Why do need to create a separate Spring-servlet.xml(Dispatcher Servlet) file in my Spring application? Why we can not keep all the request mapping in web.xml(Deployment Descriptor file)?
J2EE specification drives what content has to be available inside web.xml. Web.xml provides URL to Servlet mapping where as Spring dispatcher servlet with help of its own configuration file provides mapping of request URL with controller class.
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I'm studying about spring boot and dispatcher servlet.
but I have no idea where is the exact location of dispatcher servlet.
I saw two pictures describe dispatcher servlet and web container, but they are different.
I've been looking for an answer for this one, but I can't seem to find a good answer.
Q. Exact location of dispatcher servlet.
first one, dispatcher servlet located in servlet container.
second one, dispatcher servlet located in spring container.
which one is right?
located in servlet container
located in spring container
DispatcherServlet class located in package "org.springframework.web.servlet" (spring-mvc.jar). Not in Tomcat container
What is the difference between DispatcherServlet and ContextLoaderListener in Spring framework? Do we need to configure both of them in web.xml when we are using spring framework?
AFAIK each DispatcherServlet will have a WebApplicationContext. By default the DispatcherServlet looks for a spring configuration file named [appname]-servlet.xml under WEB-INF folder.
Do we need to configure DispatcherServlet?
Yes, every spring application should configure DispatcherServlet as it is the one through which all the requests are routed. It decides the appropriate method of the controller class to handle the request. Once controller returns the model along with the logical view, DispatcherServlet takes the help of ViewResolver to resolve the view (generally JSPs) and will pass the model data to the view, which is finally rendered on the browser.
Do we need to configure ContextLoaderListener?
No, this is not mandatory. Spring applications can live with out ContextLoaderListener.
Why do we need ContextLoaderListener?
Usually when we build multi-tier applications we don't want to clutter all the beans in one config file [appname]-servlet.xml. For example if you configure spring security you wanted to include all those beans in security-context.xml, in the same way all the beans belonging to service layer are configured in applicationContext.xml and some would like to configure beans belonging to DAO layer in dao-context.xml. So when you configure all these beans in different context files, you need to let know spring that these files exist as spring only knows about [appname]-servlet.xml. ContextLoaderListener will help spring recognize all the other context files.
Hope this helps!
The root WebApplicationContext is a Spring Application Context shared across the application.
A DispatcherServlet instance actually has its own
WebApplicationContext.
One can have multiple DispatcherServlet instances in an application, and each will have its own WebApplicationContext.
The root WebApplicationContext is shared across
the application, so if you have a root WebApplicationContext and
multiple DispatcherServlets, the DispatcherServlets will share the
root WebApplicationContext.
However, for a simple Spring MVC application, one can even have a situation where there is no need to have a root WebApplicationContext. A DispatcherServlet would still have its own WebApplicationContext, but it doesn’t actually need to have a parent root WebApplicationContext.
So, which beans should go in the root Web Application Context and which beans should go in the DispatcherServlet’s Web Application Context?
Well, general beans such as services and DAOs make their way in root Web Application Context, and more web-specific beans such as controllers are included in DispatcherServlet’s Web Application Context.
When DispatcherServlet starts up, it creates a Spring application context and starts
loading it with beans declared in the configuration files or classes that it’s given.
But in Spring web applications, there’s often another application context. This
other application context is created by ContextLoaderListener
Whereas DispatcherServlet is expected to load beans containing web components
such as controllers, view resolvers, and handler mappings, ContextLoaderListener is
expected to load the other beans in your application. These beans are typically the
middle-tier and data-tier components that drive the back end of the application.
Good luck!
So we decided to deploy our application no more as a war on the usual tomcat, but from an embedded jetty. My app uses context:property-placeholder to resolve properties from a file. Now I'd need to pass some (or all) properties programatically before starting jetty. Is there a way that allows me to set some properties by code, before running jetty, instead of relying on the .properties file? For example as Servlet params?
You can use ServletContextPropertyPlaceholderConfigurer. This PropertyPlaceholderConfigurer extract the properties from the servlet context init params.
From Spring Javadocs:
Subclass of PropertyPlaceholderConfigurer that resolves placeholders as ServletContext init parameters (that is, web.xml context-param entries).
But this class is deprecated from Spring version 3.1.
From version 3.1 you don't need to use any special configuration because all Web Based servlet context use the class org.springframework.web.context.support.StandardServletEnvironment that resolve properties from servlet context params by default.
I am using Resteasy and Spring for my project. As Resteasy document said: http://docs.jboss.org/resteasy/docs/3.0.1.Final/userguide/html_single/index.html#RESTEasy_Spring_Integration.
I need to add a listener in the web.xml file:
<listener>
<listener-class>org.jboss.resteasy.plugins.server.servlet.ResteasyBootstrap</listener-class>
<listener>
<listener-class>org.jboss.resteasy.plugins.spring.SpringContextLoaderListener</listener-class>
However, in my project we also used a cms called magnolia, and magnolia also has an implementation for SpringContextLoaderListener. If I put both context listener. The magnolia won't be started when I run the app.
So according to the Resteasy document said:
If you do not use a Spring ContextLoaderListener to create your bean factories, then you can manually register the RESTeasy BeanFactoryPostProcessor by allocating an instance of org.jboss.resteasy.plugins.spring.SpringBeanProcessor. You can obtain instances of a ResteasyProviderFactory and Registry from the ServletContext attributes org.jboss.resteasy.spi.ResteasyProviderFactory and org.jboss.resteasy.spi.Registry. (Really the string FQN of these classes). There is also a org.jboss.resteasy.plugins.spring.SpringBeanProcessorServletAware, that will automatically inject references to the Registry and ResteasyProviderFactory from the Servlet Context. (that is, if you have used RestasyBootstrap to bootstrap Resteasy).
Does anyone knows how can I achieve that without using Resteasy ContextLoaderListener? What do I need to put in my spring applicationContext xml file?
I've also had problem with RestEasy SpringContextListener (properties placeholders ${...} weren't processed - RESTEASY-787, Spring java config didn't work etc.).
So it's enough to drop RestEasy SpringContextListener and use default org.springframework.web.context.ContextLoaderListener or whatever listener you need to. You just have to define Spring bean in your Spring XML configuration like this:
<bean class="org.jboss.resteasy.plugins.spring.SpringBeanProcessorServletAware"/>
Than RestEasy should work even without their special SpringContextListener. It works for me.
I'm creating a simple Spring MVC app with a DAO layer. Now I want to access the Spring JdbcTemplate beans that I've initialized in the dispatcher servlet. I've been using FileSystemXmlApplicationContext to get to my dispatcher servlet till now, but I realized its not a good practice for MVC app when I need to deploy it elsewhere.
Can somebody let me know if I can use XmlWebApplicationContext or ClassPathXmlApplicationContext to get hold of the dispatcher servlet config file which resides in the WEB-INF folder?
I don't want to extend any ApplicationAware interface and I've also not got access to servlet context, as I'm using ModelAttribute annotations to get the data from beans in JSPs. Also, I don't have any applicationContext.xml in my web-app.