What is OGNL and how it is used in Struts 2x ?

For expressions, the framework uses OGNL (Object Graph Navigation Language)

• An expression (EL) and binding language for getting and setting properties of Java objects
• Normally the same expression is used for both getting and setting the value of a property
• Easy to learn, yet powerful
• Incrementally compiled expressions - fast !
• Embedded everywhere – views, ValueStack, *.xml
• Independent Open Source project - http: //www.ognl.org

      |

      |-- application

      |

      |-- session

      |

      |-- value stack(root)

context map ---|

      |-- request

      |

      |-- parameters

      |

      |-- attributes (searches page in order : request > session > application)

      |

In expression, the properties of the root object can be referenced without any special "marker" notion.

<s:property value="postalCode"/>

References to other objects are marked with a pound sign (#).

<s:property value="#session.mySessionPropKey"/>

OGNL examples

user.name

getUser().getName()

user.toString()

getUser().toString()

item.categories[0]

First element of Categories collection

@com.example.Test@foo()

Calls the static foo() method of com.example.Test class.

name in {null, "fred"}

True: if name is null or "fred"

categories.{name}

Calls getName() on each category in the collection, returning a new collection (projection)