struts unit best pdf for struts java.pptx

FULL STACK DEVELOPMENT II
Prof. UMA BHARTI , Assistant Professor
IT & Computer Science

Data Science Overview
UNIT -4
Java Struts

What you learn in this unit ?
1. Introduction
2. Features
3. Example
4. Interceptors: custom, params,execAndWait, prepare, modelDriven, exception
, fileUpload ,value stack, Action Context, Action Invocation,
5. Components
6. Struts architecture
7. struts configuration
8. Struts Validation

1. Introduction
 Struts is an open-source web application framework developed by Apache Software
Foundation, it is used to create a web application based on servlet and JSP.
 It depends on the MVC (Model View Controller) framework.
 Struts are thoroughly useful in building J2EE (Java 2 Platform, Enterprise Edition) applications
because struts take advantage of J2EE design patterns.
 Struts follows these J2EE design patterns including MVC and JSP custom tag libraries. In struts,
the composite view manages the layout of its sub-views and can implement a template,
making persistent look and feel easier to achieve and customize across the entire application.
 A composite view is made up by using other reusable sub-views such that a small change that
happens in a sub-view is automatically updated in every composite view.
 Struts consist of a set of custom tag libraries. Struts also support utility classes.

1. Introduction
The main purpose of the struts framework is to
provision separation of concerns between the
business logic and the presentation logic (view),
making it easier to manage and develop large-
scale web applications.

Features of Struts
Struts have the following features:
•Struts encourages good design practices and modeling because the
framework is designed with “time-proven” design patterns.
•Struts is almost simple, so easy to learn and use.
•It supports many convenient features such as input validation and
internationalization.
•It takes much of the complexity out as instead of building your own MVC
framework, you can use struts.

Features of Struts
Struts have the following features:
•Struts is very well integrated with J2EE.
•Struts has large user community.
•It is flexible and extensible; it is easy for the existing web applications to adapt
the struts framework.
•Struts provide good tag libraries.
•It allows capturing input form data into JavaBean objects called Action forms.
•It also hands over standard error handling both programmatically and
declaratively.

STRUTS Example
Prerequisites:
 Before creating your Struts2 project it is important to make sure that you have the Apache Tomcat server
installed and configured with the Eclipse IDE.
• Create a dynamic web project and set it up with the struts2 framework. Refer to “
Create and Setup Struts2 Dynamic Web Application in Eclipse” for the same.
Now, if the above conditions are fulfilled and your web application is configured with the struts2 then follow
the steps given below.

STRUTS Example
Step by Step Implementation
1] web.xml file
Create a web.xml file under the webapp/WEB-INF folder and copy the following code in web.xml. This file is
created by default if you have checked the Generate web.xml deployment descriptor option at the time of
creating a dynamic web project. Now copy the following code in the web.xml file.

STRUTS Example
web.xml
file
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
id="WebApp_ID" version="4.0">
<display-name>Struts2 Hello World Example</display-name>
<welcome-file-list>
<welcome-file>login.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>

STRUTS Example
2] Result Pages
We need JSP pages to display the final
result, this page will be called by the
Struts 2 framework where a predefined
action will be called and this mapping is
defined in the struts.xml file. We are
using Struts 2 UI tags to create our JSP
pages. To create a JSP file, right-click on
the webapp folder in the project
explorer and select New >JSP File. Refer
to the below image

STRUTS Example
login.jsp file
A JSP login page to
display the username
and password input
fields and submit
button. Copy the
following code into
the login.jsp file.
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Login Page</title>
</head>
<body bgColor="lightBlue">
<s:form action="Welcome">
<s:textfield name="userName" label="User Name" />
<s:password name="password" label="Password" />
<s:submit value="Say Hello" />
</s:form>
</body>
</html>

STRUTS Example
welcome.jsp file
Create a welcome.jsp file
under the webapp folder.
This file displays a
welcome message to the
user. Copy the following
code into the file.
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Welcome Page</title>
</head>
<body>
<h2> Hello World Example in Struts 2</h2>
<h3> Hello <s:property value="userName"/> !!! </h3>
</body>
</html>

STRUTS Example
3] Action class: WelcomeAction.java
A Struts2 Action class is used to declare all
the business logic inside. Our application has
only one Action class whereas
our WelcomeAction class extends
ActionSupport class. It is good to extend
ActionSupport class as it provides a default
implementation for most common tasks.
Create a WelcomeAction.java file and Copy
the following code into the file.
package com.GeeksforGeeks.struts2;
import com.opensymphony.xwork2.ActionSupport;
public class WelcomeAction extends ActionSupport {
// Java bean to hold the form parameters
private String userName;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
// All struts logic goes here
public String execute() {
return SUCCESS;
}
}

