给Swing程序添加一个动态显示内存情况的状态条

 

cpoy from http://yanhua.blog.techweb.com.cn/archives/2006/200691815392.shtml#cmt

在前面的文章中我们提到过Eclipse可以显示一个动态显示内存使用情况的状态条，而且还有一个按钮可以手工进行垃圾回收，昨天我看到OSWorkflow的设计器也有这么一个功能，那到底是怎么实现的呢？其实一点都不难，我们只要写一个特殊的JPanel就可以了！

 

class MemoryPanel extends JPanel  {   //状态条的颜色   private Color edgeColor = new Color(82, 115, 214);   private Color centerColor = new Color(180, 200, 230);

   public void paint(Graphics g)   {    super.paint(g);    //得到当前组件（JPanel）的大小    Dimension dimension = getSize();    //得到各边框的宽度    Insets insets = getInsets();    int left = insets.left;    int top = insets.top;        //得到内存使用状态信息    Runtime runtime = Runtime.getRuntime();    long freeMemory = runtime.freeMemory();    long totalMemory = runtime.totalMemory();        //组件（JPanel）除去左、右边框后的宽度    int insideWidth = dimension.width - (insets.left + insets.right);    //内存使用量的显示宽度    int usedAmount = insideWidth - (int) (((long) insideWidth * freeMemory) / totalMemory);    int insideHeight = dimension.height - (insets.bottom + insets.top);        Graphics2D g2 = (Graphics2D) g;    //设置渐变效果的画笔    g2.setPaint(new GradientPaint(left, top, edgeColor, left, insideHeight / 2, centerColor, true));    g.fillRect(left, top, usedAmount, insideHeight);    g.setColor(getBackground());    g.fillRect(left + usedAmount, top, insideWidth - usedAmount, insideHeight);    g.setFont(getFont());    g.setColor(Color.black);    //显示状态的文字    String memory = (Long.toString((totalMemory - freeMemory) / 1048576L) + "M of " + Long.toString(totalMemory / 1048576L) + 'M');    //确定文字的显示位置    FontMetrics fontmetrics = g.getFontMetrics();    int stringWidth = fontmetrics.charsWidth(memory.toCharArray(), 0, memory.length());    int stringHeight = fontmetrics.getHeight() - fontmetrics.getDescent();    //显示文字    g.drawString(memory, left + (insideWidth - stringWidth) / 2, top + (insideHeight + stringHeight) / 2);   }  }

有了这个JPanel，我们可以把它加到一个Frame或另一个Panel上去了。

  final MemoryPanel memoryPanel = new MemoryPanel();  memoryPanel.setPreferredSize(new Dimension(100, 15));  memoryPanel.setMaximumSize(new Dimension(100, 15));  memoryPanel.setMinimumSize(new Dimension(100, 15));  staPanel.add(memoryPanel,BorderLayout.EAST);

然后再启动一个计时器以便能让上面的JPanel实时更新。

Timer timer = new Timer(2000, new ActionListener()  {   public void actionPerformed(ActionEvent actionevent)   {    memoryPanel.repaint();   }  });  timer.start();

至于那个可以人工进行垃圾回收的小垃圾桶就更好做了，做一个带图标的JButton，在它的事件处理中进行垃圾回收并再调用一下上面那个JPanel的repaint()方法就可以了。

gcButton.addActionListener(new ActionListener(){

   public void actionPerformed(ActionEvent e)   {    System.gc();    memoryPanel.repaint();   }  });

是不是很简单呢？