org.springframework.web.util.ExpressionEvaluationUtils Maven / Gradle / Ivy
/*
* Copyright 2002-2011 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 javax.servlet.ServletContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.el.ELException;
import org.springframework.util.Assert;
/**
* Convenience methods for accessing JSP 2.0's
* {@link javax.servlet.jsp.el.ExpressionEvaluator}.
*
* The evaluation methods check if the value contains "${" before
* invoking the EL evaluator, treating the value as "normal" expression
* (i.e. a literal String value) else.
*
*
See {@link #isSpringJspExpressionSupportActive} for guidelines
* on when to use Spring's JSP expression support as opposed to the
* built-in expression support in JSP 2.0+ containers.
*
* @author Juergen Hoeller
* @author Alef Arendsen
* @since 11.07.2003
* @see javax.servlet.jsp.el.ExpressionEvaluator#evaluate
*/
public abstract class ExpressionEvaluationUtils {
/**
* Expression support parameter at the servlet context level
* (i.e. a context-param in web.xml): "springJspExpressionSupport".
*/
public static final String EXPRESSION_SUPPORT_CONTEXT_PARAM = "springJspExpressionSupport";
public static final String EXPRESSION_PREFIX = "${";
public static final String EXPRESSION_SUFFIX = "}";
/**
* Check whether Spring's JSP expression support is actually active.
*
Note that JSP 2.0+ containers come with expression support themselves:
* However, it will only be active for web applications declaring Servlet 2.4
* or higher in their web.xml deployment descriptor.
*
If a web.xml context-param named "springJspExpressionSupport" is
* found, its boolean value will be taken to decide whether this support is active.
* If not found, for backwards compatibility with Servlet 2.3 applications,
* Spring's expression support will remain active by default.
*
Recommendations: Explicitly set "springJspExpressionSupport" to "false"
* in order to prevent double evaluation for Servlet 2.4+ based applications.
* @param pageContext current JSP PageContext
* @return true if active (ExpressionEvaluationUtils will actually evaluate expressions);
* false if not active (ExpressionEvaluationUtils will return given values as-is,
* relying on the JSP container pre-evaluating values before passing them to JSP tag attributes)
*/
public static boolean isSpringJspExpressionSupportActive(PageContext pageContext) {
ServletContext sc = pageContext.getServletContext();
String springJspExpressionSupport = sc.getInitParameter(EXPRESSION_SUPPORT_CONTEXT_PARAM);
if (springJspExpressionSupport != null) {
return Boolean.valueOf(springJspExpressionSupport);
}
return true;
}
/**
* Check if the given expression value is an EL expression.
* @param value the expression to check
* @return true if the expression is an EL expression,
* false otherwise
*/
public static boolean isExpressionLanguage(String value) {
return (value != null && value.contains(EXPRESSION_PREFIX));
}
/**
* 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 (isSpringJspExpressionSupportActive(pageContext) && 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 (isSpringJspExpressionSupportActive(pageContext) && 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 (isSpringJspExpressionSupportActive(pageContext) && 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 (isSpringJspExpressionSupportActive(pageContext) && isExpressionLanguage(attrValue)) {
return (Integer) doEvaluate(attrName, attrValue, Integer.class, pageContext);
}
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 (isSpringJspExpressionSupportActive(pageContext) && isExpressionLanguage(attrValue)) {
return (Boolean) doEvaluate(attrName, attrValue, Boolean.class, pageContext);
}
else {
return Boolean.valueOf(attrValue);
}
}
/**
* Actually evaluate the given expression (be it EL or a literal String value)
* to an Object of a given type. Supports concatenated expressions,
* for example: "${var1}text${var2}"
* @param attrName name of the attribute
* @param attrValue value of the attribute
* @param resultClass class that the result should have
* @param pageContext current JSP PageContext
* @return the result of the evaluation
* @throws JspException in case of parsing errors
*/
private static Object doEvaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
throws JspException {
Assert.notNull(attrValue, "Attribute value must not be null");
Assert.notNull(resultClass, "Result class must not be null");
Assert.notNull(pageContext, "PageContext must not be null");
try {
if (resultClass.isAssignableFrom(String.class)) {
StringBuilder resultValue = null;
int exprPrefixIndex;
int exprSuffixIndex = 0;
do {
exprPrefixIndex = attrValue.indexOf(EXPRESSION_PREFIX, exprSuffixIndex);
if (exprPrefixIndex != -1) {
int prevExprSuffixIndex = exprSuffixIndex;
exprSuffixIndex = attrValue.indexOf(EXPRESSION_SUFFIX, exprPrefixIndex + EXPRESSION_PREFIX.length());
String expr;
if (exprSuffixIndex != -1) {
exprSuffixIndex += EXPRESSION_SUFFIX.length();
expr = attrValue.substring(exprPrefixIndex, exprSuffixIndex);
}
else {
expr = attrValue.substring(exprPrefixIndex);
}
if (expr.length() == attrValue.length()) {
// A single expression without static prefix or suffix ->
// parse it with the specified result class rather than String.
return evaluateExpression(attrValue, resultClass, pageContext);
}
else {
// We actually need to concatenate partial expressions into a String.
if (resultValue == null) {
resultValue = new StringBuilder();
}
resultValue.append(attrValue.substring(prevExprSuffixIndex, exprPrefixIndex));
resultValue.append(evaluateExpression(expr, String.class, pageContext));
}
}
else {
if (resultValue == null) {
resultValue = new StringBuilder();
}
resultValue.append(attrValue.substring(exprSuffixIndex));
}
}
while (exprPrefixIndex != -1 && exprSuffixIndex != -1);
return resultValue.toString();
}
else {
return evaluateExpression(attrValue, resultClass, pageContext);
}
}
catch (ELException ex) {
throw new JspException("Parsing of JSP EL expression failed for attribute '" + attrName + "'", ex);
}
}
private static Object evaluateExpression(String exprValue, Class resultClass, PageContext pageContext)
throws ELException {
return pageContext.getExpressionEvaluator().evaluate(
exprValue, resultClass, pageContext.getVariableResolver(), null);
}
}