expressionevaluationutils.java

spring framework 2.5.4源代码

/*
 * Copyright 2002-2007 the original author or authors.
 *
 * 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.springframework.web.util;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.el.ELException;
import javax.servlet.jsp.el.Expression;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;

import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * Convenience methods for transparent access to JSP 2.0's built-in
 * {@link javax.servlet.jsp.el.ExpressionEvaluator} or the standalone
 * {@link org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager}
 * of Jakarta's JSTL implementation.
 *
 * <p>Automatically detects JSP 2.0 or Jakarta JSTL, preferring the JSP 2.0
 * mechanism if available. Also detects the JSP 2.0 API being present but
 * the runtime JSP engine not actually supporting JSP 2.0, falling back to
 * the Jakarta JSTL in this case. Throws an exception when encountering actual
 * EL expressions if neither JSP 2.0 nor the Jakarta JSTL is available.
 *
 * <p>In the case of JSP 2.0, this class will by default use standard
 * <code>evaluate</code> calls. If your application server happens to be
 * inefficient in that respect, consider setting Spring's "cacheJspExpressions"
 * context-param in <code>web.xml</code> to "true", which will use
 * <code>parseExpression</code> calls with cached Expression objects instead.
 *
 * <p>The evaluation methods check if the value contains "${" before
 * invoking the EL evaluator, treating the value as "normal" expression
 * (i.e. a literal String value) else.
 *
 * <p>Note: The evaluation methods do not have a runtime dependency on
 * JSP 2.0 or on Jakarta's JSTL implementation, as long as they are not
 * asked to process actual EL expressions. This allows for using EL-aware
 * tags with Java-based JSP expressions instead, for example.
 *
 * @author Juergen Hoeller
 * @author Alef Arendsen
 * @since 11.07.2003
 * @see javax.servlet.jsp.el.ExpressionEvaluator#evaluate
 * @see javax.servlet.jsp.el.ExpressionEvaluator#parseExpression
 * @see org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager
 */
public abstract class ExpressionEvaluationUtils {

	/**
	 * JSP 2.0 expression cache parameter at the servlet context level
	 * (i.e. a context-param in <code>web.xml</code>): "cacheJspExpressions".
	 */
	public static final String EXPRESSION_CACHE_CONTEXT_PARAM = "cacheJspExpressions";

	public static final String EXPRESSION_PREFIX = "${";

	public static final String EXPRESSION_SUFFIX = "}";


	private static final String EXPRESSION_CACHE_FLAG_CONTEXT_ATTR =
			ExpressionEvaluationUtils.class.getName() + ".CACHE_JSP_EXPRESSIONS";

	private static final String EXPRESSION_CACHE_MAP_CONTEXT_ATTR =
			ExpressionEvaluationUtils.class.getName() + ".JSP_EXPRESSION_CACHE";

	private static final String JSP_20_CLASS_NAME =
			"javax.servlet.jsp.el.ExpressionEvaluator";

	private static final String JAKARTA_JSTL_CLASS_NAME =
			"org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager";


	private static final Log logger = LogFactory.getLog(ExpressionEvaluationUtils.class);

	private static ExpressionEvaluationHelper helper;


	static {
		ClassLoader cl = ExpressionEvaluationUtils.class.getClassLoader();
		if (ClassUtils.isPresent(JSP_20_CLASS_NAME, cl)) {
			logger.debug("Found JSP 2.0 ExpressionEvaluator");
			if (ClassUtils.isPresent(JAKARTA_JSTL_CLASS_NAME, cl)) {
				logger.debug("Found Jakarta JSTL ExpressionEvaluatorManager");
				helper = new Jsp20ExpressionEvaluationHelper(new JakartaExpressionEvaluationHelper());
			}
			else {
				helper = new Jsp20ExpressionEvaluationHelper(new NoExpressionEvaluationHelper());
			}
		}
		else if (ClassUtils.isPresent(JAKARTA_JSTL_CLASS_NAME, cl)) {
			logger.debug("Found Jakarta JSTL ExpressionEvaluatorManager");
			helper = new JakartaExpressionEvaluationHelper();
		}
		else {
			logger.debug("JSP expression evaluation not available");
			helper = new NoExpressionEvaluationHelper();
		}
	}


