Skip to main content

Struts2 - How Struts2 works

The struts2 provides a cleaner implementation of MVC. These clean lines are only possible with the help of a few other key architectural components(ActionContext, Interceptors,  OGNL,  and ValueStack) that participate in processing every request.

The ValueStack is a storage area for all application domain data that will be needed during the processing of a request. You could think of it as a piece of scratch paper where the framework does its work while solving the problems of request processing . Rather than passing the data around, Struts2  keeps it in a convenient, central location - ValueStack.

OGNL is the tool that allows us to access the data we put in that central repository. More specifically, it is an expression language that allows you to reference and manipulate the data on the ValueStack.

ValueStack and OGNL don't belong to any of the individual framework components. Both interceptors and results can use OGNL to target values on the ValueStack. IThe data in the ValueStack follows the request processing through all phases; it slices through the whole length of the framework. It can do this because it is stored in a ThreadLocal context called the ActionContext.

ActionContext contains all of the data that makes up the context in which an action occurs. This includes the ValueStack but also includes stuff the framework itself will use internally, such as the request , session, and application maps from the Servlet API.  You can focus on the ActionContext as the ThreadLocal home of the ValueStack. The use of ThreadLocal makes the ActionContext, and thus the ValueStack, accessible from anywhere in the same thread of execution. Since Struts2's processing of each request occurs in a single thread, the ValueStack is available from any point the framework's handling of a request.

Typically, it is considered bad form to obtain the contents of the ActionContext yourself. The framework provides many elegant ways to interact with that data without actually touching the ActionContext, or the ValueStack, yourself. Primarily, you will use OGNL to do this.


Comments

Popular posts from this blog

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold highlighted in example below) which resolve the problems.   example:
<band height="20" splitType="Stretch"> <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/> …

JasperReports - Configuration Reference

Spring - Operations with jdbcTemplate

This class manages all the database communication and exception handling using a java.sql.Connection that is obtained from the provided DataSource. JdbcTemplate is a stateless and threadsafe class and you can safely instantiate a single instance to be used for each DAO.


Use of Callback Methods
JdbcTemplate is based on a template style of programming common to many other parts of Spring. Some method calls are handled entirely by the JdbcTemplate, while others require the calling class to provide callback methods that contain the implementation for parts of the JDBC workflow. This is another form of Inversion of Control. Your application code hands over the responsibility of managing the database access to the template class. The template class in turn calls back to your application code when it needs some detail processing filled in. These callback methods are allowed to throw a java.sql.SQLException, since the framework will be able to catch this exception and use its built-in excepti…