[LOG4J2-1217] Layout option to limit length of text

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.1
• Fix Version/s: 2.6
• Component/s: Pattern Converters
• Flags: Patch
• Assignee: Matt Sicker
• Reporter: Thies Wellpott
• Created: 09/Dec/15 11:09
• Updated: 03/Mar/16 07:35
• Resolved: 03/Mar/16 04:33

Description

PatternLayout does not provide the ability to limit the length of the text without space padding (with the numbers directly after the %).

The following Converter provides this possibility:
%maxLen{pattern}{max. length}, e.g. %maxLen{%m}{90}
use %maxLen or %maxLength

MaxLengthConverter.java

package de.ittw.log4j;

import java.util.List;

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.apache.logging.log4j.core.pattern.ConverterKeys;
import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;
import org.apache.logging.log4j.core.pattern.PatternConverter;
import org.apache.logging.log4j.core.pattern.PatternFormatter;
import org.apache.logging.log4j.core.pattern.PatternParser;

/**
 * Max length pattern converter. Limit contained text to a maximum length.
 * On invalid length the default value 100 is used (and an error message is logged).
 * If max length is greater than 20, an abbreviated text will get ellipsis ("...") appended.
 * Example usage (for email subject):
 *    "%maxLen{[AppName, ${hostName}, ${web:contextPath}] %p: %c{1} - %m%notEmpty{ =>%ex{short}}}{160}"
 *
 * @author Thies Wellpott
 */
@Plugin(name = "maxLength", category = PatternConverter.CATEGORY)
@ConverterKeys({ "maxLength", "maxLen" })
public final class MaxLengthConverter extends LogEventPatternConverter
{

    /**
     * Gets an instance of the class.
     *
     * @param config
     *            The current Configuration.
     * @param options
     *            pattern options, an array of two elements: pattern, max length (defaults to 100 on invalid value).
     * @return instance of class.
     */
    public static MaxLengthConverter newInstance(final Configuration config, final String[] options) {
        if (options.length != 2) {
            LOGGER.error("Incorrect number of options on maxLength: expected 2 received {}: {}", options.length, options);
            return null;
        }
        if (options[0] == null) {
            LOGGER.error("No pattern supplied on maxLength");
            return null;
        }
        if (options[1] == null) {
            LOGGER.error("No length supplied on maxLength");
            return null;
        }
        final PatternParser parser = PatternLayout.createPatternParser(config);
        final List<PatternFormatter> formatters = parser.parse(options[0]);
        return new MaxLengthConverter(formatters, AbstractAppender.parseInt(options[1], 100));
    }


    private final List<PatternFormatter> formatters;
    private final int maxLength;

    /**
     * Construct the converter.
     *
     * @param formatters
     *            The PatternFormatters to generate the text to manipulate.
     * @param maxLength
     *            The max. length of the resultung string. Ellipses ("...") is appended on shorted string, if greater than 20.
     */
    private MaxLengthConverter(final List<PatternFormatter> formatters, final int maxLength) {
        super("MaxLength", "maxLength");
        this.maxLength = maxLength;
        this.formatters = formatters;
        LOGGER.trace("new MaxLengthConverter with {}", maxLength);
    }


    @Override
    public void format(final LogEvent event, final StringBuilder toAppendTo) {
        final StringBuilder buf = new StringBuilder();
        for (final PatternFormatter formatter : formatters) {
            formatter.format(event, buf);
            if (buf.length() > maxLength) {        // stop early
                break;
            }
        }
        if (buf.length() > maxLength) {
            buf.setLength(maxLength);
            if (maxLength > 20) {        // only append ellipses if length is not very short
                buf.append("...");
            }
        }
        toAppendTo.append(buf);
    }

}

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