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There are 3 main types of requests that get processed by a Servlet. They are:
• Get
• Post
• Put
Each of them have a corresponding doXXX() method in the Servlet class which would be:
• doGet
• doPost
• doPut
You must override either of these methods based on the type of requests that would be processed by your servlet
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What is doGet method in servlet?
The doGet() method is the method inside a servlet that gets called every time a request from a jsp page is submitted. The control first reaches the doGet() method of the servlet and then the servlet decides what functionality to invoke based on the submit request. The get method called when the type of page submission is "GET" There is another way of submitting requests from a jsp page is "POST" and when that happens it calls the doPost() method inside the servlet.
What is doPost in servlet?
doPost() is the method in the servlet that is used to service the Http requests submitted using the Post option. HTML forms can be submitted in two ways using the Get method and the Post method. You can specify the method while declaring the form itself. So you will have two methods in the servlet doGet() and doPost() each for one of them
What is difference between GET and POST in servlets in java?
The difference between a GET and a POST is the way data is transferred to a servlet. With a GET, the URL will show each name/value pair on the query string in the URL. For example, if you had a form with a field named 'foo,' and when submitted had a value of 'bar,' the URL might be something like this: http://www.example.com/servlet?foo=bar With a POST, this information is not visible in the URL. Instead, it is transferred in the HTTP headers. As far as the actual servlet is concerned, there is not a great deal of difference when it comes to getting the parameters. Whether you use a GET or a POST, you still use request.getParameter("foo"); to get the value. The method used in the Servlet for processing either a GET or a POST is different too. If you use a GET, the method that is called is doGet(HttpServletRequest, HttpServletResponse). The doGet method is also called if there is no GET or POST data. If you use a POST, the method called is doPost(HttpServletRequest, HttpServletResponse).
Why do you use superclass init method inside your init method in a servlet?
Because, that is how all Java classes work. When a class is initialized/created all the classes it extends from (its super classes) need to be initialized as well.
What is servlet mapping?
A Servlet Mapping is a directive in the web.xml that tells the Servlet Container which class to use when a particular Servlet is called. A Servlet is a class within your Java Web Application. Let's say you have a servlet called MyServlet in the com.example.servlet package. You would need to have a Servlet Mapping pointing the path "/MyServlet" to the "com.example.servlet.MyServlet" class. Without the servlet mapping, you would not be able to invoke your servlet because the Servlet container would not know where it is. JSPs are different - they do not need mappings like this. JSPs exist within the WebRoot of the application, so they are always available. Servlets exist in the WEB-INF\Classes directory once your application is deployed.
How does Apache httpd work?
Tomcat is a servlet container, and the following is how a servlet container works The init, service, and destroy methods are the servlet's lifecycle methods. The init method is called once by the servlet container after the servlet class has been instantiated to indicate to the servlet that it being placed into service. The init method must complete successfully before the servlet can receive any requests. A servlet programmer can override this method to write initialization code that needs to run only once, such as loading a database driver, initializing values, and so on. In other cases, this method is normally left blank. The service method is then called by the servlet container to allow the servlet to respond to a request. The servlet container passes a javax.servlet.ServletRequest object and a javax.servlet.ServletResponse object. The ServletRequest object contains the client's HTTP request information and the ServletResponse encapsulates the servlet's response. These two objects enable you to write custom code that determines how the servlet services the client request. The servlet container calls the destroy method before removing a servlet instance from service. This normally happens when the servlet container is shut down or when the servlet container needs some free memory. This method is called only after all threads within the servlet's service method have exited or after a timeout period has passed. After the servlet container calls destroy, it will not call the service method again on this servlet. The destroy method gives the servlet an opportunity to clean up any resources that are being held (for example, memory, file handles, and threads) and make sure that any persistent state is synchronized with the servlet's current state in memory. For Better Picture, Visit below article full of images to clear the concept : http://shivasoft.in/blog/java/servlet/how-container-handles-the-servlet-request/
Why must you override the hashcode method while overriding the equals method?
Because, if two objects are supposed to be equal as per the equals() method, then the value returned by the hashCode() method must also be the same. This will not be the case if you override only the equals method and this can have some confusing effects when using those objects with hash related collections. So it is always a good idea to override the hashCode() method if you are providing an implementation for the equals method.
What is doGet method in servlet?