	/**
	 * Check if the given expression value is an EL expression.
	 * @param value the expression to check
	 * @return <code>true</code> if the expression is an EL expression,
	 * <code>false</code> otherwise
	 */
	public static boolean isExpressionLanguage(String value) {
		return (value != null && value.indexOf(EXPRESSION_PREFIX) != -1);
	}

	/**
	 * Evaluate the given expression (be it EL or a literal String value)
	 * to an Object of a given type,
	 * @param attrName name of the attribute (typically a JSP tag attribute)
	 * @param attrValue value of the attribute
	 * @param resultClass class that the result should have (String, Integer, Boolean)
	 * @param pageContext current JSP PageContext
	 * @return the result of the evaluation
	 * @throws JspException in case of parsing errors, also in case of type mismatch
	 * if the passed-in literal value is not an EL expression and not assignable to
	 * the result class
	 */
	public static Object evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
	    throws JspException {

		if (isExpressionLanguage(attrValue)) {
			return doEvaluate(attrName, attrValue, resultClass, pageContext);
		}
		else if (attrValue != null && resultClass != null && !resultClass.isInstance(attrValue)) {
			throw new JspException("Attribute value \"" + attrValue + "\" is neither a JSP EL expression nor " +
					"assignable to result class [" + resultClass.getName() + "]");
		}
		else {
			return attrValue;
		}
	}

	/**
	 * Evaluate the given expression (be it EL or a literal String value) to an Object.
	 * @param attrName name of the attribute (typically a JSP tag attribute)
	 * @param attrValue value of the attribute
	 * @param pageContext current JSP PageContext
	 * @return the result of the evaluation
	 * @throws JspException in case of parsing errors
	 */
	public static Object evaluate(String attrName, String attrValue, PageContext pageContext)
	    throws JspException {

		if (isExpressionLanguage(attrValue)) {
			return doEvaluate(attrName, attrValue, Object.class, pageContext);
		}
		else {
			return attrValue;
		}
	}

	/**
	 * Evaluate the given expression (be it EL or a literal String value) to a String.
	 * @param attrName name of the attribute (typically a JSP tag attribute)
	 * @param attrValue value of the attribute
	 * @param pageContext current JSP PageContext
	 * @return the result of the evaluation
	 * @throws JspException in case of parsing errors
	 */
	public static String evaluateString(String attrName, String attrValue, PageContext pageContext)
	    throws JspException {

		if (isExpressionLanguage(attrValue)) {
			return (String) doEvaluate(attrName, attrValue, String.class, pageContext);
		}
		else {
			return attrValue;
		}
	}

	/**
	 * Evaluate the given expression (be it EL or a literal String value) to an integer.
	 * @param attrName name of the attribute (typically a JSP tag attribute)
	 * @param attrValue value of the attribute
	 * @param pageContext current JSP PageContext
	 * @return the result of the evaluation
	 * @throws JspException in case of parsing errors
	 */
	public static int evaluateInteger(String attrName, String attrValue, PageContext pageContext)
			throws JspException {

		if (isExpressionLanguage(attrValue)) {
			return ((Integer) doEvaluate(attrName, attrValue, Integer.class, pageContext)).intValue();
		}
		else {
			return Integer.parseInt(attrValue);
		}
	}

	/**
	 * Evaluate the given expression (be it EL or a literal String value) to a boolean.
	 * @param attrName name of the attribute (typically a JSP tag attribute)
	 * @param attrValue value of the attribute
	 * @param pageContext current JSP PageContext
	 * @return the result of the evaluation
	 * @throws JspException in case of parsing errors
	 */
	public static boolean evaluateBoolean(String attrName, String attrValue, PageContext pageContext)
	    throws JspException {

		if (isExpressionLanguage(attrValue)) {