javax.servlet

Class GenericServlet

java.lang.Object

javax.servlet.GenericServlet

All Implemented Interfaces:

java.io.Serializable, Servlet, ServletConfig

Direct Known Subclasses:

HttpServlet

public abstract class GenericServlet
extends java.lang.Object
implements Servlet, ServletConfig, java.io.Serializable

Defines a generic, protocol-independent servlet. To write an HTTP servlet for use on the Web, extend 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.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GenericServlet() Does nothing.

Method Summary

Modifier and Type	Method and Description
void	destroy() Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.
java.lang.String	getInitParameter(java.lang.String name) Returns a String containing the value of the named initialization parameter, or null if the parameter does not exist.
java.util.Enumeration<java.lang.String>	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.
ServletConfig	getServletConfig() Returns this servlet's ServletConfig object.
ServletContext	getServletContext() Returns a reference to the ServletContext in which this servlet is running.
java.lang.String	getServletInfo() Returns information about the servlet, such as author, version, and copyright.
java.lang.String	getServletName() Returns the name of this servlet instance.
void	init() A convenience method which can be overridden so that there's no need to call super.init(config).
void	init(ServletConfig config) Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
void	log(java.lang.String msg) Writes the specified message to a servlet log file, prepended by the servlet's name.
void	log(java.lang.String message, java.lang.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 void	service(ServletRequest req, ServletResponse res) Called by the servlet container to allow the servlet to respond to a request.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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 Servlet.destroy().

Specified by:

destroy in interface Servlet

getInitParameter

public java.lang.String getInitParameter(java.lang.String name)

Returns a String containing the value of the named initialization parameter, or null if the parameter does not exist. See ServletConfig.getInitParameter(java.lang.String).

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

Specified by:

getInitParameter in interface ServletConfig

Parameters:

name - a String specifying the name of the initialization parameter

Returns:

String a String containing the value of the initialization parameter

getInitParameterNames

public java.util.Enumeration<java.lang.String> 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 ServletConfig.getInitParameterNames().

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

Specified by:

getInitParameterNames in interface ServletConfig

Returns:

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

getServletConfig

public ServletConfig getServletConfig()

Returns this servlet's ServletConfig object.

Specified by:

getServletConfig in interface Servlet

Returns:

ServletConfig the ServletConfig object that initialized this servlet

See Also:

Servlet.init(javax.servlet.ServletConfig)

getServletContext

public ServletContext getServletContext()

Returns a reference to the ServletContext in which this servlet is running. See ServletConfig.getServletContext().

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

Specified by:

getServletContext in interface ServletConfig

Returns:

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

See Also:

ServletContext

getServletInfo

public java.lang.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 Servlet.getServletInfo().

Specified by:

getServletInfo in interface Servlet

Returns:

String information about this servlet, by default an empty string

init

public void init(ServletConfig config)
          throws ServletException

Called by the servlet container to indicate to a servlet that the servlet is being placed into service. See Servlet.init(javax.servlet.ServletConfig).

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

Specified by:

init in interface Servlet

Parameters:

config - the ServletConfig object that contains configuration information for this servlet

Throws:

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

See Also:

UnavailableException

init

public void init()
          throws ServletException

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

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

Throws:

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

log

public void log(java.lang.String msg)

Writes the specified message to a servlet log file, prepended by the servlet's name. See ServletContext.log(String).

Parameters:

msg - a String specifying the message to be written to the log file

log

public void log(java.lang.String message,
                java.lang.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 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)
                      throws ServletException,
                             java.io.IOException

Called by the servlet container to allow the servlet to respond to a request. See Servlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse).

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

Specified by:

service in interface Servlet

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

java.io.IOException - if an input or output exception occurs

getServletName

public java.lang.String getServletName()

Returns the name of this servlet instance. See ServletConfig.getServletName().

Specified by:

getServletName in interface ServletConfig

Returns:

the name of this servlet instance