Overwritting properties files
dbpassword=password
database=localhost
dbuser=user1

dbpassword=password
database=localhost
dbuser=user2

prop.setProperty("dbuser", "user2");

prop.store(new FileOutputStream("app.properties",true), null);

prop.store(new FileOutputStream("app.properties",false), null);

The  example, PropertiesTest, creates a Properties object and initializes it from myProperties.txt .

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PropertiesTest then uses System.setProperties to install the new Properties objects as the current set of system properties.


import java.io.FileInputStream;
import java.util.Properties;

public class PropertiesTest {
    public static void main(String[] args)
        throws Exception {

        // set up new properties object
        // from file "myProperties.txt"

        Properties p =
            new Properties(System.getProperties());
        p.load(propFile);

        // set the system properties
        System.setProperties(p);
        // display new properties
        System.getProperties().list(System.out);
    }
}
Note how PropertiesTest creates the Properties object, p, which is used as the argument to setProperties:

Properties p = new Properties(System.getProperties());