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Jakarta Standard Tag Library Implementation
/*
* Copyright (c) 1997-2020 Oracle and/or its affiliates. All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.taglibs.standard.tag.el.fmt;
import jakarta.servlet.jsp.JspException;
import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;
import org.apache.taglibs.standard.tag.common.fmt.ParamSupport;
/**
* A handler for <param> that accepts message arguments as
* Strings and evaluates them as expressions at runtime.
*
* @author Jan Luehe
*/
public class ParamTag extends ParamSupport {
//*********************************************************************
// 'Private' state (implementation details)
private String value_; // stores EL-based property
//*********************************************************************
// Constructor
/**
* Constructs a new ParamTag. As with TagSupport, subclasses
* should not provide other constructors and are expected to call
* the superclass constructor
*/
public ParamTag() {
super();
init();
}
//*********************************************************************
// Tag logic
// evaluates expression and chains to parent
public int doStartTag() throws JspException {
// evaluate any expressions we were passed, once per invocation
evaluateExpressions();
// chain to the parent implementation
return super.doStartTag();
}
// Releases any resources we may have (or inherit)
public void release() {
super.release();
init();
}
//*********************************************************************
// Accessor methods
// for EL-based attribute
public void setValue(String value_) {
this.value_ = value_;
this.valueSpecified = true;
}
//*********************************************************************
// Private (utility) methods
// (re)initializes state (during release() or construction)
private void init() {
// null implies "no expression"
value_ = null;
}
// Evaluates expressions as necessary
private void evaluateExpressions() throws JspException {
/*
* Note: we don't check for type mismatches here; we assume
* the expression evaluator will return the expected type
* (by virtue of knowledge we give it about what that type is).
* A ClassCastException here is truly unexpected, so we let it
* propagate up.
*/
if (value_ != null) {
value = ExpressionEvaluatorManager.evaluate(
"value", value_, Object.class, this, pageContext);
}
}
}