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
*/
public 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
*/
public 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
*/
public 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
*/
public 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.
*/
public void destroy();
}