2024年4月8日发(作者：)

Java Unified Expression Language

Table of contents

1 Welcome to JUEL!.................................................................................................................................2

2 2

2.1 .3

2.2 3

2.2.1 4

2.2.2 5

2.2.3 6

2.3 7

2.3.1 8

2.3.2 .8

2.4 9

2.5 9

2.6 12

3 14

3.1 History 14

Copyright © 2006-2009 Odysseus Software GmbH. All rights reserved.

Java Unified Expression Language

1. Welcome to JUEL!

JUEL is an implementation of the Unified Expression Language (EL), specified as part of the JSP 2.1 standard

(JSR-245), which has been introduced in JEE5. Additionally, JUEL 2.2 implements the JSP 2.2 maintenance

release specification for full JEE6 compliance.

Motivation

Once, the EL started as part of JSTL. Then, the EL made its way into the JSP 2.0 standard. Now, though

part of JSP 2.1, the EL API has been separated into package

and all dependencies to the core

JSP classes have been removed.

In other words: the EL is ready for use in non-JSP applications!

Features

JUEL provides a lightweight and efficient implementation of the Unified Expression Language.

•High Performance – Parsing expressions is certainly the expected performance bottleneck. JUEL uses a

hand-coded parser which is up to 10 times faster than the previously used (javacc) generated parser!

Once built, expression trees are evaluated at highest speed.

•Pluggable Cache – Even if JUELs parser is fast, parsing expressions is relative expensive. Therefore, it's

best to parse an expression string only once. JUEL provides a default caching mechanism which should

be sufficient in most cases. However, JUEL allows to plug in your own cache easily.

•Small Footprint – JUEL has been carefully designed to minimize memory usage as well as code size.

•Method Invocations – JUEL supports method invocations as in

${s('[0-9]+')}

. Methods are

resolved and invoked using the EL's resolver mechanism. As of JUEL 2.2, method invocations are enabled

by default.

•VarArg Calls – JUEL supports Java 5 VarArgs in function and method invocations. E.g., binding

(String, )

to function

format

allows for

${format('Hey %s','Joe')}

. As of

JUEL 2.2, VarArgs are enabled by default.

•Pluggable – JUEL can be configured to be transparently detected as EL implementation by a Java runtime

environment or JEE application server. Using JUEL does not require an application to explicitly reference

any of the JUEL specific implementation classes.

Status

JUEL is considered production stable. The code is well tested (80% coverage) and feature complete.

Availability

JUEL is licensed under the Apache License 2.0.

Requirements

JUEL requires Java 5 or later.

2. JUEL Guide

This guide gives a brief introduction to JUEL. However, this is not an EL tutorial. Before using JUEL,

we strongly recommend to get familiar with the Unified EL basics by taking a look at the specification

document, which is available here.

The JUEL guide divides into the following sections:

Copyright © 2006-2009 Odysseus Software GmbH. All rights reserved.

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