JSP+Servlet实现生成登录验证码示例

package servlet;

import java.awt.basicstroke;
import java.awt.color;
import java.awt.font;
import java.awt.graphics;
import java.awt.graphics2d;
import java.awt.geom.affinetransform;
import java.awt.geom.line2d;
import java.awt.image.bufferedimage;
import java.io.ioexception;
import java.io.printwriter;
import java.util.random;

import javax.imageio.imageio;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import javax.servlet.http.httpsession;

public class picturecheckcode extends httpservlet {

   private static final long serialversionuid = 1l; 

    public picturecheckcode() { 
      super(); 
    } 

    public void destroy() { 
      super.destroy();  
    } 

    public void init() throws servletexception { 
      super.init(); 
    } 
    /*该方法主要作用是获得随机生成的颜色*/  
    public color getrandcolor(int s,int e){ 
      random random=new random (); 
      if(s>255) s=255; 
      if(e>255) e=255; 
      int r,g,b; 
      r=s+random.nextint(e-s);  //随机生成rgb颜色中的r值 
      g=s+random.nextint(e-s);  //随机生成rgb颜色中的g值 
      b=s+random.nextint(e-s);  //随机生成rgb颜色中的b值 
      return new color(r,g,b); 
    } 

  public void doget(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {
    system.out.println("this is doget method");
    this.dopost(request, response);

  }

  public void dopost(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {

    //设置不缓存图片 
    response.setheader("pragma", "no-cache"); 
    response.setheader("cache-control", "no-cache"); 
    response.setdateheader("expires", 0); 
    //指定生成的响应图片,一定不能缺少这句话,否则错误. 
    response.setcontenttype("image/jpeg"); 
    int width=80,height=35;   //指定生成验证码的宽度和高度 
    bufferedimage image=new bufferedimage(width,height,bufferedimage.type_int_rgb); //创建bufferedimage对象,其作用相当于一图片 
    graphics g=image.getgraphics();   //创建graphics对象,其作用相当于画笔 
    graphics2d g2d=(graphics2d)g;    //创建grapchics2d对象 
    random random=new random(); 
    font mfont=new font("楷体",font.bold,16); //定义字体样式 
    g.setcolor(getrandcolor(200,250)); 
    g.fillrect(0, 0, width, height);  //绘制背景 
    g.setfont(mfont);          //设置字体 
    g.setcolor(getrandcolor(180,200)); 

