src/main/java/org/apache/log4j/pattern/ThrowableInformationPatternConverter.java

/*
 * 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.pattern;

import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.spi.ThrowableInformation;


/**
 * Outputs the ThrowableInformation portion of the LoggingEvent.
 * By default, outputs the full stack trace.  %throwable{none}
 * or %throwable{0} suppresses the stack trace. %throwable{short}
 * or %throwable{1} outputs just the first line.  %throwable{n}
 * will output n lines for a positive integer or drop the last
 * -n lines for a negative integer.
 *
 * @author Paul Smith
 *
 */
public class ThrowableInformationPatternConverter
  extends LoggingEventPatternConverter {

  /**
   * Maximum lines of stack trace to output.
   */
  private int maxLines = Integer.MAX_VALUE;

  /**
   * Private constructor.
   * @param options options, may be null.
   */
  private ThrowableInformationPatternConverter(
    final String[] options) {
    super("Throwable", "throwable");

    if ((options != null) && (options.length > 0)) {
      if("none".equals(options[0])) {
          maxLines = 0;
      } else if("short".equals(options[0])) {
          maxLines = 1;
      } else {
          try {
              maxLines = Integer.parseInt(options[0]);
          } catch(NumberFormatException ex) {
              maxLines = Integer.MAX_VALUE;
          }
      }
    }
  }

  /**
   * Gets an instance of the class.
    * @param options pattern options, may be null.  If first element is "short",
   * only the first line of the throwable will be formatted.
   * @return instance of class.
   */
  public static ThrowableInformationPatternConverter newInstance(
    final String[] options) {
    return new ThrowableInformationPatternConverter(options);
  }

  /**
   * {@inheritDoc}
   */
  public void format(final LoggingEvent event, final StringBuffer toAppendTo) {
    if (maxLines != 0) {
      ThrowableInformation information = event.getThrowableInformation();

      if (information != null) {
        String[] stringRep = information.getThrowableStrRep();

        int length = stringRep.length;
        if (maxLines < 0) {
            length += maxLines;
        } else if (length > maxLines) {
            length = maxLines;
        }

        for (int i = 0; i < length; i++) {
            String string = stringRep[i];
            toAppendTo.append(string).append("\n");
        }
      }
    }
  }

  /**
   * This converter obviously handles throwables.
   * @return true.
   */
  public boolean handlesThrowable() {
    return true;
  }
}