錯誤在JSP

Question

我對jsp的提交工作類型和我寫這樣的代碼：

<form action="processInfo.jsp"> 
    <input type="submit" name="Kill" value="Kill" /> 
</form> 
<% 
    String s = request.getParameter("Kill"); 
    if (s != null) { 
     System.out.println("ok"); 
    } 
%> 

，但這個錯誤已經出現了，我dpn't知道爲什麼。

ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/SystemMonitoring_v1.2].[jsp]] (http--127.0.0.1-8080-1) Servlet.service() for servlet jsp threw exception: java.lang.NumberFormatException: null 
at java.lang.Long.parseLong(Long.java:372) [rt.jar:1.6.0_13] 
at java.lang.Long.parseLong(Long.java:461) [rt.jar:1.6.0_13] 
at org.apache.jsp.processInfo_jsp._jspService(processInfo_jsp.java:64) 
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) [jbossweb-7.0.13.Final.jar:] 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final] 
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369) [jbossweb-7.0.13.Final.jar:] 
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:326) [jbossweb-7.0.13.Final.jar:] 
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:253) [jbossweb-7.0.13.Final.jar:] 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final] 
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.13.Final.jar:] 
at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:153) [jboss-as-web-7.1.1.Final.jar:7.1.1.Final] 
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.13.Final.jar:] 
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.13.Final.jar:] 
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.13.Final.jar:] 
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:671) [jbossweb-7.0.13.Final.jar:] 
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:930) [jbossweb-7.0.13.Final.jar:] 
at java.lang.Thread.run(Thread.java:619) [rt.jar:1.6.0_13] 

的我不明白，你能不能幫我請

Answer 1

在exception看，我看到某處jsp你正在做

Long.parseLong(someStringVariable); 

和someStringVariable是null 。所以解析之前檢查nullLong

if(someStringVariable != null) { 
    Long.parseLong(someStringVariable); 
} 

注：

• 即使someStringVariable不爲空，Long.parseLong(someStringVariable)仍可能拋出異常，如果字符串不是可解析的格式
• 而建議使用JSTL in JSP並將所有解析邏輯保留到Servlets中

Answer 2

您正在嘗試格式化爲空。嘗試檢查它是否爲空。

包括標籤，

<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %> 

，並格式化這樣的價值，

<fmt:parseNumber var="i" type="number" value="${inputValue}" /> 
<p>Parsed Number : <c:out value="${i}" /></p>