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package org.apache.taglibs.standard.lang.support;
import java.util.HashMap;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;
import org.apache.taglibs.standard.lang.jstl.Coercions;
import org.apache.taglibs.standard.lang.jstl.ELException;
import org.apache.taglibs.standard.lang.jstl.Logger;
/**
* <p>A conduit to the JSTL EL. Based on...</p>
*
* <p>An implementation of the ExpressionEvaluatorManager called for by
* the JSTL rev1 draft. This class is responsible for delegating a
* request for expression evaluating to the particular, "active"
* ExpressionEvaluator for the given point in the PageContext object
* passed in.</p>
*
* @author Shawn Bayern
*/
public class ExpressionEvaluatorManager {
//*********************************************************************
// Constants
public static final String EVALUATOR_CLASS =
"org.apache.taglibs.standard.lang.jstl.Evaluator";
// private static final String EVALUATOR_PARAMETER =
// "javax.servlet.jsp.jstl.temp.ExpressionEvaluatorClass";
//*********************************************************************
// Internal, static state
private static HashMap nameMap = new HashMap();
private static Logger logger = new Logger(System.out);
//*********************************************************************
// Public static methods
/**
* Invokes the evaluate() method on the "active" ExpressionEvaluator
* for the given pageContext.
*/
public static Object evaluate(String attributeName,
String expression,
Class expectedType,
Tag tag,
PageContext pageContext)
throws JspException
{
// the evaluator we'll use
ExpressionEvaluator target = getEvaluatorByName(EVALUATOR_CLASS);
// delegate the call
return (target.evaluate(
attributeName, expression, expectedType, tag, pageContext));
}
/**
* Invokes the evaluate() method on the "active" ExpressionEvaluator
* for the given pageContext.
*/
public static Object evaluate(String attributeName,
String expression,
Class expectedType,
PageContext pageContext)
throws JspException
{
// the evaluator we'll use
ExpressionEvaluator target = getEvaluatorByName(EVALUATOR_CLASS);
// delegate the call
return (target.evaluate(
attributeName, expression, expectedType, null, pageContext));
}
/**
* Gets an ExpressionEvaluator from the cache, or seeds the cache
* if we haven't seen a particular ExpressionEvaluator before.
*/
public static
ExpressionEvaluator getEvaluatorByName(String name)
throws JspException {
Object oEvaluator = nameMap.get(name);
if (oEvaluator != null) {
return ((ExpressionEvaluator) oEvaluator);
}
try {
synchronized (nameMap) {
oEvaluator = nameMap.get(name);
if (oEvaluator != null) {
return ((ExpressionEvaluator) oEvaluator);
}
ExpressionEvaluator e = (ExpressionEvaluator)
Class.forName(name).newInstance();
nameMap.put(name, e);
return (e);
}
} catch (ClassCastException ex) {
// just to display a better error message
throw new JspException("invalid ExpressionEvaluator: " +
ex.toString(), ex);
} catch (ClassNotFoundException ex) {
throw new JspException("couldn't find ExpressionEvaluator: " +
ex.toString(), ex);
} catch (IllegalAccessException ex) {
throw new JspException("couldn't access ExpressionEvaluator: " +
ex.toString(), ex);
} catch (InstantiationException ex) {
throw new JspException(
"couldn't instantiate ExpressionEvaluator: " +
ex.toString(), ex);
}
}
/** Performs a type conversion according to the EL's rules. */
public static Object coerce(Object value, Class classe)
throws JspException {
try {
// just delegate the call
return Coercions.coerce(value, classe, logger);
} catch (ELException ex) {
throw new JspException(ex);
}
}
}
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