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:
- The servlet is constructed, then initialized with the
- Any calls from clients to the
servicemethod are handled.
- The servlet is taken out of service, then destroyed with the
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.
Method SummaryModifier and TypeMethodDescription
destroy()Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.Returns a
ServletConfigobject, which contains initialization and startup parameters for this servlet.Returns information about the servlet, such as author, version, and copyright.
voidCalled by the servlet container to indicate to a servlet that the servlet is being placed into service.
voidCalled by the servlet container to allow the servlet to respond to a request.
initCalled by the servlet container to indicate to a servlet that the servlet is being placed into service.
The servlet container calls the
initmethod exactly once after instantiating the servlet. The
initmethod must complete successfully before the servlet can receive any requests.
The servlet container cannot place the servlet into service if the
- Throws a
- Does not return within a time period defined by the Web server
- Throws a
getServletConfigServletConfig getServletConfig()Returns a
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
ServletConfigobject so that this method can return it. The
GenericServletclass, which implements this interface, already does this.
ServletConfigobject that initializes this servlet
- See Also:
serviceCalled 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.
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
IOException- if an input or output exception occurs
getServletInfoString 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.).
Stringcontaining servlet information
destroyvoid 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's
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.