HTTP状态500 - java.lang.NumberFormatException：null

Question

我正在创建一个标准的动态Web项目，包括一个Servlet，一个过滤器来过滤请求和jsp页面。 我从welcome.jsp中获取书籍的数量，并根据计数我在add.jsp上填充输入框。我想过滤通过add.jsp传来的数据。当我通过Regex验证数据时，显示错误。我的流程也是正确的，即从开始的FILTER - > CONTROLLER - > FILTER - > PAGE等等。

错误： java.lang.NumberFormatException：空

完整跟踪是这样的：

---

HTTP Status 500 - java.lang.NumberFormatException: null 

type Exception report 

message java.lang.NumberFormatException: null 

description The server encountered an internal error that prevented it from fulfilling this request. 

exception 

org.apache.jasper.JasperException: java.lang.NumberFormatException: null 
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549) 
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470) 
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) 
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728) 
    com.filter.RequestFilter.doFilter(RequestFilter.java:107) 

root cause 

java.lang.NumberFormatException: null 
    java.lang.Integer.parseInt(Unknown Source) 
    java.lang.Integer.parseInt(Unknown Source) 
    org.apache.jsp.WEB_002dINF.add_jsp._jspService(add_jsp.java:139) 
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728) 
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) 
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) 
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728) 
    com.filter.RequestFilter.doFilter(RequestFilter.java:107) 

---

的代码，其中其表现是：

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { 
    // TODO Auto-generated method stub 
    // place your code here 
    boolean flag = true; 
    HttpServletRequest httpServletRequest = (HttpServletRequest) request; 
    HttpServletResponse httpResponse = (HttpServletResponse) response; 
    httpServletRequest.getServletPath(); 
    System.out.println(httpServletRequest.getServletPath()); 


    String address = InetAddress.getLocalHost().getHostAddress(); 
    System.out.println(address); 


    // For the first time (Welcome page) i will be 0 so that it will perform first if 

    if(i == 0) 
    { 
     System.out.println(i); 
     if(verify(address)) 
     { 
      chain.doFilter(request, response); 
      i++; 
     } 

     else 
     { 
      RequestDispatcher requestDispatcher = httpServletRequest.getServletContext().getRequestDispatcher("/WEB-INF/forbidden.jsp"); 
      requestDispatcher.forward(request, response); 
      return; 
     } 

    } 

    // For the second time (Controller) i will be 1 so that it will perform first if 


    else if(i == 1) 
    { 
     System.out.println(i); 
     i++; 
     System.out.println("after ++"+i); 
     chain.doFilter(request, response); 
    } 

    // For the second time (add page) i will be 2 so that it will perform first if 


    else if(i == 2) 
    { 

     if(specialChara(httpServletRequest)) 
      { 
       System.out.println(i); 
       System.out.println("done"); 
       i++; 
       chain.doFilter(request, response); 
      } 

      else 
      { 
       System.out.println(i); 
       flag = false; 
       System.out.println(""+httpServletRequest.toString()+ "\n"+httpResponse.toString()); 
       RequestDispatcher requestDispatcher = httpServletRequest.getServletContext().getRequestDispatcher("/WEB-INF/add.jsp"); 
       requestDispatcher.forward(request, response); 

      } 
    } 

    // For the third time (Controller) i will be 2 so that it will perform first if 

    else if(i == 3) 
    { 
     System.out.println(i); 
     i++; 
     chain.doFilter(request, response); 
     i = 0; 
    } 

它给e rror在循环中forward（）的行，其中我= 2。 可能是什么问题？ add.jsp的

链接https://docs.google.com/document/d/1fOzymYvlLXS577DrSrznRoeBnI7_hMmuqzFoK02xKoU/edit?usp=sharing

Answer 1

从堆栈跟踪似乎问题不在于你的java类，而是你的JSP。我的猜测是在线

int no = Integer.parseInt(request.getParameter("no")); 

似乎不是null.Also最好使用和其他条件标签，而不是在JSP中使用scriptlet。