为Logback创建OutputstreamAppender

Question

对于我的LogBack记录器，我试图以编程方式创建一个写入ByteArrayOutputStream的OutputStreamAppender。以下是我到目前为止所拥有的：

// Destination stream
ByteArrayOutputStream printStream = new ByteArrayOutputStream();
 
// Get LoggerContext from SLF4J
LoggerContext context = (LoggerContext)LoggerFactory.getILoggerFactory();
 
// Encoder
PatternLayoutEncoder encoder = new PatternLayoutEncoder();
encoder.setContext(context);
encoder.setPattern("%d{HH:mm:ss} %-5level %logger{36} - %msg%n");
encoder.start();
 
// OutputStreamAppender
OutputStreamAppender<ILoggingEvent> appender= new OutputStreamAppender<>();
appender.setName( "OutputStream Appender" );
appender.setContext(context);
appender.setOutputStream(printStream);
appender.setEncoder(encoder);
 
appender.start();
 
Logger log = context.getLogger(this.getClass());
log.addAppender(appender);
 
log.info( "text from logger");

// Output to stdout logback status
StatusPrinter.print(context);

根据我所读到的一切，这应该是正确的。日志中没有任何内容写入流，而且OutputStreamAppender无法根据StatusPrinter的输出正确初始化。

15:26:30,330 |-WARN in ch.qos.logback.core.OutputStreamAppender[OutputStream Appender] - Encoder has not been set. Cannot invoke its init method.
15:26:30,335 |-ERROR in ch.qos.logback.core.OutputStreamAppender[OutputStream Appender] - Appender [OutputStream Appender] failed to append. java.lang.NullPointerException
    at java.lang.NullPointerException
    at  at ch.qos.logback.core.encoder.LayoutWrappingEncoder.doEncode(LayoutWrappingEncoder.java:135)
    at  at ch.qos.logback.core.OutputStreamAppender.writeOut(OutputStreamAppender.java:188)
    at  at ch.qos.logback.core.OutputStreamAppender.subAppend(OutputStreamAppender.java:212)
    at  at ch.qos.logback.core.OutputStreamAppender.append(OutputStreamAppender.java:103)
    at  at ch.qos.logback.core.UnsynchronizedAppenderBase.doAppend(UnsynchronizedAppenderBase.java:88)
    at  at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:48)
    at  at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:272)
    at  at ch.qos.logback.classic.Logger.callAppenders(Logger.java:259)
    at  at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:441)
    at  at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:395)
    at  at ch.qos.logback.classic.Logger.info(Logger.java:599)

我对LayoutWrappingEncoder.doEncode(LayoutWrappingEncoder)的警告和NPE感到困惑。我正在把编码器设置在附件上。

Answer 1

在查看了源代码之后，我发现编码器必须在输出流之前设置：

OutputStreamAppender<ILoggingEvent> appender= new OutputStreamAppender<>();
appender.setName( "OutputStream Appender" );
appender.setContext(context);
appender.setEncoder(encoder);  // <-- must be set before outputstream
appender.setOutputStream(printStream);