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Redirecting System.out to somewhere else (Java)

At times you want the output of all the System.out.println and other System.out print stuff in a log file or in a UI window somewhere. To do this, you need to wrap PrintStream, and call System.setOut and System.setErr

Example Wrapper class that provides the tee function:

public class LogCapture extends PrintStream {
   
    private File outFile;
    private PrintStream filePrint;
    private boolean canLog = false;
   
    public LogCapture(PrintStream original, String logFile) {
        super(original);
        outFile = new File(logFile);
        try {
            if (!outFile.exists())
                outFile.createNewFile();
            filePrint = new PrintStream(outFile);
            if(outFile.canWrite())
                canLog = true;
            else
                canLog = false;
        } catch (Exception e) {
            e.printStackTrace();
            canLog = false;
        }
    }
   
    @Override
    public void write(byte buf[], int off, int len) {
        try {
            super.write(buf, off, len);
            if (canLog)
                filePrint.write(buf, off, len);
        } catch (Exception e) {
        }
    }
   
    @Override
    public void flush() {
        super.flush();
        filePrint.flush();
    }
}

To use:
[cc lang=”java”]
LogCapture logger = new LogCapture(System.out, logFile);
System.setOut(logger);
System.setErr(logger);

Posted in Java. Tagged with , , , .

By James
March 3, 2012

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