Get live Log4J messages

开发者_JAVA技巧How do I get what is being written by log4j in central class which monitors all log4j logs in the application?

Thanks

Edit: I wish I would not have to read it from the log file since it would use more resources

You can implement your own Appender and copy all logs on it using the normal config:

log4j.rootLogger=WARN, file, other

log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=${catalina.home}/logs/log.log
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=10
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{ISO8601} %p %t %c - %m%n

log4j.appender.other=class.path.of.your.Appender

maybe your requirement is same with me. I just write a relevant class to realize it.

public class FixedBufferAppender extends AppenderSkeleton {
    private LimitTailSizeList ll;

    public FixedBufferAppender(PatternLayout layOut, int size) {
        this.layout = layOut;
        ll = new LimitTailSizeList(size);
    }

    protected void append(LoggingEvent event) {
        String log = this.layout.format(event);
        ll.add(log);
    }

    public String getLatentLog() {
        StringBuffer sb = new StringBuffer(100000);
        for (Iterator iterator = ll.iterator(); iterator.hasNext();) {
            String log = (String) iterator.next();
            sb.append(log);
        }
        return sb.toString();
    }

    public void close() {
        ll.clear();
        ll = null;
        this.closed = true;
    }

    public boolean requiresLayout() {
        return true;
    }
}

public class LimitTailSizeList extends ArrayList {
    private int limitSize;

    public LimitTailSizeList(int limitSize){
        this.limitSize= limitSize;
    }

    public boolean add(Object o) {
        boolean add = super.add(o);
        if (size() > limitSize) {
            removeRange(0, size() - limitSize);
        }
        return add;
    }

    private void initAppender(int maxTailLine) {
        fba = new FixedBufferAppender(
            new PatternLayout("%d [%X{requestURIWithQueryString}] %-5p -[%t] %m  [%c{1}:%M %L] %n"),
            maxTailLine);
        Logger.getRootLogger().removeAppender("UI_APPENDER");
        fba.setName("UI_APPENDER");
        fba.setThreshold(org.apache.log4j.Level.DEBUG);
        Logger.getRootLogger().addAppender(fba);
    }
}

By providing log4j configuration that outputs log messages into a file or any other location.