What is Struts?
Struts Frame work is the implementation of Model-View-Controller (MVC) design pattern for the JSP. Struts are maintained as a part of Apache Jakarta project and are open source. Struts Framework is suited for the application of any size. Latest version of struts can be downloaded from http://jakarta.apache.org/. We are using jakarta-struts-1.1 and jakarta-tomcat-5.0.4 for this tutorial.
What is Model-View-Controller (MVC) Architecture?
Model-View-Controller architecture is all about dividing application components into three different categories Model, View and the Controller. Components of the MVC architecture have unique responsibility and each component is independent of the other component. Changes in one component will have no or less impact on other component. Responsibilities of the components are:
Model: Model is responsible for providing the data from the database and saving the data into the data store. All the business logic is implemented in the Model. Data entered by the user through View are check in the model before saving into the database. Data access, Data validation and the data saving logic are part of Model.
View: View represents the user view of the application and is responsible for taking the input from the user, dispatching the request to the controller and then receiving response from the controller and displaying the result to the user. HTML, JSPs, Custom Tag Libraries and Resources files are the part of view component.
Controller: Controller is intermediary between Model and View. Controller is responsible for receiving the request from client. Once request is received from client it executes the appropriate business logic from the Model and then produce the output to the user using the View component. ActionServlet, Action, ActionForm and struts-config.xml are the part of Controller.
Setting up Development Environment
Installing JDK:
Download JDK 1.4 or above from sun site. Follow the instruction given in the installation manual and install JDK.
Installing Tomcat:
Download Tomcat from the apache site and install it. I have downloaded jakarta-tomcat-5.0.4 and installed for this tutorial. To test your installation goes to your installation directory/bin and issue startup command to run the server. Open browser and type http://localhost:8080/ to test the server. It should display the welcome page. If not consult tomcat documentation before going further.
Installing Struts Application:
Download latest version of Struts from the official site of Struts http://jakarta.apache.org/struts. Extract the file into your favorite directory and copy struts-blank.war, struts-documentation.war and struts-example.war from "jakarta-struts-1.1\webapps" directtory into "jakarta-tomcat-5.0.4\webapps" directory.
struts-blank.war is the blank struts application which is useful in creating struts application from scratch. We will use this file to create our web application.
struts-documentation.war contains API and important documents for the struts application development.
struts-example.war is simple MailReader Demonstration Application.
Developing First Struts Application
Rename struts-blank.war to struts-tutorial.war from jakarta-tomcat-5.0.4\webapps and copy it to the "jakarta-tomcat-5.0.4\webapps" directory. Tomcat automatically extracts the file and loads the application.
Note: I have decided to use JBoss 3.2.3 for next parts as it is very easy to deploy the application in JBoss and I have developed the Ant script for easy deployment of the tutorial. The hot deployment feature of JBoss is very useful and it pickups the new ear files and deploys automatically.
You can download JBoss 3.2.3 from jboss.org. For installing and how to use JBoss please have a look at http://www.roseindia.net/jboss/index.shtml.
Difference between Model 1 and Model 2 architecture:
Features of MVC1:
- Html or JSP files are used to code the presentation. To retrieve the data JavaBean can be used.
- In MVC-1 architecture all the view, control elements are implemented using Servlets or Jsp.
- In MVC-1 there is tight coupling between page and model as data access is usually done using Custom tag or through java bean call.
Features of MVC2:
- The MVC-2 architecture removes the page centric property of MVC-1 architecture by separating Presentation, control logic and the application state.
- In MVC-2 architecture there is only one controller which receives all the request for the application and is responsible for taking appropriate action in response to each request.
What is Struts - Struts Architecture
In this section we will discuss about Architecture. Struts are famous for its robust Architecture and it is being used for developing small and big software projects.
Struts are an open source framework used for developing J2EE web applications using Model View Controller (MVC) design pattern. It uses and extends the Java Servlet API to encourage developers
to adopt an MVC architecture. Struts framework provides three key components:
- A request handler provided by the application developer that is used to map to a particular URI.
