What does `ServletContext.getRealPath('/')` do, and why should I avoid using it in modern Java EE applications?

What does servletcontext.getRealPath("/") mean and when should I use it?

Introduction

In a Java servlet application, the ServletContext#getRealPath() method is used to convert a relative web content path to an absolute disk file system path. The specified path can be either a file or a directory within the web content. However, this method should be used with caution and is generally discouraged in modern Java EE development.

Usage of getRealPath("/")

The / in getRealPath("/") represents the root of the web content directory. It is the absolute file system path to the directory containing the web application's web.xml file. For example, in the following project structure:

YourWebProject/
    src/
    :
    web/
        META-INF/
        WEB-INF/
        index.jsp
        login.jsp
        :

If you execute getRealPath("/"), it would return the file system path to the web directory, such as /path/to/server/work/folder/some.war/web.

Caution and Limitations

While getRealPath() can be useful in certain situations, it has several limitations and is generally discouraged for the following reasons:

• Writes are not persistent: Changes made to files written using getRealPath() will be lost during redeployment of the WAR file.
• Expansion dependence: The reliability of getRealPath() depends on the server's configuration for expanding WAR files. If the WAR is not expanded to the disk file system, getRealPath() may return incorrect or null paths.
• No portable use cases: There are usually more portable and dependable alternatives to using getRealPath().

Alternatives to getRealPath()

Instead of using getRealPath(), consider these alternatives:

• Use ServletContext#getResourceAsStream() to obtain an InputStream for a resource within the web content.
• Use ServletContext#getResourcePaths() to retrieve a list of available resource paths.
• Use ServletContext#getResource() to obtain a URL for a resource.
• For file uploads or temporary file creation, refer to the "See also" links below.

See Also

• [getResourceAsStream() vs FileInputStream](https://stackoverflow.com/questions/4212943/resource-as-inputstream-in-java-best-practice)
• [Recommended way to save uploaded files in a servlet application](https://stackoverflow.com/questions/5797716/recommended-way-to-save-uploaded-files-in-a-servlet-application)
• [Simple ways to keep data on redeployment of Java EE 7 web application](https://stackoverflow.com/questions/11736935/simple-ways-to-keep-data-on-redeployment-of-java-ee-7-web-application)

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