java - Struts2, I have a NullPointerException report -

struts.xml:

<package name="backpower" namespace="/backpower" extends="struts-default">     <default-interceptor-ref name="defaultstack"></default-interceptor-ref>     <!-- backup battery manager -->     <action name="backpower" class="com.cps.backpower.action.backpoweraction">         <result name="addbattery">/web-inf/views/backpower/info/addbattery.jsp</result>         <result name="editbattery">/web-inf/views/backpower/info/editbattery.jsp</result>         <result>/web-inf/views/backpower/info/list.jsp</result>     </action> </package> 

add.jsp:

    <div class="form-actions">         <button name="method:save" type="submit" class="btn btn-primary">             save         </button>         <button type="reset" class="btn">             reset         </button>     </div> 

my backpoweraction class

public class backpoweraction extends basemanageaction{  private static final long serialversionuid=1l; public backpowerservice backpowerservice; public paginationsupport backpowerpagination; public pagetip pagetip; public backpowerinfo backpowerinfo; public long id;   public string execute() throws exception{     return search(); }  public string search(){     string hql="from backpowerinfo 1=1";     backpowerpagination=backpowerservice.getpage(hql,getpageno(),getpagesize());     return success; }  public void setbackpowerinfo(backpowerinfo backpowerinfo){     this.backpowerinfo=backpowerinfo; }  public string add(){     return "addbattery"; }  public string save() {     if (backpowerinfo.getid() == null) {         try {             backpowerservice.save(backpowerinfo);             return success;         } catch (exception e) {             return add();         }     } else {         try {             backpowerservice.update(backpowerinfo.getid(),backpowerinfo.getname(),backpowerinfo.getlocation(),backpowerinfo.getmanager());             pagetip.setok(true);             pagetip.settip("修改用户信息成功");             return search();         } catch (exception e) {             e.printstacktrace();             pagetip.setok(false);             pagetip.settip("修改用户信息失败");             return edit();         }     }  }  public string edit() {     backpowerinfo=backpowerservice.findbyid(getid());      return "editbattery"; }  public string del() throws exception {     try {         backpowerservice.delete(getid());         pagetip.setok(true);         pagetip.settip("删除成功");     } catch (exception e) {         pagetip.setok(false);         pagetip.settip("删除失败");     }     return search(); }  public backpowerinfo getbackpowerinfo(){     return backpowerinfo; }     public paginationsupport getbackpowerpagination(){      return backpowerpagination; }  public void setbackpowerpagination(paginationsupport backpowerpagination){     this.backpowerpagination=backpowerpagination; }  public backpowerservice getbackpowerservice(){     return backpowerservice; }  public void setbackpowerservice(backpowerservice backpowerservice){     this.backpowerservice=backpowerservice; }  public pagetip getpagetip(){     return pagetip; }  public void setpagetip(pagetip pagetip){     this.pagetip=pagetip; }  public long getid(){     return id; }  public void setid(long id){     this.id=id; } } 

java.lang.nullpointerexception
com.cps.backpower.action.backpoweraction.save(backpoweraction.java:39)

when click save button on web page, gives struts2 problem report, wrong, how should correct it?

i think backpowerinfo null in code.

you haven't populated or instantiated before calling getters.