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package javax.servlet;

import java.io.IOException;
import java.util.Enumeration;
import java.util.ResourceBundle;


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


GenericFilter implements the Filter
and FilterConfig interfaces. GenericFilter
may be directly extended by a filter, although it's more common to extend
a protocol-specific subclass such as HttpFilter.

GenericFilter makes writing filters
easier. It provides simple versions of the lifecycle methods 
init and destroy and of the methods 
in the FilterConfig interface.

To write a generic filter, you need only
override the abstract doFilter method. 

Author:	Various
Since:Servlet 4.0
/**
 *
 * <p>Defines a generic, protocol-independent
 * filter. To write an HTTP filter for use on the
 * Web, extend {@link javax.servlet.http.HttpFilter} instead.</p>
 *
 * <p><code>GenericFilter</code> implements the <code>Filter</code>
 * and <code>FilterConfig</code> interfaces. <code>GenericFilter</code>
 * may be directly extended by a filter, although it's more common to extend
 * a protocol-specific subclass such as <code>HttpFilter</code>.
 *
 * <p><code>GenericFilter</code> makes writing filters
 * easier. It provides simple versions of the lifecycle methods 
 * <code>init</code> and <code>destroy</code> and of the methods 
 * in the <code>FilterConfig</code> interface.
 *
 * <p>To write a generic filter, you need only
 * override the abstract <code>doFilter</code> method. 
 *
 * @author 	Various
 * 
 * @since Servlet 4.0
 */

 
public abstract class GenericFilter 
    implements Filter, FilterConfig, java.io.Serializable
{
    private static final String LSTRING_FILE = "javax.servlet.LocalStrings";
    private static final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    private transient FilterConfig config;
    

    
Does nothing. All of the filter initialization
is done by one of the init methods.


Since:Servlet 4.0
/**
     *
     * <p>Does nothing. All of the filter initialization
     * is done by one of the <code>init</code> methods.</p>
     *
     * @since Servlet 4.0
     */
    public GenericFilter() { }
    
    
    
Returns a String containing the value of the named
initialization parameter, or null if the parameter does not exist. See FilterConfig.getInitParameter.


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

Params:
  • name – 		a String specifying the name 
			of the initialization parameter
Returns:String 		a String containing the value
			of the initialization parameter
Since:Servlet 4.0
/**
     * <p>Returns a <code>String</code> containing the value of the named
     * initialization parameter, or <code>null</code> if the parameter does
     * not exist.  See {@link FilterConfig#getInitParameter}.</p>
     *
     * <p>This method is supplied for convenience. It gets the 
     * value of the named parameter from the servlet's 
     * <code>ServletConfig</code> object.
     *
     * @param name 		a <code>String</code> specifying the name 
     *				of the initialization parameter
     *
     * @return String 		a <code>String</code> containing the value
     *				of the initialization parameter
     *
     * @since Servlet 4.0
     *
     */ 
    @Override
    public String getInitParameter(String name) {
        FilterConfig fc = getFilterConfig();
        if (fc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.filter_config_not_initialized"));
        }

        return fc.getInitParameter(name);
    }
    
    
   
Returns the names of the filter's initialization parameters 
as an Enumeration of String objects,
or an empty Enumeration if the filter has no initialization parameters. See FilterConfig.getInitParameterNames.


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

Returns:Enumeration 	an enumeration of String
			objects containing the names of 
			the filter's initialization parameters
Since:Servlet 4.0
/**
    * <p>Returns the names of the filter's initialization parameters 
    * as an <code>Enumeration</code> of <code>String</code> objects,
    * or an empty <code>Enumeration</code> if the filter has no
    * initialization parameters.  See {@link
    * FilterConfig#getInitParameterNames}.</p>
    *
    * <p>This method is supplied for convenience. It gets the 
    * parameter names from the filter's <code>FilterConfig</code> object. 
    *
    * @return Enumeration 	an enumeration of <code>String</code>
    *				objects containing the names of 
    *				the filter's initialization parameters
    *
    * @since Servlet 4.0
    */
    @Override
    public Enumeration<String> getInitParameterNames() {
        FilterConfig fc = getFilterConfig();
        if (fc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.filter_config_not_initialized"));
        }

        return fc.getInitParameterNames();
    }   
     

    
Returns this servlet's ServletConfig object.


