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Almost every Web-based business application requires data storage in various databases. For Struts 2 beginners, the biggest challenge while developing a Web application is displaying the data stored in their database to the presentation page of the browser.
Developing the best approach for handling data can require a lot of effort. Great applications require a good user interface (UI) and good back-end implementation. The power of Struts 2 lies in its ability to provide clean implementation of the Model-View-Controller (MVC) pattern with the following features:
- Actions
- Part of the framework's architecture, Actions provides clean implementation by keeping all the business logic in one place. Actions serves as a channel of automatic transfer of data from the request to result pages.
- Results
- A UI that represents the user's requirements from the application onto the Web browser.
- Interceptors
- Remove the overhead of Actions
and improve performance by implementing common operations, such as
validations, logging statements, and error checks, which are common to
multiple Actions.
Interceptors are called at both post-processing and pre-processing. For one action request, there can be a stack of Interceptors.
- ValueStack
- An object that holds all the data that gets associated during the processing of a request.
Figure 1 shows the components of the Struts 2 framework.
Figure 1. Struts 2 Action, Interceptor, and Result
In this article, learn about dynamic data handling in a Web-based application. You will explore how to send user data at run time with a few special use cases, such as pre-filling a form with user data values and setting the UI field to display a default value from a list of values. The article focuses on the implementation details of the flow of dynamic data between Struts 2 Action classes and the result pages.
Dynamic data handling using Struts 2 ValueStack
ValueStack, one of the powerful features of Struts 2, holds all the
data during processing of a request. Action classes also store data
in the form of beans. (In Struts 2 you use getter and setter methods.) Once
the data is stored in the action class objects, Struts 2 puts that data onto the
ValueStack in the form of the Action object.
ValueStack stores a stack
of objects, and this data will be exposed to the other parts of the
framework.
In Figure 2, the action class sets the values of two variables using
getter and setter methods. This data will be saved to the ValueStack
during processing of requests. HelloWorld.jsp will get the values of
these variables from the ValueStack and display the values using the
<s:property> tag from the Struts 2 tag library.
Figure 2. Data on ValueStack
Static data versus dynamic data
If data that will be displayed on the UI is known in advance, it can be called static data. Static data can be handled easily by coding it directly in JavaServer Pages (JSP). Figure 3 shows a static data situation.
Figure 3. Static data
If a user wants to display the data retrieved from the user
database, you need a mechanism to appropriately handle the data in the Action
and JSP and to display the data on the UI. With Struts 2, the building
blocks for this type of scenario are the Action class and ValueStack.
By using getter and setter methods, the Action class will save the user
values onto the ValueStack. After that, a JSP will get the values of
matching variable names and display them on the UI. See Figure 4.
Figure 4. Dynamic data
Setting UI fields and tags with user data
Struts 2 provides a tag library that displays data in rich and reusable HTML to help you create interactive, form-based applications. Struts 2 comes with generic tags (control tags and data tags) and UI tags. UI tags are designed to get data from the ValueStack (action added data onto the ValueStack) or from data tags. The following is an example of the Struts 2 UI tag <select tag>.
- Write the
Actionclass to display the data onto the UI, as shown in Listing 1.
Listing 1. Write theActionclass to display the data onto the UIpublic class DisplayAction extends ActionSupport { private List state = new ArrayList(); private List status = new ArrayList(); public String execute() { setState(this.state); setStatus(this.status); return "success"; } //getter and setter method for state variable// public List getState() { return state; } public void setState(List state) { //implement the application specific logic to retrieve the data from the database here// //Here for displaying the data on UI, we are using few hardcoded values// state.add("Defect"); state.add("Task"); state.add("User Stories"); } public List getStatus() { return status; } public void setStatus(List status) { //implement the application specific logic to retrieve the data from the database here// //Here for displaying the data on UI, we are using few hardcoded values// status.add("New"); status.add("Fixed") status.add("Resolved"); status.add("Closed"); } }
In this example, the
DisplayActionclass sets theArrayListobject's state and status with a few values. TheActionclass will save this data onto the ValueStack, which JSP will use to display on the UI. - To handle the data on the JSP side, you need to write <select>
tags that will get the values of
stateandstatus, as follows in Listing 2:
Listing 2. Write <select> tags that will get the values ofstateandstatus<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <%@ taglib prefix="s" uri="/struts-tags" %> <html> <title>Sample Display Page</title> <body> <s:select list="%{status}" name="Status"></s:select> <s:select list="%{state}" name="State"></s:select> </body> </html>
- Configure the
Actionand JSP with struts.xml mapping, as shown in Listing 3.
