java - 创建用于注销的OutputstreamAppender

对于LogBack记录器，我试图以编程方式创建一个写入ByteArrayOutputStream的OutputStreamAppender。这是我到目前为止的内容:

// Destination stream
ByteArrayOutputStream stream = 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);

根据我阅读的所有内容，这应该是正确的。记录器中的任何内容均未写入流，并且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)

我被LayoutWrappingEncoder.doEncode(LayoutWrappingEncoder)的警告和NPE困扰了。我在Appender上设置了编码器。

最佳答案

仔细查看源代码后，我发现必须在输出流之前设置编码器:

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