What's the difference between # , % and $ signs in Struts tags?

expression, java, jsp, ognl, struts2

Solution

Use of # (pound sign)

OGNL is used to refer to objects in the ActionContext as follows:

- `objectName`: object in the ValueStack (default/root object in the OGNL context), such as an Action property

- `#objectName`: object in the ActionContext but outside of the ValueStack, specifically...

- `#objectName`: ActionContext object that has been created using the Struts2 data tags with the default action scope (e.g., `<s:set name="foo" value="'Testing'" />`, referenced by `<s:property value="#foo" />`)

- `#parameters.objectName`: request parameter

- `#request.objectName`: request-scoped attribute

- `#session.objectName`: session-scoped attribute

- `#application.objectName`: application-scoped attribute

- `#attr.objectName`: attribute in page, request, session, or application scope (searched in that order)

The scoped map references above (parameters, request, session, and application) can be made one of two ways:

- `#scopeName.objectName` or

- `#scopeName['objectName']`

Use of % (percent sign)

`%{ OGNL expression }` is used to force OGNL evaluation of an attribute that would normally be interpreted as a String literal.

Example: `<s:property value="myProperty" default="%{myDynamicDefaultValue}" />`

Use of @ (at sign)

The @ symbol is used to make references to static properties and methods. Note that you may need to enable this in your Struts2 properties: `struts.ognl.allowStaticMethodAccess=true`

Examples:

@my.package.ClassName@MY_STATIC_PROPERTY
@my.package.ClassName@myStaticMethod

Use of $ (dollar sign)

Struts2 OGNL does not make special use of the dollar sign. However, it can be used to evaluate normal JSTL expressions. For example:

Struts2: `<h1><s:property value="#pageTitle" /></h1>` (is equivalent to...) JSTL: `<h1>${pageTitle}</h1>`

Problem

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