    //绘制100条颜色和位置全部为随机产生的线条,该线条为2f 
    for(int i=0;i<100;i++){ 
      int x=random.nextint(width-1); 
      int y=random.nextint(height-1); 
      int x1=random.nextint(6)+1; 
      int y1=random.nextint(12)+1; 
      basicstroke bs=new basicstroke(2f,basicstroke.cap_butt,basicstroke.join_bevel); //定制线条样式 
      line2d line=new line2d.double(x,y,x+x1,y+y1); 
      g2d.setstroke(bs); 
      g2d.draw(line);   //绘制直线 
    } 
    //输出由英文，数字，和中文随机组成的验证文字，具体的组合方式根据生成随机数确定。 
    string srand=""; 
    string ctmp=""; 
    int itmp=0; 
    //制定输出的验证码为四位 
    for(int i=0;i<4;i++){ 
      switch(random.nextint(3)){ 
        case 1:   //生成a-z的字母 
           itmp=random.nextint(26)+65; 
           ctmp=string.valueof((char)itmp); 
           break; 
        case 2:   //生成汉字 
           string[] rbase={"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"};  
           //生成第一位区码 
           int r1=random.nextint(3)+11; 
           string str_r1=rbase[r1]; 
           //生成第二位区码 
           int r2; 
           if(r1==13){ 
             r2=random.nextint(7);   
           }else{ 
             r2=random.nextint(16); 
           } 
           string str_r2=rbase[r2]; 
           //生成第一位位码 
           int r3=random.nextint(6)+10; 
           string str_r3=rbase[r3]; 
           //生成第二位位码 
           int r4; 
           if(r3==10){ 
             r4=random.nextint(15)+1; 
           }else if(r3==15){ 
             r4=random.nextint(15); 
           }else{ 
             r4=random.nextint(16); 
           } 
           string str_r4=rbase[r4]; 
           //将生成的机内码转换为汉字 
           byte[] bytes=new byte[2]; 
           //将生成的区码保存到字节数组的第一个元素中 
           string str_12=str_r1+str_r2; 
           int templow=integer.parseint(str_12, 16); 
           bytes[0]=(byte) templow; 
           //将生成的位码保存到字节数组的第二个元素中 
           string str_34=str_r3+str_r4; 
           int temphigh=integer.parseint(str_34, 16); 
           bytes[1]=(byte)temphigh; 
           ctmp=new string(bytes); 
           break; 
        default: 
           itmp=random.nextint(10)+48; 
           ctmp=string.valueof((char)itmp); 
           break; 
      } 
      srand+=ctmp; 
      color color=new color(20+random.nextint(110),20+random.nextint(110),random.nextint(110)); 
      g.setcolor(color); 
      //将生成的随机数进行随机缩放并旋转制定角度 ps.建议不要对文字进行缩放与旋转,因为这样图片可能不正常显示 
      /*将文字旋转制定角度*/ 
      graphics2d g2d_word=(graphics2d)g; 
      affinetransform trans=new affinetransform(); 
      trans.rotate((45)*3.14/180,15*i+8,7); 
      /*缩放文字*/ 
      float scalesize=random.nextfloat()+0.8f; 
      if(scalesize>1f) scalesize=1f; 
      trans.scale(scalesize, scalesize); 
      g2d_word.settransform(trans); 
      g.drawstring(ctmp, 15*i+18, 14); 
    } 
    httpsession session=request.getsession(true); 
    session.setattribute("randcheckcode", srand); 
    system.out.println(srand);
    g.dispose();  //释放g所占用的系统资源 
    imageio.write(image,"jpeg",response.getoutputstream()); //输出图片 
  }

}

<servlet>
  <description>this is the description of my j2ee component</description>
  <display-name>this is the display name of my j2ee component</display-name>
  <servlet-name>picturecheckcode</servlet-name>
  <servlet-class>servlet.picturecheckcode</servlet-class>
 </servlet>

<servlet-mapping>
  <servlet-name>picturecheckcode</servlet-name>
  <url-pattern>/picturecheckcode</url-pattern>
 </servlet-mapping>

<%@ page language="java" import="java.util.*" pageencoding="utf-8"%>

<!doctype html public "-//w3c//dtd html 4.01 transitional//en">
<html>
<head>

<title>登录页面</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="this is my page">
<script language="javascript">
  function myreload() {
    document.getelementbyid("createcheckcode").src = document
        .getelementbyid("createcheckcode").src
        + "?nocache=" + new date().gettime();
  }
</script>

</head>

<body>
  <form action="loginservlet" method="get">
      <p class="font tdheight">
        验证码：<input type="text" name="checkcode"
          style="width:70px;height:35px;"> <img
          src="picturecheckcode" id="createcheckcode" align="middle"
          style="margin-top:-10px;"> <br> <a href=""
          onclick="myreload()"
          style="font-size:12px;color:red;margin-left:156px;"> 看不清,换一个</a>
      </p>
      <br><input type="submit" value="提交"
            class="font" style="width:240px;height:35px;background:#f19e28">

    </form>
</body>
</html>

public void doget(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {

    string code = request.getparameter("checkcode");
    httpsession session = request.getsession();
    if (!code.equals(session.getattribute("randcheckcode"))) {
      request.setattribute("errormsg", "验证码不正确");
    } 
    system.out.println(request.getattribute("errormsg"));
  }