Package org.appng.el

Class ExpressionEvaluator

  • public final class ExpressionEvaluator
extends Object
    Used for evaluating expressions that conform the Expression Language 2.2 syntax.
    A valid expression must start with ${ and end with }. A list of the allowed operators an be found here.

    Example: 

     Map<String, Object> parameters = new HashMap<String, Object>();
 parameters.put("intValue", 5);
 parameters.put("stringValue", "foobar");
 ExpressionEvaluator ee = new ExpressionEvaluator(parameters);
 org.junit.Assert.assertEquals("foobar", ee.evaluate("${stringValue}", String.class));
 org.junit.Assert.assertEquals(Integer.valueOf(5), ee.evaluate("${intValue}", Integer.class));
 org.junit.Assert.assertTrue(ee.evaluate("${intValue eq (3+2)}"));
 org.junit.Assert.assertTrue(ee.evaluate("${(1 eq (2/2)) && (2<3)}"));
 org.junit.Assert.assertTrue(ee.evaluate("${stringValue.length() == 6}"));
    Author:
    Matthias Müller

    • Constructor Detail

      • ExpressionEvaluator

        public ExpressionEvaluator​(Map<String,​?> variables)
        Creates a new ExpressionEvaluator using the given variables.
        Parameters:
        variables - a Map of variables to use

      • ExpressionEvaluator

        public ExpressionEvaluator​(javax.el.VariableMapper variableMapper)
        Creates a new ExpressionEvaluator using the given VariableMapper.
        Parameters:
        variableMapper - the VariableMapper to use

    • Method Detail

      • evaluate

        public final <T> T evaluate​(String expression,
                            Class<T> targetType)
        Evaluates the given expression to an object of the given targetType
        Parameters:
        expression - the expression to parse
        targetType - the expected target type
        Returns:
        an object of the given type
        Throws:
        NullPointerException - if targetType is null
        javax.el.ELException - if the expression has syntactical errors

      • evaluate

        public final boolean evaluate​(String expression)
        Evaluates the given expression to a boolean.
        Parameters:
        expression - the expression to evaluate
        Returns:
        evaluation result

      • addFunction

        public final void addFunction​(String prefix,
                              String name,
                              Method method)
        Adds a prefixed function to this ExpressionEvaluator. The given Method must be static.
        Example: 
         ExpressionEvaluator ee = ...;
 ee.addFunction("math","max", Math.class.getMethod("max", int.class, int.class));
 org.junit.Assert.assertEquals(Integer.valueOf(47), ee.evaluate("${math:max(47,11)}", Integer.class));
        Parameters:
        prefix - the prefix for the method
        name - the name of the method
        method - the Method to add as a function

      • addFunction

        public final void addFunction​(String name,
                              Method method)
        Adds a function to this ExpressionEvaluator. The given Method must be static.
        static.
        Example: 
         ExpressionEvaluator ee = ...;
 ee.addFunction("max", Math.class.getMethod("max", int.class, int.class));
 org.junit.Assert.assertEquals(Integer.valueOf(47), ee.evaluate("${max(47,11)}", Integer.class));
        Parameters:
        name - the name of the method
        method - the Method to add as a function

      • setVariable

        public final void setVariable​(String name,
                              Object value)
        Sets the variable with the given name to the given value.
        Parameters:
        name - the name of the variable
        value - the value of the variable (must not be null)

      • isExpression

        public boolean isExpression​(String value)
        Checks whether the given String is a valid expression (starts with ${ and ends with }).
        Parameters:
        value - the String to check
        Returns:
        true if the given value is a valid expression, false otherwise

      • getString

        public String getString​(String expression)
        Evaluates the given expression to a String, if possible.
        Parameters:
        expression - the expression to evaluate
        Returns:
        • the String evaluated from the expression, in cases it's a valid expression
        • the given expression itself, otherwise
        See Also:
        isExpression(String)

      • getBoolean

        public Boolean getBoolean​(String expression)
        Evaluates the given expression to a Boolean, if possible.
        Parameters:
        expression - the expression to evaluate
        Returns:
        • the Boolean evaluated from the expression, in cases it's a valid expression
        • Boolean.valueOf(expression) if the expression is not null but is not a valid expression
        • null if the expression is null
        See Also:
        isExpression(String)