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package javax.servlet.jsp.jstl.core;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;
/**
* <p>Abstract class that facilitates implementation of conditional actions
* where the boolean result is exposed as a JSP scoped variable. The
* boolean result may then be used as the test condition in a <c:when>
* action.</p>
*
* <p>This base class provides support for:</p>
*
* <ul>
* <li> Conditional processing of the action's body based on the returned value
* of the abstract method <tt>condition()</tt>.</li>
* <li> Storing the result of <tt>condition()</tt> as a <tt>Boolean</tt> object
* into a JSP scoped variable identified by attributes <tt>var</tt> and
* <tt>scope</tt>.
* </ul>
*
* @author Shawn Bayern
*/
public abstract class ConditionalTagSupport
extends TagSupport
{
//*********************************************************************
// Abstract methods
/**
* <p>Subclasses implement this method to compute the boolean result
* of the conditional action. This method is invoked once per tag invocation
* by <tt>doStartTag()</tt>.
*
* @return a boolean representing the condition that a particular subclass
* uses to drive its conditional logic.
*/
protected abstract boolean condition() throws JspTagException;
//*********************************************************************
// Constructor
/**
* Base constructor to initialize local state. As with <tt>TagSupport</tt>,
* subclasses should not implement constructors with arguments, and
* no-argument constructors implemented by subclasses must call the
* superclass constructor.
*/
public ConditionalTagSupport() {
super();
init();
}
//*********************************************************************
// Lifecycle management and implementation of conditional behavior
/**
* Includes its body if <tt>condition()</tt> evaluates to true.
*/
public int doStartTag() throws JspException {
// execute our condition() method once per invocation
result = condition();
// expose variables if appropriate
exposeVariables();
// handle conditional behavior
if (result)
return EVAL_BODY_INCLUDE;
else
return SKIP_BODY;
}
/**
* Releases any resources this ConditionalTagSupport may have (or inherit).
*/
public void release() {
super.release();
init();
}
//*********************************************************************
// Private state
private boolean result; // the saved result of condition()
private String var; // scoped attribute name
private int scope; // scoped attribute scope
//*********************************************************************
// Accessors
/**
* Sets the 'var' attribute.
*
* @param var Name of the exported scoped variable storing the result of
* <tt>condition()</tt>.
*/
public void setVar(String var) {
this.var = var;
}
/**
* Sets the 'scope' attribute.
*
* @param scope Scope of the 'var' attribute
*/
public void setScope(String scope) {
if (scope.equalsIgnoreCase("page"))
this.scope = PageContext.PAGE_SCOPE;
else if (scope.equalsIgnoreCase("request"))
this.scope = PageContext.REQUEST_SCOPE;
else if (scope.equalsIgnoreCase("session"))
this.scope = PageContext.SESSION_SCOPE;
else if (scope.equalsIgnoreCase("application"))
this.scope = PageContext.APPLICATION_SCOPE;
// TODO: Add error handling? Needs direction from spec.
}
//*********************************************************************
// Utility methods
// expose attributes if we have a non-null 'var'
private void exposeVariables() {
if (var != null)
pageContext.setAttribute(var, Boolean.valueOf(result), scope);
}
// initializes internal state
private void init() {
result = false; // not really necessary
var = null;
scope = PageContext.PAGE_SCOPE;
}
}
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