When to use WEB-INF and when to use META-INF?

In the root of a Java application's archive, you often find the directories WEB-INF and META-INF. Both directories store various metadata files about the application, usually in text formats like YAML, XML, JSON, or plain text.

META-INF is used in archives of all types. The main file in this directory is MANIFEST.MF, which we discussed earlier. It also contains:

• Declarations of SPI providers;
• Archive signatures: .SF, .DSA, .RSA files;
• INDEX.LIST with hints for the loader about the locations of packages.
• Occasionally (though not often), applications place their static resources here since this directory is included in the classpath and is accessible at runtime.

WEB-INF is used only in web archives (.war). It does not replace but rather complements META-INF. It contains:

• The main file of the web application, web.xml;
• Tag descriptor files .TLD;
• A classes/ subdirectory with the web application's classes;
• A lib/ subdirectory with .jar dependency libraries;
• A tag/ subdirectory with tag files.