Question

Example.properties

user=somePerson
env=linux
file=mpg

properties.java class

propertiestTest.java
   {
     Properties props = new Properties();
     props.setProperty("user", "GodIsUser");
     final File propsFile = new File(someDir/Example.properties");

     props.store(new FileOutputStream(propsFile), "");
}

reseult of Example.properties

user=GodIsUser

and all other entries are deleted

Answer 1

You need to populate it from the file first using props.load:

final File propsFile = new File("someDir/Example.properties");
Properties props = new Properties();
props.load(new FileInputStream(propsFile));
// make changes
props.save(new FileOutputStream(propsFile), "");