The Preferences API provided in the java.util.prefs package can be used to store and retrieve application configurations. The main class is the Preferences class. Using this class you can manage the preference data such as storing, retrieving, removing and clearing the preference data.
Preferences are key-value pairs of data. You can store a string, int, boolean and other primitive data type. You can use the get() method to retrieve value associated with a key from preference node and the put() method to store a value associated with a key in the preference node. To remove a value associated with a key from preference node you can use the remove() method. And if you want to clear the keys from the preference node you can use the clear() method.
The actual storage of these preference data is dependent on the platform. For example in Windows OSes it stored in the Windows Registry. What you have to know that this Preferences API is not intended to use for storing application data, you will only use it to store configurations of your applications.
Let’s see an example of using the Preferences API.
package org.kodejava.util.prefs;
import java.util.prefs.BackingStoreException;
import java.util.prefs.Preferences;
public class PreferencesExample {
public static void main(String[] args) {
PreferencesExample demo = new PreferencesExample();
demo.setPreferences();
}
private void setPreferences() {
// Define a node to store the preference data.
Preferences pref = Preferences.userRoot().node(getClass().getName());
String key1 = "KEY1";
String key2 = "KEY2";
String key3 = "KEY3";
// Read the value of KEY1, return an empty string if the value
// hasn't been set previously.
String key1Value = pref.get(key1, "");
System.out.println("KEY1: " + key1Value);
// Read the value of KEY2 as an integer, if the value hasn't
// been set previously return -1.
int key2Value = pref.getInt(key2, -1);
System.out.println("KEY2: " + key2Value);
// Read the value of KEY3, return true if no value was set
// previously.
boolean key3Value = pref.getBoolean(key3, true);
System.out.println("KEY3: " + key3Value);
// Set the values for all the preference key above.
if (key1Value.equals("")) {
pref.put(key1, "January");
}
if (key2Value == -1) {
pref.putInt(key2, 1000);
}
if (key3Value) {
pref.putBoolean(key3, false);
}
printKeys(pref);
// Remove KEY1 from the preference data.
pref.remove(key1);
printKeys(pref);
try {
// Remove all preference data of this node.
pref.clear();
} catch (BackingStoreException e) {
e.printStackTrace();
}
printKeys(pref);
}
/**
* Print Keys in the preference node.
* @param pref Preference node.
*/
private void printKeys(Preferences pref) {
System.out.println("PreferencesExample.printKeys");
try {
String[] keys = pref.keys();
for (String key : keys) {
System.out.println("Key = " + key);
}
} catch (BackingStoreException e) {
e.printStackTrace();
}
System.out.println("============================");
}
}
Here are the output you’ll get when running the example above:
KEY1:
KEY2: -1
KEY3: true
PreferencesExample.printKeys
Key = KEY1
Key = KEY2
Key = KEY3
============================
PreferencesExample.printKeys
Key = KEY2
Key = KEY3
============================
PreferencesExample.printKeys
============================
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