org.appng.el

Class ExpressionEvaluator

java.lang.Object

org.appng.el.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 Summary

Constructors

Constructor and Description
ExpressionEvaluator(Map<String,?> variables) Creates a new ExpressionEvaluator using the given variables.
ExpressionEvaluator(javax.el.VariableMapper variableMapper) Creates a new ExpressionEvaluator using the given VariableMapper.

Method Summary

Modifier and Type	Method and Description
void	addFunction(String name, Method method) Adds a function to this ExpressionEvaluator.
void	addFunction(String prefix, String name, Method method) Adds a prefixed function to this ExpressionEvaluator.
boolean	evaluate(String expression) Evaluates the given expression to a boolean.
<T> T	evaluate(String expression, Class<T> targetType) Evaluates the given expression to an object of the given targetType
Boolean	getBoolean(String expression) Evaluates the given expression to a Boolean, if possible.
String	getString(String expression) Evaluates the given expression to a String, if possible.
boolean	isExpression(String value) Checks whether the given String is a valid expression (starts with ${ and ends with }).
void	setVariable(String name, Object value) Sets the variable with the given name to the given value.
void	setVariables(Map<String,?> variables) Calls setVariable(String, Object) for each entry of the given map.

Methods inherited from class java.lang.Object

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

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)

setVariables

public final void setVariables(Map<String,?> variables)

Calls setVariable(String, Object) for each entry of the given map.

Parameters:

variables - a Map of variables

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)