java.lang.NullPointerException探讨

xuefeifangpei 2003-04-07 08:46:56

strSQL="select * FROM data where ";
if(!tousu_start_date1.trim().equals("") && !tousu_end_date1.trim().equals(""))
strSQL=strSQL+" tousu_date between #"+tousu_start_date1+"# and #"+tousu_end_date1+"# order by tousu_date desc";
if(!tousu_class1.trim().equals("") )
strSQL=strSQL+" and tousu_class like '%"+tousu_class1+"%' ";
if(!depart1.trim().equals("") )
strSQL=strSQL+" and depart = '"+depart1+"' ";
if(!handle1.trim().equals("") )
strSQL=strSQL+" and handle = '"+handle1+"' ";
if(!details1.trim().equals("") )
strSQL=strSQL+" and details like '%"+details1+"%' ";
if(!person1.trim().equals("") )
strSQL=strSQL+" and person = '"+person1+"' ";
我做了个查询怎么有时候报如下错误:如果把if条件语句换个顺序,在输入不通类别时它报同样下面的错

java.lang.NullPointerException
at _0002fsql_0005fok_0002ejspsql_0005fok_jsp_57._jspService(_0002fsql_0005fok_0002ejspsql_0005fok_jsp_57.java:210)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:184)

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切换为时间正序

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xuefeifangpei 2003-04-08

我这样做了还是不行哦
tousu_end_date1=request.getParameter("tousu_end_date");
if (tousu_end_date1 ==null)
tousu_end_date1 ="";
depart1=request.getParameter("depart");
if (depart1 ==null)
depart1 ="";
details1=request.getParameter("details");
if (details1 ==null)
details1 ="";
handle1=request.getParameter("handle");
if (handle1 ==null)
handle1 ="";
person1=request.getParameter("person");
if (person1 ==null)
person1 ="";
tousu_class1=request.getParameter("tousu_class");
if (tousu_class1 ==null)
tousu_class1 ="";
strSQL="select * FROM data where ";

if(!tousu_class1.trim().equals(""))
strSQL=strSQL+" and tousu_class like '%"+tousu_class1+"%' ";
if(!depart1.trim().equals("") )
strSQL=strSQL+" depart = '"+depart1+"' ";
if( !handle1.trim().equals("") )
strSQL=strSQL+" and handle = '"+handle1+"' ";
if( !details1.trim().equals("") )
strSQL=strSQL+" and details like '%"+details1+"%' ";
if( !person1.trim().equals("") )
strSQL=strSQL+" and person = '"+person1+"' ";
if(!tousu_start_date1.trim().equals("") && !tousu_end_date1.trim().equals("") )
strSQL=strSQL+" and tousu_date between #"+tousu_start_date1+"# and #"+tousu_end_date1+"# order by tousu_date desc";

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dybine 2003-04-08

如果对象==null, trim()方法和equals("")方法都会抛出空指针异常

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凋零的老树 2003-04-08

原因很简单
tousu_start_date1 是null
所以执行
if(!tousu_start_date1.trim().equals("") && !tousu_end_date1.trim().equals("")) 肯定提示空指针错误
解决方法：
在前面加一句
if (tousu_start_date1 ==null)
tousu_start_date1 ="";
注意你的每一个做类似操作的变量都必须这样做

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xuefeifangpei 2003-04-08

这样写对么??但是还是不行哦??
strSQL="select * FROM data where ";
if( tousu_class1!=null && !tousu_class1.trim().equals("all"))
strSQL=strSQL+" tousu_class like '%"+tousu_class1+"%' ";
if(depart1!=null && !depart1.trim().equals("all") )
strSQL=strSQL+" and depart = '"+depart1+"' ";
if( handle1!=null && !handle1.trim().equals("all") )
strSQL=strSQL+" and handle = '"+handle1+"' ";
if( details1!=null && !details1.trim().equals("") )
strSQL=strSQL+" and details like '%"+details1+"%' ";
if( person1!=null && !person1.trim().equals("all") )
strSQL=strSQL+" and person = '"+person1+"' ";
if(!tousu_start_date1.trim().equals("") && !tousu_end_date1.trim().equals("") )
strSQL=strSQL+" and tousu_date between #"+tousu_start_date1+"# and #"+tousu_end_date1+"# order by tousu_date desc";

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qiri07 2003-04-07

http://expert.csdn.net/Expert/topic/1481/1481192.xml?temp=.7586328

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farawayMemory 2003-04-07

order by 从句应在 where 条件句之后

建议将以下if语句置后!
/*******************
if(!tousu_start_date1.trim().equals("") && !tousu_end_date1.trim().equals(""))
strSQL=strSQL+" tousu_date between #"+tousu_start_date1+"# and #"+tousu_end_date1+"# order by tousu_date desc";
/*******************

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