jakarta.servlet.Servlet Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jakarta.servlet;
import java.io.IOException;
/**
* Defines methods that all servlets must implement.
*
* A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web
* clients, usually across HTTP, the HyperText Transfer Protocol.
*
* To implement this interface, you can write a generic servlet that extends jakarta.servlet.GenericServlet
* or an HTTP servlet that extends jakarta.servlet.http.HttpServlet.
*
* This interface defines methods to initialize a servlet, to service requests, and to remove a servlet from the server.
* These are known as life-cycle methods and are called in the following sequence:
*
* - The servlet is constructed, then initialized with the
init method.
* - Any calls from clients to the
service method are handled.
* - The servlet is taken out of service, then destroyed with the
destroy method, then garbage collected
* and finalized.
*
*
* In addition to the life-cycle methods, this interface provides the getServletConfig method, which the
* servlet can use to get any startup information, and the getServletInfo method, which allows the servlet
* to return basic information about itself, such as author, version, and copyright.
*
* @see GenericServlet
* @see jakarta.servlet.http.HttpServlet
*/
public interface Servlet {
/**
* Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
*
* The servlet container calls the init method exactly once after instantiating the servlet. The
* init method must complete successfully before the servlet can receive any requests.
*
* The servlet container cannot place the servlet into service if the init method
*
* - Throws a
ServletException
* - Does not return within a time period defined by the Web server
*
*
* @param config a ServletConfig object containing the servlet's configuration and initialization
* parameters
*
* @exception ServletException if an exception has occurred that interferes with the servlet's normal operation
*
* @see UnavailableException
* @see #getServletConfig
*/
void init(ServletConfig config) throws ServletException;
/**
* Returns a {@link ServletConfig} object, which contains initialization and startup parameters for this servlet.
* The ServletConfig object returned is the one passed to the init method.
*
* Implementations of this interface are responsible for storing the ServletConfig object so that this
* method can return it. The {@link GenericServlet} class, which implements this interface, already does this.
*
* @return the ServletConfig object that initializes this servlet
*
* @see #init
*/
ServletConfig getServletConfig();
/**
* Called by the servlet container to allow the servlet to respond to a request.
*
* This method is only called after the servlet's init() method has completed successfully.
*
* The status code of the response always should be set for a servlet that throws or sends an error.
*
* Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently.
* Developers must be aware to synchronize access to any shared resources such as files, network connections, and as
* well as the servlet's class and instance variables. More information on multithreaded programming in Java is
* available in the Java tutorial on
* multi-threaded programming.
*
* @param req the ServletRequest object that contains the client's request
* @param res the ServletResponse object that contains the servlet's response
*
* @exception ServletException if an exception occurs that interferes with the servlet's normal operation
* @exception IOException if an input or output exception occurs
*/
void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;
/**
* Returns information about the servlet, such as author, version, and copyright.
*
* The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).
*
* @return a String containing servlet information
*/
String getServletInfo();
/**
* Called by the servlet container to indicate to a servlet that the servlet is being taken out of service. This
* method is only called once all threads within the servlet's service method have exited or after a
* timeout period has passed. After the servlet container calls this method, it will not call the
* service method again on this servlet.
*
* This method gives the servlet an opportunity to clean up any resources that are being held (for example, memory,
* file handles, threads) and make sure that any persistent state is synchronized with the servlet's current state
* in memory.
*/
void destroy();
}