NullPointerException的异常，请教一下

来源：百度知道 编辑：UC知道 时间：2024/06/16 13:48:26
请问一下这个空指针是什么原因，在这里谢谢了
2008-2-20 21:55:21 org.apache.catalina.core.ApplicationDispatcher invoke
严重: Servlet.service() for servlet debugjsp threw exception
java.lang.NullPointerException
at org.apache.jsp.PetDisplay_jsp._jspService(org.apache.jsp.PetDisplay_jsp:114)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.ApplicationD

肯定是使用了什么值为null的对象，并试图使用该对象的方法，就会产生nullpointerexception
String petName = "";
if (request.getParameter("petName") != null)
petName = request.getParameter("petName");
String petOwner = "";
if (request.getParameter("petOwner") != null)
petOwner = request.getParameter("petOwner");
这部分不用判断是否为空了
因为你都复制了“”！=null

list = new PetDAO().search(petName, petOwner); 这句话可能得到的是个null