Difference between applicationContext xml and spring-servlet xml in Spring Framework

Question

Are applicationContext xml and spring-servlet xml related anyhow in Spring Framework  Will the properties files declared in applicationContext xml be available to DispatcherServlet  On a related note  why do I need a  -servlet xml at all  Why is applicationContext xml alone insufficient

User · Answer

In Servlet technology if you want to pass any input to a particular servlet then you need to pass in init param like below code.

 <servlet>
    <servlet-name>DBController</servlet-name>
    <servlet-class>com.test.controller.DBController</servlet-class>
    <init-param>
        <param-name>username</param-name>
        <param-value>John</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>DBController</servlet-name>
    <url-pattern>/DBController</url-pattern>
</servlet-mapping>

If you want to pass some in put that is common for all servlets then that time you need to configure context param. Example

 <context-param>
    <param-name>email</param-name>
    <param-value>admin@example.com</param-value>
</context-param>

SO exactly like this when ever we are working with Spring MVC we need to provide some information to Predefined servlet provided by Spring that is DispatcherServlet through init param. So the configuration is as fallows, here we are providing the spring-servlet.xml as init parameter to DispatcherServlet.

 <?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>Spring MVC App</display-name>

    <servlet>
        <servlet-name>SpringController</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>SpringController</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>
</web-app>

Again we need some context param. That is applicable for whole application. So we can provide the root context that is applicationcontext.xml The configuration is like this:

    <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/applicationcontext.xml</param-value>
</context-param>
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<servlet>
        <servlet-name>SpringController</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>SpringController</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>

User · Answer

Scenario 1 In client application  application is not web application  e g may be swing app  private static ApplicationContext context   new  ClassPathXmlApplicationContext  quot test-client xml quot     context getBean name    No need of web xml  ApplicationContext as container for getting bean service  No need for web server container  In test-client xml there can be  Simple bean with no remoting  bean with  remoting  Conclusion  In Scenario 1 applicationContext and DispatcherServlet are not related  Scenario 2 In a server application  application deployed in server e g Tomcat   Accessed service via remoting from client program  e g Swing app  Define listener in web xml  lt listener gt       lt listener-class gt org springframework web context ContextLoaderListener lt  listener-class gt   lt  listener gt   At server startup ContextLoaderListener instantiates beans defined in applicationContext xml  Assuming you have defined the following in applicationContext xml   lt import resource  quot test1 xml quot    gt   lt import resource  quot test2 xml quot    gt   lt import resource  quot test3 xml quot    gt   lt import resource  quot test4 xml quot    gt   The beans are instantiated from all four configuration files test1 xml  test2 xml  test3 xml  test4 xml  Conclusion  In Scenario 2 applicationContext and DispatcherServlet are not related  Scenario 3 In a web application with spring MVC  In web xml define   lt servlet gt       lt servlet-name gt springweb lt  servlet-name gt       lt servlet-class gt org springframework web servlet DispatcherServlet lt  servlet-class gt       lt  servlet gt    lt servlet-mapping gt       lt servlet-name gt springweb lt  servlet-name gt       lt url-pattern gt   action lt  url-pattern gt   lt  servlet-mapping gt   When Tomcat starts  beans defined in springweb-servlet xml are instantiated  DispatcherServlet extends FrameworkServlet  In FrameworkServlet bean instantiation takes place for springweb   In our case springweb is FrameworkServlet  Conclusion  In Scenario 3 applicationContext and DispatcherServlet are not related  Scenario 4 In web application with spring MVC  springweb-servlet xml for servlet and applicationContext xml for accessing the business service within the server program or for accessing DB service in another server program  In web xml the following are defined   lt listener gt       lt listener-class gt org springframework web context ContextLoaderListener lt  listener-class gt   lt  listener gt    lt servlet gt       lt servlet-name gt springweb lt  servlet-name gt       lt servlet-class gt org springframework web servlet DispatcherServlet lt  servlet-class gt           lt  servlet gt    lt servlet-mapping gt       lt servlet-name gt springweb lt  servlet-name gt       lt url-pattern gt   action lt  url-pattern gt   lt  servlet-mapping gt   At server startup  ContextLoaderListener instantiates beans defined in applicationContext xml  assuming you have declared herein   lt import resource  quot test1 xml quot    gt   lt import resource  quot test2 xml quot    gt   lt import resource  quot test3 xml quot    gt   lt import resource  quot test4 xml quot    gt   The beans are all  instantiated from all four test1 xml  test2 xml  test3 xml  test4 xml  After the completion of bean instantiation defined in applicationContext xml  beans defined in springweb-servlet xml are instantiated  So the instantiation order is  the root  application context   then FrameworkServlet  Now it should be clear why they are important in which scenario

User · Answer

In simple words    applicationContext xml defines the beans that are shared among all the servlets  If your application have more than one servlet  then defining the common resources in the applicationContext xml would make more sense   spring-servlet xml defines the beans that are related only to that servlet  Here it is the dispatcher servlet  So  your Spring MVC controllers must be defined in this file   There is nothing wrong in defining all the beans in the spring-servlet xml if you are running only one servlet in your web application

User · Answer

Application contexts provide a means for resolving text messages  including support for i18n of those messages  Application contexts provide a generic way to load file resources  such as images  Application contexts can publish events to beans that are registered as listeners  Certain operations on the container or beans in the container  which have to be handled in a programmatic fashion with a bean factory  can be handled declaratively in an application context  ResourceLoader support  Spring   s Resource interface us a flexible generic abstraction for handling low-level resources  An application context itself is a ResourceLoader  Hence provides an application with access to deployment-specific Resource instances  MessageSource support  The application context implements MessageSource  an interface used to obtain localized messages  with the actual implementation being pluggable

User · Answer

One more point I want to add  In spring-servlet xml we include component scan for Controller package  In following example we include filter annotation for controller package    lt  -- Scans for annotated  Controllers in the classpath -- gt   lt context component-scan base-package  org test web  use-default-filters  false  gt       lt context include-filter type  annotation  expression  org springframework stereotype Controller   gt   lt  context component-scan gt    In applicationcontext xml we add filter for remaining package excluding controller    lt context component-scan base-package  org test  gt           lt context exclude-filter type  annotation  expression  org springframework stereotype Controller   gt       lt  context component-scan gt

User · Answer

Spring lets you define multiple contexts in a parent-child hierarchy   The applicationContext xml defines the beans for the  root webapp context   i e  the context associated with the webapp   The spring-servlet xml  or whatever else you call it  defines the beans for one servlet s app context   There can be many of these in a webapp  one per Spring servlet  e g  spring1-servlet xml for servlet spring1  spring2-servlet xml for servlet spring2    Beans in spring-servlet xml can reference beans in applicationContext xml  but not vice versa   All Spring MVC controllers must go in the spring-servlet xml context   In most simple cases  the applicationContext xml context is unnecessary  It is generally used to contain beans that are shared between all servlets in a webapp  If you only have one servlet  then there s not really much point  unless you have a specific use for it

[java] Difference between applicationContext.xml and spring-servlet.xml in Spring Framework

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