javax.servlet
Interface Servlet

All Known Subinterfaces:

HttpJspPage, JspPage

All Known Implementing Classes:

GenericServlet

public abstract interface Servlet

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 javax.servlet.GenericServlet or an HTTP servlet that extends javax.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:

1. The servlet is created, then initialized with the init method.
2. Any calls from clients to the service method are handled.
3. The servlet is 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.

Version:

$Version$

Author:

Various

See Also:

GenericServlet, HttpServlet

Method Summary

void	destroy() Removes the servlet from service after all threads within its service method have exited or a timeout period has passed.
ServletConfig	getServletConfig() Returns a ServletConfig object, which contains initialization and startup parameters for this servlet.
java.lang.String	getServletInfo() Returns information about the servlet, such as author, version, and copyright.
void	init(ServletConfig config) Initializes the servlet and places it into service.
void	service(ServletRequest req, ServletResponse res) Allows the servlet to respond to a request after the servlet has been initialized with the init method.

Method Detail

init

public void init(ServletConfig config)
          throws ServletException

Initializes the servlet and places it into service.

The host servlet engine 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 engine cannot place the servlet into service if the init method

1. Throws a ServletException
2. Does not return within a time period defined by the Web server

Parameters:

config - a ServletConfig object containing the servlet's configuration and initialization parameters

Throws:

ServletException - if an exception has occurred that interferes with the servlet's normal operation

See Also:

UnavailableException, getServletConfig()

getServletConfig

public ServletConfig getServletConfig()

Returns a ServletConfig object, which contains initialization and startup parameters for this servlet. The ServletConfig object returned is the one passed to the init method.

You are responsible for storing the ServletConfig object so that this method can access it. For your convenience, the GenericServlet class, which implements this interface, already does this.

Returns:

the ServletConfig object that initializes this servlet

See Also:

init(javax.servlet.ServletConfig)

service

public void service(ServletRequest req,
                    ServletResponse res)
             throws ServletException,
                    java.io.IOException

Allows the servlet to respond to a request after the servlet has been initialized with the init method.

The servlet engine can block pending requests to this method until the servlet is initialized. Likewise, once this servlet is removed from service (when the servlet engine calls its destroy method), you cannot call its service method.

Servlets typically run inside multithreaded servlet engines that can handle multiple requests concurrently. You must synchronize access to any shared resources such as network connections or the servlet's class and instance variables. You can find more information on multithreaded programming in Java in the Java tutorial on multi-threaded programming.

Parameters:

req - the ServletRequest object that contains the client's request

res - the ServletResponse object that contains the servlet's response

Throws:

ServletException - if an exception occurs that interferes with the servlet's normal operation

java.io.IOException - if an input or output exception occurs

getServletInfo

public java.lang.String getServletInfo()

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, and so on).

Returns:

a String containing servlet information

destroy

public void destroy()

Removes the servlet from service after all threads within its service method have exited or a timeout period has passed. After the servlet engine calls this method, it cannot call the service method 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.