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Interface Servlet

All Known Subinterfaces:

HttpJspPage,JspPage

All Known Implementing Classes:

GenericServlet

public interfaceServlet

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 extendsjavax.servlet.GenericServlet or an HTTP servlet that extendsjavax.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 constructed, then initialized with theinit method.
2. Any calls from clients to theservice method are handled.
3. The servlet is taken out of service, then destroyed with thedestroy method, then garbage collected and finalized.

In addition to the life-cycle methods, this interface provides thegetServletConfig method, which the servlet can use to get any startup information, and thegetServletInfo method, which allows the servlet to return basic information about itself, such as author, version, and copyright.

See Also:

GenericServlet,HttpServlet

init

public voidinit(ServletConfig config)          throwsServletException

Called by the servlet container to indicate to a servlet that the servlet is being placed into service.

The servlet container calls theinit method exactly once after instantiating the servlet. Theinit method must complete successfully before the servlet can receive any requests.

The servlet container cannot place the servlet into service if theinit method

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

Parameters:

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

Throws:

ServletException - if an exception has occurred thatinterferes with the servlet's normaloperation

See Also:

UnavailableException,getServletConfig()

getServletConfig

publicServletConfiggetServletConfig()

Returns aServletConfig object, which contains initialization and startup parameters for this servlet. TheServletConfig object returned is the one passed to theinit method.

Implementations of this interface are responsible for storing theServletConfig object so that this method can return it. TheGenericServlet class, which implements this interface, already does this.

Returns:

theServletConfig objectthat initializes this servlet

See Also:

init(javax.servlet.ServletConfig)

service

public voidservice(ServletRequest req,ServletResponse res)             throwsServletException,                    java.io.IOException

Called by the servlet container to allow the servlet to respond to a request.

This method is only called after the servlet'sinit() 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.

Parameters:

req - theServletRequest object that containsthe client's request

res - theServletResponse object that containsthe servlet's response

Throws:

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

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

getServletInfo

public java.lang.StringgetServletInfo()

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.).

Returns:

aString containing servlet information

destroy

public voiddestroy()

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'sservice method have exited or after a timeout period has passed. After the servlet container calls this method, it will not call theservice 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.