Dinesh on Java

Struts2

Struts 2 OGNL, ActionInvocation, ActionContext

The Object Graph Navigation Language (OGNL) is an expression language. It simplifies the accessibility of data stored in the ActionContext.

The struts framework sets the ValueStack as the root object of OGNL. Notice that action object is pushed into the ValueStack. We can direct access the action property.

<s:property value="username"/>

Here, username is the property key
.
The struts framework places other objects in ActionContext also e.g. map representing the request, session, application scopes.

To get these values i.e. not the action property, we need to use # notation. For example to get the data from session scope, we need to use #session as given in the following example:

<s:property name="#session.username"/>

(or)

<s:property name="#session['username']"/>

Struts 2 ActionInvocation

The ActionInvocation represents the execution state of an action. It holds the action and interceptors objects.

The struts framework provides ActionInvocation interface to deal with ActionInvocation. It provides many methods, some of them can be used to get the instance of ValueStack, ActionProxy, ActionContext, Result etc.

Methods of ActionInvocation Interface

The commonly used methods of ActionInvocation interface are as follows:
1)public ActionContext getInvocationContext() returns the ActionContext object associated with the ActionInvocation.
2)public ActionProxy getProxy() returns the ActionProxy instance holding this ActionInvocation.
3)public ValueStack getStack() returns the instance of ValueStack.
4)public Action getAction() returns the instance of Action associated with this ActionInvocation.
5)public void invoke() invokes the next resource in processing this ActionInvocation.
6)public Result getResult() returns the instance of Result.

**Struts 2 ActionContex–**

The ActionContext is a container of objects in which action is executed. The values stored in the ActionContext are unique per thread (i.e. ThreadLocal). So we don’t need to make our action thread safe.

We can get the reference of ActionContext by calling the getContext() method of ActionContext class. It is a static factory method. For example:

ActionContext context = ActionContext.getContext();

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!