关于ant中一个属性mapped

<target name="jspc" depends="init, copy_needed">
    <copy todir="${jsp_temp}/jsp">
        <fileset dir="${webroot}/jsp">
        <exclude name="onlinehelp/**"/> 
        <exclude name="WebHelp/**"/>         
        </fileset>
      </copy>    
      <copy file="${webroot}/index.jsp" todir="${jsp_temp}"/>
      
      <taskdef classname="org.apache.jasper.JspC" name="jasper2" > 
      <classpath id="jspc.classpath"> 
        <pathelement location="${java.home}/lib/tools.jar"/>          
        <pathelement location="${tomcat_lib}/ant.jar" />
        <pathelement location="${tomcat_lib}/jasper-runtime.jar" /> 
        <pathelement location="${tomcat_lib}/jasper-compiler.jar" /> 
        <!-- The two jars for Jboss3.2.6
        <pathelement location="${tomcat_lib}/servlet-api.jar" />
        <pathelement location="${tomcat_lib}/jsp-api.jar" />
        -->
        <pathelement location="${jboss_server_lib}/javax.servlet.jar" />
        <pathelement location="${jboss_server_lib}/javax.servlet.jsp.jar"/>
        <pathelement location="${tomcat_lib}/commons-logging.jar" />
        <pathelement location="${tomcat_lib}/commons-el.jar"/>
        <pathelement location="${extjar}/xercesImpl.jar" />
        <pathelement location="${extjar}/xml-apis.jar" />
        <pathelement location="${extjar}/struts.jar"/>
        <pathelement location="${extjar}/ncs.jar" />
        <pathelement location="./lib/ivan.jar"/>
        <pathelement location="${jsp_temp}/ivanweb.jar"/>        
        <pathelement location="${tmghome}/lib/tmgclientapi.jar"/>
<!--Add apache commons lang-->
<pathelement path="${extjar}/commons-lang-2.0.jar"/>      </classpath>      
    </taskdef>     <jasper2 
             validateXml="false" 
             uriroot="${jsp_temp}" 
             package="com.timogen.web.ivan.jsp"
             outputDir="${jsp_temp}/src"
             compile="true"
             addWebXmlMappings="true" 
             mapped="true"
             webXmlFragment="${jsp_temp}/generated_web.xml"/> 
    </target>