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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:
init
method.
service
method are handled.
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.
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 |
public void init(ServletConfig config) throws ServletException
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
ServletException
config
- a ServletConfig
object
containing the servlet's
configuration and initialization parametersUnavailableException
,
getServletConfig()
public ServletConfig getServletConfig()
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.
ServletConfig
object
that initializes this servletinit(javax.servlet.ServletConfig)
public void service(ServletRequest req, ServletResponse res) throws ServletException, java.io.IOException
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.
req
- the ServletRequest
object that contains
the client's requestres
- the ServletResponse
object that contains
the servlet's responsepublic java.lang.String getServletInfo()
The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, and so on).
String
containing servlet informationpublic void destroy()
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.
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