Interface Servlet
- All Known Implementing Classes:
GenericServlet
,HttpServlet
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:
- The servlet is constructed, then initialized with the
init
method. - Any calls from clients to the
service
method are handled. - The servlet is taken out of service, then 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.
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionvoid
destroy()
Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.Returns aServletConfig
object, which contains initialization and startup parameters for this servlet.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.
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Method Details
-
init
Called by the servlet container to indicate to a servlet that the servlet is being placed into service.The servlet container calls the
init
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 the
init
method- Throws a
ServletException
- 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 that interferes with the servlet's normal operation- See Also:
- Throws a
-
getServletConfig
ServletConfig getServletConfig()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 the
ServletConfig
object so that this method can return it. TheGenericServlet
class, which implements this interface, already does this.- Returns:
- the
ServletConfig
object that initializes this servlet - See Also:
-
service
Called by the servlet container to allow the servlet to respond to a request.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.
- Parameters:
req
- theServletRequest
object that contains the client's requestres
- theServletResponse
object that contains the servlet's response- Throws:
ServletException
- if an exception occurs that interferes with the servlet's normal operationIOException
- if an input or output exception occurs
-
getServletInfo
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, etc.).
- Returns:
- a
String
containing servlet information
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destroy
void destroy()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.
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