判断是否为授权用户

boolean  flag=false;  
                       String  username=(String)  request.getAttribute("user");  
                       List  list0=this.getPatchuserService().findallpatchuser();  
                       Iterator  it=list0.iterator();  
                       while(it.hasNext()){  
                                   Patchuser  pu=(Patchuser)  it.next();  
                                   if(username.equals((String)pu.getUsename())  ¦  ¦username==(String)pu.getUsename())flag=true;  
                       }  
                       if(flag){  
                                   List  list=this.getPubdocService().findallpubdocs();  
                                               request.getSession().setAttribute("pubdoclist",  list);              
                                               return  mapping.findForward("managePubdoc");  
                       }else{  
                                   return  mapping.findForward("error");  
                       }  
 
 
this.getPatchuserService().findallpatchuser();返回所有授权用户  这个方法经过测试好用  并且授权用户为Patchuser类型  
可是怎么有错误  java.lang.NullPointerException  
           com.yourcompany.struts.action.ManagepubAction.execute(ManagepubAction.java:47)  
这个第47行就是  
if(username.equals((String)pu.getUsename())  ¦  ¦username==(String)pu.getUsename())  
这行  大家帮我看看怎么回事