javax.servlet.GenericServlet Maven / Gradle / Ivy
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* JBoss, Home of Professional Open Source.
* Copyright 2007, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
import java.util.ResourceBundle;
/**
* 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.
*
* @author Various
*/
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable
{
private static final String LSTRING_FILE = "javax.servlet.LocalStrings";
private static ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE);
private transient ServletConfig config;
/**
* Does nothing. All of the servlet initialization is done by one of the
* init methods.
*/
public GenericServlet()
{
}
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being taken out of service. See {@link Servlet#destroy}.
*/
public void destroy()
{
}
/**
* 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.
*
* @param name
* a String specifying the name of the
* initialization parameter
* @return String a String containing the value of the
* initialization parameter
*/
public String getInitParameter(String name)
{
ServletConfig sc = getServletConfig();
if (sc == null)
{
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getInitParameter(name);
}
/**
* 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.
*
* @return Enumeration an enumeration of String objects
* containing the names of the servlet's initialization parameters
*/
public Enumeration getInitParameterNames()
{
ServletConfig sc = getServletConfig();
if (sc == null)
{
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getInitParameterNames();
}
/**
* Returns this servlet's {@link ServletConfig} object.
*
* @return ServletConfig the ServletConfig object that
* initialized this servlet
*/
public ServletConfig getServletConfig()
{
return config;
}
/**
* 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.
*
* @return ServletContext the ServletContext object passed to
* this servlet by the init method
*/
public ServletContext getServletContext()
{
ServletConfig sc = getServletConfig();
if (sc == null)
{
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getServletContext();
}
/**
* 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}.
*
* @return String information about this servlet, by default an empty string
*/
public String getServletInfo()
{
return "";
}
/**
* 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).
*
* @param config
* the ServletConfig object that contains
* configutation information for this servlet
* @exception ServletException
* if an exception occurs that interrupts the servlet's normal
* operation
* @see UnavailableException
*/
public void init(ServletConfig config) throws ServletException
{
this.config = config;
this.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}.
*
* @exception ServletException
* if an exception occurs that interrupts the servlet's normal
* operation
*/
public void init() throws ServletException
{
}
/**
* Writes the specified message to a servlet log file, prepended by the
* servlet's name. See {@link ServletContext#log(String)}.
*
* @param msg
* a String specifying the message to be written to
* the log file
*/
public void log(String msg)
{
getServletContext().log(getServletName() + ": " + msg);
}
/**
* 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)}.
*
* @param message
* a String that describes the error or exception
* @param t
* the java.lang.Throwable error or exception
*/
public void log(String message, Throwable t)
{
getServletContext().log(getServletName() + ": " + message, t);
}
/**
* 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.
*
* @param req
* the ServletRequest object that contains the
* client's request
* @param res
* the ServletResponse object that will contain the
* servlet's response
* @exception ServletException
* if an exception occurs that interferes with the servlet's
* normal operation occurred
* @exception IOException
* if an input or output exception occurs
*/
public abstract void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;
/**
* Returns the name of this servlet instance. See
* {@link ServletConfig#getServletName}.
*
* @return the name of this servlet instance
*/
public String getServletName()
{
ServletConfig sc = getServletConfig();
if (sc == null)
{
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getServletName();
}
}