What is called first doGet or doPost? [duplicate] - http

Question

This question already has answers here:
doGet and doPost in Servlets
(5 answers)
Closed 1 year ago.
I have question about doGet doPost priorities (if there are any). Here is my HelloServlet class:
public class HelloServlet extends HttpServlet {
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
#Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getWriter().println("Hello, World Post!");
}
#Override
public void init() throws ServletException {
System.out.println("Servlet " + this.getServletName() + " has started.");
}
#Override
public void destroy() {
System.out.println("Servlet " + this.getServletName() + " has stopped.");
}
This class is mapped to the /greeting URL. When I try to access this page now, everything is fine. But when I change the doPost and doGet methods I gives me an error: HTTP Status 405 - HTTP method GET is not supported by this URL. Everytime I read about doGet and doPost I assume these methods are interchangeable. So what is the problem with this version of these methods?
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
#Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.getWriter().println("Hello, World Post!");
}
This of course caused no exception because doGet is present, but it will not do any work. When I remove doGet method it throws the exception.
Can you please tell me what exactly happens in the moment I use my code URL? http://localhost:8080/greeting
Why the client just cannot use the doPost method to obtain the data from the server when doGet is completely missing?
Thank you!
UPDATE WEB.xml file
<display-name>Hello World Application</display-name>
<servlet>
<servlet-name>helloServlet</servlet-name>
<servlet-class>com.wrox.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>helloServlet</servlet-name>
<url-pattern>/greeting</url-pattern>
</servlet-mapping>

Answer 1

If you do not specify the request method by default it will be GET which means doGet() will be called.
example: http://www.anywebsite.com is a default GET request.
But you have to specify your request is a POST request to execute doPost()
example:
<form action="/servlet" method="POST">
<input type="text" name="something"
</form>

Answer 2

if you have not mentioned in then default it call doGet method But if you have to specify your request is a POST in below code as like then tomcat call the service method where service method decide where request should go
<form action="/servlet" method="POST">
<input type="text" name="something"
</form>
The protected service method checks the type of request, if request type is get, it calls doGet method, if request type is post, it calls doPost method, so on. Let's see the internal code:
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String method = req.getMethod();
if(method.equals("GET"))
{
long lastModified = getLastModified(req);
if(lastModified == -1L)
{
doGet(req, resp);
}
//rest of the code
}
}