Loading properties files from classpath

You could load resources using ClassLoader.getResourceAsStream() or Class.getResourceAsStream(). Important thing to note is that Class.getResourceAsStream (String) delegates the call to ClassLoader.getResourceAsStream(String). You can see the same below.

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public InputStream getResourceAsStream(String name) {
	name = resolveName(name);
	ClassLoader cl = getClassLoader0();
	if (cl==null) {
		// A system class.
		return ClassLoader.getSystemResourceAsStream(name);
	}
	return cl.getResourceAsStream(name);
}

resolveName(name) will add a package name prefix if the name is not absolute. Remove leading “/”  if name is absolute. What does this mean? This means that if we pass just “test.properties” to getResourceAsStream it will resolve it to “com/my/test.properties” (assuming your current package is com.my). If we pass “/test.properties” it will assume you’re passing an absolute path and remove “/” making it just “test.properties”. Remember your classpath must have “com/my/test.properties” or “test.properties” depending on what you pass to getResourceAsStream(). Now, if you are using ClassLoader.getSystemResourceAsStream() directly we know from the above code that it expects absolute paths without the “/” in the beginning.

Here is a sample folder structure and App.java the reads properties files from the classpath. Remember that the src/main/resources folder must be added (and usually is added) to the classpath.

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package com.my;
 
import java.io.InputStream;
import java.util.Properties;
 
public class App
{
	public static void main( String[] args )
	{
 
		String var = null;
		Properties properties = new Properties();
 
		try {
 
			InputStream in = App.class.getResourceAsStream("test.properties");
			properties.load(in);
			var = properties.getProperty("my.prop");
			System.out.println(var);
 
			in = App.class.getResourceAsStream("/test2.properties");
			properties.load(in);
			var = properties.getProperty("my.prop");
			System.out.println(var);
 
		} catch (Exception e) {
			e.printStackTrace();
		}
 
	}
}