We will learn
annotations in struts 2 using the hello user example. In this example we will
get the user name and display a welcome message to the user. There are two
versions of this example, in the first one we will see how to do this by using
the intelligent defaults provided by the struts 2 framework. We will not do any
configuration in this example except the deployment descriptor.
The example is
created using ecilpse. The war file of this example is also provided at the end
of this tutorial so that you can try it yourself.
So lets start, you
need to have the following jar files in the WEB-INF/lib directory.
commons-fileupload-1
commons-io-2
commons-logging-1
freemarker-13
junit-1
ognl-11
spring-test-6
struts2-convention-plugin-6
struts2-core-6
xwork-2
You can definitely save a lot of time
by having the correct versions of these jar files in the lib directory. The struts2-convention-plugin-6 jar file is needed if your are using annotations.
This is the
directory structure of the hello user example.
Now we will create the index page.
This page is simple, we use the struts tags to create the page. Thetextfield tag is used to create the textfiled and the submit tag is used to create the submit button. The index.jsp page contains the
following code.
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC
"-//W3C//DTD HTML 01 Transitional//EN" "http://www.worg/TR/html4/loose.dtd">
<%@taglib
uri="/struts-tags" prefix="s" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Hello World</title>
</head>
<body>
<s:form action="welcome-user" >
<s:textfield name="userName" label="User Name" />
<s:submit />
</s:form>
</body>
</html>
Note the URL value
of the action attribute in the form tag. In the end we will see how everything
relates together.
We compose the welcome message in the execute()
method of the WelcomeUser class and we
return "success". The
WelcomeUser class contains the following code.
package com.vaannila.action;
import com.opensymphony.xworkActionSupport;
public class WelcomeUser extends ActionSupport{
private String
userName;
private String message;
public String
execute() {
message = "Welcome
" + userName;
return SUCCESS;
}
public void setUserName(String userName) {
this.userName = userName;
}
public void setMessage(String message) {
this.message = message;
}
public String
getUserName() {
return userName;
}
public String
getMessage() {
return message;
}
}
Note the class
name, can you find any similarities between the action URL and the class name?
if yes got the concept, if no don't worry you will learn what it is in the
coming pages.
We display the welcome message to the
user using the welcome-user.jsp page. The content of the page is very simple, we just display the
message. The important thing to note here is the name of the page.
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC
"-//W3C//DTD HTML 01 Transitional//EN" "http://www.worg/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<title>Welcome User</title>
</head>
<body>
<h1>${message}</h1>
</body>
</html>
Now we will
configure the web.xml for the struts 2 framework. We need to specify the filter
and the filter mapping here. Except this there is no need to have any other XML
configuration files.
<?xml version="0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.worg/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_xsd"xsi:schemaLocation="http://java.sun.com/xml/ns/javaeehttp://java.sun.com/xml/ns/javaee/web-app_2_xsd" id="WebApp_ID"version="5">
<display-name>Struts2Example1</display-name>
<filter>
<filter-name>struts2</filter-name>
<filter-class>
org.apache.strutsdispatcher.ng.filter.
StrutsPrepareAndExecuteFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
Now the coding part is complete. You
can run the example by using the following URL "http://localhost:8080/Struts2Example1/"
Enter a user name
and submit the form, you will see the following welcome-user.jsp page.
The example works
fine. Now lets see how the example works.
The Convention
plug-in is the one which does everything in
the background. The Convention plug-in does the following things.
·
By default the Convention plug-in
looks for the action classes inside the following packages strut, struts2, action or
actions. Here our package name is
com.vaannila.action. Any package that matches these names will be considered as the root
package for the Convention plug-in.
·
The action class should either
implement com.opensymphony.xworkAction interface or the name of the action class should end with Action. Here we extend our WelcomeUser class fromcom.opensymphony.xworkActionSupport which
inturn implements com.opensymphony.xworkAction.
·
The Convention plug-in uses the
action class name to map the action URL. Here our action class name is WelcomeUser and the URL is welcome-user. The plug-in converts the camel case class name to dashes to get the
request URL.
·
Now the Convention plug-in knows
which Action class to call for a particular request. The next step is to find
which result to forward based on the return value of the execute method. By
default the Convention plug-in will look for result pages in WEB-INF/content directory.
·
Now the Convention plug-in knows where
to look for results, but it doesn't know which file to display inside the
content directory. The Convention plug-in finds this with the help of the
result code returned by the Action class. If "success" is returned then the Convention plug-in will look for a file name welcome-user-success.jsp or welcome-user.jsp .
It need not be a jsp file it can be even a velocity or freemaker files. If the result value is "input" it will look for a file name welcome-user-input.jsp or
welcome-user-input.vm or welcome-user-input.ftl.
Download Struts 2 all examples source code
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