無法編譯jsp

Question

我無法編譯jsp並得到以下錯誤。

org.apache.jasper.JasperException: Unable to compile class for JSP: 

An error occurred at line: 8 in the jsp file: /jsp/org_1/Alpha.jsp
Duplicate local variable applicationURL
5: <%@ page import="java.util.*" %>
6: <%@ page import="org.apache.log4j.Logger" %>
7: <%
8:      String applicationURL = (String) session.getAttribute("appURL");
9:      String cntxtName = "";
10:         
11:         if(null != applicationURL)


An error occurred at line: 9 in the jsp file: /jsp/org_1/Alpha.jsp
Duplicate local variable cntxtName
6: <%@ page import="org.apache.log4j.Logger" %>
7: <%
8:      String applicationURL = (String) session.getAttribute("appURL");
9:      String cntxtName = "";
10:         
11:         if(null != applicationURL)
12:         {


 Stacktrace:
at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:92)
at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:330)
at org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:415)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:308)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:286)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:273)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:566)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:316)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:336)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:557)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:481)
at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
at org.apache.jsp.jsp.org_005f1.Beta_jsp._jspService(Beta_jsp.java:135)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:336)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1063)
at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:386)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:229)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1063)
at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:386)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:229)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.tcs.ddf.servlets.gamma.checkBrowser(gamma.java:180)
at com.tcs.ddf.servlets.gamma.doFilter(gamma.java:40)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
at java.lang.Thread.run(Unknown Source)

我的jsp看起來像這樣：

 <%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>
 <%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>
 <%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>
 <%@ page import="java.util.*" %>
 <%@ page import="org.apache.log4j.Logger" %>
  <%
    String applicationURL = (String) session.getAttribute("appURL");
    String cntxtName = "";

    if(null != applicationURL)
    {
        cntxtName = applicationURL+"abc/";
    }
    else
    {
        cntxtName = "/abc/";
    }

    session.setAttribute("cntxtName",cntxtName);
     %>
  <head> 

我已經檢查過字符串變量applicationURL和cntxtName都沒有在其他任何地方使用過。 那么為什么我會得到Duplicate local variable error。 請提出解決方案。

Answer 1

當其他包含的JSP文件已在當前jsp文件中聲明相同的局部變量時，通常會發生Duplicate local variable異常。
欲了解更多信息，請訪問： http ： //www.appperfect.com/support/java-coding-rules/jsp.html#rule1 。
因此，請確保您在包含的jsp文件中沒有相同的變量。

注意：
避免在JSP中編寫腳本總是好的（因為@duffymo告訴你使用JSTL）

Answer 2

避免在JSP中使用Scriptlets <% %> 。 使用JSTL ， EL它比scriptlet更簡單，代碼更少。

//get the value of appURL from session and set to variable applicationURL
<c:set var="applicationURL" value="${sessionScope.appURL}"></c:set>

//set the variable cntxtName default value to avoid else part
<c:set var="cntx" value="/abc/"></c:set>

//there is no if else so use 
<c:choose>
  <c:when test="${not empty applicationURL}">     //empty also checks for null as well
    <c:set var="cntxtName" value="${applicationURL}${cntx}" scope="session"></c:set>
  </c:when> 
  <c:otherwise>
    <c:set var="cntxtName" value="${cntx}" scope="session"></c:set>
  </c:otherwise>  
</c:choose>       

要運行上面的代碼，您需要在類路徑中使用jstl-1.2.jar 。 在JSP中添加

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

相關鏈接

• JSTL核心
• 標簽集
• 如何避免JSP-Files中的Java代碼？