- A response handler which is used to transfer the control to another resource which will be responsible for completing the response.
- A tag library which helps developers to create the interactive form based applications with server pages.
Struts provide you the basic infrastructure for implementing MVC allowing the developers to concentrate on the business logic.
MVC Architecture
The main aim of the MVC architecture is to separate the business logic and application data from the presentation data to the user.
Here are the reasons why we should use the MVC design pattern.
- They are reusable: When the problems recur, there is no need to invent a new solution; we just have to follow the pattern and adapt it as necessary.
- They are expressive: By using the MVC design pattern our application becomes more expressive.
1). Model: The model object knows about all the data that need to be displayed. It is model who is aware about all the operations that can be applied to transform that object. It only represents the data of an application. The model represents enterprise data and the business rules that govern access to and updates of this data. Model is not aware about the presentation data and how that data will be displayed to the browser.
2). View: The view represents the presentation of the application. The view object refers to the model. It uses the query methods of the model to obtain the contents and renders it. The view is not dependent on the application logic. It remains same if there is any modification in the business logic. In other words, we can say that it is the responsibility of the of the view's to maintain the consistency in its presentation when the model changes.
3). Controller: Whenever the user sends a request for something then it always go through the controller. The controller is responsible for intercepting the requests from view and passes it to the model for the appropriate action. After the action has been taken on the data, the controller is responsible for directing the appropriate view to the user. In GUIs, the views and the controllers often work very closely together.
Overview of the Struts Framework
The Struts framework is composed of approximately 300 classes and interfaces which are organized in about 12 top level packages. Along with the utility and helper classes framework also provides the classes and interfaces for working with controller and presentation by the help of the custom tag libraries. It is entirely on to us which model we want to choose. The view of the Struts architecture is given below:
The Struts Controller Components:
Whenever a user request for something, then the request is handled by the Struts Action Servlet. When the ActionServlet receives the request, it intercepts the URL and based on the Struts Configuration files, it gives the handling of the request to the Action class. Action class is a part of the controller and is responsible for communicating with the model layer.
The Struts View Components:
The view components are responsible for presenting information to the users and accepting the input from them. They are responsible for displaying the information provided by the model components. Mostly we use the Java Server Pages (JSP) for the view presentation. To extend the capability of the view we can use the Custom tags, java script
etc.
The Struts model component:
The model components provide a model of the business logic behind a Struts program. It provides interfaces to databases or back- ends systems. Model components are generally a java class. There is not any such defined format for a Model component, so it is possible for us to reuse Java code which is written for other projects. We should choose the model according to our client requirement.
How Struts Works
The basic purpose of the Java Servlets in struts is to handle requests made by the client or by web browsers. In struts JavaServerPages (JSP) are used to design the dynamic web pages. In struts, servlets helps to route request which has been made by the web browsers to the appropriate ServerPage. The use of servlet as a router helps to make the web applications easier to design, create, and maintain. Struts is purely based on the Model- View- Controller (MVC) design pattern. It is one of the best and most well developed design patterns in use. By using the MVC architecture we break the processing in three sections named Model, the View, and the Controller. Below we are describing the working of struts.
- As we all are well aware of the fact that each application we develop has a deployment descriptor i.e. WEB-INF/web.xml. This is the file which the container reads.
This file has all the configuration information which we have defined for our web application. The configuration information includes the index file, the default welcome page, the mapping of our servlets including path and the extension name, any init parameters, information related to the context elements.
In the file WEB-INF/web.xml of struts application we need to configure the Struts ActionServlet which handles the entire request made by the web browsers to a given mapping. ActionServlet is the central component of the Struts controller. This servlet extends the HttpServlet. This servlet basically performs two important things. First is : When the container gets start, it reads the Struts Configuration files and loads it into memory in the init() method. You will know more about the Struts Configuration files below. Second point is: It intercepts the HTTP request in the doGet() and doPost() method and handles it appropriately.
