提高Java程序内存效率

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提高Java程序内存效率

原创:忘记理想 2004-11-1

我们都知道Java程序之所以被广大程序员青睐,很大的一个原因是因为Java有GC(垃圾收集),不用程序员花很大的精力来解决内存释放和泄漏问题。而这些问题总是C/C++程序员需要花很大精力来认真地面对的。

问题总是双面的,GC给我们带来了很大的快乐,释放了程序员很多的精力和时间,但是在某些时候也会给我们带来一些小小的麻烦。Java里的Object并非交给GC去释放就可高枕无忧了,下面从JDK1.4的Demo中Java2D的Memory Monitor说起。

先看看Memory Monitor单独运行的效果。

可以看到因为有个While循环,GC释放内存有一定的时间,在这个时间中间,内存消耗的很厉害。峰值达到923K。程序代码的如下:

//SysGcMain.java Created on 9:15:59

package com.gx2.system;

/**

 * @author Frank Gao  @version 1.00

 * Copy right by GX2 Studio 2003

 * Copyright (c) 2003 Sun Microsystems, Inc. All  Rights Reserved.

 *

 * Redistribution and use in source……以后省略

 */

 

/*

 * @(#)MemoryMonitor.java   1.32 03/01/23

 */

 

import java.awt.*;

import java.awt.event.*;

import java.awt.image.BufferedImage;

import java.awt.geom.Line2D;

import java.awt.geom.Rectangle2D;

import java.util.Date;

import javax.swing.*;

import javax.swing.border.EtchedBorder;

import javax.swing.border.TitledBorder;

 

 

/**

 * Tracks Memory allocated & used, displayed in graph form.

 */

public class SysGcMain extends JPanel {

 

    static JCheckBox dateStampCB = new JCheckBox("Output Date Stamp");

    public Surface surf;

    JPanel controls;

    boolean doControls;

    JTextField tf;

 

    public SysGcMain() {

        setLayout(new BorderLayout());

        setBorder(new TitledBorder(new EtchedBorder(), "Memory Monitor"));

        add(surf = new Surface());

        controls = new JPanel();

        controls.setPreferredSize(new Dimension(135,80));

        Font font = new Font("serif", Font.PLAIN, 10);

        JLabel label = new JLabel("Sample Rate");

        label.setFont(font);

        label.setForeground(Color.black);

        controls.add(label);

        tf = new JTextField("1000");

        tf.setPreferredSize(new Dimension(45,20));

        controls.add(tf);

        controls.add(label = new JLabel("ms"));

        label.setFont(font);

        label.setForeground(Color.black);

        controls.add(dateStampCB);

        dateStampCB.setFont(font);

        addMouseListener(new MouseAdapter() {

            public void mouseClicked(MouseEvent e) {

               removeAll();

               if ((doControls = !doControls)) {

                   surf.stop();

                   add(controls);

               } else {

                   try {

                       surf.sleepAmount = Long.parseLong(tf.getText().trim());

                   } catch (Exception ex) {}

                   surf.start();

                   add(surf);

               }

               validate();

               repaint();

            }

        });

    }

 

 

    public class Surface extends JPanel implements Runnable {

 

        public Thread thread;

        public long sleepAmount = 1000;

        private int w, h;

        private BufferedImage bimg;

        private Graphics2D big;

        private Font font = new Font("Times New Roman", Font.PLAIN, 11);

        private Runtime r = Runtime.getRuntime();

        private int columnInc;

        private int pts[];

        private int ptNum;

        private int ascent, descent;

        private float freeMemory, totalMemory;

        private Rectangle graphOutlineRect = new Rectangle();

        private Rectangle2D mfRect = new Rectangle2D.Float();

        private Rectangle2D muRect = new Rectangle2D.Float();

        private Line2D graphLine = new Line2D.Float();

        private Color graphColor = new Color(46, 139, 87);

        private Color mfColor = new Color(0, 100, 0);

        private String usedStr;

     

 

        public Surface() {

            setBackground(Color.black);

            addMouseListener(new MouseAdapter() {

                public void mouseClicked(MouseEvent e) {

                    if (thread == null) start(); else stop();

                }

            });

        }

 

        public Dimension getMinimumSize() {

            return getPreferredSize();

        }

 

        public Dimension getMaximumSize() {

            return getPreferredSize();

        }

 

        public Dimension getPreferredSize() {

            return new Dimension(135,80);

        }

 

           

        public void paint(Graphics g) {

 

            if (big == null) {

                return;

            }

 

            big.setBackground(getBackground());

            big.clearRect(0,0,w,h);

 

            float freeMemory = (float) r.freeMemory();

            float totalMemory = (float) r.totalMemory();

 

            // .. Draw allocated and used strings ..

            big.setColor(Color.green);

            big.drawString(String.valueOf((int) totalMemory/1024) + "K allocated",  4.0f, (float) ascent+0.5f);

            usedStr = String.valueOf(((int) (totalMemory - freeMemory))/1024)

                + "K used";

            big.drawString(usedStr, 4, h-descent);

 

            // Calculate remaining size

            float ssH = ascent + descent;

            float remainingHeight = (float) (h - (ssH*2) - 0.5f);

            float blockHeight = remainingHeight/10;

            float blockWidth = 20.0f;

            float remainingWidth = (float) (w - blockWidth - 10);

 

            // .. Memory Free ..

