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 () 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. |
Method Detail |
public 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 parameters
UnavailableException
,
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.
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 servlet
init(javax.servlet.ServletConfig)
public 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. 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 request
res
- the
ServletResponse
object that contains the servlet's response
public java.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 information
public void 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.