Life Cycle of a Servlet (Servlet Life Cycle)
- 1) Servlet class is loaded The classloader is responsible to load the servlet class. ...
- 2) Servlet instance is created The web container creates the instance of a servlet after loading the servlet class. ...
- 3) init method is invoked The web container calls the init method only once after creating the servlet instance. ...
- 4) service method is invoked ...
- 5) destroy method is invoked ...
What is the life cycle of a servlet?
Life Cycle of a Servlet (Servlet Life Cycle) 1 Servlet class is loaded. The classloader is responsible to load the servlet class. ... 2 Servlet instance is created. The web container creates the instance of a servlet after loading the servlet class. ... 3 init method is invoked. ... 4 service method is invoked. ... 5 destroy method is invoked. ...
What are the different methods of servlet?
There are as follows: 1 init () method : A servlet’s life begins here . ... 2 service () method : The service () method is the most important method to perform that provides the connection between client and server. ... 3 destroy () method : The destroy () method is called only once. ...
What is the difference between servlet class and Servlet instance?
The servlet class is loaded when the first request for the servlet is received by the web container. The web container creates the instance of a servlet after loading the servlet class. The servlet instance is created only once in the servlet life cycle. The web container calls the init method only once after creating the servlet instance.
When is the Servlet class loaded in a web container?
The servlet class is loaded when the first request for the servlet is received by the web container. The web container creates the instance of a servlet after loading the servlet class. The servlet instance is created only once in the servlet life cycle.
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What is the first phase of servlet life cycle?
Initialization is the first phase of the Servlet life cycle and represents the creation and initialization of resources the Servlet may need to service requests.
Which are lifecycle methods of servlet interface?
The init, service and destroy are the life cycle methods of servlet.
How many types are there in servlet?
There are two main types of Servlet. They are Generic and HTTP servlets. We can use the constructor method to initialize the Servlets with the help of init() and the destructor method to remove the servlet from the resources using destroy().
Which of the following is not a servlet life cycle method?
Explanation: Pausing the servlet for a given amount of time is not a part of the servlet lifecycle. A servlet can be checked, invoked and destroyed but it cannot be paused.
Which is not life cycle method of servlet Mcq?
1 Answer. Right choice is (d) Pausing the servlet for a given period of time. Explanation: Pausing the servlet for a given amount of time is not a part of the servlet lifecycle.
Which of the following are interfaces in servlet?
Interfaces in javax. servlet packageServlet.ServletRequest.ServletResponse.RequestDispatcher.ServletConfig.ServletContext.SingleThreadModel.Filter.More items...
What are the methods of servlet class Mcq?
Servlets MCQ Quiz Answerssession.getAttribute(String name)session.alterAttribute(String name)C. session.updateAttribute(String name)D. session.setAttribute(String name)
Which of the following are the life cycle method of JSP?
Instantiation(Object of the generated Servlet is created) Initialization(jspInit() method is invoked by the container) Request processing(_jspService()is invoked by the container) JSP Cleanup (jspDestroy() method is invoked by the container)
What maintains the life cycle of a servlet instance?
The web container maintains the life cycle of a servlet instance. Let's see the life cycle of the servlet:
How often is a servlet created?
The web container creates the instance of a servlet after loading the servlet class. The servlet instance is created only once in the servlet life cycle.
How many states does a servlet have?
As displayed in the above diagram, there are three states of a servlet: new, ready and end. The servlet is in new state if servlet instance is created. After invoking the init () method, Servlet comes in the ready state. In the ready state, servlet performs all the tasks. When the web container invokes the destroy () method, it shifts to the end state.
What are the phases of servlet life cycle?
What are the phases of the Servlet life cycle? The servlet life cycle contains five phases: 1. load a servlet class: The class Classloader is responsible to load the servlet class .ClassLoader object is designed to load a class just once. It is loaded, when the first request for the servlet is received by the web container.
What are the three methods that are central to the life cycle of a servlet?
There are three methods which are central to the life cycle of a servlet. They are init (), service () and destroy () methods. They are implemented by every servlet and are invoked at a specific time by the server. Do Check:
How many life cycle methods are there in servlet?
There are three life cycle methods in servlet and they are given in detail
How many times does a servlet call destroy?
5. Destroy () method: This method is called only once in the entire life cycle of a servlet. The servlet calls the destroy () method after the servlet has been taken out of service and all pending requests have been completed or timed out.
What is the second phase of a servlet life cycle?
The second phase of a servlet life cycle is the service phase. This phase of the servlet life cycle represents all the interactions carried out along with the requests that are handled by the servlet until it is destroyed. The service phase of the servlet life cycle corresponds to the service () method of the Servlet interface. The service () method of a servlet is invoked once for every request.
Why are servlets better than CGI?
