使用java.util.logging打印线程名称

Question

是否可以在java.util.logging.Logger生成的日志语句中打印线程名称？一种替代方法是执行以下操作:

logger.info(thread.getName() + " some useful info");

但它是重复的,日志框架应该处理它.

Answer 1

令人尴尬,但看起来java.util.logging不能这样做......

默认情况下java.util.logging.SimpleFormatter根本无法记录线程名称.该java.util.logging.FileHandler支架几个模板占位符,它们都不是线程名.

java.util.logging.XMLFormatter 是最接近的,但只记录线程ID:

<record>
  <date>2011-07-31T13:15:32</date>
  <millis>1312110932680</millis>
  <sequence>0</sequence>
  <logger></logger>
  <level>INFO</level>
  <class>java.util.logging.LogManager$RootLogger</class>
  <method>log</method>
  <thread>10</thread>
  <message>Test</message>
</record>

如果你认为我们正在接近 - 我们不是.LogRecordclass只保存线程ID,而不是它的名字 - 不是很有用.

Answer 2

有习俗 Formatter

幸运的是，LogRecord包含生成日志消息的线程的 ID。我们可以LogRecord在编写自定义Formatter. 一旦我们有了它，我们只需要通过它的 ID 获取线程名称。

有几种方法可以获取Thread与该 ID 对应的对象，这是我的：

static Optional<Thread> getThread(long threadId) {
    return Thread.getAllStackTraces().keySet().stream()
            .filter(t -> t.getId() == threadId)
            .findFirst();
}

以下是Formatter仅打印线程名称和日志消息的最小值：

private static Formatter getMinimalFormatter() {
    return new Formatter() {

        @Override
        public String format(LogRecord record) {

            int threadId = record.getThreadID();
            String threadName = getThread(threadId)
                    .map(Thread::getName)
                    .orElseGet(() -> "Thread with ID " + threadId);

            return threadName + ": " + record.getMessage() + "\n";
        }
    };
}

要使用自定义格式化程序，还有不同的选项，一种方法是修改默认值ConsoleHandler：

public static void main(final String... args) {

    getDefaultConsoleHandler().ifPresentOrElse(
            consoleHandler -> consoleHandler.setFormatter(getMinimalFormatter()),
            () -> System.err.println("Could not get default ConsoleHandler"));

    Logger log = Logger.getLogger(MyClass.class.getName());
    log.info("Hello from the main thread");
    SwingUtilities.invokeLater(() -> log.info("Hello from the event dispatch thread"));
}

static Optional<Handler> getDefaultConsoleHandler() {
    // All the loggers inherit configuration from the root logger. See:
    // https://docs.oracle.com/javase/8/docs/technotes/guides/logging/overview.html#a1.3
    var rootLogger = Logger.getLogger("")
    // The root logger's first handler is the default ConsoleHandler
    return first(Arrays.asList(rootLogger.getHandlers()));
}

static <T> Optional<T> first(List<T> list) {
    return list.isEmpty() ?
            Optional.empty() :
            Optional.ofNullable(list.get(0));
}

Formatter然后你的minimal应该产生包含线程名称的以下日志消息：

main：来自主线程的你好

和

AWT-EventQueue-0：来自事件调度线程的Hello

这是一个Formatter显示如何记录线程名称和日志消息的更多信息：

private static Formatter getCustomFormatter() {
    return new Formatter() {

        @Override
        public String format(LogRecord record) {

            var dateTime = ZonedDateTime.ofInstant(record.getInstant(), ZoneId.systemDefault());

            int threadId = record.getThreadID();
            String threadName = getThread(threadId)
                    .map(Thread::getName)
                    .orElse("Thread with ID " + threadId);

            // See also: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Formatter.html
            var formatString = "%1$tF %1$tT %2$-7s [%3$s] %4$s.%5$s: %6$s %n%7$s";

            return String.format(
                    formatString,
                    dateTime,
                    record.getLevel().getName(),
                    threadName,
                    record.getSourceClassName(),
                    record.getSourceMethodName(),
                    record.getMessage(),
                    stackTraceToString(record)
            );
        }
    };
}

private static String stackTraceToString(LogRecord record) {
    final String throwableAsString;
    if (record.getThrown() != null) {
        var stringWriter = new StringWriter();
        var printWriter = new PrintWriter(stringWriter);
        printWriter.println();
        record.getThrown().printStackTrace(printWriter);
        printWriter.close();
        throwableAsString = stringWriter.toString();
    } else {
        throwableAsString = "";
    }
    return throwableAsString;
}

这Formatter会产生这样的日志消息：

2019-04-27 13:21:01 INFO [AWT-EventQueue-0] package.ClassName.method：日志消息