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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  package org.apache.log4j.helpers;
    18
    19  import org.apache.log4j.spi.LoggingEvent;
    20  import org.apache.log4j.pattern.LogEvent;
    21
    22  import java.lang.reflect.Method;
    23  import java.util.Set;
    24  import java.io.ByteArrayOutputStream;
    25  import java.io.ObjectOutputStream;
    26  import java.io.ByteArrayInputStream;
    27  import java.io.ObjectInputStream;
    28
    29
    30  public final class MDCKeySetExtractor {
    31      private final Method getKeySetMethod;
    32      public static final MDCKeySetExtractor INSTANCE =
    33              new MDCKeySetExtractor();
    34
    35
    36      private MDCKeySetExtractor() {
    37          //
    38          //  log4j 1.2.15 and later will have method to get names
    39          //     of all keys in MDC
    40          //
    41        Method getMethod = null;
    42
    43          try {
    44             getMethod = LoggingEvent.class.getMethod(
    45                        "getPropertyKeySet", null);
    46          } catch(Exception ex) {
    47              getMethod = null;
    48          }
    49        getKeySetMethod = getMethod;
    50
    51      }
    52
    53      public Set getPropertyKeySet(final LoggingEvent event) throws Exception {
    54          //
    55          //  MDC keys are not visible prior to log4j 1.2.15
    56          //
    57          Set keySet = null;
    58          if (getKeySetMethod != null) {
    59                keySet = (Set) getKeySetMethod.invoke(event, null);
    60          } else {
    61              //
    62              //  for 1.2.14 and earlier could serialize and
    63              //    extract MDC content
    64                ByteArrayOutputStream outBytes = new ByteArrayOutputStream();
    65                ObjectOutputStream os = new ObjectOutputStream(outBytes);
    66                os.writeObject(event);
    67                os.close();
    68
    69                byte[] raw = outBytes.toByteArray();
    70                //
    71                //   bytes 6 and 7 should be the length of the original classname
    72                //     should be the same as our substitute class name
    73                final String subClassName = LogEvent.class.getName();
    74                if (raw[6] == 0 || raw[7] == subClassName.length()) {
    75                    //
    76                    //  manipulate stream to use our class name
    77                    //
    78                    for (int i = 0; i < subClassName.length(); i++) {
    79                        raw[8 + i] = (byte) subClassName.charAt(i);
    80                    }
    81                    ByteArrayInputStream inBytes = new ByteArrayInputStream(raw);
    82                    ObjectInputStream is = new ObjectInputStream(inBytes);
    83                    Object cracked = is.readObject();
    84                    if (cracked instanceof LogEvent) {
    85                        keySet = ((LogEvent) cracked).getPropertyKeySet();
    86                    }
    87                    is.close();
    88                }
    89          }
    90          return keySet;
    91      }
    92  }