Different ways of loading a file as an InputStream

java

class-loading

file-input-stream

resource-loading

byNikita Barsukov·Sep 16, 2024

Load a file as an InputStream using ClassLoader for classpath resources:

// Summoning the spirit of the classpath
InputStream classPathStream = getClass().getClassLoader().getResourceAsStream("config.properties");

Or use FileInputStream for file system resources:

// Grabbing the file, nails and all
InputStream fileSystemStream = new FileInputStream("/etc/config.properties");

Stores data from files in respective InputStreams, ready for engaging action.

Brushing up on `getResourceAsStream()`

The method getResourceAsStream() has multiple facades, depending on the context under which it is summoned.

The relative path interpretation comes into effect in case the method is invoked through a class instance. In contrast, when the lamp is rubbed via the class loader, absolute paths from the classpath root are assumed.

For those walking along the ancient tombs of pre-8 Tomcat versions, be wary of the changing behaviors of getResourceAsStream(). Remember to consult the source code or magical documentation scrolls to guide your journey.

Always beware of the treacherous /. In Class.getResourceAsStream(), it claims the absolute path, but loses its individuality, enabling the call to ClassLoader.getResourceAsStream().

Selecting your resource loading weapon

Every adventurer needs to select the right weapon depending on the quest at hand:

For the explorers wandering within the barriers of the classloader, the poisoned arrow of getClass().getResourceAsStream() is a trusty friend.
Should you be venturing into the unknown lands of the filesystem, the sharp blade of FileInputStream is your ally.

However, for those brave souls who dare to explore the realms of unknown application servers like Tomcat, remember the golden rule - when in doubt, use Thread.currentThread().getContextClassLoader().getResourceAsStream().

Gather the troubleshooting scrolls

Battles are never without obstacles. Here are some solutions to vanquish common foes:

To pacify the specter of Missing Resources, ensure you've got your maps right. Even a misplaced dot or slash could lead to a null InputStream.
When battling the many-headed hydra of Server Quirks, seek wisdom from the documentation of these server monsters.
Seek advice from the ghostly figures of the Tomcat or the knowledge-packed scrolls of StackOverflow threads to conquer the dark magic of Class Loading.
As you travel from a peaceful village of your local environment to the bustling town of production or navigate the changing landscapes of Tomcat configurations, stay vigilant.

Navigating the edge of the map

Different challenges call for different strategies:

Dynamic Resources: If your treasure map keeps changing, consider dynamic loading techniques.
Performance Considerations: If your battles involve massive armies, tune your resource access for efficiency.
Security Implications: Remember, treasures have traps. Make sure you access sensitive files securely.

Unveiling the legend of resource loading

Here's the legend translating the mysterious symbols of resource loading:

FileInputStream for External Files: This is for brave adventurers who prefer reading inscription runes directly from the rock walls.
Classpath-based Resources: These are for scholars who prefer accessing ancient scrolls from their own monastery.
Accessing Jar Resources: If you're looking to decode the content of ancient sealed jars, this is your key.
Application Server Environment: For wanderers strolling around the bustling city markets, this method ensures you always find your way back.