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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();
}
}