How To: Dynamically-defined properties in Java

Question

How can I define some properties dynamically in Java. For now, I'm using a properties file, but I need to change these properties before installation, so these properties should be set in a file outside the jar (or install) file.

These properties define my IBatis connection.

Answer 1

Keep going with the .properties and load the file as a resource.

If it is in the classpath it would be found.

What I use, because it is much easier to me is a resource bundle instead.

edit

If the file is in your classpath you can loaded it either as a resource with: Some.class.loadResource(...) or what I do is use a ResourceBundle which does basically the same.

For instance if I have:

import java.util.ResourceBundle;

public class ResourceBundleTest {
    public static void main( String [] args ) {
        ResourceBundle bundle = ResourceBundle.getBundle("connection");
        for( String key: bundle.keySet() ){
            System.out.printf("bundle[%s]=%s%n",key, bundle.getString(key));
        }
    }
}

I can load that file if is in the class path. The property is outside, in "some/nested/dir"

$ls -l some/nested/dir/
total 8
-rw-r--r--  1 oscarreyes  staff  35 Jun 25 12:06 connection.properties
$cat some/nested/dir/connection.properties 
name=Oscar
lastName=Reyes
age=0x1F

If I run it without adding that directory to my classpath it wont work:

$java ResourceBundleTest 
Exception in thread "main" java.util.MissingResourceException: Can't find bundle for base name connection, locale es_ES
    at java.ut...ceBundle.java:1427)
    at java.ut...urceBundle.java:1250)
    at java.ut...ceBundle.java:705)
    at Resourc...st.java:6)

But if I add the directory to my classpath, then the file will be found easily.

$java -cp some/nested/dir/:.  ResourceBundleTest 
bundle[lastName]=Reyes
bundle[age]=0x1F
bundle[name]=Oscar
$

In a similar fashion, you can have a .jar file, and put your .properties file wherever you want, you just have to include it in your classpath.

The equivalent using properties would be:

import java.util.Properties;

public class LoadProperties {
    public static void main( String [] args ) throws java.io.IOException {
        Properties properties = new Properties();
        properties.load( LoadProperties.class.getResourceAsStream("connection.properties"));
        properties.list( System.out );
    }
}

But for some reason I prefer the resource bundle.