This is something which I want to do in properties file
#Comments about key Value pair 1
Key_1=value_1
#Comments about key Value pair 2
Key_2=value_2
#Com
You can use the Apache Commons Configuration to write and read Properties files, specifically the setComment() function in a PropertiesConfigurationLayout which allows you to specify a comment for each property.
Note that above links refer to Commons Configuration v1.x, while v2.0 has been released in the meantime, which has different package names.