Question

I have a jsp to which a servlet passes an object (a collection). the object becomes a session attribute:

session.setAttribute("groupList", request.getAttribute("groups"));

I use a tag to recursively generate a menu from the content of this collection:

<c:forEach items="${groupList}" var="emp" begin="0" end="10">
        <tag:menuRenderer groupList="${groupList}" />
    </c:forEach>

Those items in the are objects of a class Group. This class contains a list of subgroups subGroups and a list of objects of a different class called students.

My problem is that I can not access this list of students in my tag.
This is the tag code:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib tagdir="/WEB-INF/tags" prefix="tag"%>
<%@ taglib uri='http://java.sun.com/jsp/jstl/functions' prefix='fn' %>
<%@ attribute name="groupList" type="java.util.Collection"%>

<c:forEach var="item" items="${groupList}">

    <li><c:out value="${item.name}" /></li>
    <br>

    <!-- ##### here #### -->
    <li><c:out value="${fn:length(item.students)}" />   <!-- #### doesn't work ####-->
    <li><c:out value="${fn:length(item.subGroups)}" />  <!-- ####     works    #### -->

    <ul>
        <tag:menuRenderer groupList="${item.subGroups}" />
    </ul>
</c:forEach>

The call to item.students causes an exception, but I can’t see what exactly it is because the strack trace only shows where the exception is thrown in the jsp:

SEVERE: Servlet.service() for servlet jsp threw exception
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:186)
    at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:137)
    at org.hibernate.collection.internal.PersistentSet.size(PersistentSet.java:156)
    at org.apache.taglibs.standard.functions.Functions.length(Functions.java:202)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.el.parser.AstFunction.getValue(AstFunction.java:112)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:986)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fout_005f1(webmenuRenderer_tag.java:202)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fforEach_005f0(webmenuRenderer_tag.java:143)
    at org.apache.jsp.tag.webmenuRenderer_tag.doTag(webmenuRenderer_tag.java:97)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_tag_005fmenuRenderer_005f0(webmenuRenderer_tag.java:240)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fforEach_005f0(webmenuRenderer_tag.java:153)
    at org.apache.jsp.tag.webmenuRenderer_tag.doTag(webmenuRenderer_tag.java:97)
    at org.apache.jsp.testMenu2_jsp._jspx_meth_tag_005fmenuRenderer_005f0(testMenu2_jsp.java:173)
    at org.apache.jsp.testMenu2_jsp._jspx_meth_c_005fforEach_005f0(testMenu2_jsp.java:138)
    at org.apache.jsp.testMenu2_jsp._jspService(testMenu2_jsp.java:90)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at myPackage.controller.ControllerServlet.doGet(ControllerServlet.java:38)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Nov 29, 2012 5:50:36 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Hello] in context with path [/HibernateTest] threw exception [An exception occurred processing JSP page /testMenu2.jsp at line 19

16: 
17: <ul>
18:     <c:forEach items="${treeMap}" var="emp" begin="0" end="10">
19:         <tag:menuRenderer treeMap="${treeMap}" />
20:     </c:forEach>
21: </ul>
22: 


Stacktrace:] with root cause
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:186)
    at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:137)
    at org.hibernate.collection.internal.PersistentSet.size(PersistentSet.java:156)
    at org.apache.taglibs.standard.functions.Functions.length(Functions.java:202)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.el.parser.AstFunction.getValue(AstFunction.java:112)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:986)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fout_005f1(webmenuRenderer_tag.java:202)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fforEach_005f0(webmenuRenderer_tag.java:143)
    at org.apache.jsp.tag.webmenuRenderer_tag.doTag(webmenuRenderer_tag.java:97)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_tag_005fmenuRenderer_005f0(webmenuRenderer_tag.java:240)
    at org.apache.jsp.tag.webmenuRenderer_tag._jspx_meth_c_005fforEach_005f0(webmenuRenderer_tag.java:153)
    at org.apache.jsp.tag.webmenuRenderer_tag.doTag(webmenuRenderer_tag.java:97)
    at org.apache.jsp.testMenu2_jsp._jspx_meth_tag_005fmenuRenderer_005f0(testMenu2_jsp.java:173)
    at org.apache.jsp.testMenu2_jsp._jspx_meth_c_005fforEach_005f0(testMenu2_jsp.java:138)
    at org.apache.jsp.testMenu2_jsp._jspService(testMenu2_jsp.java:90)
    // and so on

I’d be very happy if somebody could tell me why this doesn’t work!
Do I have to import something?

Thanks in advance! 🙂

Answer 1

The students collection probably comes from a lazy one-to-many relationship and you’re trying to access it in the web tier in which no Hibernate session is active. You should declare the relationship as EAGER in order to have the collection loaded at query time.