用JSP生成JPEG图片

一、前言

本文原作者为Tony Wang ，该文章涉及到文件的读写和jpg图片的自动生成。利用jsp+servlet的技术，jsp调用servlet生成图片。

二、首文件index.jsp如下：

<%--

Author: Tony Wang

E-mail:
Date: 2001-01-01
如果对程序有什么疑问，可以和我联系，
另外程序如果有什么bug，麻烦指出！！
*/
import java.io.*;
import java.util.*;
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
{
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 void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException
{
doGet(request,response);
}

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;
}
}

五、在index.jsp目录下建立question.txt和count.txt文件分别用来保存投票的问题和投票的数量，用户投票后，就修改count.txt的值。

为了对原作者表示感谢，这2个文件内容不变化，如下：

question.txt:

Yes,I think so!

No,I dont think so!

Sorry,I dont know the answer!

count.txt:

12

9

5

9

六、目录结构：

(1)jsp文件和txt文件同一个目录

(2).java文件是servlet目录下

七、测试：

http：//[server:port]/dir/index.jsp