Saturday, September 8, 2012

Improving java.util.Properties

The Java built-in java.util.Properties class could really use some love. I have written a slightly improved version called timemachine.scheduler.support.Props, and below are some features that I use often.

You can use it as a "String Map" of properties

Props props1 = new Props();
props1.put("foo", "bar");

// It can load from/to the Java Properties
Props props2 = new Props(System.getProperties());
java.util.Properties javaProps = props3.toProperties();

// It can load from/to a basic java.util.Map
Props props3 = new Props(System.getenv());

// Props is a HashMap<String, String>, so no need to convert. Just use it
for(Map.Entry<String, String> entry : props3.entrySet())
    System.our.println(entry.getKey() + ": " + entry.getValue());

You can load from a file in a single line

Props props1 = new Props("config.properties");
Props props2 = new Props("/path/to/config.properties");
Props props3 = new Props(new java.net.URL("http://myhost/config/config.properties"));
Props props4 = new Props(ClasspathURLStreamHandler.createURL("classpath://config/config.properties"));

// You can re-load on top of existing instance to override values
props4.load("config2.properties");

NOTE: The ClasspathURLStreamHandler is a utility class from the same package under timemachine.scheduler.support that can load any resources that's in the classpath.

You can get many basic types conversion

Props props = new Props();
props.put("str", "foo");
props.put("num", "123");
props.put("dec", "99.99");
props.put("flag", "true");

String str = props.getString("str");
int num = props.getInt("num");
double dec = props.getDouble("dec");
boolean flag = props.getBoolean("flag");

// You can even get default value when key is not found too
int num2 = props.getInt("num2", -1);

You can auto expand ${variable} from any existing properties

Props props = new Props(System.getProperties());
props.put("configDir", "${user.home}/myapp/config");
props.expandVariables();

// The ${user.home} should be expanded to actual user home dir value.
File dir = new File(props.get("configDir"));

There you have it. You see more code than words in this post, but I believe simple code speak louder than words and docs. I find these features very convenient and practical for many Java applications to use. I wish the JDK would provide these out of the box, and make the java.util.Properties more developer friendly.