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| <document xmlns="http://maven.apache.org/XDOC/2.0" |
| xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
| xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd"> |
| |
| <properties> |
| <title>Apache Commons OGNL - Object Graph Navigation Library</title> |
| <author>Apache Commons community (dev AT apache DOT org)</author> |
| </properties> |
| |
| <body> |
| <section name="Apache Commons OGNL - Object Graph Navigation Library"> |
| <p> |
| OGNL stands for Object-Graph Navigation Language; it is an expression language for getting and setting |
| properties of Java objects, plus other extras such as list projection and selection and lambda expressions. |
| You use the same expression for both getting and setting the value of a property. |
| </p> |
| |
| <p> |
| The <code>Ognl</code> class contains convenience methods for evaluating OGNL expressions. You can do this in two |
| stages, parsing an expression into an internal form and then using that internal form to either set or get the |
| value of a property; or you can do it in a single stage, and get or set a property using the String form of the |
| expression directly. |
| </p> |
| |
| <p> |
| OGNL started out as a way to set up associations between UI components and controllers using property names. As the |
| desire for more complicated associations grew, Drew Davidson created what he called KVCL, for Key-Value Coding |
| Language, egged on by Luke Blanshard. Luke then reimplemented the language using ANTLR, came up with the new name, |
| and, egged on by Drew, filled it out to its current state. Later on Luke again reimplemented the language using |
| JavaCC. Further maintenance on all the code is done by Drew (with spiritual guidance from Luke). |
| </p> |
| |
| <p> |
| We pronounce OGNL as a word, like the last syllables of a drunken pronunciation of "<i>orthogonal</i>". |
| </p> |
| </section> |
| |
| <section name="Introduction"> |
| <p> |
| Many people have asked exactly what <code>OGNL</code> is good for. Several of the uses to which <code>OGNL</code> |
| has been applied are: |
| </p> |
| <ul> |
| <li> |
| A binding language between GUI elements (textfield, combobox, etc.) to model objects. Transformations are made |
| easier by <code>OGNL</code>'s TypeConverter mechanism to convert values from one type to another (String to |
| numeric types, for example); |
| </li> |
| <li> |
| A data source language to map between table columns and a Swing TableModel; |
| </li> |
| <li> |
| A binding language between web components and the underlying model objects; |
| </li> |
| <li> |
| A more expressive replacement for the property-getting language used by the Apache Commons BeanUtils package or |
| JSTL's EL (which only allow simple property navigation and rudimentary indexed properties). |
| </li> |
| </ul> |
| <p> |
| Most of what you can do in Java is possible in <code>OGNL</code>, plus other extras such as list <i>projection</i>, |
| <i>selection</i> and <i>lambda expressions</i>. |
| </p> |
| </section> |
| |
| </body> |
| |
| </document> |
