Logback output to stream.

StreamingKMeansTest.java

    ByteArrayOutputStream bs = new ByteArrayOutputStream(2048);

    LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
    lc.reset();
    lc.setName("context");
    lc.start();

    PatternLayoutEncoder encoder = new PatternLayoutEncoder();
    encoder.setContext(lc);
    encoder.setPattern("%message\n");
    encoder.setImmediateFlush(true);
    encoder.setCharset(Charset.defaultCharset());
    encoder.start();

    OutputStreamAppender<ILoggingEvent> appender = new OutputStreamAppender<ILoggingEvent>();
    appender.setContext(lc);
    appender.setOutputStream(bs);
    appender.setName("appender");
    appender.setEncoder(encoder);
    appender.start();

    Logger l = lc.getLogger("test");
    l.addAppender(appender);
    l.setLevel(Level.DEBUG);

    assertThat(lc.isStarted(), is(true));
    assertThat(encoder.isStarted(), is(true));
    assertThat(appender.isStarted(), is(true));

    l.debug("Hello!");

Hi, i had a similar problem and i found your solution. For me it didn't work either (like you said on the mailing list). So i used StatusPrinter.print(lc); to see whats happening here. This told me something like "OutputStreamAppender[appender] - Encoder has not been set. Cannot invoke its init method".
After a little bit of testing i just moved line 19 ( appender.setEncoder(encoder); ) before line 16 ( appender.setContext(lc); ) and it worked!

OutputStreamAppender<ILoggingEvent> appender = 
    new OutputStreamAppender<ILoggingEvent>();
appender.setEncoder(encoder);
appender.setContext(lc);
appender.setOutputStream(bs);
appender.setName("appender");
appender.start();