Intellij IDEA 报错java.lang.NoClassDefFoundError

逃离我推掉我的手 2022-06-05 04:43 296阅读 0赞

入坑，踩坑，填坑……  
今天在Idea写一个简单地基于Servlet的验证码小页面

package com.dream.servlet.response;
    
    import cn.dsna.util.images.ValidateCode;
    
    import javax.imageio.ImageIO;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.awt.*;
    import java.awt.image.BufferedImage;
    import java.io.IOException;
    import java.util.Random;
    
    /** * Created by Dream on 2017/11/15. */
    public class IdentifyCode extends HttpServlet { 
        public void doGet(HttpServletRequest request, HttpServletResponse response)throws IOException{
    // produceCode(request,response);
            //使用ValidateCode jar包中现成的验证码类
            ValidateCode vc = new ValidateCode(110,25,4,9);
            vc.write(response.getOutputStream());
        }
        public void doPost(HttpServletRequest request,HttpServletResponse response)throws IOException{
            doGet(request,response);
        }
        //自己写方法实现验证码
        private void produceCode(HttpServletRequest request,HttpServletResponse response)throws IOException{
            int width = 110;
            int height = 25;
            //创建一个图像对象
            BufferedImage img = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
            //创建一个画笔
            Graphics g = img.getGraphics();
            //填充内部颜色
            g.setColor(Color.PINK);
            g.fillRect(1,1,width-2,height-2);
            //画边框
            g.setColor(Color.RED);
            g.drawRect(0,0,width-1,height-1);
            //设置文本样式
            g.setColor(Color.BLUE);
            g.setFont(new Font("宋体",Font.BOLD|Font.ITALIC,15));
            //写随机数字
            Random r = new Random();
            int position = 20;
            for(int i=0;i<4;i++){
                g.drawString(r.nextInt(10)+"",position,20);
                position+=20;
            }
            //画干扰线
            g.setColor(Color.CYAN);
            for(int i=0;i<5;i++){
                g.drawLine(r.nextInt(width),r.nextInt(height),r.nextInt(width),r.nextInt(height));
            }
            ImageIO.write(img,"jpg",response.getOutputStream());
        }
    }

其中produceCode()是自己写的方法，ValidateCode是一个可以产生验证码的现成类，但是，就是在我引入该类的jar包准备用这个类的时候，结果报出了如下错误  
![SouthEast][]  
内心很崩溃，明明引入了该jar包，但是仍然报该类找不到的异常，黑人问号脸….  
![这里写图片描述][SouthEast 1]  
其实是因为jar包未被部署，那么在进行页面请求的时候，就会找不到jar包，那么就会报错…..  
解决方案如下：  
Projecture—>Artifacts–>选择打包部署项目—->Output Layout–>Web-INF—->查看下面是否有lib目录(如果没有lib目录，可自行创建)—>右边的jar包添加到lib目录下  
以上，即可解决ClassNotFound的异常  
![这里写图片描述][SouthEast 2]

[SouthEast]: /images/20220605/3211f09db377404791d494c80a9228a6.png
[SouthEast 1]: /images/20220605/f4b7d3e1610d409093023f830d7335d6.png
[SouthEast 2]: /images/20220605/dfc8f1b3e35c4e409517ef30190fb2da.png