The primary reason why servlets and JavaServer Pages (JSP) outperform traditional CGI is the servlet life cycle. Servlets have a three-phase life cycle, namely initialization, service, and destruction. initialization and destruction are called only once in the entire lifecycle while service is can call multiple times in lifecycle.
How does a server spawn a new thread?
It is possible that the server spawns a new thread by reusing an idle thread from a thread pool. The service () method verifies the HTTP request type (GET, POST, PUT, DELETE) and accordingly calls the doGet (), doPost (), doPut (), doDelete () methods. A normal request for a URL or a request from an HTML form that has no METHOD specified results in a GET request. Apart from the GET request, an HTML form can also specify POST as the request method type. The following code snippet explains the implementation of the POST method:
How to read server specific initialization parameters?
When you need to read the initialization parameters, you have to first obtain a ServletConfig object by using the getServletConfig () method, and then call the getInitParameter () method on the result . The following code snippet shows how to obtain a ServletConfig object:
When is init called?
As mentioned earlier, the init () method is called when a servlet is created for the first time. It will not be called again for other user requests. Therefore, the init () method is used only for one-time initializations. A servlet is normally created when a user invokes a URL corresponding to the servlet, for the first time; however, the servlet is loaded on the server when a Servlet container maps the user request to the servlet. The following code snippet shows the init () method definition:
When is a servlet created?
The servlet is normally created when a user first invokes a URL corresponding to the servlet, but you can also specify that the servlet be loaded when the server is first started.
What is servlet service?
The servlet calls service () method to process a client's request.
How does a servlet handle multiple requests?
Then the servlet container handles multiple requests by spawning multiple threads, each thread executing the service () method of a single instance of the servlet.
How to call servlets?
Servlets - Life Cycle 1 The servlet is initialized by calling the init () method. 2 The servlet calls service () method to process a client's request. 3 The servlet is terminated by calling the destroy () method. 4 Finally, servlet is garbage collected by the garbage collector of the JVM.
What is the destroy method in servlet?
The destroy () method is called only once at the end of the life cycle of a servlet. This method gives your servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities.
What is the service method?
The service () method is the main method to perform the actual task. The servlet container (i.e. web server) calls the service () method to handle requests coming from the client ( browsers) and to write the formatted response back to the client.
When is init called?
The init () Method. The init method is called only once. It is called only when the servlet is created, and not called for any user requests afterwards. So, it is used for one-time initializations, just as with the init method of applets.
How is the life cycle of a servlet controlled?
The life cycle of a servlet is controlled by the container in which the servlet has been deployed.
How does a servlet initialize?
The container initializes the servlet by invoking its init() method , passing an object implementing the ServletConfig interface. In the init() method, the servlet can read configuration parameters from the deployment descriptor or perform any other one-time activities, so the init() method is invoked once and only once by the servlet container.
What is servlet loading?
Servlet class loading: For each servlet defined in the deployment descriptor of the Web application, the servlet container locates and loads a class of the type of the servlet. This can happen when the servlet engine itself is started, or later when a client request is actually delegated to the servlet.
Initialization
After creating servlet instance container creates ServletConfig object and config object have got config parameters as specified in web.xml related to the particular servlet (ServletConfig will be studied in next chapter). These config parameters are used to do initialization operations.
Service
The web container calls the service method each time when request for the servlet is received. If servlet is not initialized, it follows the first three steps as described above then calls the service method. If servlet is initialized, it calls the service method. Notice that servlet is initialized only once.
Finalization
When server is shutdown, destroy () method will be called do following cleanup operation:
Destruction
Container destroys all the servlet instances by calling destroy () method on each instance.
At server start up following things will happen
Container reads the web.xml file i.e. using the SAX parser container reads the data from web.xml document and converts the data into java objects. If any errors are found while parsing the document then SAXParserException will be thrown. If SAXParserException comes at server start up, then it means that deployment is not successful.
Once server is shutdown following things will happen
Container destroys all the servlet instances, ServletConfig objects, filter instances, ServletContext object, Thread pool by calling destroy () method on each instance.
The init() Method
The service() Method
The doGet() Method
- A GET request results from a normal request for a URL or from an HTML form that has no METHOD specified and it should be handled by doGet() method.
The doPost() Method
- A POST request results from an HTML form that specifically lists POST as the METHOD and it should be handled by doPost() method.
The destroy() Method
- The destroy() method is called only once at the end of the life cycle of a servlet. This method gives your servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities. After the destroy() method is called, the servlet object is marked for garbage collection. The destroy method definition looks li…
Architecture Diagram
- The following figure depicts a typical servlet life-cycle scenario. 1. First the HTTP requests coming to the server are delegated to the servlet container. 2. The servlet container loads the servlet before invoking the service() method. 3. Then the servlet container handles multiple requests by spawning multiple threads, each thread executing the s...