public interface Servlet
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
Modifier and Type | Method and Description |
---|---|
void |
destroy()
Called by the servlet container to indicate to a servlet that the
servlet is being taken out of service.
|
ServletConfig |
getServletConfig()
Returns a
ServletConfig object, which contains
initialization and startup parameters for this servlet. |
String |
getServletInfo()
Returns information about the servlet, such
as author, version, and copyright.
|
void |
init(ServletConfig config)
Called by the servlet container to indicate to a servlet that the
servlet is being placed into service.
|
void |
service(ServletRequest req,
ServletResponse res)
Called by the servlet container to allow the servlet to respond to
a request.
|
void init(ServletConfig config) throws ServletException
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
ServletException
config
- a ServletConfig
object
containing the servlet's
configuration and initialization parametersServletException
- if an exception has occurred that
interferes with the servlet's normal
operationUnavailableException
,
getServletConfig()
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.
Implementations of this interface are responsible for storing the
ServletConfig
object so that this
method can return it. The GenericServlet
class, which implements this interface, already does this.
ServletConfig
object
that initializes this servletinit(javax.servlet.ServletConfig)
void service(ServletRequest req, ServletResponse res) throws ServletException, IOException
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.
req
- the ServletRequest
object that contains
the client's requestres
- the ServletResponse
object that contains
the servlet's responseServletException
- if an exception occurs that interferes
with the servlet's normal operationIOException
- if an input or output exception occursString getServletInfo()
The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).
String
containing servlet informationvoid destroy()
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.
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