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

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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

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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);
    }
}

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