有段代码不明白，请解释，谢谢！分不够马上加！！！！

Question

package com.mine.struts.action;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;import org.hibernate.Session;
import org.hibernate.Transaction;
import com.mine.hiber.SessionFactory;
import com.mine.hiber.T3;
import com.mine.struts.form.RegForm;
public class RegAction extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) 
{
         RegForm regForm = (RegForm) form;// TODO Auto-generated method stub
         Session sessiont3=SessionFactory.getSession();
        Transaction tx=sessiont3.beginTransaction();
             String msg=null;
             
               
    return mapping.findForward("success");
}
}
请问这段代码错在那里，总是提示错误：javax.servlet.ServletException: java.lang.NullPointerException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:523)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause java.lang.NullPointerException
com.mine.struts.action.RegAction.execute(RegAction.java:71)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

Answer 1

RegAction.java:71行有空指针看看是哪一行 自己打印一下日志 看什么是null

Answer 2

找上面给出的代码看,可能session出现了NullPointerException

Answer 3

ding ding ding ding 

Answer 4

其实Debug一下就什么都有了。也没多少代码呀。

Answer 5

debug上面的代码,看看哪个引用是空的.

Answer 6

如何debug啊，我刚开始学，能告诉我吗，谢谢！如果分不够的话，我立刻加！！

Answer 7

靠!折腾了我这么久,贴出来参考下:import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Comparator;class Item {
private String name;
private int salary;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getSalary() {
return salary;
}
public void setSalary(int salary) {
this.salary = salary;
}
}
class MyComparator implements Comparator { public int compare(Object o1, Object o2) {
Item c1=(Item)o1;
Item c2=(Item)o2;
if (c1.getSalary() >c2.getSalary()) {
return 1;
} else if (c1.getSalary() == c2.getSalary()) {
return 0;
} else {
return -1;
}
}
}
public class Person{
public static void main(String[] args){
List<Item> list=new ArrayList<Item>();
for(int i=0;i<10;i++){
Item p=new Item();
p.setName("n"+i);
p.setSalary(i%7);
list.add(p);
}
System.out.println("----------排序前---------");
System.out.println("    name          salary");
for(int i=0;i<list.size();i++){
System.out.println("    "+list.get(i).getName()+"            "+list.get(i).getSalary());
} MyComparator mc=new MyComparator();
Collections.sort(list,mc);

System.out.println("----------排序后---------");
System.out.println("    name          salary");
for(int i=0;i<list.size();i++){
System.out.println("    "+list.get(i).getName()+"            "+list.get(i).getSalary());
}
for(int i=0;i<list.size();){
String names=list.get(i).getName();
while(i+1<list.size()&&list.get(i).getSalary()==list.get(i+1).getSalary()){
names+=","+list.get(i+1).getName();
i++;
}
i++;
System.out.println(names+"  salary:"+list.get(i-1).getSalary()+" 元");
}
}
}

Answer 8

请问如何debug上面的代码，谢谢了！

Answer 9

可能是Session里面为空,自己调试调试

Answer 10

RegAction.java:71行 有空指针 看看是哪一行 自己打印一下日志 看什么是null