STRUTS Example
4] Struts configuration file: struts.xml
We need a mapping between URL to
action mapping. The struts.xml maps
the WelcomeAction class, and
the welcome.jsp together. The
mapping tells the Struts 2 framework
which class will respond to the user’s
action (the URL), which method of
that class will be executed, and what
view to render based on the String
result that method returns. So we will
now create a struts.xml file under
the src/main/java folder. Copy the
following code into struts.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.custom.i18n.resources" value="WelcomeAction" />
<package name="default" extends="struts-default" namespace="/">
<action name="Welcome"
class="com.GeeksforGeeks.struts2.WelcomeAction" >
<result name="success">welcome.jsp</result>
<result name="input">login.jsp</result>
</action>
</package>
</struts>

STRUTS Example
Your project structure should now look like this:

STRUTS Example
5] Run your application
To run your application in
Eclipse: Right-click on
project -> run as -> run on
server

STRUTS Example
After you enter the
username and
password you’ll get the
following screen:

STRUTS Example
Output:
When we run our application,
you will see a web page opened
on your Eclipse IDE like this:

INTERCEPATOR
Interceptor is an object that is invoked at the
preprocessing and postprocessing of a request. In Struts
2, interceptor is used to perform operations such as
validation, exception handling, internationalization,
displaying intermediate result etc.

A
ADVANTGE OF INTERCEPATOR
8) clearSession It unbinds the HttpSession object.
9) debugging It provides support of debugging.
10) externalRef
11) execAndWait It sends an intermediate waiting page for the result.
12) exception It maps exception to a result.
13) fileUpload It provides support to file upload in struts 2.
14) i18n It provides support to internationalization and localization.

A
15) jsonValidation It provides support to asynchronous validation.
16) logger It outputs the action name.
17) store It stores and retrieves action messages, action errors or field errors for action that
implements ValidationAware interface.
18) modelDriven It makes other model object as the default object of valuestack.
19) scopedModelDriven It is similar to ModelDriven but works for action that implements ScopedModelDriven.
20) params It populates the action properties with the request parameters.
21) actionMappingParams
22) prepare It performs preparation logic if action implements Preparable interface.
23) profiling It supports action profiling.
24) roles It supports role-based action.
25) scope It is used to store the action state in the session or application scope.

A
26) servletConfig It provides access to maps representing HttpServletRequest and
HttpServletResponse.
27) sessionAutowiring
28) staticParams It maps static properties to action properties.
29) timer It outputs the time needed to execute an action.
30) token It prevents duplication submission of request.
31) tokenSession It prevents duplication submission of request.
32) validation It provides support to input validation.
33) workflow It calls the validate method of action class if action class implements Validateable
interface.
34) annotationWorkflow
35) multiselect

Custom Interceptor
In struts 2, we can create the custom interceptor by implementing the Interceptor
interface in a class and overriding its three life cycle method.
For creating the custom interceptor, Interceptor interface must be implemented. It has
three methods:
1. public void init() It is invoked only once and used to initialize the interceptor.
2. public String intercept(ActionInvocation ai) It is invoked at each request, it is used to
define the request processing logic. If it returns string, result page will be invoked, if
it returns invoke() method of ActionInvocation interface, next interceptor or action
will be invoked.
3. public void destroy() It is invoked only once and used to destroy the interceptor.

Example to create Custom Interceptor
In this example, we are going to create custom interceptor that converts
request processing data into uppercase letter.
You need to follow 2 steps to create custom interceptor
1. Create an interceptor (must implement Interceptor interface)
2. Define the entry of interceptor in the struts.xml file
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1) Create an interceptor (must implement Interceptor interface)
By this interceptor, we are converting the name property of action
class into uppercase letter.
The getStack() method of ActionInvocation returns the reference of
ValueStack.
We are getting the value set in the name property
by findString method of ValueStack.
The set method of ValueStack sets the name property by the
specified value. In such case, we are converting the value of name
property into uppercase letter and storing it into the valuestack.
The invoke method of ActionInvocation returns the information of
next resource.

