空指针异常怎么处理 求高人帮忙啊！！！1急在线等

指针异常myeclipse

解决方案 »

  1.   

      out.write("          <td width=\"266\" height=\"342\" align=\"center\" valign=\"top\" bgcolor=\"#CCCCCC\">\r\n");
          out.write("\t\t  <form id=\"form5\" name=\"form5\" method=\"post\" action=\"ShowFlowers.jsp?flowername=");
          out.print(str );
          out.write("&flowerkind=");
          out.print(flower1.getFlowerKind());
      

  2.   

    index_jsp.java:337   apache-tomcat-6.0.37\work\Catalina\localhost  这个路径下找到 jsp 的java文件 。看看337 是什么 ，就找到错了
      

  3.   

    这是Java
    package org.apache.jsp;import javax.servlet.*;
    import javax.servlet.http.*;
    import javax.servlet.jsp.*;
    import java.util.*;
    import ustc.edu.user.*;
    import ustc.edu.flower.*;
    import ustc.edu.cart.*;public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
        implements org.apache.jasper.runtime.JspSourceDependent {  private static final javax.servlet.jsp.JspFactory _jspxFactory =
              javax.servlet.jsp.JspFactory.getDefaultFactory();  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;  private javax.el.ExpressionFactory _el_expressionfactory;
      private org.apache.tomcat.InstanceManager _jsp_instancemanager;  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
        return _jspx_dependants;
      }  public void _jspInit() {
        _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
        _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
      }  public void _jspDestroy() {
      }  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
            throws java.io.IOException, javax.servlet.ServletException {    final javax.servlet.jsp.PageContext pageContext;
        javax.servlet.http.HttpSession session = null;
        final javax.servlet.ServletContext application;
        final javax.servlet.ServletConfig config;
        javax.servlet.jsp.JspWriter out = null;
        final java.lang.Object page = this;
        javax.servlet.jsp.JspWriter _jspx_out = null;
        javax.servlet.jsp.PageContext _jspx_page_context = null;
        try {
          response.setContentType("text/html; charset=utf-8");
          pageContext = _jspxFactory.getPageContext(this, request, response,
           null, true, 8192, true);
          _jspx_page_context = pageContext;
          application = pageContext.getServletContext();
          config = pageContext.getServletConfig();
          session = pageContext.getSession();
          out = pageContext.getOut();
          _jspx_out = out;      out.write("\r\n");
          out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\r\n");
          out.write("<html xmlns=\"http://www.w3.org/1999/xhtml\">\r\n");
          out.write("\r\n");request.setCharacterEncoding("utf-8");Flower flower1 = FlowerMgr.getInstance().loadFlowerByFlowerId(1);
    Flower flower2 = FlowerMgr.getInstance().loadFlowerByFlowerId(17);
    Flower flower3 = FlowerMgr.getInstance().loadFlowerByFlowerId(18);
    Flower flower4 = FlowerMgr.getInstance().loadFlowerByFlowerId(16);String action = request.getParameter("action");
    if(action != null && action.equals("exit")) {
    session.removeAttribute("user");
    session.removeAttribute("cart");
    }
    else if(action != null && action.equals("login")) {
    User user = (User)session.getAttribute("user");
    if(user!=null){
    response.sendRedirect("AlreadyLogin.jsp");
    return;
    } String username = request.getParameter("username");
    String password = request.getParameter("password");
    User u = null;
    Cart c=null;
    try {
    u = User.check(username, password);
    } catch (UserNotFoundException e) {
    response.sendRedirect("LoginFailure.jsp");
    return;
    } catch (PasswordNotCorrectException e) {
    response.sendRedirect("LoginFailure.jsp");
    return;
    }
    session.setAttribute("user", u);
    session.setAttribute("cart", c);
    }String guest = "游客";
    User user = (User)session.getAttribute("user");
    if(user != null){
    guest = user.getUserName();
    }ArrayList<String> flowerkinds = FlowerMgr.getInstance().getFlowerKinds();String str = "";
      

  4.   

    337是这个
         out.write("&flowerkind=");
          out.print(flower1.getFlowerKind());
      

  5.   

    话说 方法里需不需要set和get方法呢
      

  6.   

    把 这句先注释掉 
      out.print(flower1.getFlowerKind());//  out.print(flower1.getFlowerKind());然后再跑跑看
      

  7.   

    flowerid值为空，你检查一下，你传过来的有没有正确值呀
      

  8.   

    所有对象在使用前先判断是否为null，这样可以避免空指针异常！
      

  9.   

    我现在就是想知道 我应该改那个文件 是当前的 index.JSP 文件 还是 后台路径下找到 jsp 的java文件  ......
      

  10.   

    后台那个是jsp编译的java文件，你改jsp
      

  11.   

    往页面刷出内容   out.flush();
      

  12.   

    应该怎么该这个JSP  求代码 
      

  13.   

    先找到空指针错误在哪一行，用debug调试，或者打印输出。然后将代码注释，看确定是哪一行出现的错误。方法就是：先找到病根，在开方子。这样贴代码，没有意义呀