Programming Tutorials

store() and load() example in Java

By: Kamini in Java Tutorials on 2007-09-14  

One of the most useful aspects of Properties is that the information contained in a Properties object can be easily stored to or loaded from disk with the store() and load() methods. At any time, you can write a Properties object to a stream or read it back. This makes property lists especially convenient for implementing simple databases.

For example, the following program uses a property list to create a simple computerized telephone book that stores names and phone numbers. To find a person's number, you enter his or her name. The program uses the store() and load() methods to store and retrieve the list. When the program executes, it first tries to load the list from a file called phonebook.dat. If this file exists, the list is loaded. You can then add to the list. If you do, the new list is saved when you terminate the program. Notice how little code is required to implement a small, but functional, computerized phone book.

/* A simple telephone number database that uses
a property list. */
import java.io.*;
import java.util.*;

class Phonebook {
    public static void main(String args[])
            throws IOException {
        Properties ht = new Properties();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String name, number;
        FileInputStream fin = null;
        boolean changed = false;
        // Try to open phonebook.dat file.
        try {
            fin = new FileInputStream("phonebook.dat");
        } catch (FileNotFoundException e) {
            // ignore missing file
        }
        /*
         * If phonebook file already exists,
         * load existing telephone numbers.
         */
        try {
            if (fin != null) {
                ht.load(fin);
                fin.close();
            }
        } catch (IOException e) {
            System.out.println("Error reading file.");
        }
        // Let user enter new names and numbers.
        do {
            System.out.println("Enter new name" +
                    " ('quit' to stop): ");
            name = br.readLine();
            if (name.equals("quit"))
                continue;
            System.out.println("Enter number: ");
            number = br.readLine();
            ht.put(name, number);
            changed = true;
        } while (!name.equals("quit"));
        // If phone book data has changed, save it.
        if (changed) {
            FileOutputStream fout = new FileOutputStream("phonebook.dat");
            ht.store(fout, "Telephone Book");
            fout.close();
        }
        // Look up numbers given a name.
        do {
            System.out.println("Enter name to find" +
                    " ('quit' to quit): ");
            name = br.readLine();
            if (name.equals("quit"))
                continue;
            number = (String) ht.get(name);
            System.out.println(number);
        } while (!name.equals("quit"));
    }
}

Sample output:

Enter new name ('quit' to stop): 
Gandhi
Enter number: 
18
Enter new name ('quit' to stop): 
Teresa
Enter number: 
89
Enter new name ('quit' to stop): 
quit
Enter name to find ('quit' to quit): 
Enter name to find ('quit' to quit):
Gandhi
18
Enter name to find ('quit' to quit):
quit