- In struts application we have another xml file which is a Struts configuration file named as struts.config.xml. The name of this file can be changed. The name of the struts configuration file can be configured in the web.xml file. This file is placed under the WEB-INF directory of the web application. It is an XML document that describes all or part of Struts application. This file has all the information about many types of Struts resources and configures their interaction. This file is used to associate paths with the controller components of your application., known as Action classes like <action path ="/login" type = "LoginAction">. This tag tells the Struts ActionServlet that whenever the incoming request is http://myhost/myapp/login.do, then it must invoke the controller component LoginAction. Above, you can see that we have written .do in the URL. This mapping is done to tell the web application that whenever a request is received with the .do extension then it should be appended to the URL.
- For each action we also have to configure Struts with the names of the resulting pages that will be shown as a result of that action. In our application there can be more than one view which depends on the result of an action. One can be for a success and the other for the failure. If the result action is "success" then the action tells the ActionServlet that the action has been successfully accomplished or vice- versa. The struts knows how to forward the specific page to the concerned destination. The model which we want to use is entirely to you, the model is called from within the controller components.
- Action can also get associate with a JavaBean in our Struts configuration file. Java bean is nothing but a class having getter and setter methods that can be used to communicate between the view and the controller layer. These java beans are validated by invoking the validate() method on the ActionForm by the help of the Struts system. The client sends the request by the normal form submission by using Get or Post method, and the Struts system updates that data in the Bean before calling the controller components.
- The view we use in the struts can be either Jsp page, Velocity templates, XSLT pages etc. In struts there are set of JSP tags which has been bundled with the struts distribution, but it is not mandatory to use only Jsp tags, even plain HTML files can be used within our Struts application but the disadvantage of using the html is that it can't take the full advantage of all the dynamic features provided in the struts framework.
The framework includes a set of custom tag libraries that facilitate in creating the user interfaces that can interact gracefully with ActionForm beans. The struts Jsp taglibs has a number of generic and struts specific tags tags which helps you to use dynamic data in your view. These tags helps us to interact with your controller without writing much java code inside your jsp. These tags are used create forms, internally forward to other pages by interacting with the bean and helps us to invoke other actions of the web application.
There are many tags provided to you in the struts frameworks which helps you in sending error messages, internationalization etc.
Note: The points we have described above will be in effect if and only if when the ActionServlet is handling the request. When the request is submitted to the container which call the ActionServlet, make sure that the extension of the file which we want to access should have the extension .do.
Struts working:
Process flow:
web.xml : Whenever the container gets start up the first work it does is to check the web.xml file and determine what struts action Servlets exist. The container is responsible for mapping all the file request to the correct action Servlet.
A Request : This is the second step performed by the container after checking the web.xml file. In this the user submits a form within a browser and the request is intercepted by the controller.
The Controller : This is the heart of the container. Most Struts application will have only one controller that is ActionServlet which is responsible for directing several Actions. The controller determines what action is required and sends the information to be processed by an action Bean. The key advantage of having a controller is its ability to control the flow of logic through the highly controlled, centralized points.
struts.config.xml : Struts has a configuration file to store mappings of actions. By using this file there is no need to hard code the module which will be called within a component. The one more responsibility of the controller is to check the struts.config.xml file to determine which module to be called upon an action request. Struts only reads the struts.config.xml file upon start up.
Model : The model is basically a business logic part which takes the response from the user and stores the result for the duration of the process. This is a great place to perform the preprocessing of the data received from request. It is possible to reuse the same model for many page requests. Struts provides the ActionForm and the Action classes which can be extended to create the model objects.
View : The view in struts framework is mainly a jsp page which is responsible for producing the output to the user.
Struts tag libraries : These are struts components helps us to integrate the struts framework within the project's logic. These struts tag libraries are used within the JSP page. This means that the controller and the model part can't make use of the tag library but instead use the struts class library for strut process control.