MyInterceptor.java
1.package com;
2.import com.opensymphony.xwork2.ActionInvocation;
3.import com.opensymphony.xwork2.interceptor.Interceptor;
4.import com.opensymphony.xwork2.util.ValueStack;
5.
6.public class MyInterceptor implements Interceptor{
7.
8. public void init() {}
9. public String intercept(ActionInvocation ai) throws Except
ion {
10. ValueStack stack=ai.getStack();
11. String s=stack.findString("name");
12.
13. stack.set("name",s.toUpperCase());
14. return ai.invoke();
15. }
16. public void destroy() {}
17.}

2) Define the entry of interceptor in the struts.xml file
To define the interceptor, we need to declare an interceptor first. The interceptors element of
package is used to specify interceptors. The interceptor element of interceptors is used to
define the custom interceptor. Here, we are defining the custom interceptor by upper.
The interceptor-ref subelement of action specifies the interceptor that
will be applied for this action. Here, we are specifying the defaultstack
interceptors and upper interceptor.

struts.xml
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts
Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>
<package name="abc" extends="struts-default">
<interceptors>
<interceptor name="upper" class="com.MyInterceptor"></interceptor>
</interceptors>
<action name="login" class="com.Login">
<interceptor-ref name="defaultStack"></interceptor-ref>
<interceptor-ref name="upper"></interceptor-ref>
<result>welcome.jsp</result>
</action>
</package>
</struts>

Other Required Resources
The other required resources are
index.jsp
Login.java
welcome.jsp

1) Create form to get input (index.jsp)
index.jsp
This jsp page creates a form using struts UI tags. It receives name from the user.
<%@ taglib uri="/struts-tags" prefix="s" %>
<s:form action="login">
<s:textfield name="name" label="Name"></s:textfield>
<s:submit value="login"></s:submit>
</s:form>

2) Create the action class
It is the simple action class
containing name property with
its setter and getter methods.
Login.java
package com;
public class Login {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String execute(){
return "success";
}
}

3) Create view component
This jsp page displays the name input by the user.
welcome.jsp
Welcome, <s:property value="name"/>

Params Interceptor
The params interceptor also known as parameters interceptor is used to set
all parameters on the valuestack.
It is found in the default stack bydefault. So you don't need to specify it
explicitely.
Internal working of params interceptor
It gets all parameters by calling the getParameters() method of
ActionContext and sets it on the valuestack by calling the setValue()
method of ValueStack.
Parameters of params interceptor

There are 4 parameters defined for params interceptor.
Parameter Description
ordered It is true bydefault but can be used to
top-down the property setter
behaviour.
paramNameMaxLength specifies the maximum length for the
parameter. The default length is 100
characters bydefault. The parameters
length more that 100 will be ignored.
excludeParams specifies the unallowed parameter
names. You can specify multiple
names separated with comma.
acceptParamNames specifies the accepted parameter
names.

Example of params interceptor
<action name="login" class="com.javatpoint.Login">
<interceptor-ref name="params"/>
<result name="success">login-success.jsp</result>
</action>

Struts 2 defaultStack interceptors
The params
interceptor is found
in the default stack.
You don't need to
specify interceptors
found in the default-
stack. The
defaultStack
interceptors are as
follows:
<interceptor-stack name="defaultStack">
<interceptor-ref name="exception"/>
<interceptor-ref name="alias"/>
<interceptor-ref name="servletConfig"/>
<interceptor-ref name="prepare"/>
<interceptor-ref name="i18n"/>
<interceptor-ref name="chain"/>
<interceptor-ref name="debugging"/>
<interceptor-ref name="profiling"/>
<interceptor-ref name="scopedModelDriven"/>
<interceptor-ref name="modelDriven"/>
<interceptor-ref name="fileUpload"/>
<interceptor-ref name="checkbox"/>
<interceptor-ref name="staticParams"/>
<interceptor-ref name="actionMappingParams"/>
<interceptor-ref name="params">
<param name="excludeParams">dojo..*,^struts..*</param>
</interceptor-ref>
<interceptor-ref name="conversionError"/>
<interceptor-ref name="validation">
<param name="excludeMethods">input,back,cancel,browse</param>
</interceptor-ref>
<interceptor-ref name="workflow">
<param name="excludeMethods">input,back,cancel,browse</param>
</interceptor-ref>
</interceptor-stack>

execAndWait interceptor
The execAndWait interceptor also known as execute and wait interceptor is used to display the intermediate
result.
It is recommended to use for long running action.
It is not found in the default stack bydefault. So you need to specify it explicitely.
If you don't specify "wait" result, struts framework displays an intermediate result until your request is
completed. For the custom intermediate result, you need to define "wait" result in struts.xml file. In your page,
you can display processing image etc. So, it is better to specify the custom result.
Parameters of execAndWait interceptor