Returns:FilterConfig 	the FilterConfig object
			that initialized this filter
Since:Servlet 4.0
/**
     * <p>Returns this servlet's {@link ServletConfig} object.</p>
     *
     * @return FilterConfig 	the <code>FilterConfig</code> object
     *				that initialized this filter
     *
     * @since Servlet 4.0
     */    
    public FilterConfig getFilterConfig() {
	return config;
    }
 
    
    
Returns a reference to the ServletContext in which this filter is running. See FilterConfig.getServletContext.


This method is supplied for convenience. It gets the 
context from the filter's FilterConfig object.

Returns:ServletContext 	the ServletContext object
			passed to this filter by the init
			method
Since:Servlet 4.0
/**
     * <p>Returns a reference to the {@link ServletContext} in which this filter
     * is running.  See {@link FilterConfig#getServletContext}.</p>
     *
     * <p>This method is supplied for convenience. It gets the 
     * context from the filter's <code>FilterConfig</code> object.
     *
     * @return ServletContext 	the <code>ServletContext</code> object
     *				passed to this filter by the <code>init</code>
     *				method
     *
     * @since Servlet 4.0
     */
    @Override
    public ServletContext getServletContext() {
        FilterConfig sc = getFilterConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.filter_config_not_initialized"));
        }

        return sc.getServletContext();
    }


    
Called by the servlet container to indicate to a filter that it is being placed into service. See Filter.init.


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

Params:
  • config – 			the FilterConfig object
				that contains configuration
				information for this filter
Throws:
  • ServletException – 	if an exception occurs that
				interrupts the servlet's normal
				operation
See Also:
Since:Servlet 4.0
/**
     * <p>Called by the servlet container to indicate to a filter that
     * it is being placed into service.  See {@link Filter#init}.</p>
     * 
     * <p>This implementation stores the {@link FilterConfig}
     * object it receives from the servlet container for later use.
     * When overriding this form of the method, call 
     * <code>super.init(config)</code>.
     * 
     * @param config 			the <code>FilterConfig</code> object
     *					that contains configuration
     *					information for this filter
     *
     * @exception ServletException 	if an exception occurs that
     *					interrupts the servlet's normal
     *					operation
     * 
     * @see 				UnavailableException
     *
     * @since Servlet 4.0
     */
    @Override
    public void init(FilterConfig 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 init(FilterConfig), simply override this method and it will be called by GenericFilter.init(FilterConfig config).
The FilterConfig object can still be retrieved via getFilterConfig. 
Throws:
  • ServletException – 	if an exception occurs that
				interrupts the servlet's
				normal operation
Since:Servlet 4.0
/**
     * <p>A convenience method which can be overridden so that there's no need
     * to call <code>super.init(config)</code>.</p>
     *
     * <p>Instead of overriding {@link #init(FilterConfig)}, simply override
     * this method and it will be called by
     * <code>GenericFilter.init(FilterConfig config)</code>.
     * The <code>FilterConfig</code> object can still be retrieved via {@link
     * #getFilterConfig}. 
     * 
     * @exception ServletException 	if an exception occurs that
     *					interrupts the servlet's
     *					normal operation
     *
     * @since Servlet 4.0
     */
    public void init() throws ServletException {

    }
    

    
Returns the name of this filter instance. See FilterConfig.getFilterName.


Returns:         the name of this filter instance
Since:Servlet 4.0
/**
     * <p>Returns the name of this filter instance.
     * See {@link FilterConfig#getFilterName}.</p>
     *
     * @return          the name of this filter instance
     *
     * @since Servlet 4.0
     */
    @Override
    public String getFilterName() {
        FilterConfig sc = getFilterConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getFilterName();
    }
}