验证码校验

1.首先考虑过滤器是否过滤后台访问验证码图片方法
2.equalsIgnoreCase（对比字符串是否相等与大小写无关）

一、前台：
1.这里是jsp页面的标签：
<script src="../styles/js/jquery-3.2.1.min.js" type="text/javascript"></script>
<link href="../styles/css/doctorlogin.css" rel="stylesheet" />
<link rel='stylesheet' href='../styles/bootstrap/css/bootstrap.min.css'>
2.下面是script，直接拿过来用就行，注意往后台跳转的地址要改成自己的，用我的也可以.
function reload(){
document.getElementById("image").src="<%=request.getContextPath() %>/picCheck/imageServlet?date="+new Date().getTime();
$("#checkcode").val(""); // 将验证码清空
}

function verificationcode(){
var text=$.trim($("#checkcode").val());

var sp=$('#span').val();

$.post("${pageContext.request.contextPath}/Verification/verificationServlet",{op:text},function(data){
data=parseInt($.trim(data));
if(data>0){
$("#span").text("验证成功!").css("color","green");
}else{
/* $("#span").text("验证失败!").css("color","red"); */
if(text==""){
$("#span").text("验证为空，请重新输入!").css("color","red");
}else{
$("#span").text("验证码错误").css("color","red");
}



reload(); //验证失败后需要更换验证码
}
});
$("#checkcode").val(""); // 将验证码清空
}
3.这里是 body 体部分(标签里面的class都是我的设计的静态css样式，不想设计的可以忽略)
<div class="home">
<div class="home_login">

<h4 class="title"><strong>爱你么么哒医院管理系统๑乛◡乛๑</strong></h3>
<input type="text" name="checkcode" id="checkcode" class="home_login_button3" placeholder="请输入验证码"/><br />
<div>
<img src="<%=request.getContextPath() %>/picCheck/imageServlet" alt="验证码" id="image" class="home_login_check_code"/>
<a href="javascript:reload();" class="home_login_button3_font"><label>换一张</label></a><br>
<span id="span"> </span>
</div>
<button type="button" class="home_login_button1" onclick="javascript:verificationcode()" >提交</button>

</div>
</div>
二、下面是后台部分(后台（controller层）一共有两部分，一个是编写验证码的controller，一个是判断验证码是否正确的controller)
1.判断验证码是否正确的controller层（拿来直接用就行）
/**
*
*/
package mvct.Controller;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

/**
* @author zhouxingxing
* @package mvct.Controller
* @Description TODO
* @date：2018年4月25日下午4:09:22
*/
@Controller
@RequestMapping("Verification")
public class PicCodeVerificationServletController extends HttpServlet {

/**
*
*/
private static final long serialVersionUID = 1L;

@RequestMapping("/verificationServlet")
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");

HttpSession session =request.getSession();
String verificationCode = (String)session.getAttribute("verificationCode");
String checkcode = request.getParameter("op");
PrintWriter out = response.getWriter();
if(checkcode.equals(verificationCode)){
out.println(1);
}else{
out.println(0);
}
out.flush();
out.close();
}





}

2.编写验证码的controller(直接拿过来用即可)
/**
*
*/
package mvct.Controller;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
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;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

/**
* @author zhouxingxing
* @package mvct.Controller
* @Description TODO
* @date：2018年4月25日下午4:00:23
*/
@Controller
@RequestMapping("/picCheck")
public class PicCheckController extends HttpServlet {

/**
*
*/
private static final long serialVersionUID = 1L;

@ResponseBody
@RequestMapping("/imageServlet")
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");

BufferedImage bfi = new BufferedImage(80,25,BufferedImage.TYPE_INT_RGB);
Graphics g = bfi.getGraphics();
g.fillRect(0, 0, 80, 25);

//验证码字符范围
char[] ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".toCharArray();
Random r = new Random();
int index;
StringBuffer sb = new StringBuffer(); //保存字符串
for(int i=0; i<4; i++){
index = r.nextInt(ch.length);
g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255)));
Font font = new Font("宋体", 30, 20);
g.setFont(font);
g.drawString(ch[index]+"", (i*20)+2, 23);
sb.append(ch[index]);
}

// 添加噪点
int area = (int) (0.02 * 80 * 25);
for(int i=0; i<area; ++i){
int x = (int)(Math.random() * 80);
int y = (int)(Math.random() * 25);
bfi.setRGB(x, y, (int)(Math.random() * 255));
}

//设置验证码中的干扰线
for (int i = 0; i < 6; i++) {
//随机获取干扰线的起点和终点
int xstart = (int)(Math.random() * 80);
int ystart = (int)(Math.random() * 25);
int xend = (int)(Math.random() * 80);
int yend = (int)(Math.random() * 25);
g.setColor(interLine(1, 255));
g.drawLine(xstart, ystart, xend, yend);
}
HttpSession session = request.getSession(); //保存到session
session.setAttribute("verificationCode", sb.toString());
ImageIO.write(bfi, "JPG", response.getOutputStream()); //写到输出流
}



/**
* 获取随机的颜色值，r,g,b的取值在Low到High之间
* @param L 左区间
* @param R 右区间
* @return 返回随机颜色值
*/
private static Color interLine(int Low, int High){
if(Low > 255)
Low = 255;
if(High > 255)
High = 255;
if(Low < 0)
Low = 0;
if(High < 0)
High = 0;
int interval = High - Low;
int r = Low + (int)(Math.random() * interval);
int g = Low + (int)(Math.random() * interval);
int b = Low + (int)(Math.random() * interval);
return new Color(r, g, b);
}

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原文：https://blog.csdn.net/qq_36831718/article/details/80095770