Red n' Black: Login application, using Spring MVC

This article builds on ??. We will be using Spring MVC to create a simple form. The data filled in the form will be sent to the model. The model ??. We will not do form validation.

fold

Table of Contents

The spring tag library.

Get the spring.tld from spring download and put it in \WEB-INF\tlds.
Update the web.xml to use this tld

\WEB-INF\web.xml

...
    <taglib>
        <taglib-uri>/spring</taglib-uri>
        <taglib-location>/WEB-INF/spring.tld</taglib-location>
    </taglib>
...

The view.

Command object.

The command object is bound to the input tag in the form on the front end.
The command object is passed to the validator.
If the validator passes the command object it is passed to the controller.
If the validator does not pass the command object, ??.

package com.check.spring.mvc;
 
public class LoginCredentials {
    private String Username;
    private String Password;
    public String getPassword() {
        return Password;
    }
    public void setPassword(String password) {
        Password = password;
    }
    public String getUsername() {
        return Username;
    }
    public void setUsername(String username) {
        Username = username;
    } 
}

Validator object.

Implements the Validator object of spring framework.
Validator class gets control after the submit on the form.
A validate() method of the object is called with the command object and errors object as parameter.
What does this supports() do ??

package com.check.spring.mvc;
 
import org.springframework.validation.Errors;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;
 
public class LoginCredentialsValidator implements Validator {
 
    LoginCredentials loginCredentials;
 
    @Override
    public boolean supports(Class clazz) {
        return LoginCredentials.class.isAssignableFrom(clazz);
    }
 
    @Override
    public void validate(Object commandObject, Errors errors) {
 
        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "userName",
                "Field is required.");
        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "password",
                "Field is required.");
 
        loginCredentials = (LoginCredentials) commandObject;
 
        if ((loginCredentials.getPassword() != "password")&&
            (loginCredentials.getUsername() != "partha")){
            errors.reject("Credentials provided are not correct.");
        }
    }
}

\WEB-INF\dispatcher-servlet.xml

...
    <bean id="LoginCredentialsValidator"
        class="com.check.spring.mvc.LoginCredentialsValidator" />
...

LoginFormController

Extends the SimpleFormController class.
The onSubmit method gets control.
What is the formBackingObject?? doing?

Step1 : Getting a useless Login form shown in the webpage.

Create the basic JSP.

It does not do anything.
There is no action associated with it.
CheckSpringMVC101\WEB-INF\jsp\loginForm.jsp

<html>
<head><title>Login please.</title></head>
<body>
<table>
<tr><td>Username:</td><td><input type="text" name="username" /></td></tr>
<tr><td>Password:</td><td><input type="password" name="password" /></td></tr>
<tr><td colspan=2><input type="submit" /></td></tr>
</table>
</body>
</html>

Create an almost empty SimpleFormController.

CheckSpringMVC101\WEB-INF\src\com\check\spring\mvc\login\LoginFormController.java

package com.check.spring.mvc.login;
 
import org.springframework.web.servlet.mvc.SimpleFormController;
 
public class LoginFormController extends SimpleFormController {
}

Create a POJO command object.

There is simply nothing here.
However the command object is required for the SimpleFormController.
CheckSpringMVC101\WEB-INF\src\com\check\spring\mvc\login\LoginCredentials.java

package com.check.spring.mvc.login;
 
public class LoginCredentials {
}

Tie the view, controller and the command object.

CheckSpringMVC101\WEB-INF\dispatcher-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" 
"http://www.springframework.org/dtd/spring-beans.dtd">
 
<beans>
 
    <bean id="Login"
        class="com.check.spring.mvc.login.LoginFormController">
        <property name="sessionForm">
            <value>true</value>
        </property>
        <property name="commandName">
            <value>credentials</value>
        </property>
        <property name="commandClass">
            <value>com.check.spring.mvc.login.LoginCredentials</value>
        </property>
        <property name="formView">
            <value>/WEB-INF/jsp/loginForm.jsp</value>
        </property>
    </bean>
 
    <bean id="urlMapping"
        class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="urlMap">
            <map>
                <entry key="/login.do">
                    <ref bean="Login" />
                </entry>
            </map>
        </property>
    </bean>
 
</beans>

Run the application.

