(KeyEvent.VK_F);
JMenuItem fileExitMenuItem = new JMenuItem("Exit",
KeyEvent.VK_X);
fileExitMenuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionExit();
}
});
fileMenu.add(fileExitMenuItem);
menuBar.add(fileMenu);
setJMenuBar(menuBar);
// Set up add panel.
JPanel addPanel = new JPanel();
addTextField = new JTextField(30);
addPanel.add(addTextField);
JButton addButton = new JButton("Add Download");
addButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionAdd();
}
});
addPanel.add(addButton);
// Set up Downloads table.
tableModel = new DownloadsTableModel();
table = new JTable(tableModel);
table.getSelectionModel().addListSelectionListener(new
ListSelectionListener() {
public void valueChanged(ListSelectionEvent e) {
tableSelectionChanged();
}
});
// Allow only one row at a time to be selected.
table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
// Set up ProgressBar as renderer for progress column.
ProgressRenderer renderer = new ProgressRenderer(0, 100);
renderer.setStringPainted(true); // show progress text
table.setDefaultRenderer(JProgressBar.class, renderer);
// Set table's row height large enough to fit JProgressBar.
table.setRowHeight(
(int) renderer.getPreferredSize().getHeight());
// Set up downloads panel.
JPanel downloadsPanel = new JPanel();
downloadsPanel.setBorder(
BorderFactory.createTitledBorder("Downloads"));
downloadsPanel.setLayout(new BorderLayout());
downloadsPanel.add(new JScrollPane(table),
BorderLayout.CENTER);
// Set up buttons panel.
JPanel buttonsPanel = new JPanel();
pauseButton = new JButton("Pause");
pauseButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionPause();
}
});
pauseButton.setEnabled(false);
buttonsPanel.add(pauseButton);
resumeButton = new JButton("Resume");
resumeButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionResume();
}
});
resumeButton.setEnabled(false);
buttonsPanel.add(resumeButton);
cancelButton = new JButton("Cancel");
cancelButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionCancel();
}
});
cancelButton.setEnabled(false);
buttonsPanel.add(cancelButton);
clearButton = new JButton("Clear");
clearButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
actionClear();
}
});
clearButton.setEnabled(false);
buttonsPanel.add(clearButton);
// Add panels to display.
getContentPane().setLayout(new BorderLayout());
getContentPane().add(addPanel, BorderLayout.NORTH);
getContentPane().add(downloadsPanel, BorderLayout.CENTER);
getContentPane().add(buttonsPanel, BorderLayout.SOUTH);
}
// Exit this program.
private void actionExit() {
System.exit(0);
}
// Add a new download.
private void actionAdd() {
URL verifiedUrl = verifyUrl(addTextField.getText());
if (verifiedUrl != null) {
tableModel.addDownload(new Download(verifiedUrl));
addTextField.setText(""); // reset add text field
} else {
JOptionPane.showMessageDialog(this,
"Invalid Download URL", "Error",
JOptionPane.ERROR_MESSAGE);
}
}
// Verify download URL.
private URL verifyUrl(String url) {
// Only allow HTTP URLs.
if (!url.toLowerCase().startsWith("http://"))
return null;
// Verify format of URL.
URL verifiedUrl = null;
try {
verifiedUrl = new URL(url);
} catch (Exception e) {
return null;
}
// Make sure URL specifies a file.
if (verifiedUrl.getFile().length() < 2)
return null;
return verifiedUrl;
}
// Called when table row selection changes.
private void tableSelectionChanged() {
/* Unregister from receiving notifications
from the last selected download. */
if (selectedDownload != null)
selectedDownload.deleteObserver(DownloadManager.this);
/* If not in the middle of clearing a download,
set the selected download and register to
receive notifications from it. */
if (!clearing) {
selectedDownload =
tableModel.getDownload(table.getSelectedRow());
selectedDownload.addObserver(DownloadManager.this);
updateButtons();
}
}
// Pause the selected download.
private void actionPause() {
selectedDownload.pause();
updateButtons();
}
// Resume the selected download.
private void actionResume() {
selectedDownload.resume();
updateButtons();
}
// Cancel the selected download.
private void actionCancel() {
selectedDownload.cancel();
updateButtons();
}
// Clear the selected download.
