July 2019
Intermediate to advanced
480 pages
9h 35m
Chinese
Content preview from 持續交付｜使用Java
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| 第十三章
我們建議在盡可能高的級別（最接近呼叫或用戶發起的操作）上面 log 錯誤。試著在呼
叫堆疊中多次 log 單一錯誤經常在 log 中加入雜訊，讓你難以追蹤問題。
防範“過度
log
”
log 級別真正強大之處在於，它們可讓你在部署或運行期修改 log 的數
量。例如，如果 app 沒有按照預期執行，運維人員可以啟用更精細的 log
級別，例如
DEBUG
，以獲得更多的資訊。但是，產生額外的 dubug 問題會
降低性能，諷刺的是，當你開始尋找問題時，很多問題就會消失，原因通
常是時機（timing）和記憶體的使用模式會隨著額外的 log 而改變，我們
也看過一個 app 在啟用 log 時完全崩潰，因為它在生產環境中產生 log 敘
句需要極大量的記憶體（相關的
TRACE
敘句一直以來都只在嚴格控制下的
開發環境中使用，而且資料量很少）。
Java 生態系統有好幾種 log 框架可供你選擇。接下來要介紹兩種最熱門的：SLF4J（與
Logback）以及 Log4j 2。
別發明自己的
logger
請不要試著實作你自己的 log 框架，或採取同樣糟糕的做法，直接使用
System.out.println
。現代的 Java log 框架已經有了高度的發展，相較於
直接將細節 echo 到控制台（在容器環境中可能存在，也可能不存在），
它們提供了更多的彈性。
SLF4J
Simple Logging Facade for Java（SLF4J）（
https://www.slf4j.org/
）旨在提供各種
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