How to access objects in EL expression language ${}

Question

If I have a

ArrayList<Person> persons

How do I access it in EL?

<c:foreach items="${what goes here??}" var="person">${person.title}</c:foreach>

Tomblin

Answer 1

The expression ${foo} uses behind the scenes JspContext#findAttribute() which searches for attributes in PageContext, HttpServletRequest, HttpSession and ServletContext in this order by their getAttribute("foo") method whereby foo from ${foo} thus represents the attribute name "foo" and returns the first non-null object.

So, if you do in a servlet

ArrayList<Person> persons = getItSomehow();
request.setAttribute("persons", persons); // It's now available by ${persons}
request.getRequestDispatcher("/WEB-INF/persons.jsp").forward(request, response);

And call this servlet by URL, then you'll be able to iterate over it in page.jsp as follows:

<c:foreach items="${persons}" var="person">
    ${person.title}
<c:forEach>

The above is also equally valid when you put it in the session scope instead

request.getSession().setAttribute("persons", persons);

or even in the application scope

getServletContext().setAttribute("persons", persons);

EL will for title in ${person.title} implicitly look for a public instance (not static!) method prefixed with get in Person class like below:

public String getTitle() {
    return title;
}

The field title does not necessarily need to exist in the class (so you can even return a hardcoded string and keep using ${person.title}), and it does not necessarily need to be an instance field (so it can also be a static field, as long as the getter method itself isn't static).

Only boolean (not Boolean!) getters have a special treatment; EL will implicitly look for a public method prefixed with is. E.g. for a ${person.awesome}:

public boolean isAwesome() {
    return awesome;
}

See also:

• Our EL wiki page
• How do servlets work? Instantiation, sessions, shared variables and multithreading
• How to avoid Java code in JSP files?
• Show JDBC ResultSet in HTML in JSP page using MVC and DAO pattern
• Use EL ${XY} directly in scriptlet <% XY %>
• How does Java expression language resolve boolean attributes? (in JSF 1.2)

Edinburgh

Thank you, especially the behind the scenes information as that really really helped me. – Tomblin

Answer 2

<c:forEach var="item" items="${names}"> ${item.title}  </c:forEach>

names should be in the set as attribute available for the view

Bunin

when you say "set" are you refering to <c:set>? – Tomblin

you can set it in no. of ways. but it should be available to that page – Bunin

Note that the syntax is wrong. You seem to have copypasted from Ashish. – Edinburgh

@Edinburgh agree about syntax. and did you check time log about copying stuff :) – Bunin

Sorry, I didn't expect that you was the first who made the mistake :) (it is still incorrect though) – Edinburgh

Answer 3

If you are using Servlets or action class for creating your list and then forwarding it to your JSP, then you must be having following line in your servlet or action class.

ArrayList<Person> names = "get from somewhere";

request.setAttribute("personNames",names);  

<c:foreach var="item" items="${personNames}"> ${item.title} </c:foreach>

Cami

If I were to put this in the session would it be any different? – Tomblin

@robertlewis2001 You will have to fetch the list from the session Scope from instead of the request scope. It should become items="{sessionScope.personNames}". – Cami

Note that the syntax is wrong. As to the last comment, it's not necessary to explicitly mention the scope. – Edinburgh