Java: Properties Class

A Properties object is a persistent Hashtable that stores key–value pairs of Strings. By "persistent", we mean that the Properties object can be written to an output stream (possibly a file) and read back in through an input stream. A common use of Properties objects in prior versions of Java was to maintain application-configuration data or user preferences for applications.

import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.io.IOException;

import java.util.Properties;
import java.util.Set;

public class PropertiesTest {
    public static void main(String[] args) {
        Properties table = new Properties();

        // set properties
        table.setProperty("color", "blue");
        table.setProperty("width", "200");

        System.out.println("After setting properties");
        listProperties(table);

        // replace property value
        table.setProperty("color", "red");

        System.out.println("After replacing properties");
        listProperties(table);

        saveProperties(table);

        table.clear(); // empty table

        System.out.println("After clearing properties");
        listProperties(table);

        loadProperties(table);

        // get value of property color
        Object value = table.getProperty("color");

        // check if value is in table
        if (value != null)
            System.out.printf("Property color's value is %s%n", value);
        else
            System.out.println("Property color is not in table");
    }

    // save properties to a file

    private static void saveProperties(Properties props) {
        // save contents of table
        try {
            FileOutputStream output = new FileOutputStream("props.dat");
            props.store(output, "Sample Properties"); // save properties
            output.close();
            System.out.println("After saving properties");
            listProperties(props);
        } catch (IOException ioException) {
            ioException.printStackTrace();
        }
    }

    // load properties from a file

    private static void loadProperties(Properties props) {
        // load contents of table
        try {
            FileInputStream input = new FileInputStream("props.dat");
            props.load(input); // load properties
            input.close();
            System.out.println("After loading properties");
            listProperties(props);
        } catch (IOException ioException) {
            ioException.printStackTrace();
        }
    }

    // output property values

    private static void listProperties(Properties props) {
        Set<object> keys = props.keySet(); // get property names

        // output name/value pairs
        for (Object key : keys)
            System.out.printf("%s\t%s%n", key, props.getProperty((String)key));

        System.out.println();
    }
}


OUTPUT
After setting properties
color blue
width 200

After replacing properties
color red
width 200

After saving properties
color red
width 200

After clearing properties

After loading properties
color red
width 200

Property color's value is red