如何解决这个空NullPointerException?

Question

下面这几句代码提示有NullPointerException问题:
其中cwdfMap是一个Map对象 String sDF=cwdfMap.get(CWZBDM).toString();
 double dfValue=Double.parseDouble(sDF);提示错误就是在String sDF =cwdfMap.get(CWZBDM).toString()这行.
但是我在输出的时候这里面是都有值的,
其中有两个是0.00那么为什么会有这种错误提示呢?

Answer 1

我输出看了里面都有值,为什么还提示说NullPointerException

Answer 2

cwdfMap.put(CWZBDM,sValue)在这里我是通过另一个方法initCwdfMap来对Map进行初始化的.首先从数据表当中读出记录,然后把字段名为cwzbdm,的值写入map的key,而把另一个字段的值写入map的value

Answer 3

public boolean saveScoreToDB(HttpServletRequest req,HttpServletResponse res){
      HttpSession session = req.getSession(false);//获取session
      String PJLX=(String)session.getAttribute("RWLB");//评级类型
      String PJXH=(String)session.getAttribute("PJXH");//评级序号
      String PJJD=(String)session.getAttribute("PJJD");//评级阶段
      String RWBH=(String)session.getAttribute("SPRWBH");//任务编号
      String LCXH=(String)session.getAttribute("activityId");//流程序号
      //避免空指针
      PJLX=PJLX==null?"":PJLX;
      PJXH=PJXH==null?"":PJXH;
      PJJD=PJJD==null?"":PJJD;
      RWBH=RWBH==null?"":RWBH;
      LCXH=LCXH==null?"":LCXH;
      if(PJJD.equals("")){
         ErrMsg="程序出错,session中取得的PJJD不能为空!";
         YwdzAssist.alert(res,req,ErrMsg,"");
         return false ;
      }
      String sql="",sql1="",sql2="";
      sql="select * from Loan.XT_CWZBHYGXQZ where HYDM='" + HYDM + "' and PJMX In('01','11')";
      System.out.println(sql);
      System.out.println("PJLX="+PJLX+";PJXH="+PJXH+"PJJD="+PJJD+"RWBH="+RWBH+"LCXH="+LCXH);
      DBManage DB=new DBManage();
      DB.setAutoCommit(false);//设置不自动提交
      ResultSet rs=null;
      this.totalScore=0;
      try{
        rs=DB.sqlQuery(sql);
        if(initCwdfMap()){
         while(rs.next()){
            String CWZBDM=rs.getString("CWZBDM").trim();
            String CWYSDM=rs.getString("CWYSDM").trim();
            String sDF= "";            
            sDF=cwdfMap.get(CWZBDM).toString();//取出得分 
            
            double dfValue=Double.parseDouble(sDF);
            totalScore=totalScore + dfValue;
            System.out.println("CWZBDM="+CWZBDM+"-----------CWYSDM="+CWYSDM);
            System.out.println("sDF="+sDF);
            System.out.println("dfValue="+dfValue);
            
