This is how you are able to load and read external file properties:

import java.io.InputStream;
import java.util.Properties;

InputStream inputStream = getClass().getClassLoader().getResourceAsStream("/custom.properties");
Properties customProperties = new Properties();
try {
    customProperties.load(inputStream);
} catch (IOException e) {
    e.printStackTrace();
    logger.error("IOException caught while reading properties file: " + e.getMessage());
}

if( customProperties.get("prop1") != null )
    boolean prop1 = Boolean.parseBoolean((String) customProperties.get("prop1"));