slf4j日志中的palceholder

// Good
logger.error("Logger1: ", e);
[main] ERROR  - Logger1: 
java.lang.NullPointerException
	at com.kaven.test.logger.PlaceHolderTest.main(PlaceHolderTest.java:11)

// 占位符不能解析
logger.error("Logger2: {}", e);
[main] ERROR  - Logger2: {}
java.lang.NullPointerException
	at com.kaven.test.logger.PlaceHolderTest.main(PlaceHolderTest.java:11)

// 占位符能解析，但是没有了堆栈信息(使用了toString())
logger.error("Logger2: {}, {}", 3, e);
[main] ERROR  - Logger2: 3, java.lang.NullPointerException
 
// toString()
logger.error("Logger3: " + e);
[main] ERROR  - Logger3: java.lang.NullPointerException

// getMessage()
logger.error("Logger4: " + e.getMessage());
[main] ERROR  - Logger4: null