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Improving java.util.Properties

09.14.2012
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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.get("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.

Published at DZone with permission of Zemian Deng, author and DZone MVB. (source)

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

Comments

Emmanuel Bourg replied on Sun, 2012/09/16 - 8:10am

If you want to save some time you can even use the Apache Commons Configuration API, it does the same things and much more (multiple formats, smart type conversion, automatic reloading, configuration composed from several sources...) :

http://commons.apache.org/configuration

And it's supported by a very nice and helpful community :)

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