+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.log4j.spi;
+
+
+
+/**
+ Users should extend this class to implement customized logging
+ event filtering. Note that {@link org.apache.log4j.Category} and {@link
+ org.apache.log4j.AppenderSkeleton}, the parent class of all standard
+ appenders, have built-in filtering rules. It is suggested that you
+ first use and understand the built-in rules before rushing to write
+ your own custom filters.
+
+ <p>This abstract class assumes and also imposes that filters be
+ organized in a linear chain. The {@link #decide
+ decide(LoggingEvent)} method of each filter is called sequentially,
+ in the order of their addition to the chain.
+
+ <p>The {@link #decide decide(LoggingEvent)} method must return one
+ of the integer constants {@link #DENY}, {@link #NEUTRAL} or {@link
+ #ACCEPT}.
+
+ <p>If the value {@link #DENY} is returned, then the log event is
+ dropped immediately without consulting with the remaining
+ filters.
+
+ <p>If the value {@link #NEUTRAL} is returned, then the next filter
+ in the chain is consulted. If there are no more filters in the
+ chain, then the log event is logged. Thus, in the presence of no
+ filters, the default behaviour is to log all logging events.
+
+ <p>If the value {@link #ACCEPT} is returned, then the log
+ event is logged without consulting the remaining filters.
+
+ <p>The philosophy of log4j filters is largely inspired from the
+ Linux ipchains.
+
+ <p>Note that filtering is only supported by the {@link
+ org.apache.log4j.xml.DOMConfigurator DOMConfigurator}. The {@link
+ org.apache.log4j.PropertyConfigurator PropertyConfigurator} does not
+ support filters.
+
+ @author Ceki Gülcü
+ @since 0.9.0 */
+public abstract class Filter implements OptionHandler {
+
+ /**
+ Points to the next filter in the filter chain.
+
+ @deprecated As of 1.2.12, use {@link #getNext} and {@link #setNext} instead
+ */
+ public Filter next;
+
+ /**
+ The log event must be dropped immediately without consulting
+ with the remaining filters, if any, in the chain. */
+ public static final int DENY = -1;
+
+ /**
+ This filter is neutral with respect to the log event. The
+ remaining filters, if any, should be consulted for a final decision.
+ */
+ public static final int NEUTRAL = 0;
+
+ /**
+ The log event must be logged immediately without consulting with
+ the remaining filters, if any, in the chain. */
+ public static final int ACCEPT = 1;
+
+
+ /**
+ Usually filters options become active when set. We provide a
+ default do-nothing implementation for convenience.
+ */
+ public
+ void activateOptions() {
+ }
+
+
+
+ /**
+ <p>If the decision is <code>DENY</code>, then the event will be
+ dropped. If the decision is <code>NEUTRAL</code>, then the next
+ filter, if any, will be invoked. If the decision is ACCEPT then
+ the event will be logged without consulting with other filters in
+ the chain.
+
+ @param event The LoggingEvent to decide upon.
+ @return decision The decision of the filter. */
+ abstract
+ public
+ int decide(LoggingEvent event);
+
+ /**
+ * Set the next filter pointer.
+ */
+ public void setNext(Filter next) {
+ this.next = next;
+ }
+
+ /**
+ * Return the pointer to the next filter;
+ */
+ public Filter getNext() {
+ return next;
+ }
+
+}