Logback: the reliable, generic, fast and flexible logging framework.
Copyright (C) 1999-2015, QOS.ch. All rights reserved.
This program and the accompanying materials are dual-licensed under
either the terms of the Eclipse Public License v1.0 as published by
the Eclipse Foundation
  or (per the licensee's choosing)
under the terms of the GNU Lesser General Public License version 2.1
as published by the Free Software Foundation.
/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.classic.pattern;

import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.Context;
import ch.qos.logback.core.pattern.Converter;
import ch.qos.logback.core.pattern.ConverterUtil;
import ch.qos.logback.core.pattern.PostCompileProcessor;

public class EnsureExceptionHandling implements PostCompileProcessor<ILoggingEvent> {

    
This implementation checks if any of the converters in the chain handles exceptions. If not, then this method adds a ExtendedThrowableProxyConverter instance to the end of the chain. 

This allows appenders using this layout to output exception information
event if the user forgets to add %ex to the pattern. Note that the
appenders defined in the Core package are not aware of exceptions nor
LoggingEvents.

If for some reason the user wishes to NOT print exceptions, then she can
add %nopex to the pattern.
/**
     * This implementation checks if any of the converters in the chain handles
     * exceptions. If not, then this method adds a
     * {@link ExtendedThrowableProxyConverter} instance to the end of the chain.
     * <p>
     * This allows appenders using this layout to output exception information
     * event if the user forgets to add %ex to the pattern. Note that the
     * appenders defined in the Core package are not aware of exceptions nor
     * LoggingEvents.
     * <p>
     * If for some reason the user wishes to NOT print exceptions, then she can
     * add %nopex to the pattern.
     * 
     * 
     */
    public void process(Context context, Converter<ILoggingEvent> head) {
        if (head == null) {
            // this should never happen
            throw new IllegalArgumentException("cannot process empty chain");
        }
        if (!chainHandlesThrowable(head)) {
            Converter<ILoggingEvent> tail = ConverterUtil.findTail(head);
            Converter<ILoggingEvent> exConverter = null;
            LoggerContext loggerContext = (LoggerContext) context;
            if (loggerContext.isPackagingDataEnabled()) {
                exConverter = new ExtendedThrowableProxyConverter();
            } else {
                exConverter = new ThrowableProxyConverter();
            }
            tail.setNext(exConverter);
        }
    }

    
This method computes whether a chain of converters handles exceptions or
not.
Params:
head – 
               The first element of the chain
Returns:
true if can handle throwables contained in logging events/**
     * This method computes whether a chain of converters handles exceptions or
     * not.
     * 
     * @param head
     *                The first element of the chain
     * @return true if can handle throwables contained in logging events
     */
    public boolean chainHandlesThrowable(Converter<ILoggingEvent> head) {
        Converter<ILoggingEvent> c = head;
        while (c != null) {
            if (c instanceof ThrowableHandlingConverter) {
                return true;
            }
            c = c.getNext();
        }
        return false;
    }
}