public double getProperty(String key, double defaultValue) {
		String property = properties.getProperty(key);
		if (property != null) {
			return Double.parseDouble(property);
		}
		else {
			return defaultValue;
		}
	}
Return the property for the key, or the default value if the
property doesn't exist.
@param key The key.
@param defaultValue The default value.
@return The property or default value.
spring-xd-messagebus-spi/src/main/java/org/springframework/xd/dirt/integration/bus/AbstractBusPropertiesAccessor.java