No mapping found for HTTP request - spring

Question

I am back with working in Springs. I used to work in Springs but blindly, didn't understand much. I used to get a lot of errors, very basic ones, and I am getting them again.
My problem is that, I don't know how the configuration of the Spring-MVC work.
What happens when I run the project from my STS?
I am working on the spring template project in STS.
I am getting this when I run the project.
WARN : org.springframework.web.servlet.PageNotFound - No mapping found for HTTP request with URI [/common/] in DispatcherServlet with name 'appServlet'
I am totally fed up and broken.
Just 2 months of break from work, I am back at the starting block.
I don't want to post my code and make the question specific.
I want an answer that explains the way in which the server executes a spring project. Right from the running of an application(basic hello world application) to the display of the home page.
This will be helpful for all the beginners.
I tried searching for such an explanation in the net but I didn't get any proper explanation, but got a lot of basic samples. Those samples are easy to understand but are not explaining the way in which the server goes about.
Note: I am looking for an answer that explains the Springs concept. From the running of an application to the display of a home page. What all happens in this process? Where does the server start with? How does it go about?

Answer 1

Here is the flow initially servlet container loads the web.xml file.In web.xml we will specify that all the requests are handled by the spring FrontController that is DispatcherServlet.
We include it by adding the following code
<servlet>
<servlet-name>dispatcher</servlet-name>
<servletclass>org.springframework.web.servlet.DispatcherServlet</servletclass>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>*.htm</url-pattern>
</servlet-mapping>
Here it indicate if the url request is of *.htm it is handled by dispatcherServlet then dispatcherServlet load dispatcher-servlet.xml . Where we need to mention the mapping to controller by writing the specific url request such as
<bean name="/insert.htm" class="com.controller.MyController"></bean>
So in bean we mention that for request of /insert.htm it tells the servlet to look in the mentioned class.You need use the Annotation of #RequestMapping above the method for ex
#RequestMapping("/insert.htm")
public ModelAndView insert(HttpServletRequest req,Student student)
{
String name=req.getParameter("name");
int id=Integer.parseInt(req.getParameter("id"));
student.setId(id);
return new ModelAndView("display","Student",student);//It returns a view named display with modelclass name as `Student` and model object student
}
So when a Request url of /insert.htm appears it executes the above method it returns a ModelAndView object nothing but an view.It again goes to dispatcher-servlet.xml and looks for view Resolver the normal code that is to be added is
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver"
p:prefix="/WEB-INF/jsp/"
p:suffix=".jsp" />
So from this it gets the logical view name and appends the prefix and suffix to it .Finally it displays the content in the view.so it looks for display in view resolver prefixes and suffixes the things and finally returns /WEB-INF/jsp/display.jsp .Which displays the jsp content

Answer 2

You are mapping your Spring servlet only for requests that end with .htm. The request for the root of your application does not end with .htm and so, it does not get picked up by Spring. Edit your web.xml as follows, in order to use Spring for all requests:
<servlet-mapping>
<servlet-name>appServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
Then, use this as the controller:
package com.mkyong.common;
#Controller
public class HomeController {
#RequestMapping(value = "/", method = RequestMethod.GET)
public ModelAndView helloWorld() {
ModelAndView model = new ModelAndView("index");
model.addObject("msg", "hello world");
return model;
}
}
The controller intercepts the requests for the context root of the application, adds the msg attribute to the model and redirects to the index view.
So, you need to add the index.jsp file in the /WEB-INF/views/ directory. Inside your jsp, you will be able to use the value of the msg attribute.

Answer 3

From what every you have posted you do no have a request mapping for the url /common/.
You will have to create another request mapping function like the one below in your controller class and create a view file also.
#RequestMapping(value = "/common/", method = RequestMethod.GET)
public ModelAndView common(HttpServletRequest request,
HttpServletResponse response) {
ModelAndView model = new ModelAndView("common");
model.addObject("msg", "hello world");
return model;
}