Stop Tomcat. Start Tomcat.
Hit http://localhost:8080/CheckSpringMVC101/login.do.

Step 2: Create command object, bind that with the view and receive data in controller.

Get the spring tld.

Fetch the spring.tld from Spring download and put it in CheckSpringMVC101\WEB-INF\tlds.
Update the web.xml to use the tld.
CheckSpringMVC101\WEB-INF\web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC '-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN'
 'http://java.sun.com/dtd/web-app_2_3.dtd'>
 
<web-app>
 
    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>*.do</url-pattern>
    </servlet-mapping>
 
    <taglib>
        <taglib-uri>/spring</taglib-uri>
        <taglib-location>/WEB-INF/tlds/spring.tld</taglib-location>
    </taglib>
 
</web-app>

Tie the view with command object.

Import the spring taglib.
Create a form in the JSP with method post.
Use the <spring:bind> tag to bind input elements inside form to the command object properties.
CheckSpringMVC101\WEB-INF\jsp\loginForm.jsp

<%@ taglib prefix="spring" uri="/spring" %>
 
<html>
 
<head><title>Login please.</title></head>
<body>
<form method="post">
<table>
<tr><td>Username:</td>
<spring:bind path="credentials.username">
<td><input type="text" name="username" /></td>
</spring:bind>
</tr>
<tr><td>Password:</td>
<spring:bind path="credentials.password">
<td><input type="password" name="password" /></td>
</spring:bind>
</tr>
<tr><td colspan=2><input type="submit" /></td></tr>
</table>
</form>
</body>
</html>

Update the command object to be able to handle form data.

Create the POJO like methods and variables.
CheckSpringMVC101\WEB-INF\src\com\check\spring\mvc\login\LoginCredentials.java

package com.check.spring.mvc.login;
 
public class LoginCredentials {
    private String username; 
    private String password;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    } 
}

Update the controller to read data from the command object.

Override the onSubmit method to get access to the command object.
At this point we are simply reading the attributes of the command object and not doing anything with them.
CheckSpringMVC101\WEB-INF\src\com\check\spring\mvc\login\LoginFormController.java

package com.check.spring.mvc.login;
 
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.SimpleFormController;
 
public class LoginFormController extends SimpleFormController {
 
    @Override
    protected ModelAndView onSubmit(Object command) throws Exception {
        LoginCredentials credentials = (LoginCredentials) command;
        System.out.println("Username: " + credentials.getUsername());
        System.out.println("Password: " + credentials.getPassword());
        return super.onSubmit(command);
    }
}

Run the application.

Stop Tomcat. Start Tomcat.
Hit http://localhost:8080/CheckSpringMVC101/login.do.
Fill in the values and hit submit.
There should be error on the browser but on the Tomcat console, the values that were provided in the form must be shown.

Step 3: Create a model using the command object and then surface the data in view.

Create a model in controller.

Tie together the view and the model.

Create a view which can fetch data from the controller.

Run the application.

Stop Tomcat. Start Tomcat.
Hit http://localhost:8080/CheckSpringMVC101/login.do.

Page tags: spring

page_revision: 20, last_edited: 1197043515|%e %b %Y, %H:%M %Z (%O ago)

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Red n' Black

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The spring tag library.

The view.

Command object.

Validator object.

LoginFormController

Step1 : Getting a useless Login form shown in the webpage.

Create the basic JSP.

Create an almost empty SimpleFormController.

Create a POJO command object.

Tie the view, controller and the command object.

Run the application.

Step 2: Create command object, bind that with the view and receive data in controller.

Get the spring tld.

Tie the view with command object.

Update the command object to be able to handle form data.

Update the controller to read data from the command object.

Run the application.

Step 3: Create a model using the command object and then surface the data in view.

Create a model in controller.

Tie together the view and the model.

Create a view which can fetch data from the controller.

Run the application.