How to Choose the Right Method for Loading Files as InputStreams in Java?

Loading Files as InputStreams: Different Approaches and When to Use Them

When it comes to loading files as InputStreams, there are several methods that can be employed, each with its own nuances. This article delves into the differences between three commonly used approaches:

• Class.getResourceAsStream(fileName):

  This method interprets the fileName as a path relative to the package of the class invoking it. For instance, String.class.getResourceAsStream("myfile.txt") searches for the file "myfile.txt" within the classpath at "java/lang/myfile.txt." If the path starts with a "/", it signifies an absolute path and begins the search from the classpath root.

• ClassLoader.getResourceAsStream(fileName):

  Unlike Class.getResourceAsStream(), this method treats all paths as absolute. Both String.class.getClassLoader().getResourceAsStream("myfile.txt") and String.class.getClassLoader().getResourceAsStream("/myfile.txt") search for the file "myfile.txt" in the classpath at "./myfile.txt."

• Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName):

  This method is appropriate when loading classes and files from an application server, as it uses the context classloader associated with the current thread, which handles resources deployed within the server.

When to Use Each Method:

In your specific scenario, where the file and class reside in the same jar and EAR file deployed in WebSphere 6.1, you should use Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName) because it considers the context classloader of the application server.

Warning for Tomcat 7 and Below Users:

However, be mindful of the following caveat if using Tomcat 7 or earlier. While the explanation above is generally sound, it seems that versions 6 and 7 of Tomcat handle resource normalization differently in findResource(String name) method. As a result, classLoader.getResourceAsStream("/resource.txt") and classLoader.getResourceAsStream("resource.txt") may not yield the same result in these versions. Be cautious if using these methods in earlier Tomcat versions.

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