org.springframework.web.util
Class ExpressionEvaluationUtils

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

public abstract class ExpressionEvaluationUtils
extends 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 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 String	EXPRESSION_PREFIX
static String	EXPRESSION_SUFFIX

Constructor Summary

ExpressionEvaluationUtils()

Method Summary

static Object	evaluate(String attrName, String attrValue, Class resultClass, PageContext pageContext) Evaluate the given expression (be it EL or a literal String value) to an Object of a given type,
static Object	evaluate(String attrName, String attrValue, PageContext pageContext) Evaluate the given expression (be it EL or a literal String value) to an Object.
static boolean	evaluateBoolean(String attrName, String attrValue, PageContext pageContext) Evaluate the given expression (be it EL or a literal String value) to a boolean.
static int	evaluateInteger(String attrName, String attrValue, PageContext pageContext) Evaluate the given expression (be it EL or a literal String value) to an integer.
static String	evaluateString(String attrName, String attrValue, PageContext pageContext) Evaluate the given expression (be it EL or a literal String value) to a String.
static boolean	isExpressionLanguage(String value) Check if the given expression value is an EL expression.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

EXPRESSION_CACHE_CONTEXT_PARAM

public static final 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 String EXPRESSION_PREFIX

See Also:

Constant Field Values

EXPRESSION_SUFFIX

public static final String EXPRESSION_SUFFIX

See Also:

Constant Field Values

Constructor Detail

ExpressionEvaluationUtils

public ExpressionEvaluationUtils()

Method Detail

isExpressionLanguage

public static boolean isExpressionLanguage(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 Object evaluate(String attrName,
                              String attrValue,
                              Class resultClass,
                              PageContext pageContext)
                       throws 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:

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 Object evaluate(String attrName,
                              String attrValue,
                              PageContext pageContext)
                       throws 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:

JspException - in case of parsing errors

evaluateString

public static String evaluateString(String attrName,
                                    String attrValue,
                                    PageContext pageContext)
                             throws 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:

JspException - in case of parsing errors

evaluateInteger

public static int evaluateInteger(String attrName,
                                  String attrValue,
                                  PageContext pageContext)
                           throws 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:

JspException - in case of parsing errors

evaluateBoolean

public static boolean evaluateBoolean(String attrName,
                                      String attrValue,
                                      PageContext pageContext)
                               throws 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:

JspException - in case of parsing errors