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. * *
In the case of JSP 2.0, this class will by default use standard
* evaluate calls. If your application server happens to be
* inefficient in that respect, consider setting Spring's "cacheJspExpressions"
* context-param in web.xml to "true", which will use
* parseExpression calls with cached Expression objects instead.
*
*
The evaluation methods check if the value contains "${" before * invoking the EL evaluator, treating the value as "normal" expression * (i.e. a literal String value) else. * *
Note: The evaluation methods do not have a runtime dependency on
* JSP 2.0 or on Jakarta's JSTL implementation, as long as they are not
* asked to process actual EL expressions. This allows for using EL-aware
* tags with Java-based JSP expressions instead, for example.
*
* @author Juergen Hoeller
* @author Alef Arendsen
* @since 11.07.2003
* @see javax.servlet.jsp.el.ExpressionEvaluator#evaluate
* @see javax.servlet.jsp.el.ExpressionEvaluator#parseExpression
* @see org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager
*/
public abstract class ExpressionEvaluationUtils {
/**
* Expression support parameter at the servlet context level
* (i.e. a context-param in web.xml): "springJspExpressionSupport".
*/
public static final String EXPRESSION_SUPPORT_CONTEXT_PARAM = "springJspExpressionSupport";
/**
* JSP 2.0 expression cache parameter at the servlet context level
* (i.e. a context-param in web.xml): "cacheJspExpressions".
*/
public static final String EXPRESSION_CACHE_CONTEXT_PARAM = "cacheJspExpressions";
public static final String EXPRESSION_PREFIX = "${";
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 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).booleanValue();
}
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.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 (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)).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 (isSpringJspExpressionSupportActive(pageContext) && isExpressionLanguage(attrValue)) {
return ((Boolean) doEvaluate(attrName, attrValue, Boolean.class, pageContext)).booleanValue();
}
else {
return Boolean.valueOf(attrValue).booleanValue();
}
}
/**
* 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");
if (resultClass.isAssignableFrom(String.class)) {
StringBuffer resultValue = null;
int exprPrefixIndex = -1;
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 = null;
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 helper.evaluate(attrName, attrValue, resultClass, pageContext);
}
else {
// We actually need to concatenate partial expressions into a String.
if (resultValue == null) {
resultValue = new StringBuffer();
}
resultValue.append(attrValue.substring(prevExprSuffixIndex, exprPrefixIndex));
resultValue.append(helper.evaluate(attrName, expr, String.class, pageContext));
}
}
else {
if (resultValue == null) {
resultValue = new StringBuffer();
}
resultValue.append(attrValue.substring(exprSuffixIndex));
}
}
while (exprPrefixIndex != -1 && exprSuffixIndex != -1);
return resultValue.toString();
}
else {
return helper.evaluate(attrName, attrValue, resultClass, pageContext);
}
}
/**
* Determine whether JSP 2.0 expressions are supposed to be cached
* and return the corresponding cache Map, or null if
* caching is not enabled.
* @param pageContext current JSP PageContext
* @return the cache Map, or null if caching is disabled
*/
private static Map getJspExpressionCache(PageContext pageContext) {
ServletContext servletContext = pageContext.getServletContext();
Map cacheMap = (Map) servletContext.getAttribute(EXPRESSION_CACHE_MAP_CONTEXT_ATTR);
if (cacheMap == null) {
Boolean cacheFlag = (Boolean) servletContext.getAttribute(EXPRESSION_CACHE_FLAG_CONTEXT_ATTR);
if (cacheFlag == null) {
cacheFlag = Boolean.valueOf(servletContext.getInitParameter(EXPRESSION_CACHE_CONTEXT_PARAM));
servletContext.setAttribute(EXPRESSION_CACHE_FLAG_CONTEXT_ATTR, cacheFlag);
}
if (cacheFlag.booleanValue()) {
cacheMap = Collections.synchronizedMap(new HashMap());
servletContext.setAttribute(EXPRESSION_CACHE_MAP_CONTEXT_ATTR, cacheMap);
}
}
return cacheMap;
}
/**
* Internal interface for evaluating a JSP EL expression.
*/
private static interface ExpressionEvaluationHelper {
public Object evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
throws JspException;
}
/**
* Fallback ExpressionEvaluationHelper:
* always throws an exception in case of an actual EL expression.
*/
private static class NoExpressionEvaluationHelper implements ExpressionEvaluationHelper {
public Object evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
throws JspException {
throw new JspException(
"Neither JSP 2.0 nor Jakarta JSTL available - cannot parse JSP EL expression \"" + attrValue + "\"");
}
}
/**
* Actual invocation of the Jakarta ExpressionEvaluatorManager.
* In separate inner class to avoid runtime dependency on Jakarta's
* JSTL implementation, for evaluation of non-EL expressions.
*/
private static class JakartaExpressionEvaluationHelper implements ExpressionEvaluationHelper {
public Object evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
throws JspException {
return ExpressionEvaluatorManager.evaluate(attrName, attrValue, resultClass, pageContext);
}
}
/**
* Actual invocation of the JSP 2.0 ExpressionEvaluator.
* In separate inner class to avoid runtime dependency on JSP 2.0,
* for evaluation of non-EL expressions.
*/
private static class Jsp20ExpressionEvaluationHelper implements ExpressionEvaluationHelper {
private final ExpressionEvaluationHelper fallback;
private boolean fallbackNecessary = false;
public Jsp20ExpressionEvaluationHelper(ExpressionEvaluationHelper fallback) {
this.fallback = fallback;
}
public Object evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext)
throws JspException {
if (isFallbackNecessary()) {
return this.fallback.evaluate(attrName, attrValue, resultClass, pageContext);
}
try {
Map expressionCache = getJspExpressionCache(pageContext);
if (expressionCache != null) {
// We are supposed to explicitly create and cache JSP Expression objects.
ExpressionCacheKey cacheKey = new ExpressionCacheKey(attrValue, resultClass);
Expression expr = (Expression) expressionCache.get(cacheKey);
if (expr == null) {
expr = pageContext.getExpressionEvaluator().parseExpression(attrValue, resultClass, null);
expressionCache.put(cacheKey, expr);
}
return expr.evaluate(pageContext.getVariableResolver());
}
else {
// We're simply calling the JSP 2.0 evaluate method straight away.
return pageContext.getExpressionEvaluator().evaluate(
attrValue, resultClass, pageContext.getVariableResolver(), null);
}
}
catch (ELException ex) {
throw new JspException("Parsing of JSP EL expression \"" + attrValue + "\" failed", ex);
}
catch (LinkageError err) {
logger.debug("JSP 2.0 ExpressionEvaluator API present but not implemented - using fallback", err);
setFallbackNecessary();
return this.fallback.evaluate(attrName, attrValue, resultClass, pageContext);
}
}
private synchronized boolean isFallbackNecessary() {
return this.fallbackNecessary;
}
private synchronized void setFallbackNecessary() {
this.fallbackNecessary = true;
}
}
/**
* Cache key class for JSP 2.0 Expression objects.
*/
private static class ExpressionCacheKey {
private final String value;
private final Class resultClass;
private final int hashCode;
public ExpressionCacheKey(String value, Class resultClass) {
this.value = value;
this.resultClass = resultClass;
this.hashCode = this.value.hashCode() * 29 + this.resultClass.hashCode();
}
public boolean equals(Object obj) {
if (!(obj instanceof ExpressionCacheKey)) {
return false;
}
ExpressionCacheKey other = (ExpressionCacheKey) obj;
return (this.value.equals(other.value) && this.resultClass.equals(other.resultClass));
}
public int hashCode() {
return this.hashCode;
}
}
}