            big.setColor(mfColor);

            int MemUsage = (int) ((freeMemory / totalMemory) * 10);

            int i = 0;

            for ( ; i < MemUsage ; i++) {

                mfRect.setRect(5,(float) ssH+i*blockHeight,

                                blockWidth,(float) blockHeight-1);

                big.fill(mfRect);

            }

 

            // .. Memory Used ..

            big.setColor(Color.green);

            for ( ; i < 10; i++)  {

                muRect.setRect(5,(float) ssH+i*blockHeight,

                                blockWidth,(float) blockHeight-1);

                big.fill(muRect);

            }

 

            // .. Draw History Graph ..

            big.setColor(graphColor);

            int graphX = 30;

            int graphY = (int) ssH;

            int graphW = w - graphX - 5;

            int graphH = (int) remainingHeight;

            graphOutlineRect.setRect(graphX, graphY, graphW, graphH);

            big.draw(graphOutlineRect);

 

            int graphRow = graphH/10;

 

            // .. Draw row ..

            for (int j = graphY; j <= graphH+graphY; j += graphRow) {

                graphLine.setLine(graphX,j,graphX+graphW,j);

                big.draw(graphLine);

            }

       

            // .. Draw animated column movement ..

            int graphColumn = graphW/15;

 

            if (columnInc == 0) {

                columnInc = graphColumn;

            }

 

            for (int j = graphX+columnInc; j < graphW+graphX; j+=graphColumn) {

                graphLine.setLine(j,graphY,j,graphY+graphH);

                big.draw(graphLine);

            }

 

            --columnInc;

 

            if (pts == null) {

                pts = new int[graphW];

                ptNum = 0;

            } else if (pts.length != graphW) {

                int tmp[] = null;

                if (ptNum < graphW) {    

                    tmp = new int[ptNum];

                    System.arraycopy(pts, 0, tmp, 0, tmp.length);

                } else {       

                    tmp = new int[graphW];

                    System.arraycopy(pts, pts.length-tmp.length, tmp, 0, tmp.length);

                    ptNum = tmp.length - 2;

                }

                pts = new int[graphW];

                System.arraycopy(tmp, 0, pts, 0, tmp.length);

            } else {

                big.setColor(Color.yellow);

                pts[ptNum] = (int)(graphY+graphH*(freeMemory/totalMemory));

                for (int j=graphX+graphW-ptNum, k=0;k < ptNum; k++, j++) {

                    if (k != 0) {

                        if (pts[k] != pts[k-1]) {

                            big.drawLine(j-1, pts[k-1], j, pts[k]);

                        } else {

                            big.fillRect(j, pts[k], 1, 1);

                        }

                    }

                }

                if (ptNum+2 == pts.length) {

                    // throw out oldest point

                    for (int j = 1;j < ptNum; j++) {

                        pts[j-1] = pts[j];

                    }

                    --ptNum;

                } else {

                    ptNum++;

                }

            }

            g.drawImage(bimg, 0, 0, this);

        }

 

 

        public void start() {

            thread = new Thread(this);

            thread.setPriority(Thread.MIN_PRIORITY);

            thread.setName("MemoryMonitor");

            thread.start();

        }

 

 

        public synchronized void stop() {

            thread = null;

            notify();

        }

        public void run() {

            Thread me = Thread.currentThread();

            while (thread == me && !isShowing() || getSize().width == 0) {

                try {

                    thread.sleep(500);

                } catch (InterruptedException e) { return; }

            }

   

            while (thread == me && isShowing()) {

                Dimension d = getSize();

                if (d.width != w || d.height != h) {

                    w = d.width;

                    h = d.height;

                    bimg = (BufferedImage) createImage(w, h);

                    big = bimg.createGraphics();

                    big.setFont(font);

                    FontMetrics fm = big.getFontMetrics(font);

                    ascent = (int) fm.getAscent();

                    descent = (int) fm.getDescent();

                }

                repaint();

                try {

                    thread.sleep(sleepAmount);

                } catch (InterruptedException e) { break; }

                if (SysGcMain.dateStampCB.isSelected()) {

                     System.out.println(new Date().toString() + " " + usedStr);

                }

                //add by 忘记理想 2004-11-1

                // 不强制GC的话,因为while循环,内存会消耗的很厉害

                // 加上下面两句,可以保证内存消耗平稳

               

             Runtime.getRuntime().freeMemory();

             Runtime.getRuntime().gc();

            }

            thread = null;

        }

    }

 

 

    public static void main(String s[]) {

        final SysGcMain demo = new SysGcMain();

        WindowListener l = new WindowAdapter() {

            public void windowClosing(WindowEvent e) {System.exit(0);}

            public void windowDeiconified(WindowEvent e) { demo.surf.start(); }

            public void windowIconified(WindowEvent e) { demo.surf.stop(); }

        };

        JButton button = new JButton("Force GC");

        button.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent event){

             Runtime.getRuntime().freeMemory();

             Runtime.getRuntime().gc();

        }

        });

       

        JFrame f = new JFrame("Frank Gao - MemoryMonitor");

        f.addWindowListener(l);

        f.getContentPane().add("Center", demo);

        f.getContentPane().add(button,BorderLayout.SOUTH);

        f.pack();

        f.setSize(new Dimension(200,200));

        f.setVisible(true);

        demo.surf.start();

    }

}

在while循环中加入强制gc,内存峰值得到了很好的控制维持水平。

Runtime.getRuntime().freeMemory();

Runtime.getRuntime().gc();

 

 

由此可以考虑在,程序while等比较好内存的地方采用上述方法,降低内存峰值,提高内存效率。

 

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