What is the Purpose of the WEB-INF Directory in a Java EE Web Application?

What is WEB-INF Used for in a Java EE Web Application?

The WEB-INF directory is a vital component of a Java EE web application. Defined in the Servlet 2.4 specification, it serves as a container for resources that are not intended for public access.

According to the specification, "The WEB-INF node is not part of the public document tree of the application. No file contained in the WEB-INF directory may be served directly to a client by the container." This ensures that sensitive resources and configurations remain inaccessible from outside the application.

Common Contents of WEB-INF

Typically, WEB-INF contains the following resources:

• web.xml: The web application deployment descriptor that defines servlets, filters, and other application settings.
• Resource files: Properties files, XML files, and other resources necessary for application functionality.
• JSP views: JavaServer Pages (JSP) files that render dynamic content.
• Tag libraries: Custom tag libraries for extending JSP syntax.

Flexibility with JSP Files

While JSP files are commonly placed in WEB-INF, they can technically reside elsewhere. However, for accessibility by the servlet code, deploying them within WEB-INF is recommended.

Additional Elements for WAR Files

The WAR (Web Application Archive) files, described in Wikipedia, include additional folders:

• WEB-INF/classes: Contains compiled Java classes.
• WEB-INF/lib: Contains JAR libraries used by the application.

Build Process and WAR Structure

It's essential to distinguish between the project structure and the final WAR file structure. While some resources may be placed directly into the WEB-INF folder, others, such as compiled classes and libraries, are managed by a build process.

Example

For instance, Apache Maven defines defaults for mapping resources from the project structure to the WAR file. In this case, the src/main/java and src/main/resources directories will be automatically compiled and copied into the WEB-INF/classes folder for class loading.

Conclusion

WEB-INF is a critical directory in Java EE web applications, providing a secure and accessible repository for resources essential for application functionality while protecting sensitive information from external access.

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