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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();
}
}