There are 3 parameters defined for execAndWait interceptor
delay specifies the initial delay time.
Bydefault, no initial delay is set.
delaySleepInterval used only with delay. It specifies the
time interval in milliseconds to check
that background process is
completed. It is set to 100
milliseconds bydefault.
threadPriority specifies the priority of the thread.
The default is
Thread.NORM_PRIORITY.

Example of execAndWait interceptor without wait result
<interceptor-ref name="execAndWait"/>
</action>

Example of execAndWait interceptor with wait result
<interceptor-ref name="execAndWait"/>
<result name="wait">myintermediatepage.jsp</result>
</action>

myintermediatepage.jsp
Let's write the code for intermediate result. The s:url tag will forward the request to specified url.
<html>
<head>
<title>wait</title>
<meta http-equiv="refresh" content="0.5;url='<s:url includeParams="all" />'">
</head>
<body>
<p>your request is processing...</p>
<img src="processing.gif"/>
</body>
</html>

Output
It will be refreshed at 0.5
seconds.

Prepare Interceptor
The prepare interceptor calls prepre()
method on the action if it
implements Preparable interface. It calls
prepare() method before the execute()
method.
To use the prepare interceptor, you need to
implement Preparable interface in your
action class and override its method
prepare.
It is found in the default stack bydefault. So
you don't need to specify it explicitely.
Parameters of prepare interceptor
There is only 1 parameter defined for prepare
interceptor.
alwaysInvokePrepare It is set to true bydefault.

Example of prepare interceptor
<action name="login" class="com.javatpoint.LoginAction">
<interceptor-ref name="prepare"/>
</action>

Action class
package com.javatpoint;
import com.opensymphony.xwork2.Preparable;
public class LoginAction implements Preparable{
private String name,password;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public void prepare() throws Exception {
System.out.println("preparation logic");
}
System.out.println("actual logic");
return "success";
}
}

ModelDriven Interceptor
The modelDriven interceptor makes other model object as the
default object of valuestack.
Bydefault, action object is the default object of valuestack.
To use the modelDriven interceptor, you need to
implement ModelDriven interface in your action class and
override its method getModel().
It is found in the default stack bydefault. So you don't need to
specify it explicitely.

Example of modelDriven interceptor
<action name="login" class="com.javatpoint.LoginAction">
<interceptor-ref name="modelDriven"/>
</action>

Full example of modelDriven interceptor
File: index.jsp
<s:password name="password" label="Password"></s:password>
</s:form>

File: struts.xml
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//
EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>
<package name="abc" extends="struts-default" >
<result name="success" >/login-success.jsp</result>
<result name="error">/login-error.jsp</result>
</action>
</package>
</struts>

File: Login.java package com.javatpoint;
import com.opensymphony.xwork2.ModelDriven;
public class Login implements ModelDriven<User>{
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public User getModel(){
user=new User();
return user;
}
if(user.getPassword().equals("admin")){
return "success";
}
else{
return "error";
}
}
}

File: User.java
public class User {
//getters and setters
}
File: login-success.jsp
Welcome, <s:property value="name"/>

File: login-error.jsp
Sorry, username or password error!
<jsp:include page="index.jsp"></jsp:include>

Exception Handling
• In our web application, there might occur exception at any point.
To overcome this problem, struts 2 provides a mechanism of global exception handling where we
can display a global result to the user.
Struts 2 automatically log the uncaught exceptions and redirects the user to the error handler page.
Understanding the internal working of exception
interceptor
If there occurs exception, it is wrapped in ExceptionHolder and pushed in
the valuestack so that we can easily access exception object from the
result.

There are 3 parameters defined for exception interceptor. All are optional.
logEnabled specifies log should be enabled or
not. You can pass true or false.
logLevel specifies the log level. It may be
trace, debug, info, warn, error, fatal.
Default log level is debug.
logCategory specifies the log category eg.
com.mycompany.app. The default is
com.opensymphony.xwork2.intercept
or.ExceptionMappingInterceptor..