The doGet() method is the method inside a servlet that gets called every time a request from a jsp page is submitted. The control first reaches the doGet() method of the servlet and then the servlet decides what functionality to invoke based on the submit request. The get method called when the type of page submission is "GET" There is another way of submitting requests from a jsp page is "POST" and when that happens it calls the doPost() method inside the servlet.
Can you override an instance method and make it final?
No. Once a method is declared final in a class, no derivative of that class can override that method.
How do you get servlet context instance to servlet?
You can get the ServletContext instance in a servlet by using the getServletContext() method provided by the HttpServlet class, which is the base class for servlets. This method returns the ServletContext object associated with the servlet. For example: ServletContext context = getServletContext();
Describe the life cycle of servelet?
Each servlet has the same life cycle: * A server loads and initializes the servlet * The servlet handles zero or more client requests * The server removes the servlet (some servers do this step only when they shut down) == When a server loads a servlet, the server runs the servlet's init method. Initialization completes before client requests are handled and before the servlet is destroyed. Even though most servlets are run in multi-threaded servers, servlets have no concurrency issues during servlet initialization. The server calls the init method once, when the server loads the servlet, and will not call the init method again unless the server is reloading the servlet. The server can not reload a servlet until after the server has destroyed the servlet by calling the destroy method. == After initialization, the servlet is able to handle client requests. This part of the servlet life cycle was handled in the previous lesson. == Servlets run until the server are destroys them, for example, at the request of a system administrator. When a server destroys a servlet, the server runs the servlet's destroy method. The method is run once; the server will not run that servlet again until after the server reloads and reinitializes the servlet. When the destroy method runs, another thread might be running a service request. The Handling Service Threads at Servlet Termination lesson shows you how to provide a clean shutdown when there could be long-running threads still running service requests.
What is doPost in servlet?
doPost() is the method in the servlet that is used to service the Http requests submitted using the Post option. HTML forms can be submitted in two ways using the Get method and the Post method. You can specify the method while declaring the form itself. So you will have two methods in the servlet doGet() and doPost() each for one of them
Can you override the life cycle methods of a JSP?
You cannot override the jspService() method but you can override the jspInit() and jspDestroy() methods
How is hiding method different from overriding method in c sharp?
Hiding means a class cannot see the definition. Overriding implies that a class must see that to "override"
What are the rules for overriding a method in Java?
Realistically, the only real rule is that you may NOT override a method which has been declared 'final' by a superclass. By inference, you of course cannot extended a class that has itself been declared 'final', so no method in a final class can be overridden.In addition to the above restriction on whether you are permitted to override a method, there are several restrictions which you must obey when creating an override method:The scope (visibility) of the method may not be more restrictive than the one being overridden. For example, a method which is declared 'public' cannot be overridden with one which is declared 'package' or 'private'The override method's declared exceptions must be a subset of the original (i.e. you can removed Exceptions to be handled, but never add new ones that aren't a subtype of already existing Exceptions).The return type must either stay the same, or be a subclass of the original method's return type.And, of course, the declaration of arguments (type and number) must not change; otherwise, you are writing an Overloaded method, not an Overridden method.
Why no need of main in servlet?
I think you mean: why isn't there a function required in a servlet like the following? public static void main(String[] args) { } Because the main() method is what the Java VM 'boots up' into...it's the first thing the JVM executes. A servlet, however, is running inside a servlet container (e.g., Tomcat), which is running inside a JVM. *That* JVM gets started with a main() method, but unless you intend to run your servlet from the commandline, there's no explicit need for a main() method.
Generic Servlet and HTTP Servlet?
javax.servlet.GenericServletSignature: public abstract class GenericServlet extends java.lang.Object implements Servlet, ServletConfig, java.io.SerializableGenericServlet defines a generic, protocol-independent servlet.GenericServlet gives a blueprint and makes writing servlet easier.GenericServlet provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface.GenericServlet implements the log method, declared in the ServletContext interface.To write a generic servlet, it is sufficient to override the abstract service method.javax.servlet.http.HttpServletSignature: public abstract class HttpServlet extends GenericServlet implements java.io.SerializableHttpServlet defines a HTTP protocol specific servlet.HttpServlet gives a blueprint for Http servlet and makes writing them easier.HttpServlet extends the GenericServlet and hence inherits the properties GenericServlet.
