请问老师我这是什么错误

代码：

package com.imooc.code;

import javax.servlet.http.HttpServletResponse;
import java.util.Random;

public class CaptcahCode {


    public static String drawImage(HttpServletResponse response){
        StringBuilder builder=new StringBuilder();
        for (int i = 0; i <5; i++) {
            builder.append(randowChar());
        }
        String code=builder.toString();
        System.out.println(code);
        return null;
    }
    private static char randowChar(){
        String string="QWERTYUIOPASDFGHJKLZXCVBNM0123456789";
        Random random=new Random();
        return string.charAt(random.nextInt(string.length()));
    }

    public static void main(String[] args) {
        CaptcahCode.drawImage(null);
    }
}

控制台：

D:\jdk\bin\java.exe -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:20898,suspend=y,server=n -javaagent:C:\Users\81456\.IntelliJIdea2018.3\system\captureAgent\debugger-agent.jar -Dfile.encoding=UTF-8 -classpath "D:\jdk\jre\lib\charsets.jar;D:\jdk\jre\lib\deploy.jar;D:\jdk\jre\lib\ext\access-bridge-32.jar;D:\jdk\jre\lib\ext\cldrdata.jar;D:\jdk\jre\lib\ext\dnsns.jar;D:\jdk\jre\lib\ext\jaccess.jar;D:\jdk\jre\lib\ext\jfxrt.jar;D:\jdk\jre\lib\ext\localedata.jar;D:\jdk\jre\lib\ext\nashorn.jar;D:\jdk\jre\lib\ext\sunec.jar;D:\jdk\jre\lib\ext\sunjce_provider.jar;D:\jdk\jre\lib\ext\sunmscapi.jar;D:\jdk\jre\lib\ext\sunpkcs11.jar;D:\jdk\jre\lib\ext\zipfs.jar;D:\jdk\jre\lib\javaws.jar;D:\jdk\jre\lib\jce.jar;D:\jdk\jre\lib\jfr.jar;D:\jdk\jre\lib\jfxswt.jar;D:\jdk\jre\lib\jsse.jar;D:\jdk\jre\lib\management-agent.jar;D:\jdk\jre\lib\plugin.jar;D:\jdk\jre\lib\resources.jar;D:\jdk\jre\lib\rt.jar;C:\Users\81456\IdeaProjects\imooccode\out\production\imooccode;D:\idea\IntelliJ IDEA 2018.3.1\lib\idea_rt.jar" com.imooc.code.CaptcahCode

Connected to the target VM, address: '127.0.0.1:20898', transport: 'socket'

java.lang.NoClassDefFoundError: javax/servlet/http/HttpServletResponse

at java.lang.Class.getDeclaredMethods0(Native Method)

at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)

at java.lang.Class.privateGetMethodRecursive(Class.java:3048)

at java.lang.Class.getMethod0(Class.java:3018)

at java.lang.Class.getMethod(Class.java:1784)

at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)

at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)

Caused by: java.lang.ClassNotFoundException: javax.servlet.http.HttpServletResponse

at java.net.URLClassLoader.findClass(URLClassLoader.java:381)

at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)

at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

... 7 more

Disconnected from the target VM, address: '127.0.0.1:20898', transport: 'socket'

Error: A JNI error has occurred, please check your installation and try again

Exception in thread "main" 

Process finished with exit code 1