javax.servlet

Class GenericServlet

public abstract class GenericServlet extends Object implements Servlet, ServletConfig, Serializable

Defines a generic, protocol-independent servlet. To write an HTTP servlet for use on the Web, extend {@link javax.servlet.http.HttpServlet} instead.

GenericServlet implements the Servlet and ServletConfig interfaces. GenericServlet may be directly extended by a servlet, although it's more common to extend a protocol-specific subclass such as HttpServlet.

GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface. GenericServlet also implements the log method, declared in the ServletContext interface.

To write a generic servlet, you need only override the abstract service method.

Version: $Rev: 46019 $ $Date: 2005/03/15 10:03:20 $

Constructor Summary
GenericServlet()
Does nothing.
Method Summary
voiddestroy()
Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.
StringgetInitParameter(String name)
Returns a String containing the value of the named initialization parameter, or null if the parameter does not exist.
EnumerationgetInitParameterNames()
Returns the names of the servlet's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the servlet has no initialization parameters.
ServletConfiggetServletConfig()
Returns this servlet's {@link ServletConfig} object.
ServletContextgetServletContext()
Returns a reference to the {@link ServletContext} in which this servlet is running.
StringgetServletInfo()
Returns information about the servlet, such as author, version, and copyright.
StringgetServletName()
Returns the name of this servlet instance.
voidinit(ServletConfig config)
Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
voidinit()
A convenience method which can be overridden so that there's no need to call super.init(config).
voidlog(String msg)
Writes the specified message to a servlet log file, prepended by the servlet's name.
voidlog(String message, Throwable t)
Writes an explanatory message and a stack trace for a given Throwable exception to the servlet log file, prepended by the servlet's name.
abstract voidservice(ServletRequest req, ServletResponse res)
Called by the servlet container to allow the servlet to respond to a request.

Constructor Detail

GenericServlet

public GenericServlet()
Does nothing. All of the servlet initialization is done by one of the init methods.

Method Detail

destroy

public void destroy()
Called by the servlet container to indicate to a servlet that the servlet is being taken out of service. See {@link Servlet#destroy}.

getInitParameter

public String getInitParameter(String name)
Returns a String containing the value of the named initialization parameter, or null if the parameter does not exist. See {@link ServletConfig#getInitParameter}.

This method is supplied for convenience. It gets the value of the named parameter from the servlet's ServletConfig object.

Parameters: name a String specifying the name of the initialization parameter

Returns: String a String containing the value of the initalization parameter

getInitParameterNames

public Enumeration getInitParameterNames()
Returns the names of the servlet's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the servlet has no initialization parameters. See {@link ServletConfig#getInitParameterNames}.

This method is supplied for convenience. It gets the parameter names from the servlet's ServletConfig object.

Returns: Enumeration an enumeration of String objects containing the names of the servlet's initialization parameters

getServletConfig

public ServletConfig getServletConfig()
Returns this servlet's {@link ServletConfig} object.

Returns: ServletConfig the ServletConfig object that initialized this servlet

getServletContext

public ServletContext getServletContext()
Returns a reference to the {@link ServletContext} in which this servlet is running. See {@link ServletConfig#getServletContext}.

This method is supplied for convenience. It gets the context from the servlet's ServletConfig object.

Returns: ServletContext the ServletContext object passed to this servlet by the init method

getServletInfo

public String getServletInfo()
Returns information about the servlet, such as author, version, and copyright. By default, this method returns an empty string. Override this method to have it return a meaningful value. See {@link Servlet#getServletInfo}.

Returns: String information about this servlet, by default an empty string

getServletName

public String getServletName()
Returns the name of this servlet instance. See {@link ServletConfig#getServletName}.

Returns: the name of this servlet instance

init

public void init(ServletConfig config)
Called by the servlet container to indicate to a servlet that the servlet is being placed into service. See {@link Servlet#init}.

This implementation stores the {@link ServletConfig} object it receives from the servlet container for later use. When overriding this form of the method, call super.init(config).

Parameters: config the ServletConfig object that contains configutation information for this servlet

Throws: ServletException if an exception occurs that interrupts the servlet's normal operation

See Also: UnavailableException

init

public void init()
A convenience method which can be overridden so that there's no need to call super.init(config).

Instead of overriding {@link #init(ServletConfig)}, simply override this method and it will be called by GenericServlet.init(ServletConfig config). The ServletConfig object can still be retrieved via {@link #getServletConfig}.

Throws: ServletException if an exception occurs that interrupts the servlet's normal operation

log

public void log(String msg)
Writes the specified message to a servlet log file, prepended by the servlet's name. See {@link ServletContext#log(String)}.

Parameters: msg a String specifying the message to be written to the log file

log

public void log(String message, Throwable t)
Writes an explanatory message and a stack trace for a given Throwable exception to the servlet log file, prepended by the servlet's name. See {@link ServletContext#log(String, Throwable)}.

Parameters: message a String that describes the error or exception t the java.lang.Throwable error or exception

service

public abstract void service(ServletRequest req, ServletResponse res)
Called by the servlet container to allow the servlet to respond to a request. See {@link Servlet#service}.

This method is declared abstract so subclasses, such as HttpServlet, must override it.

Parameters: req the ServletRequest object that contains the client's request res the ServletResponse object that will contain the servlet's response

Throws: ServletException if an exception occurs that interferes with the servlet's normal operation occurred IOException if an input or output exception occurs

Copyright © 2004 Mortbay Consulting Pty. Ltd. All Rights Reserved.