private void actionClear() {
clearing = true;
tableModel.clearDownload(table.getSelectedRow());
clearing = false;
selectedDownload = null;
updateButtons();
}
/* Update each button's state based off of the
currently selected download's status. */
private void updateButtons() {
if (selectedDownload != null) {
int status = selectedDownload.getStatus();
switch (status) {
case Download.DOWNLOADING:
pauseButton.setEnabled(true);
resumeButton.setEnabled(false);
cancelButton.setEnabled(true);
clearButton.setEnabled(false);
break;
case Download.PAUSED:
pauseButton.setEnabled(false);
resumeButton.setEnabled(true);
cancelButton.setEnabled(true);
clearButton.setEnabled(false);
break;
case Download.ERROR:
pauseButton.setEnabled(false);
resumeButton.setEnabled(true);
cancelButton.setEnabled(false);
clearButton.setEnabled(true);
break;
default: // COMPLETE or CANCELLED
pauseButton.setEnabled(false);
resumeButton.setEnabled(false);
cancelButton.setEnabled(false);
clearButton.setEnabled(true);
}
} else {
// No download is selected in table.
pauseButton.setEnabled(false);
resumeButton.setEnabled(false);
cancelButton.setEnabled(false);
clearButton.setEnabled(false);
}
}
/* Update is called when a Download notifies its
observers of any changes. */
public void update(Observable o, Object arg) {
// Update buttons if the selected download has changed.
if (selectedDownload != null && selectedDownload.equals(o))
updateButtons();
}
// Run the Download Manager.
public static void main(String[] args) {
DownloadManager manager = new DownloadManager();
manager.show();
}
}
DownloadTableModel.java
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;
// This class manages the download table's data.
class DownloadsTableModel extends AbstractTableModel
implements Observer {
// These are the names for the table's columns.
private static final String[] columnNames = {"URL", "Size",
"Progress", "Status"};
// These are the classes for each column's values.
private static final Class[] columnClasses = {String.class,
String.class, JProgressBar.class, String.class};
// The table's list of downloads.
private ArrayList downloadList = new ArrayList();
// Add a new download to the table.
public void addDownload(Download download) {
// Register to be notified when the download changes.
download.addObserver(this);
downloadList.add(download);
// Fire table row insertion notification to table.
fireTableRowsInserted(getRowCount() - 1, getRowCount() - 1);
}
// Get a download for the specified row.
public Download getDownload(int row) {
return (Download) downloadList.get(row);
}
// Remove a download from the list.
public void clearDownload(int row) {
downloadList.remove(row);
// Fire table row deletion notification to table.
fireTableRowsDeleted(row, row);
}
// Get table's column count.
public int getColumnCount() {
return columnNames.length;
}
// Get a column's name.
public String getColumnName(int col) {
return columnNames[col];
}
// Get a column's class.
public Class getColumnClass(int col) {
return columnClasses[col];
}
// Get table's row count.
public int getRowCount() {
return downloadList.size();
}
// Get value for a specific row and column combination.
public Object getValueAt(int row, int col) {
Download download = (Download) downloadList.get(row);
switch (col) {
case 0: // URL
return download.getUrl();
case 1: // Size
int size = download.getSize();
return (size == -1) ? "" : Integer.toString(size);
case 2: // Progress
return new Float(download.getProgress());
case 3: // Status
return Download.STATUSES[download.getStatus()];
}
return "";
}
/* Update is called when a Download notifies its
observers of any changes */
public void update(Observable o, Object arg) {
int index = downloadList.indexOf(o);
// Fire table row update notification to table.
fireTableRowsUpdated(index, index);
}
}
ProgressRenderer.java
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;
// This class renders a JProgressBar in a table cell.
class ProgressRenderer extends JProgressBar
implements TableCellRenderer {
// Constructor for ProgressRenderer.
public ProgressRenderer(int min, int max) {
super(min, max);
}
/* Returns this JProgressBar as the renderer
for the given table cell. */
public Component getTableCellRendererComponent(
JTable table, Object value, boolean isSelected,
boolean hasFocus, int row, int column) {
// Set JProgressBar's percent complete value.
setValue((int) ((Float) value).floatValue());
return this;
}
}
import javax.swing.*;
import javax.swing.table.*;
// This class renders a JProgressBar in a table cell.
class ProgressRenderer extends JProgressBar
implements TableCellRenderer {
// Constructor for ProgressRenderer.
public ProgressRenderer(int min, int max) {
super(min, max);
}
/* Returns this JProgressBar as the renderer
for the given table cell. */
public Component getTableCellRendererComponent(
JTable table, Object value, boolean isSelected,
boolean hasFocus, int row, int column) {
// Set JProgressBar's percent complete value.
setValue((int) ((Float) value).floatValue());
return this;
}
}
Source: www.java-tips.org
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