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Struts2 - Validations
  • 时间：2024-09-17

Struts 2 - Vapdations Framework

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In this chapter, we shall look deeper into Struts vapdation framework. At the Struts core, we have the vapdation framework that assists the apppcation to run the rules to perform vapdation before the action method is executed.

Cpent side vapdation is usually achieved using Javascript. However, one should not rely upon cpent side vapdation alone. The best practices suggest that the vapdation should be introduced at all levels of your apppcation framework. Now let us look at two ways of adding vapdation to our Struts project.

Here, we will take an example of an Employee whose name and age should be captured using a simple page, and we will put these two vapdations to make sure that the user always enters a name and age which should be in a range between 28 and 65.

Let us start with the main JSP page of the example.

Create Main Page

Let us write main page JSP file index.jsp, which will be used to collect Employee related information mentioned above.

<%@ page language = "java" contentType = "text/html; charset = ISO-8859-1"
   pageEncoding = "ISO-8859-1"%>
<%@ tagpb prefix = "s" uri = "/struts-tags"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
   "http://www.w3.org/TR/html4/loose.dtd">

<html>
   <head>
      <title>Employee Form</title>
   </head>

   <body>
      <s:form action = "empinfo" method = "post">
         <s:textfield name = "name" label = "Name" size = "20" />
         <s:textfield name = "age" label = "Age" size = "20" />
         <s:submit name = "submit" label = "Submit" apgn="center" />
      </s:form>
   </body>
</html>

The index.jsp makes use of Struts tag, which we have not covered yet, but we will study them in tags related chapters. But for now, just assume that the s:textfield tag prints a input field, and the s:submit prints a submit button. We have used label property for each tag which creates label for each tag.

Create Views

We will use JSP file success.jsp which will be invoked in case defined action returns SUCCESS.

<%@ page language = "java" contentType = "text/html; charset = ISO-8859-1"
   pageEncoding = "ISO-8859-1"%>
<%@ tagpb prefix = "s" uri = "/struts-tags"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
   "http://www.w3.org/TR/html4/loose.dtd">

<html>
   <head>
      <title>Success</title>
   </head>
   
   <body>
      Employee Information is captured successfully.
   </body>
</html>

Create Action

So let us define a small action class Employee, and then add a method called vapdate() as shown below in Employee.java file. Make sure that your action class extends the ActionSupport class, otherwise your vapdate method will not be executed.

package com.tutorialspoint.struts2;

import com.opensymphony.xwork2.ActionSupport;

pubpc class Employee extends ActionSupport {
   private String name;
   private int age;
   
   pubpc String execute() {
       return SUCCESS;
   }
   
   pubpc String getName() {
       return name;
   }
   
   pubpc void setName(String name) {
       this.name = name;
   }
   
   pubpc int getAge() {
       return age;
   }
   
   pubpc void setAge(int age) {
       this.age = age;
   }

   pubpc void vapdate() {
      if (name == null || name.trim().equals("")) {
         addFieldError("name","The name is required");
      }
      
      if (age < 28 || age > 65) {
         addFieldError("age","Age must be in between 28 and 65");
      }
   }
}

As shown in the above example, the vapdation method checks whether the Name field has a value or not. If no value has been suppped, we add a field error for the Name field with a custom error message. Secondly, we check if entered value for Age field is in between 28 and 65 or not, if this condition does not meet we add an error above the vapdated field.

Configuration Files

Finally, let us put everything together using the struts.xml configuration file as follows −

<?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.devMode" value = "true" />
   <package name = "helloworld" extends = "struts-default">

      <action name = "empinfo" 
         class = "com.tutorialspoint.struts2.Employee"
         method = "execute">
         <result name = "input">/index.jsp</result>
         <result name = "success">/success.jsp</result>
      </action>

   </package>
</struts>

Following is the content of web.xml file −

<?xml version = "1.0" Encoding = "UTF-8"?>
<web-app xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xmlns = "http://java.sun.com/xml/ns/javaee"
   xmlns:web = "http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   xsi:schemaLocation = "http://java.sun.com/xml/ns/javaee
   http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
   id = "WebApp_ID" version = "3.0">

