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 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:
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. |
java.lang.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 container will
ensure that actions performed in the init
method will be visible to any threads that subsequently call
the service
method according to the rules in JSR-133 (i.e. there is a 'happens before' relationship
between init
and service
).
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(jakarta.servlet.ServletConfig)
void service(ServletRequest req, ServletResponse res) throws ServletException, java.io.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.
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 operationjava.io.IOException
- if an input or output exception occursjava.lang.String 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.