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I have a application which allows user to make a search.

Based on the search criteria entered, a service call to DAO function is made (pattern jsp event -> interceptors -> processors -> services -> DAO -> database) and list of results is returned back which gets displayed in myView.jsp

Code as below is used to read the TO data in JSP:

<jsp:usebean id="myTO" type="com.myPackage.MyTO" scope="session"/>

and in the body something like

<%= myTo.getSomething() =%>

Each item on the list is clickable for details. So on clicking item 2 on the list, another call will be made with item 2's id to fetch more details on item 2.

Depending on type of item, the details are fetched in different TO's. e.g. Type1TO, Type2TO.

So detailed data on item is returned in one such TO.

Issue is: I am displaying the details in the same JSP. So the returnURL of the second request gets forwarded to myView.JSP

So I have put a line like 

<jsp:usebean id="type1TO" type="com.myPackage.Type1TO" scope="session"/>

However this gives error during the first call of list search when above Type1TO does not yet exist. Error is something like "unable to find type1TO in scope session"

How could I solve this issue ???

Is there a way to put jsp:usebean tag in an if condition in the place where it is to be used in the body ?? Or any other solution to this ??

I am new to JSP and dealing with legacy JSP. So very advanced JSP (complex EL) might not be feasible.

Vicky
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  • My understanding was that the useBean tag would create the bean in the specified scope if it did not already exist. – Dave Newton Nov 09 '11 at 01:24
  • Is there any pre requirement for this ? Or is my way of declaration not correct ?? – Vicky Nov 09 '11 at 01:30
  • None that I'm aware of. I could be remembering incorrectly. – Dave Newton Nov 09 '11 at 01:33
  • Ok. Let's say JSP creates instance on its own in the first call. Will that be overwritten when I set the instance in the context during the second call ??? will I be able to access data ? – Vicky Nov 09 '11 at 01:40
  • It only creates the object if it doesn't already exist. Or at least I thought that's what it was supposed to do. – Dave Newton Nov 09 '11 at 02:00
  • possible duplicate of [jsp servlet exception: bean not found within scope](http://stackoverflow.com/questions/270444/jsp-servlet-exception-bean-not-found-within-scope) – BalusC Nov 09 '11 at 14:00

2 Answers2

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The following are the usages of the <usebean>:

  1. <jsp:useBean id=”connection” class=”com.myco.myapp.Connection” /> . In this example the bean with the id is made available either by creating or finding the existing one in the session
  2. <jsp:useBean id=”connection” class=”com.myco.myapp.Connection”> <jsp:setProperty name=”connection” property=”timeout” value=”33”> </jsp:useBean>. In this example, the bean is created or found, and instatiated with the setProperty if it is being created.
  3. <jsp:useBean id=”wombat” type=”my.WombatType” scope=”session”/>. In this example the existing bean is found and made available with the given type.
Ramesh PVK
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If translated to Servlet, your first code snippet will look like:

getAttribute("myTO");

Whether to use a single attribute or 'multiple attributes with if-else logic' depends on your particular case. Without understanding your particular situation, I can see the following options:

Option 1 Wherever you are setting myTO attribute, ensure you set the value to the same variable, so that you don't have to use if-else logic in jsp.

Option 2 Use scripts

<%
  com.myPackage.MyTO toObject = session.getAttribute("myTo");
  if (toObject == NULL) {
      toObject = session.getAttrbute("type1TO");
  }
%>
Ken Russell
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