            if(PJJD.equals("3")||PJJD.equals("4")){//非流程的处理
                //-----------------------------更新的sql语句--------------------------------------------
                sql1 = "update Loan.PJ_GC_CWYS set ZBDF=" + dfValue + ",BBQS1='" + BQBBQS + "',BBQS2='" + SQBBQS
                     +"' where KHBH='" + KHBH + "' and PJLX='" + PJLX+"' and PJXH=" + PJXH + " and PJJD='"
                     + PJJD + "' and CWZBDM='" + CWZBDM + "' and PJMX='01'";
                //------------------------------插入的sql语句--------------------------------------------
                sql2 ="insert into Loan.PJ_GC_CWYS(KHBH,PJLX,PJXH,PJJD,RWBH,LCXH,BBQS1,BBQS2,CWYSDM,CWZBDM,ZBDF,PJMX)"
                     +" values('" + KHBH + "','" +PJLX + "'," + PJXH + ",'" + PJJD + "','" + RWBH + "',0,'"
                     + BQBBQS + "','" + SQBBQS + "','" + CWYSDM +"','" + CWZBDM + "'," + dfValue+ ",'01')";
             }
             else {//流程的处理
                //-------------------------------更新的sql语句------------------------------------------
                int iLCXH=Integer.parseInt(LCXH)-2;
                sql1 = "update Loan.PJ_GC_CWYS set ZBDF=" + dfValue + ",BBQS1='" + BQBBQS + "',BBQS2='" + SQBBQS
                     +"' where KHBH='" + KHBH + "' and RWBH='" + RWBH + "' and LCXH=" + iLCXH + " and PJJD='"
                     + PJJD + "' and CWZBDM='" + CWZBDM + "' and PJMX='01'";
                //--------------------------------插入的sql语句------------------------------------------
                sql2 ="insert into Loan.PJ_GC_CWYS(KHBH,PJLX,PJXH,PJJD,RWBH,LCXH,BBQS1,BBQS2,CWYSDM,CWZBDM,ZBDF,PJMX)"
                     +" values('" + KHBH + "','" +PJLX + "'," + PJXH + ",'" + PJJD + "','" + RWBH + "'," + iLCXH  + ",'"
                     + BQBBQS + "','" + SQBBQS + "','" + CWYSDM + "','" + CWZBDM + "'," + dfValue+ ",'01')";
             }
            System.out.println(sql1);
            System.out.println(sql2);
             //debugPrint(sql1);
             //debugPrint(sql2); edit in 2006-06-27 batman
             //更新或插入PJ_GC_CWYS
            //System.out.println("sqlUpdateTotalCount="+DB.sqlUpdate(sql1));
             int totalCount;
             int insertCount;
             totalCount = DB.sqlUpdate(sql1);
             System.out.println("totalCount="+totalCount);
             if(totalCount <=0){ //若更新条数为0,则插入一条新记录
                insertCount = DB.sqlUpdate(sql2);
              System.out.println("insertCount="+insertCount);
              }
             
            if(!DB.getErrMsg().trim().equals("")){
             DB.rollback();
             ErrMsg="数据存入[PJ_GC_CWYS]表失败!错误原因 :"+DB.getErrMsg();
             System.out.println(ErrMsg);
             YwdzAssist.alert(res,req,ErrMsg,"");
             return false;
            }
            //超过界限,取极值
            //if(totalScore>100) totalScore=100;
            System.out.println("totalScore="+totalScore);
            if(totalScore<0) totalScore=0;
            DB.commit();//提交事务
         }
        }      }
      catch(SQLException sqlE){
         DB.rollback();//事务回滚
         ErrMsg="数据存入[PJ_GC_CWYS]表失败!错误原因 :"+sqlE.getMessage();
         System.out.println(ErrMsg);
         YwdzAssist.alert(res,req,ErrMsg,"");
         return false;
      }
      finally{
         if(rs!=null){
            try{rs.close();rs=null;}
            catch(SQLException sqlE1){}
         }
         if(DB!=null){
            DB.close();
            DB=null;
         }
      }
      return true;
  }

Answer 4

问题有可能出现在下面这句...
String CWZBDM=rs.getString("CWZBDM").trim();
你把CWZBDM输出到控制台看看它的值

Answer 5

为null时是不能toString()的！！！！！！！！！！！！！！！！！！！！

Answer 6

cwdfMap.get(CWZBDM)为null不能toString（）
差一下initCwdfMap()时有没有把CWZBDM的值的value设进去

Answer 7

这样用：
String sDF=(String)cwdfMap.get(CWZBDM);因为cwdfMap.get(CWZBDM)获得的可能是null，null.toString();肯定是异常喽；或者这样改：Object obj = cwdfMap.get(CWZBDM);
if (null != obj) {
String sDF=obj.toString();
}