Log4j具有带log4j.properties的两个输出？

Question

I want to use the Log4j API but I encountered a little problem with the configuration.

This is my LogWriter Class:

public class LogWriter {
    static Logger logger = Logger.getLogger(LogWriter.class);

    public LogWriter(String logFilePath) {
        File outFile = new File(logFilePath);
        try {
            PrintStream outStream = new PrintStream(new FileOutputStream(outFile));
            System.setOut(outStream));    
            System.setErr(outStream);
        } catch (FileNotFoundException e) {
            throw new IllegalArgumentException("File not Found");
        }
        BasicConfigurator.configure();
    }

    public void write(String infoString) {
        logger.info(infoString);
    }
}

Now this works fine, but I can't write into the Logger-File and the Console at the same time (probably because of System.setOut )

I added a log4j.properties File that looks like this:

# Root logger option
log4j.rootLogger=INFO, console

# Direct log messages to console
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.Target=System.out
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-5p- %m%n

Now my question is, how can I make my LogWriter and the log4j.properties File work together, so that the Output comes into the Logger-File and the Console? What do I have to change in my LogWriter?

Answer 1

Before installing your LogWriter , you must keep copies of the original references stored in System.out and System.err somewhere. Use them to write a new appender. Configure log4j to use this appender in log4j.appender.console .

Background: The default log4j ConsoleAppender just writes to System.out . If you change it, log4j will use whatever you supply. There is no way to configure ConsoleAppender to write somewhere else. In your LogWriter , it's not possible to distinguish between output coming from log4j and System.out.println() .

So the only solution is to write another appender which writes to the original System.out .

That said, it might be smarter to use the original ConsoleAppender and use a FileAppender instead of your own LogWriter . Just make sure you never use System.out directly anywhere in your code.