Property file : It is used to store the messages that an object or page can use. Properties files can be used to store the titles and other string data. We can create many property files to handle different languages.
Business objects : It is the place where the rules of the actual project exists. These are the modules which just regulate the day- to- day site activities.
The Response : This is the output of the View JSP object.
Understanding Struts Controller
In this section I will describe you the Controller part of the Struts Framework. I will show you how to configure the struts-config.xml file to map the request to some destination servlet or jsp file.
The class org.apache.struts.action.ActionServlet is the heart of the Struts Framework. It is the Controller part of the Struts Framework. ActionServlet is configured as Servlet in the web.xml file as shown in the following code snippets.
<!-- Standard Action Servlet Configuration (with debugging) -->
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/struts-config.xml</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>2</param-value>
</init-param>
<init-param>
<param-name>detail</param-name>
<param-value>2</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet>
This servlet is responsible for handing all the request for the Struts Framework, user can map the specific pattern of request to the ActionServlet. <servlet-mapping> tag in the web.xml file specifies the url pattern to be handled by the servlet. By default it is *.do, but it can be changed to anything. Following code form the web.xml file shows the mapping.
<!-- Standard Action Servlet Mapping -->
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
The above mapping maps all the requests ending with .do to the ActionServlet. ActionServlet uses the configuration defined in struts-config.xml file to decide the destination of the request. Action Mapping Definitions (described below) is used to map any action. For this lesson we will create Welcome.jsp file and map the "Welcome.do" request to this page.
Welcome.jsp
<%@ taglib uri="/tags/struts-bean" prefix="bean" %>
<%@ taglib uri="/tags/struts-html" prefix="html" %>
<html:html locale="true">
<head>
<title><bean:message key="welcome.title"/></title>
<html:base/>
</head>
<body bgcolor="white">
<h3><bean:message key="welcome.heading"/></h3>
<p><bean:message key="welcome.message"/></p>
</body>
</html:html>
Forwarding the Welcome.do request to Welcome.jsp
The "Action Mapping Definitions" is the most important part in the struts-config.xml. This section takes a form defined in the "Form Bean Definitions" section and maps it to an action class.
Following code under the <action-mappings> tag is used to forward the request to the Welcome.jsp.
<action path="/Welcome"
forward="/pages/Welcome.jsp"/>
To call this Welcome.jsp file we will use the following code.
<html:link page="/Welcome.do">First Request to the controller</html:link>
Once the use clicks on on First Request to the controller link on the index page, request (for Welcome.do) is sent to the Controller and the controller forwards the request to Welcome.jsp. The content of Welcome.jsp is displayed to the user.
Understanding Struts Action Class
In this lesson I will show you how to use Struts Action Class and forward a jsp file through it.
What is Action Class?
An Action class in the struts application extends Struts 'org.apache.struts.action.Action" Class. Action class acts as wrapper around the business logic and provides an inteface to the application's Model layer. It acts as glue between the View and Model layer. It also transfers the data from the view layer to the specific business process layer and finally returns the procssed data from business layer to the view layer.
An Action works as an adapter between the contents of an incoming HTTP request and the business logic that corresponds to it. Then the struts controller (ActionServlet) slects an appropriate Action and creates an instance if necessary, and finally calls execute method.
To use the Action, we need to Subclass and overwrite the execute() method. In the Action Class don't add the business process logic, instead move the database and business process logic to the process or dao layer.
The ActionServlet (commad) passes the parameterized class to Action Form using the execute() method. The return type of the execute method is ActionForward which is used by the Struts Framework to forward the request to the file as per the value of the returned ActionForward object.
Developing our Action Class?
