The Java EE 5 Tutorial

An Iteration Tag

Constructing page content that is dependent on dynamically generated data often requires the use of flow control scripting statements. By moving the flow control logic to tag handlers, flow control tags reduce the amount of scripting needed in JSP pages. Iteration is a very common flow control function and is easily handled by a custom tag.

The discussion on using tag libraries in Chapter 5, JavaServer Pages Technology introduced a tag library containing an iterator tag. The tag retrieves objects from a collection stored in a JavaBeans component and assigns them to an EL variable. The body of the tag retrieves information from the variable. As long as elements remain in the collection, the iterator tag causes the body to be reevaluated. The tag in this example is simplified to make it easy to demonstrate how to program a custom tag. web applications requiring such functionality should use the JSTL forEach tag, which is discussed in Iterator Tags.

JSP Page

The index.jsp page invokes the iterator tag to iterate through a collection of department names. Each item in the collection is assigned to the departmentName variable.

<%@ taglib uri="/tlt" prefix="tlt" %>
    <body bgcolor="white">
    <jsp:useBean id="myorg" class="myorg.Organization"/>
    <table border=2 cellspacing=3 cellpadding=3>
    <tlt:iterator var="departmentName" type="java.lang.String"
            <td><a href="list.jsp?deptName=${departmentName}">

Tag Handler

The collection is set in the tag handler by means of the group attribute. The tag handler retrieves an element from the group and passes the element back to the page in the EL variable whose name is determined by the var attribute. The variable is accessed in the calling page using the JSP expression language. After the variable is set, the tag body is evaluated with the invoke method.

public void doTag() throws JspException, IOException {
    if (iterator == null)
    while (iterator.hasNext()) {
public void setVar(String var) {
    this.var = var;
public void setGroup(Collection group) { = group;
    if(group.size() > 0)
        iterator = group.iterator();