In this short tutorial we focus on writing/reading Java Properties files without external dependencies.

Quoting Wikipedia:

.properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. They can also be used for storing strings for Internationalization and localization; these are known as Property Resource Bundles.

Each parameter is stored as a pair of strings, one storing the name of the parameter (called the key), and the other storing the value.

We usually come across properties files when dealing with configurations or translations. Those files have the following format:

\# Comment
key1 = value1
key2 = value2

Within the java.util package, we already have classes for reading and writing properties files.

Creating a Java Properties file

Properties properties = new Properties();
properties.setProperty("key1", "value1");
properties.setProperty("key2", "value2");
 
FileOutputStream fos = new FileOutputStream("C:/test.properties");
 
properties.store(fos, null);
fos.flush();

Reading from a Java Properties file

Properties prop = new Properties();
 
prop.load(new FileInputStream("C:/test.properties"));
System.out.println(prop.getProperty("key1"));