org.apache.commons.jexl2
Class UnifiedJEXL

java.lang.Object
  org.apache.commons.jexl2.UnifiedJEXL

public final class UnifiedJEXL
extends Object

An evaluator similar to the Unified EL evaluator used in JSP/JSF based on JEXL. It is intended to be used in configuration modules, XML based frameworks or JSP taglibs and facilitate the implementation of expression evaluation.

An expression can mix immediate, deferred and nested sub-expressions as well as string constants;

• The "immediate" syntax is of the form "...${jexl-expr}..."
• The "deferred" syntax is of the form "...#{jexl-expr}..."
• The "nested" syntax is of the form "...#{...${jexl-expr0}...}..."
• The "composite" syntax is of the form "...${jexl-expr0}... #{jexl-expr1}..."

Deferred & immediate expression carry different intentions:

• An immediate expression indicate that evaluation is intended to be performed close to the definition/parsing point.
• A deferred expression indicate that evaluation is intended to occur at a later stage.

For instance: "Hello ${name}, now is #{time}" is a composite "deferred" expression since one of its subexpressions is deferred. Furthermore, this (composite) expression intent is to perform two evaluations; one close to its definition and another one in a later phase.

The API reflects this feature in 2 methods, prepare and evaluate. The prepare method will evaluate the immediate subexpression and return an expression that contains only the deferred subexpressions (& constants), a prepared expression. Such a prepared expression is suitable for a later phase evaluation that may occur with a different JexlContext. Note that it is valid to call evaluate without prepare in which case the same JexlContext is used for the 2 evaluation phases.

In the most common use-case where deferred expressions are to be kept around as properties of objects, one should parse & prepare an expression before storing it and evaluate it each time the property storing it is accessed.

Note that nested expression use the JEXL syntax as in: "#{${bar}+'.charAt(2)'}" The most common mistake leading to an invalid expression being the following: "#{${bar}charAt(2)}"

Also note that methods that parse evaluate expressions may throw unchecked exceptions; The UnifiedJEXL.Exception are thrown when the engine instance is in "non-silent" mode but since these are RuntimeException, user-code should catch them where appropriate.

Since:

2.0

Nested Class Summary

static class	UnifiedJEXL.Exception The sole type of (runtime) exception the UnifiedJEXL can throw.
class	UnifiedJEXL.Expression The abstract base class for all expressions, immediate '${...}' and deferred '#{...}'.
class	UnifiedJEXL.Template A Template is a script that evaluates by writing its content through a Writer.
class	UnifiedJEXL.TemplateContext The type of context to use during evaluation of templates.

Constructor Summary

UnifiedJEXL(JexlEngine aJexl)
Creates a new instance of UnifiedJEXL with a default size cache.

UnifiedJEXL(JexlEngine aJexl, int cacheSize)
Creates a new instance of UnifiedJEXL creating a local cache.

Method Summary

void	clearCache() Clears the cache.
UnifiedJEXL.Template	createTemplate(String source) Creates a new template.
UnifiedJEXL.Template	createTemplate(String prefix, Reader source, String... parms) Creates a new template.
UnifiedJEXL.Template	createTemplate(String source, String... parms) Creates a new template.
JexlEngine	getEngine() Gets the JexlEngine underlying the UnifiedJEXL.
UnifiedJEXL.Expression	parse(String expression) Creates a a UnifiedJEXL.Expression from an expression string.
protected List<org.apache.commons.jexl2.UnifiedJEXL.TemplateBlock>	readTemplate(String prefix, Reader source) Reads lines of a template grouping them by typed blocks.
protected int	startsWith(CharSequence sequence, CharSequence pattern) Whether a sequence starts with a given set of characters (following spaces).

Methods inherited from class java.lang.Object

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

Constructor Detail

UnifiedJEXL

public UnifiedJEXL(JexlEngine aJexl)

Creates a new instance of UnifiedJEXL with a default size cache.

Parameters:

aJexl - the JexlEngine to use.

UnifiedJEXL

public UnifiedJEXL(JexlEngine aJexl,
                   int cacheSize)

Creates a new instance of UnifiedJEXL creating a local cache.

Parameters:

aJexl - the JexlEngine to use.

cacheSize - the number of expressions in this cache

Method Detail

getEngine

public JexlEngine getEngine()

Gets the JexlEngine underlying the UnifiedJEXL.

Returns:

the JexlEngine

clearCache

public void clearCache()

Clears the cache.

Since:

2.1

parse

public UnifiedJEXL.Expression parse(String expression)

Creates a a UnifiedJEXL.Expression from an expression string. Uses & fills up the expression cache if any.

If the underlying JEXL engine is silent, errors will be logged through its logger as warnings.

Parameters:

expression - the UnifiedJEXL string expression

Returns:

the UnifiedJEXL object expression, null if silent and an error occured

Throws:

UnifiedJEXL.Exception - if an error occurs and the JexlEngine is not silent

startsWith

protected int startsWith(CharSequence sequence,
                         CharSequence pattern)

Whether a sequence starts with a given set of characters (following spaces).

Space characters at beginning of line before the pattern are discarded.

Parameters:

sequence - the sequence

pattern - the pattern to match at start of sequence

Returns:

the first position after end of pattern if it matches, -1 otherwise

Since:

2.1

readTemplate

protected List<org.apache.commons.jexl2.UnifiedJEXL.TemplateBlock> readTemplate(String prefix,
                                                                                Reader source)

Reads lines of a template grouping them by typed blocks.

Parameters:

prefix - the directive prefix

source - the source reader

Returns:

the list of blocks

Since:

2.1

createTemplate

public UnifiedJEXL.Template createTemplate(String prefix,
                                           Reader source,
                                           String... parms)

Creates a new template.

Parameters:

prefix - the directive prefix

source - the source

parms - the parameter names

Returns:

the template

Since:

2.1

createTemplate

public UnifiedJEXL.Template createTemplate(String source,
                                           String... parms)

Creates a new template.

Parameters:

source - the source

parms - the parameter names

Returns:

the template

Since:

2.1

createTemplate

public UnifiedJEXL.Template createTemplate(String source)

Creates a new template.

Parameters:

source - the source

Returns:

the template

Since:

2.1