Our Action class (TestAction.java) is simple class that only forwards the TestAction.jsp. Our Action class returns the ActionForward called "testAction", which is defined in the struts-config.xml file (action mapping is show later in this page). Here is code of our Action Class:
TestAction.java
package roseindia.net;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
public class TestAction extends Action
{
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
return mapping.findForward("testAction");
}
}
Understanding Action Class
Here is the signature of the Action Class.
public ActionForward execute(ActionMapping mapping,
ActionForm form,
javax.servlet.http.HttpServletRequest request,
javax.servlet.http.HttpServletResponse response)
throws java.lang.Exception
Action Class process the specified HTTP request, and create the corresponding HTTP response (or forward to another web component that will create it), with provision for handling exceptions thrown by the business logic. Return an ActionForward instance describing where and how control should be forwarded, or null if the response has already been completed.
Parameters:
mapping - The ActionMapping used to select this instance
form - The optional ActionForm bean for this request (if any)
request - The HTTP request we are processing
response - The HTTP response we are creating
Throws:
Action class throws java.lang.Exception - if the application business logic throws an exception
Adding the Action Mapping in the struts-config.xml
To test the application we will add a link in the index.jsp
<html:link page="/TestAction.do">Test the Action</html:link>
Following code under the <action-mappings> tag is used to for mapping the TestAction class.
<action
path="/TestAction"
>
<forward name="testAction" path="/pages/TestAction.jsp"/>
</action>
To test the new application click on Test the Action link on the index page. The content of TestAction.jsp should be displayed on the user browser.
In this lesson you learned how to create Action Class and add the mappings in the struts-config.xml. Our Action Class returns the ActionForward mapping of the TestAction.jsp.
The ActionForm Class
In this lesson you will learn about the ActionForm in detail. I will show you a good example of ActionForm. This example will help you understand Struts in detail. We will create user interface to accept the address details and then validate the details on server side. On the successful validation of data, the data will be sent to model (the action class). In the Action class we can add the business processing logic but in this case we are just forwarding it to the sucess.jsp.
What is ActionForm?
An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm. ActionForm maintains the session state for web application and the ActionForm object is automatically populated on the server side with data entered from a form on the client side.
We will first create the class AddressForm which extends the ActionForm class. Here is the code of the class:
AddressForm.java
package roseindia.net;
import javax.servlet.http.HttpServletRequest;
import org.apache.struts.action.*;
/**
* @author Deepak Kumar
* @Web http://www.roseindia.net
* @Email [email protected]
*/
/**
* Form bean for the Address Entry Screen.
*
*/
public class AddressForm extends ActionForm
{
private String name=null;
private String address=null;
private String emailAddress=null;
public void setName(String name){
this.name=name;
}
public String getName(){
return this.name;
}
public void setAddress(String address){
this.address=address;
}
public String getAddress(){
return this.address;
}
public void setEmailAddress(String emailAddress){
this.emailAddress=emailAddress;
}
public String getEmailAddress(){
return this.emailAddress;
}
/**
* Reset all properties to their default values.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
*/
public void reset(ActionMapping mapping, HttpServletRequest request) {
this.name=null;
this.address=null;
this.emailAddress=null;
}
/**
* Reset all properties to their default values.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
* @return errors
*/
public ActionErrors validate(
ActionMapping mapping, HttpServletRequest request ) {
ActionErrors errors = new ActionErrors();
if( getName() == null || getName().length() < 1 ) {
errors.add("name",new ActionMessage("error.name.required"));
}
if( getAddress() == null || getAddress().length() < 1 ) {
errors.add("address",new ActionMessage("error.address.required"));
}
if( getEmailAddress() == null || getEmailAddress().length() < 1 ) {
errors.add("emailaddress",new ActionMessage("error.emailaddress.required"));
}
return errors;
}
}
The above class populates the Address Form data and validates it. The validate() method is used to validate the inputs. If any or all of the fields on the form are blank, error messages are added to the ActionMapping object. Note that we are using ActionMessage class, ActionError is now deprecated and will be removed in next version.