Listing 3. Configure theActionand JSP with struts.xml mapping<!DOCTYPE struts PUBLIC"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"> <struts> <package name="sample.exmaple" extends="struts-default"> <action name=”DisplayAction” class=”com.sample.example.DisplayAction”> <result name=”success”>/DisplayPage.jsp </result> </action> </package> </struts>
In the code examples above:
- The
Actionclass has the list variables namedstateandstatus. - Data is added in the
Actionclass by makingstateandstatusof typearraylist. <s:select>has the list parameter (mandatory) with the same name as defined in theActionclass.- Place these list variables using
%{<list-variable>}. - The name of the list variables in JSP must match the name given in the
Actionclass.
Figure 5 shows an example of the output.
Figure 5. Output 1: Display of Status list
In Figure 6, the <select> tag Status is
initialized with the values that are put in the Action class.
Figure 6. Output 2: Display of State list
The <select> tag State is also initialized
with the values that are put in the Action class.
Setting default values in prefilled UI fields
Assume a user has a list of values. From the elements in the list, the user wants to set one value as the default once the UI gets loaded.
In the following example, the user has a combo box and wants to display the last value after the UI is loaded.
- Modify the
Actionclass and add code for the default value, as shown in Listing 4.
Listing 4. Modify theActionclass and add code for the default valuepublic class DisplayAction extends ActionSupport { private List state = new ArrayList(); private List status = new ArrayList(); private String defaultState = ""; private String defaultStatus = ""; public String execute() { //set status and state list values// setState(this.state); setStatus(this.status); //set default values for state and status which //a user wants to display on the User Interface setDefaultState("Task"); setDefaultStatus("Closed"); return "success"; } //getter and setter method// public List getState() { return state; } public void setState(List state) { //implement the application specific logic to retrieve //the data from the database here// //Here for displaying the data, we are using few //hardcoded values state.add("Defect"); state.add("Task"); state.add("User Stories"); } public List getStatus() { return status; } public void setStatus(List status) { //implement the application specific logic to retrieve //the data from the database here// //Here for displaying the data, we are using few //hardcoded values// status.add("New"); status.add("Fixed"); status.add("Resolved"); status.add("Closed"); } public String getDefaultState() { return defaultState; } public void setDefaultState(String defaultState) { this.defaultState = defaultState; } public String getDefaultStatus() { return defaultStatus; } public void setDefaultStatus(String defaultStatus) { this.defaultStatus = defaultStatus; } }
In the
Actionclass above, the example adds two more getter/setter methods to set variables with the default values for the<select>tag. - The modified JSP code is shown below in Listing 5.
Listing 5. The modified JSP code<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <%@ taglib prefix="s" uri="/struts-tags" %> <html> <title>Sample Display Page</title> <body> <s:select list="%{status}" name="Status" value="%{defaultStatus}"></s:select> <s:select list="%{state}" name="State" value="%{defaultState}"></s:select> </body> </html>
The struts.xml mapping remains the same in this case.
In the code examples above:
- In the
Actionclass, the default values to be displayed are saved in two string variables. - In the JSP, these values can be handled using the
valueparameter of the<select>tag. - The name of the default value variable in the
Actionclass must match the name in the result JSP.
Figure 7 shows an example of the output.
Figure 7. Output 1: Display of Status default value
In Figure 8, Closed has been set as the default value of the Status list when the UI is loaded.
Figure 8. Output 2: Display of State default value
Task has been set as the default value of the State list when the UI is loaded.
Struts 2 is a second-generation Web application framework that has gained popularity over Java Servlets. It encompasses the commonly used MVC design pattern. Struts 2 automates common tasks, freeing you up to take advantage of the Action-to-result pages mapping using SML-based configurations. The framework covers the ground-level details of the implementation of Web-based applications and provides a piece of structural software.
In this article you learned about Struts 2 abilities as a complete framework. You explored a few of the most common use cases and the solutions provided with the powerful features of Struts 2.
Learn
- Become more familiar with Apache Struts 2, the free
open source framework for creating Java Web applications.
- Get the Struts 2 documentation: Getting started, Tutorials, FAQs, and Guides.
- Read more about ValueStack, which allows multiple beans to be pushed in and dynamic EL expressions to be evaluated against it.
- Use the Struts 2 UI Tag Reference. Struts UI tags display data in rich and
reusable HTML.
- Get Struts 2 documentation and other resources, such as security
bulletins, wikis, quick links, and tutorials.
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