org.springframework.web.util
Class ExpressionEvaluationUtils

java.lang.Object
  extended by org.springframework.web.util.ExpressionEvaluationUtils

public abstract class ExpressionEvaluationUtils
extends java.lang.Object

Convenience methods for transparent access to JSP 2.0's built-in ExpressionEvaluator or the standalone ExpressionEvaluatorManager of Jakarta's JSTL implementation.

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.

Since:
11.07.2003
Author:
Juergen Hoeller, Alef Arendsen
See Also:
ExpressionEvaluator.evaluate(java.lang.String, java.lang.Class, javax.servlet.jsp.el.VariableResolver, javax.servlet.jsp.el.FunctionMapper), ExpressionEvaluator.parseExpression(java.lang.String, java.lang.Class, javax.servlet.jsp.el.FunctionMapper), ExpressionEvaluatorManager

Field Summary
static java.lang.String EXPRESSION_CACHE_CONTEXT_PARAM
          JSP 2.0 expression cache parameter at the servlet context level (i.e. a context-param in web.xml): "cacheJspExpressions".
static java.lang.String EXPRESSION_PREFIX
           
static java.lang.String EXPRESSION_SUFFIX
           
static java.lang.String EXPRESSION_SUPPORT_CONTEXT_PARAM
          Expression support parameter at the servlet context level (i.e. a context-param in web.xml): "springJspExpressionSupport".
 
Constructor Summary
ExpressionEvaluationUtils()
           
 
Method Summary
static java.lang.Object evaluate(java.lang.String attrName, java.lang.String attrValue, java.lang.Class resultClass, javax.servlet.jsp.PageContext pageContext)
          Evaluate the given expression (be it EL or a literal String value) to an Object of a given type,
static java.lang.Object evaluate(java.lang.String attrName, java.lang.String attrValue, javax.servlet.jsp.PageContext pageContext)
          Evaluate the given expression (be it EL or a literal String value) to an Object.
static boolean evaluateBoolean(java.lang.String attrName, java.lang.String attrValue, javax.servlet.jsp.PageContext pageContext)
          Evaluate the given expression (be it EL or a literal String value) to a boolean.
static int evaluateInteger(java.lang.String attrName, java.lang.String attrValue, javax.servlet.jsp.PageContext pageContext)
          Evaluate the given expression (be it EL or a literal String value) to an integer.
static java.lang.String evaluateString(java.lang.String attrName, java.lang.String attrValue, javax.servlet.jsp.PageContext pageContext)
          Evaluate the given expression (be it EL or a literal String value) to a String.
static boolean isExpressionLanguage(java.lang.String value)
          Check if the given expression value is an EL expression.
static boolean isSpringJspExpressionSupportActive(javax.servlet.jsp.PageContext pageContext)
          Check whether Spring's JSP expression support is actually active.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

EXPRESSION_SUPPORT_CONTEXT_PARAM

public static final java.lang.String EXPRESSION_SUPPORT_CONTEXT_PARAM
Expression support parameter at the servlet context level (i.e. a context-param in web.xml): "springJspExpressionSupport".

See Also:
Constant Field Values

EXPRESSION_CACHE_CONTEXT_PARAM

public static final java.lang.String EXPRESSION_CACHE_CONTEXT_PARAM
JSP 2.0 expression cache parameter at the servlet context level (i.e. a context-param in web.xml): "cacheJspExpressions".

See Also:
Constant Field Values

EXPRESSION_PREFIX

public static final java.lang.String EXPRESSION_PREFIX
See Also:
Constant Field Values

EXPRESSION_SUFFIX

public static final java.lang.String EXPRESSION_SUFFIX
See Also:
Constant Field Values
Constructor Detail

ExpressionEvaluationUtils

public ExpressionEvaluationUtils()
Method Detail

isSpringJspExpressionSupportActive

public static boolean isSpringJspExpressionSupportActive(javax.servlet.jsp.PageContext pageContext)
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.

Parameters:
pageContext - current JSP PageContext
Returns:
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)

isExpressionLanguage

public static boolean isExpressionLanguage(java.lang.String value)
Check if the given expression value is an EL expression.

Parameters:
value - the expression to check
Returns:
true if the expression is an EL expression, false otherwise

evaluate

public static java.lang.Object evaluate(java.lang.String attrName,
                                        java.lang.String attrValue,
                                        java.lang.Class resultClass,
                                        javax.servlet.jsp.PageContext pageContext)
                                 throws javax.servlet.jsp.JspException
Evaluate the given expression (be it EL or a literal String value) to an Object of a given type,

Parameters:
attrName - name of the attribute (typically a JSP tag attribute)
attrValue - value of the attribute
resultClass - class that the result should have (String, Integer, Boolean)
pageContext - current JSP PageContext
Returns:
the result of the evaluation
Throws:
javax.servlet.jsp.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

evaluate

public static java.lang.Object evaluate(java.lang.String attrName,
                                        java.lang.String attrValue,
                                        javax.servlet.jsp.PageContext pageContext)
                                 throws javax.servlet.jsp.JspException
Evaluate the given expression (be it EL or a literal String value) to an Object.

Parameters:
attrName - name of the attribute (typically a JSP tag attribute)
attrValue - value of the attribute
pageContext - current JSP PageContext
Returns:
the result of the evaluation
Throws:
javax.servlet.jsp.JspException - in case of parsing errors

evaluateString

public static java.lang.String evaluateString(java.lang.String attrName,
                                              java.lang.String attrValue,
                                              javax.servlet.jsp.PageContext pageContext)
                                       throws javax.servlet.jsp.JspException
Evaluate the given expression (be it EL or a literal String value) to a String.

Parameters:
attrName - name of the attribute (typically a JSP tag attribute)
attrValue - value of the attribute
pageContext - current JSP PageContext
Returns:
the result of the evaluation
Throws:
javax.servlet.jsp.JspException - in case of parsing errors

evaluateInteger

public static int evaluateInteger(java.lang.String attrName,
                                  java.lang.String attrValue,
                                  javax.servlet.jsp.PageContext pageContext)
                           throws javax.servlet.jsp.JspException
Evaluate the given expression (be it EL or a literal String value) to an integer.

Parameters:
attrName - name of the attribute (typically a JSP tag attribute)
attrValue - value of the attribute
pageContext - current JSP PageContext
Returns:
the result of the evaluation
Throws:
javax.servlet.jsp.JspException - in case of parsing errors

evaluateBoolean

public static boolean evaluateBoolean(java.lang.String attrName,
                                      java.lang.String attrValue,
                                      javax.servlet.jsp.PageContext pageContext)
                               throws javax.servlet.jsp.JspException
Evaluate the given expression (be it EL or a literal String value) to a boolean.

Parameters:
attrName - name of the attribute (typically a JSP tag attribute)
attrValue - value of the attribute
pageContext - current JSP PageContext
Returns:
the result of the evaluation
Throws:
javax.servlet.jsp.JspException - in case of parsing errors


Copyright © 2002-2008 The Spring Framework.