org.apache.commons.jexl

Class ExpressionFactory

java.lang.Object

org.apache.commons.jexl.ExpressionFactory

public class ExpressionFactory
extends java.lang.Object

Creates Expression objects. To create a JEXL Expression object, pass valid JEXL syntax to the static createExpression() method:

 String jexl = "array[1]";
 Expression expression = ExpressionFactory.createExpression( jexl );
 

When an Expression object is created, the JEXL syntax is parsed and verified. If the supplied expression is neither an expression nor a reference, an exception is thrown from createException().

Since:

1.0

Version:

$Id: ExpressionFactory.java 429169 2006-08-06 18:36:29Z rahul $

Author:

Geir Magnusson Jr.

Field Summary

Fields

Modifier and Type	Field and Description
protected static ExpressionFactory	ef ExpressionFactory is a singleton and this is the private instance fufilling that pattern.
protected static org.apache.commons.logging.Log	log The Log to which all ExpressionFactory messages will be logged.
protected static Parser	parser The singleton ExpressionFactory also holds a single instance of Parser.

Constructor Summary

Constructors

Modifier	Constructor and Description
private	ExpressionFactory() Private constructor, the single instance is always obtained with a call to getInstance().

Method Summary

Modifier and Type	Method and Description
private java.lang.String	cleanExpression(java.lang.String expression) Trims the expression and adds a semi-colon if missing.
static Expression	createExpression(java.lang.String expression) Creates an Expression from a String containing valid JEXL syntax.
protected Expression	createNewExpression(java.lang.String expression) Creates a new Expression based on the expression string.
protected static ExpressionFactory	getInstance() Returns the single instance of ExpressionFactory.

Methods inherited from class java.lang.Object

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

Field Detail

log

protected static org.apache.commons.logging.Log log

The Log to which all ExpressionFactory messages will be logged.

parser

protected static Parser parser

The singleton ExpressionFactory also holds a single instance of Parser. When parsing expressions, ExpressionFactory synchronizes on Parser.

ef

protected static ExpressionFactory ef

ExpressionFactory is a singleton and this is the private instance fufilling that pattern.

Constructor Detail

ExpressionFactory

private ExpressionFactory()

Private constructor, the single instance is always obtained with a call to getInstance().

Method Detail

getInstance

protected static ExpressionFactory getInstance()

Returns the single instance of ExpressionFactory.

Returns:

the instance of ExpressionFactory.

createExpression

public static Expression createExpression(java.lang.String expression)
                                   throws java.lang.Exception

Creates an Expression from a String containing valid JEXL syntax. This method parses the expression which must contain either a reference or an expression.

Parameters:

expression - A String containing valid JEXL syntax

Returns:

An Expression object which can be evaluated with a JexlContext

Throws:

java.lang.Exception - An exception can be thrown if there is a problem parsing this expression, or if the expression is neither an expression or a reference.

createNewExpression

protected Expression createNewExpression(java.lang.String expression)
                                  throws java.lang.Exception

Creates a new Expression based on the expression string.

Parameters:

expression - valid Jexl expression

Returns:

Expression

Throws:

java.lang.Exception - for a variety of reasons - mostly malformed Jexl expression

cleanExpression

private java.lang.String cleanExpression(java.lang.String expression)

Trims the expression and adds a semi-colon if missing.

Parameters:

expression - to clean

Returns:

trimmed expression ending in a semi-colon