src/java/org/apache/log4j/filter/LocationInfoFilter.java

/*
 * Copyright 1999,2004 The Apache Software Foundation.
 * 
 * Licensed 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.filter;

import org.apache.log4j.rule.ExpressionRule;
import org.apache.log4j.rule.Rule;
import org.apache.log4j.spi.Filter;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.spi.location.LocationInfo;


/**
 * Location information is usually specified at the appender level - all events associated 
 * with an appender either create and parse stack traces or they do not.  This is
 * an expensive operation and in some cases not needed for all events associated with
 * an appender.
 * 
 * This filter creates event-level location information only if the provided expression evaluates to true.
 * 
 * For information on expression syntax, see org.apache.log4j.rule.ExpressionRule
 * 
 * @author Scott Deboy sdeboy@apache.org
 */
public class LocationInfoFilter extends Filter {
  boolean convertInFixToPostFix = true;
  String expression;
  Rule expressionRule;
  //HACK: Category is the last of the internal layers - pass this in as the class name
  //in order for parsing to work correctly
  private String className = "org.apache.log4j.Category";

  public void activateOptions() {
    expressionRule =
      ExpressionRule.getRule(expression, !convertInFixToPostFix);
  }

  public void setExpression(String expression) {
    this.expression = expression;
  }

  public String getExpression() {
    return expression;
  }

  public void setConvertInFixToPostFix(boolean convertInFixToPostFix) {
    this.convertInFixToPostFix = convertInFixToPostFix;
  }

  public boolean getConvertInFixToPostFix() {
    return convertInFixToPostFix;
  }

  /**
   * If this event does not already contain location information, 
   * evaluate the event against the expression.
   * 
   * If the expression evaluates to true, generate a LocationInfo instance 
   * by creating an exception and set this LocationInfo on the event.
   * 
   * Returns {@link Filter#NEUTRAL}
   */
  public int decide(LoggingEvent event) {
    if (!event.locationInformationExists()) {
      if (expressionRule.evaluate(event)) {
	      Throwable t = new Exception();
	      event.setLocationInformation(new LocationInfo(t, className));
      }
    }
    return Filter.NEUTRAL;
  }
}