Now we will create the Action class which is the model part of the application. Our action class simply forwards the request the Success.jsp. Here is the code of the AddressAction class:
AddressAction.java
package roseindia.net;
/**
* @author Deepak Kumar
* @Web http://www.roseindia.net
* @Email [email protected]
*/
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
public class AddressAction extends Action
{
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
return mapping.findForward("success");
}
}
Now we have to create an entry for form bean in the struts-config.xml. Add the following lines in the struts-config.xml file:
<form-bean
name="AddressForm"
/>
Add the following line in the struts-config.xml file for handling the action "/Address.do":
<action
path="/Address"
name="AddressForm"
scope="request"
validate="true"
input="/pages/Address.jsp">
<forward name="success" path="/pages/success.jsp"/>
</action>
Now create Address.jsp, which is our form for entering the address details. Code for Address.jsp is as follows:
Address.jsp
<%@ taglib uri="/tags/struts-bean" prefix="bean" %>
<%@ taglib uri="/tags/struts-html" prefix="html" %>
<html:html locale="true">
<head>
<title><bean:message key="welcome.title"/></title>
<html:base/>
</head>
<body bgcolor="white">
<html:form action="/Address">
<html:errors/>
<table>
<tr>
<td align="center" colspan="2">
<font size="4">Please Enter the Following Details</font>
</tr>
<tr>
<td align="right">
Name
</td>
<td align="left">
<html:text property="name" size="30" maxlength="30"/>
</td>
</tr>
<tr>
<td align="right">
Address
</td>
<td align="left">
<html:text property="address" size="30" maxlength="30"/>
</td>
</tr>
<tr>
<td align="right">
E-mail address
</td>
<td align="left">
<html:text property="emailAddress" size="30" maxlength="30"/>
</td>
</tr>
<tr>
<td align="right">
<html:submit>Save</html:submit>
</td>
<td align="left">
<html:cancel>Cancel</html:cancel>
</td>
</tr>
</table>
</html:form>
</body>
</html:html>
User enter the values in the form and click on the submit form. Form validation is done on the server side and error message is displays on the jsp page. To display the error on the jsp page <html:errors/> tag is used. The <html:errors/> tag displays all the errors in one go. To create text box <html:text .../> is used in jsp page.
e.g.
<html:text property="address" size="30" maxlength="30"/>
Above tag creates text box for entering the address. The address is retrieved from and later stored in the property named address in the form-bean. The tag <html:submit>Save</html:submit> creates the submit button and the tag <html:cancel>Cancel</html:cancel> is used to create the Cancel button.
Add the following line in the index.jsp to create a link for testing the Address.jsp form:
<html:link page="/pages/Address.jsp">Test the Address Form</html:link>
Build the application and click on the Test the Address Form link on the index page to test the newly created screen. You should see the following screen.
In this lesson you learned how to create data entry form using struts, validate and finally send process the business logic in the model part of the struts.
Struts HTML Tags
Struts provides HTML tag library for easy creation of user interfaces. In this lesson I will show you what all Struts HTML Tags are available to the JSP for the development of user interfaces.
To use the Struts HTML Tags we have to include the following line in our JSP file:
<%@ taglib uri="/tags/struts-html" prefix="html" %>
above code makes available the tag to the jsp.
Struts HTML Tags
<html:message key="thekey"/>
Looks up the message corresponding to the given key in the message resources and displays it.
<html:password property="prop" size="10"/>
Tag creates the password field. The string is stored in the property named prop in the form bean.
<html:text property="text1" size="5"/>
Tag creates the text field. The string is retrieved from and later stored in the property named text1 in the form bean.
<html:submit>Submit</html:submit>
Tag creates a submit button with the%
The framework includes a set of custom tag libraries that facilitate in creating the user interfaces that can interact gracefully with ActionForm beans. The struts Jsp taglibs has a number of generic and struts specific tags tags which helps you to use dynamic data in your view. These tags helps us to interact with your controller without writing much java code inside your jsp. These tags are used create forms, internally forward to other pages by interacting with the bean and helps us to invoke other actions of the web application.
There are many tags provided to you in the struts frameworks which helps you in sending error messages, internationalization etc.