使用{}的Log4j2反对使用％d或％s [英] Log4j2 using {} against using %d or %s

问题描述

在Log4j2中，以下两种方法是否同样有效，并且不会导致日志级别比DEBUG更具体的任何字符串连接?并且由于任何原因/情况，一个人会比其他人更受青睐吗?

In Log4j2, are both the following equally efficient and do not cause any string concatenation with a log level more specific than DEBUG ? And for any reason/situation will one be preferred over other ?

log.warn(String.format("Number of cars : %d",carCount));
log.warn("Number of cars : {}",carCount );

{}是否适用于任何类型的对象?

And does {} works with any type of Object ?

推荐答案

{}表示法比%s %d String格式表示法有效得多. (有

The {} notation is much more efficient than the %s %d String format notation. (There are benchmarks for this, I'll add some numbers later.)

{}表示法接受任何对象或原始值，其中%s %d ...字符串格式要求参数的类型与该格式匹配，否则将引发异常.因此，通常{}更方便.

The {} notation accepts any Object or primitive value, where the %s %d ... String format requires that the type of the parameter matches the format or an exception is thrown. So generally, {} is more convenient.

在某些情况下，您想使用String格式语法，因为它可以使您对格式进行非常细粒度的控制.如果要漂亮地打印"大量数字作为1,234,567.123，或控制小数点后的位数，则{}是不够的.

There are cases where you want to use the String format syntax, since it gives you very fine-grained control over the formatting. If you want to "pretty-print" a large number as 1,234,567.123, or control the number of digits behind the decimal point, then {} is not enough.

Log4j2允许您混合使用两种用法.可以在任何地方使用String格式语法(通过使用LogManager.getFormattedLogger)，但是也许更方便的是大多数时候使用默认的{}格式，并且仅在需要细粒度控制时才使用String格式语法使用printf方法:

Log4j2 allows you to mix both usages. It is possible to use the String format syntax everywhere (by using LogManager.getFormattedLogger), but perhaps more convenient is to use the default {} format most of the time, and only use the String format syntax when you need the fine grained control with the printf method:

logger.printf(Level.INFO, "Logging in user %1$s with birthday %2$tm %2$te,%2$tY", user.getName(), user.getBirthdayCalendar());

内部，采用{}格式，Log4j2努力避免创建字符串或其他临时对象.使用String格式语法无法做到这一点.

Internally, with the {} format Log4j2 makes an effort to avoid creating Strings or other temporary objects. This is not possible with the String format syntax.

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