Remembering installed path can be solved by setting an environment variable e.g. MYAPP_HOME. The variable can be initialized with the required value while installing so that every time the application gets loaded the variable will be set. This is a typical solution that is employed in most of the projects.
The Other Solution
The Preferences API that is provided JDK can be used to solve this typical problem. Preferences work just like properties but they are persistent unlike Properties. At the back, when a preference is written it gets stored to a backing store. When you ask for the preference, the value is then loaded from this store. On a typical Windows machine the default store is Windows registry but the store is configurable and you can change it to what ever you like e.g. a file.
Writing a preference is straight forward. Unlike properties which are String based key-value pairs the preferences have keys that are Strings but you can store values of all basic types e.g. long, boolean, double etc.
public class StaticPreferenceFactory {
public static void main(String args[]) throws Exception {
Preferences prefsRoot = Preferences.userRoot();
Preferences myPrefs = prefsRoot
.node("com.myapp.preference.staticPreferenceLoader");
myPrefs.put("fruit", "apple");
myPrefs.putDouble("price", 40);
myPrefs.putBoolean("available", false);
return prefsRoot;
}
}
Just like we have system variables and user variables. There is a system preference node that you can get by calling systemRoot() and there is a user preference node that you get calling userRoot() node. Once a preference is stored in a userNode it is not accessible to other users of the system just like user variables. You can clear the preferences written by calling the clear() API.
public class UsePreference {
public static void main(String args[]) throws Exception {
Preferences myfilePrefs = Preferences.userRoot();
myfilePrefs = myfilePrefs
.node("com.myapp.preference.staticPreferenceLoader");
System.out.println("finding fruit:"
+ myfilePrefs.get("fruit", "not found") + " available :"
+ myfilePrefs.getBoolean("available", true));
}
}
Retrieving a preference is also straight forward just like properties. The get API here takes two arguments the key, to be found, and default value, incase the value is not found.
Spring also provides PreferencesPlaceholderConfigurer that can be used to load preferences.
<bean id="preferencePlaceHolder"
class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer">
<property name="userTreePath" value="com.myapp.preference.staticPreferenceLoader" />
</bean>
<bean id="myEntity" class="info.dependencyInjection.spring.factory.MyEntity">
<property name="value" value="${fruit}" />
</bean>
For our installer problem we can store all our configuration options in Preferences while installing and the application will be only concerned about reading these values. This way we can avoid all the pains of writing to environment variables and making sure that we load the proper variables every time.
Reference: Use java.util.prefs.Preferences instead of java.util.Properties from our JCG partner Rahul Sharma at the “The road so far…” blog.