Example of exception handling in struts 2
struts.xml <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts
Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>
<package name="aa" extends="struts-default">
<global-results>
<result name="myresult">globalresult.jsp</result>
</global-results>
<global-exception-mappings>
<exception-mapping result="myresult" exception="java.lang.Exception"></exception-mapping>
</global-exception-mappings>
<action name="login" class="com.Login">
<result>welcome.jsp</result>
<result name="error">error.jsp</result>
</action>
</package>
</struts>

The global-results sub-element of package specifies the global-result for this
package.
The result sub-element of global-result specifies the result page that will be
rendered to the user as a view.
The global-exception-mappings sub-element of package specifies the exception
mapping for all the actions of this package.
The exception-mapping sub-element of global-exception-mapping maps the given
result for the given exception type. In this example, we are using the Exception
which the parent of many exception classes such as IOException,
ArithmeticException etc. It means if any exception occurs, specified result will be
invoked.

globalresult.jsp
<p>Exception Name: <s:property value="exception" /> </p>
<p>Exception Details: <s:property value="exceptionStack" /></p>
Full example of exception handling
The other required resources to complete this example are as follows:
• Input page (index.jsp)
• Action class (Login.java)
• View components (globalresult.jsp, welcome.jsp and error.jsp)

1) Create index.jsp for
input
<s:password name="password" label="Password"></s:password>
</s:form>
Login.java
package com;
public class Login {
//getters and setters
if(password.equals("struts")){
int a=12/0;//If you comment this, exception will not occur
return "success";
}else
return "error";
}

3) Create view components
There are three view components globalresult.jsp that displays the exception
message, welcome.jsp that displays the welcome message with the username
and error.jsp that displays the error message.
globalresult.jsp
1.<%@ taglib uri="/struts-tags" prefix="s" %>
2.
3.Sorry an exception occured!
4.<p>Exception Name: <s:property value="exception" /> </p>
5.<p>Exception Details: <s:property value="exceptionStack" /></p>
6.<form>
7.<input type="button" value="back" onclick="history.back()">
8.</form>
welcome.jsp
1.<%@ taglib uri="/struts-tags" prefix="s" %>
2.Welcome, <s:property value="name"/>
error.jsp
Sorry username or password error!
<jsp:include page="index.jsp"></jsp:include>

File Upload
The fileUpload interceptor automatically works for all the requests that includes files.
We can use this interceptor to control the working of file upload in struts2 such as defining allowed types,
maximum file size etc.
There are 2 parameters defined for fileupload interceptor.
maximumSize specifies maximum size of the
file to be uploaded.
allowedTypes specifies allowed types. It may
be image/png, image/jpg etc

It automatically adds 2 parameters in the request
:
String fileName represents the filename of the file.
String contentType specifies the content type of the file.

1) Create UserImage.jsp
index.jsp <%@ page contentType="text/html; charset=UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags"%>
<html>
<head>
<title>Upload User Image</title>
</head>
<body>
<h2>
Struts2 File Upload & Save Example without Database
</h2>
<s:actionerror />
<s:form action="userImage" method="post" enctype="multipart
/form-data">
<s:file name="userImage" label="Image" />
<s:submit value="Upload" align="center" />
</s:form>
</body>
</html>

2) Create SuccessUserImage.jsp
SuccessUserImage.jsp
<%@ page contentType="text/html; charset=UTF-8"%><%@ taglib prefix="s"
uri="/struts-tags"%>
<html>
<head>
<title>Success: Upload User Image</title>
</head>
<body>
<h2>
Struts2 File Upload Example
</h2>
User Image: <s:property value="userImage" /><br/>
Content Type:<s:property value="userImageContentType" /><br/>
File Name: <s:property value="userImageFileName" /><br/>
Uploaded Image: <img src="userimages/
<s:property value="userImageFileName"/>"
width="100" height="100" />

RegisterAction.java
import java.io.File;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.io.FileUtils;
import com.opensymphony.xwork2.ActionSupport;
public class FileUploadAction extends ActionSupport{
private File userImage;
private String userImageContentType;
private String userImageFileName;
public String execute() {
try {
String filePath = ServletActionContext.getServletContext().getRealPath("/").concat("userimages");
System.out.println("Image Location:" + filePath);//see the server console for actual location
File fileToCreate = new File(filePath,userImageFileName);
FileUtils.copyFile(userImage, fileToCreate);//copying source file to new file
return SUCCESS;
}
public File getUserImage() {
return userImage;
}
public void setUserImage(File userImage) {
this.userImage = userImage;
}
public String getUserImageContentType() {
return userImageContentType;
}
public void setUserImageContentType(String userImageContentType) {
this.userImageContentType = userImageContentType;
}
public String getUserImageFileName() {
return userImageFileName;
}
public void setUserImageFileName(String userImageFileName) {
this.userImageFileName = userImageFileName;
}

