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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17
    18  package org.apache.log4j.spi;
    19
    20  import org.apache.log4j.spi.LoggingEvent;
    21
    22
    23  /***
    24     Users should extend this class to implement customized logging
    25     event filtering. Note that {@link org.apache.log4j.Category} and {@link
    26     org.apache.log4j.AppenderSkeleton}, the parent class of all standard
    27     appenders, have built-in filtering rules. It is suggested that you
    28     first use and understand the built-in rules before rushing to write
    29     your own custom filters.
    30
    31     <p>This abstract class assumes and also imposes that filters be
    32     organized in a linear chain. The {@link #decide
    33     decide(LoggingEvent)} method of each filter is called sequentially,
    34     in the order of their addition to the chain.
    35
    36     <p>The {@link #decide decide(LoggingEvent)} method must return one
    37     of the integer constants {@link #DENY}, {@link #NEUTRAL} or {@link
    38     #ACCEPT}.
    39
    40     <p>If the value {@link #DENY} is returned, then the log event is
    41     dropped immediately without consulting with the remaining
    42     filters.
    43
    44     <p>If the value {@link #NEUTRAL} is returned, then the next filter
    45     in the chain is consulted. If there are no more filters in the
    46     chain, then the log event is logged. Thus, in the presence of no
    47     filters, the default behaviour is to log all logging events.
    48
    49     <p>If the value {@link #ACCEPT} is returned, then the log
    50     event is logged without consulting the remaining filters.
    51
    52     <p>The philosophy of log4j filters is largely inspired from the
    53     Linux ipchains.
    54
    55     <p>Note that filtering is only supported by the {@link
    56     org.apache.log4j.xml.DOMConfigurator DOMConfigurator}. The {@link
    57     org.apache.log4j.PropertyConfigurator PropertyConfigurator} does not
    58     support filters.
    59
    60     @author Ceki G&uuml;lc&uuml;
    61     @since 0.9.0 */
    62  public abstract class Filter implements OptionHandler {
    63
    64    /***
    65       Points to the next filter in the filter chain.
    66
    67       @deprecated As of 1.2.12, use {@link #getNext} and {@link #setNext} instead
    68     */
    69    public Filter next;
    70
    71    /***
    72       The log event must be dropped immediately without consulting
    73       with the remaining filters, if any, in the chain.  */
    74    public static final int DENY    = -1;
    75
    76    /***
    77       This filter is neutral with respect to the log event. The
    78       remaining filters, if any, should be consulted for a final decision.
    79    */
    80    public static final int NEUTRAL = 0;
    81
    82    /***
    83       The log event must be logged immediately without consulting with
    84       the remaining filters, if any, in the chain.  */
    85    public static final int ACCEPT  = 1;
    86
    87
    88    /***
    89       Usually filters options become active when set. We provide a
    90       default do-nothing implementation for convenience.
    91    */
    92    public
    93    void activateOptions() {
    94    }
    95
    96
    97
    98    /***
    99       <p>If the decision is <code>DENY</code>, then the event will be
    100      dropped. If the decision is <code>NEUTRAL</code>, then the next
    101      filter, if any, will be invoked. If the decision is ACCEPT then
    102      the event will be logged without consulting with other filters in
    103      the chain.
    104
    105      @param event The LoggingEvent to decide upon.
    106      @return decision The decision of the filter.  */
    107   abstract
    108   public
    109   int decide(LoggingEvent event);
    110
    111   /***
    112    * Set the next filter pointer.
    113    */
    114   public void setNext(Filter next) {
    115     this.next = next;
    116   }
    117
    118   /***
    119    * Return the pointer to the next filter;
    120    */
    121   public Filter getNext() {
    122         return next;
    123   }
    124
    125 }