javax.servlet.GenericFilter Maven / Gradle / Ivy
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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 {@link javax.servlet.http.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 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 4.0
*/
public GenericFilter() { }
/**
* Called by the servlet container to indicate to a filter that the
* filter is being taken out of service. See {@link Filter#destroy}.
*
*
* @since 4.0
*
*/
@Override
public void destroy() {
}
/**
* Returns a String containing the value of the named
* initialization parameter, or null if the parameter does
* not exist. See {@link FilterConfig#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
*
* @since 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 {@link
* FilterConfig#getInitParameterNames}.
*
*
*
* This method is supplied for convenience. It gets the
* parameter names from the filter's FilterConfig object.
*
*
*
* @return Enumeration an enumeration of String
* objects containing the names of
* the filter's initialization parameters
*
* @since 4.0
*/
@Override
public Enumeration getInitParameterNames() {
FilterConfig fc = getFilterConfig();
if (fc == null) {
throw new IllegalStateException(
lStrings.getString("err.filter_config_not_initialized"));
}
return fc.getInitParameterNames();
}
/**
* Returns this servlet's {@link ServletConfig} object.
*
* @return FilterConfig the FilterConfig object
* that initialized this filter
*
* @since 4.0
*/
public FilterConfig getFilterConfig() {
return config;
}
/**
* Returns a reference to the {@link ServletContext} in which this filter
* is running. See {@link FilterConfig#getServletContext}.
*
*
*
* This method is supplied for convenience. It gets the
* context from the filter's FilterConfig object.
*
*
*
* @return ServletContext the ServletContext object
* passed to this filter by the init
* method
*
* @since 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 {@link Filter#init}.
*
*
*
* This implementation stores the {@link FilterConfig}
* object it receives from the servlet container for later use.
* When overriding this form of the method, call
* super.init(config).
*
*
*
* @param config the FilterConfig object
* that contains configuration
* information for this filter
*
* @exception ServletException if an exception occurs that
* interrupts the servlet's normal
* operation
*
* @see UnavailableException
*
* @since 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 {@link #init(FilterConfig)}, simply override
* this method and it will be called by
* GenericFilter.init(FilterConfig config).
* The FilterConfig object can still be retrieved via {@link
* #getFilterConfig}.
*
*
*
* @exception ServletException if an exception occurs that
* interrupts the servlet's
* normal operation
*
* @since 4.0
*/
public void init() throws ServletException {
}
/**
* Called by the servlet container to allow the filter to respond to
* a request. See {@link Filter#doFilter}.
*
* This method is declared abstract so subclasses, such as
* HttpFilter, 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
*
* @param chain the FilterChain for invoking the next filter or the resource
*
* @exception ServletException if an exception occurs that
* interferes with the servlet's
* normal operation occurred
*
* @exception IOException if an input or output
* exception occurs
*
* @since 4.0
*/
@Override
public abstract void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException;
/**
*
Returns the name of this filter instance.
* See {@link FilterConfig#getFilterName}.
*
* @return the name of this filter instance
*
* @since 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();
}
}