jsp+servlet实现投票的大概比例功能
以下是文件index.jsp的代码：
index.jsp文件中设定了4个选项（ABCD），每个选项都通过Request对象的getRealPath()方法来从question.txt文件中获得了一个问题。当选中一个选项投票后，由VoteImage.java文件生成的图片就会显示该选项的投票比例。write.jsp文件设定了投票数值的计算方法，并将结果输出到count.txt文件中，下面是write.jsp文件的代码：package servlet;import java.io.*;import com.sun.image.codec.jpeg.*;import javax.servlet.*;import javax.servlet.http.*;import java.awt.*;import java.awt.geom.*;import java.awt.image.*;public class VoteImage extends HttpServlet {private String strFile = null;private Color color[]={Color.red,Color.black,Color.orange,Color.green};private int baseAng = 30;public void doGet(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException {System.out.println("VoteImage.doGet()");doPost(request,response);}public void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException {System.out.println("VoteImage.doPost()");strFile = request.getRealPath("count.txt");float[][] xy = new float[4][2];xy = getNumAndPercent(strFile);int[] ang = new int[4];ang[0] = (int)(xy[0][1]*360);ang[1] = (int)(xy[1][1]*360);ang[2] = (int)(xy[2][1]*360);ang[3] = 360-ang[0]-ang[1]-ang[2];response.setHeader("Cache-Control","no-store");response.setDateHeader("Expires",0);response.setContentType("image/jpeg");ServletOutputStream out=response.getOutputStream();BufferedImage image=new BufferedImage(150,100,BufferedImage.TYPE_INT_RGB);Graphics2D g=(Graphics2D)image.getGraphics();g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);g.setColor(Color.white);g.fillRect(0,0,150,100); AffineTransform at = null;Arc2D arc = null;int fromAng = baseAng;at = AffineTransform.getRotateInstance((-20*java.lang.Math.PI)/180,45,37);g.setTransform(at);int r =6;int dx = (int)(r*java.lang.Math.cos((baseAng+ang[0])/2.0*java.lang.Math.PI/180));int dy = (int)(r*java.lang.Math.sin((baseAng+ang[0])/2.0*java.lang.Math.PI/180));arc = new Arc2D.Double(10+dx,24-dy,80,50,fromAng,ang[0],Arc2D.PIE);g.setColor(color[0]);g.fill(arc);fromAng+=ang[0];for (int i=1;i<4;i++){g.setColor(color[i]);arc = new Arc2D.Double(10,24,80,50,fromAng,ang[i],Arc2D.PIE);g.fill(arc);fromAng+=ang[i];if (fromAng>360){fromAng-=360;}}at = AffineTransform.getRotateInstance(0,arc.getCenterX(),arc.getCenterY());g.setTransform(at);for (int i=0;i<4;i++){g.setColor(color[i]);g.fillRect(100,15*i+20,10,10);g.drawString((char)('A'+i)+"",120,15*i+20+8);}JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);encoder.encode(image);out.close();}public synchronized float[][] getNumAndPercent(String sFileName){float xx[][] = new float[4][2];int totalNum = 0 ;String strTemp = null;int i = 0;java.io.RandomAccessFile rf = null;try {rf = new java.io.RandomAccessFile (sFileName,"r");} catch(Exception e){System.out.println(e);System.exit(0);}for (i=0;i<4;i++){int m=0;try {strTemp = rf.readLine();} catch (Exception e){strTemp = "0";}if (strTemp == null) strTemp = "0";m = new Integer(strTemp).intValue();xx[i][0]=m;totalNum += m;}if (totalNum==0) totalNum=1;for ( i=0;i<4;i++){xx[i][1] = xx[i][0]/totalNum;}return xx;}}
当进行投票时，count.txt文件中的数据被修改，相应地VoteImage.java文件中的JSP调用servlet生成的图片比例也将被修改。
代码(vote.rar)可见附件，下载后直接用myeclipse导入即可测试。
测试效果可查看图片附件
来源：书籍《JSP实用简明教程》中第九章【JSP与Servlet编程】