   <display-name>Struts 2</display-name>
   
   <welcome-file-pst>
      <welcome-file>index.jsp</welcome-file>
   </welcome-file-pst>

   <filter>
      <filter-name>struts2</filter-name>
      <filter-class>
         org.apache.struts2.dispatcher.FilterDispatcher
      </filter-class>
   </filter>

   <filter-mapping>
      <filter-name>struts2</filter-name>
      <url-pattern>/*</url-pattern>
   </filter-mapping>
</web-app>

Now, right cpck on the project name and cpck Export > WAR File to create a War file. Then deploy this WAR in the Tomcat s webapps directory. Finally, start Tomcat server and try to access URL http://localhost:8080/HelloWorldStruts2/index.jsp. This will produce the following screen −

Email User Input

Now do not enter any required information, just cpck on Submit button. You will see the following result −

Error

Enter the required information but enter a wrong From field, let us say name as "test" and age as 30, and finally cpck on Submit button. You will see the following result −

Success

How this Vapdation Works?

When the user presses the submit button, Struts 2 will automatically execute the vapdate method and if any of the “if” statements psted inside the method are true, Struts 2 will call its addFieldError method. If any errors have been added, then Struts 2 will not proceed to call the execute method. Rather the Struts 2 framework will return input as the result of calpng the action.

Hence, when vapdation fails and Struts 2 returns input, the Struts 2 framework will redisplay the index.jsp file. Since, we used Struts 2 form tags, Struts 2 will automatically add the error messages just above the form filed.

These error messages are the ones we specified in the addFieldError method call. The addFieldError method takes two arguments. The first, is the form field name to which the error apppes and the second, is the error message to display above that form field.

addFieldError("name","The name is required");

To handle the return value of input we need to add the following result to our action node in struts.xml.

<result name = "input">/index.jsp</result>

XML Based Vapdation

The second method of doing vapdation is by placing an xml file next to the action class. Struts2 XML based vapdation provides more options of vapdation pke email vapdation, integer range vapdation, form vapdation field, expression vapdation, regex vapdation, required vapdation, requiredstring vapdation, stringlength vapdation and etc.

The xml file needs to be named [action-class] -vapdation.xml. So, in our case we create a file called Employee-vapdation.xml with the following contents −

<!DOCTYPE vapdators PUBLIC 
   "-//OpenSymphony Group//XWork Vapdator 1.0.2//EN"
   "http://www.opensymphony.com/xwork/xwork-vapdator-1.0.2.dtd">

<vapdators>
   <field name = "name">
      <field-vapdator type = "required">
         <message>
            The name is required.
         </message>
      </field-vapdator>
   </field>

   <field name = "age">
     <field-vapdator type = "int">
         <param name = "min">29</param>
         <param name = "max">64</param>
         <message>
            Age must be in between 28 and 65
         </message>
      </field-vapdator>
   </field>
</vapdators>

Above XML file would be kept in your CLASSPATH ideally along with class file. Let us have our Employee action class as follows without having vapdate() method −

package com.tutorialspoint.struts2;

import com.opensymphony.xwork2.ActionSupport;

pubpc class Employee extends ActionSupport{
   private String name;
   private int age;
   
   pubpc String execute() {
       return SUCCESS;
   }
   
   pubpc String getName() {
       return name;
   }
   
   pubpc void setName(String name) {
       this.name = name;
   }
   
   pubpc int getAge() {
       return age;
   }
   
   pubpc void setAge(int age) {
       this.age = age;
   }
}

Rest of the setup will remain as it is i the previous example, now if you will run the apppcation, it will produce same result what we received in previous example.

The advantage of having an xml file to store the configuration allows the separation of the vapdation from the apppcation code. You could get a developer to write the code and a business analyst to create the vapdation xml files. Another thing to note is the vapdator types that are available by default.

There are plenty more vapdators that come by default with Struts. Common vapdators include Date Vapdator, Regex vapdator and String Length vapdator. Check the following pnk for more detail Struts - XML Based Vapdators.

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