4) Create struts.xml
struts.xml
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<package name="fileUploadPackage" extends="struts-default">
<action name="userImage" class="com.javatpoint.FileUploadAction">
<interceptor-ref name="fileUpload">
<param name="maximumSize">2097152</param>
<param name="allowedTypes">
image/png,image/gif,image/jpeg,image/pjpeg
</param>
</interceptor-ref>
<interceptor-ref name="defaultStack"></interceptor-ref>
<result name="success">SuccessUserImage.jsp</result>
<result name="input">UserImage.jsp</result>
</action>
</package>

ActionContext
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.getContex
t();
A valueStack is simply a stack that contains application specific
objects such as action objects and other model object.
At the execution time, action is placed on the top of the stack.
We can put objects in the valuestack, query it and delete it.

ActionInvocation
ActionInvocation represen
ts the execution state of
an action. It holds the
action and interceptors
objects.
ActionInvocation Interface
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
No. Method Description
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 Architecture
The architecture and flow of struts 2 application,
is combined with many components such as
Controller, ActionProxy, ActionMapper,
Configuration Manager, ActionInvocation,
Inerceptor, Action, Result etc.
Here, we are going to understand the struts flow
by 2 ways:
struts 2 basic flow
struts 2 standard architecture and flow provided
by apache struts
Struts 2 basic flow
User sends a request for the action
Controller invokes the ActionInvocation
ActionInvocation invokes each interceptors and action
A result is generated
The result is sent back to the ActionInvocation
A HttpServletResponse is generated
Response is sent to the user

Struts standard flow (Struts architecture)
User sends a request for the action
Container maps the request in the web.xml file and gets the class
name of controller.
Container invokes the controller (StrutsPrepareAndExecuteFilter
or FilterDispatcher). Since struts2.1, it is
StrutsPrepareAndExecuteFilter. Before 2.1 it was FilterDispatcher.
Controller gets the information for the action from the
ActionMapper
Controller invokes the ActionProxy
ActionProxy gets the information of action and interceptor stack
from the configuration manager which gets the information from
the struts.xml file.
ActionProxy forwards the request to the ActionInvocation
ActionInvocation invokes each interceptors and action
A result is generated
The result is sent back to the ActionInvocation
A HttpServletResponse is generated

Configuration Files
From a Struts developer point of view,
the one required configuration file used
by the framework is web.xml.
From here, you have full control over
how Struts configures both itself and
your application. By default, Struts will
load a set of internal configuration files
to configure itself, then another set to
configure your application, however it
is possible to build an entire Struts
application without writing a single
configuration file other than web.xml.
The table lists the files that you can use
to configure the framework for your
application. Some configuration files
can be reloaded dynamically. Dynamic
reloading makes interactive
File Optional Location (relative to webapp) Purpose
web.xml no /WEB-INF/
Web deployment descriptor to
include all necessary
framework components
struts.xml yes /WEB-INF/classes/
Main configuration, contains
result/view types, action
mappings, interceptors, and so
forth
default.properties yes /WEB-INF/classes/ Framework properties
struts-default.xml yes /WEB-INF/lib/struts2-core.jar Default configuration provided
by Struts
struts-default.vm yes /WEB-INF/classes/ Default macros referenced by
velocity.properties
struts-plugin.xml yes At the root of a plugin JAR
Optional configuration files for
Plugins in the same format as
struts.xml.
struts-deferred.xml yes At the root of a plugin JAR
Optional configuration files for
Plugins, most useful for
defining extension points
velocity.properties yes /WEB-INF/classes/ Override the
default Velocity configuration

Struts 2 Validation
To avoid the wrong values, we need to perform validation on forms where user
submits some values. For example, if user writes his/her email id as abc, we need to
give error message to the user that the given email id is not correct. So that we can
have only valuable informations.
There are three ways to perform validation in struts 2.
1) By Custom Validation Here, we must implement the Validateable interface (or
extend ActionSupport class) and provide the implementation of validate method.
2) By Input Validation (built-in validators) Struts 2 provides a lot of predefined that
can be used in struts 2 application to perform validation.

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