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
or an HTTP servlet that extends
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:
servicemethod are handled.
destroymethod, 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.
|Modifier and Type||Method and Description|
Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.
Returns information about the servlet, such as author, version, and copyright.
Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
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
service method according to the rules in JSR-133 (i.e. there is a 'happens before' relationship
The servlet container cannot place the servlet into service if the
ServletConfigobject, which contains initialization and startup parameters for this servlet. The
ServletConfigobject returned is the one passed to the
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.
ServletConfigobject that initializes this servlet
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.
ServletRequestobject that contains the client's request
ServletResponseobject that contains the servlet's response
ServletException- if an exception occurs that interferes with the servlet's normal operation
java.io.IOException- if an input or output exception occurs
The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).
Stringcontaining servlet information
servicemethod have exited or after a timeout period has passed. After the servlet container calls this method, it will not call the
servicemethod 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.