What's the Best Way to Load a File as an InputStream in Java?

Different Ways of Loading a File as an InputStream

Introduction:

Java provides multiple methods to load a file as an InputStream. This article explores the differences between the following approaches:

• InputStream is = this.getClass().getClassLoader().getResourceAsStream(fileName)
• InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName)
• InputStream is = this.getClass().getResourceAsStream(fileName)

Interpretation of the fileName Parameter:

Each method interprets the fileName parameter differently. ClassLoader.getResourceAsStream() treats all paths as absolute, while Class.getResourceAsStream() considers them relative to the package of the calling class.

Appropriate Use Cases:

1. Using Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName)

This method is recommended when loading a file that is part of the application's classpath and packaged within the same JAR or EAR as the calling class. It provides access to classpath resources regardless of class or package location.

2. Using this.getClass().getResourceAsStream(fileName)

This method is suitable for loading files located in the same package as the calling class. It is especially useful when the file is packaged within a JAR and accessible via the classpath.

3. Using this.getClass().getClassLoader().getResourceAsStream(fileName)

This method is similar to Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName) but is less commonly used. It also loads files from the application's classpath, but its behavior may vary depending on the class loader's implementation.

Warning for Tomcat 7 Users:

In Tomcat 7 and below, ClassLoader.getResourceAsStream() and Class.getResourceAsStream() may not handle resource names containing slashes (/) consistently as specified by the Javadoc. Always ensure correct normalization when using these methods.

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