空指针如何处理？java.lang.NullPointerException

Question

package com.muke;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")

public class LoginServlet extends HttpServlet{

public void doGet(HttpServletRequest request,HttpServletResponse response)throws IOException{

String piccode =(String)request.getSession().getAttribute("piccode");

String checkcode = request.getParameter("checkcode");

checkcode = checkcode.toUpperCase();

response.setContentType("text/html;chsrset=gbk");

PrintWriter out = response.getWriter();

if(checkcode.equals(piccode)){

out.println("输入正确");

}

else{

out.println("输入有误");

}

out.flush();

out.close();

}

}

Answer 1

错误语句是 checkcode = checkcode.toUpperCase();