How to check if a Java ResourceBundle is loadable, without loading it?

Question

I would like to check the existence of a ResourceBundle without actually loading it.

Typically, I'm using Guice, and at initialization time, I want to check the existence, while at execution time, I want to load it. If the bundle doesn't exist, I want an early report of the inexistence of the RB.

If it was possible to get the ResourceBundle.Control instance used for a specific ResourceBundle, I would have no problem getting the basic information to build the actual resource name (using toBundleName() and toResourceName()), but it is not the case at that level.

Edit:

Ok, I found the way to do it. I'll create a ResourceBundle.Control that is extensible (using a custome addFormat(String, Class)) to store all the bundle formats, then use another method of my own to check all possible file names for a specific locale (using Class.getResource as indicated here below).

Coding speaking:

class MyControl extends ResourceBundle.Control {
  private Map<String,Class<? extends ResourceBundle>> formats = new LinkedHashMap();
  public void addFormat(String format,Class<? extends ResourceBundle> rbType) {
    formats.put(format, rbType);
  }
  public boolean resourceBundleExists(ClassLoader loader, String baseName, Locale locale) {
    for (String format: formats.keySet()) {
      // for (loop on locale hierarchy) {
        if (loader.getResource(toResourceName(toBundleName(baseName, locale), format))) {
          return true;
        }
      // }
    }
    return false;
  }
}

Answer 1

You can load the bundles, thus making your checks, and then call ResourceBundle.clearCache() so that they are loaded again next time.

This happens once (at initialization time), and it isn't such a heavy operation, so it won't be a problem.

Or you can simply try to find whether a resource is present on the classpath. For example the fallback .properties file, or the properties file for your default locale.

Finally, after having a look at the code for ResourceBundle.Control, you have the option to do what they do in the newBundle() method.

Answer 2

If the default bundle must exists you can do:

Class.getResource("/my/path/to/bundle.properties")

and it will return an URL to the file or null if it doesn't exists.

Of course use the correct class or classloader if you have many.

EDIT: if you have resources as classes you have to check also

Class.getResource("/my/path/to/bundle.class")

In Java 6 you can store resource bundles in XML. I don't know how ResourceBundle class lookups this resource, but I bet it's in the same way.

Answer 3

Something like this, maybe

ResourceBundle bundle;
public PropertiesExist() {
    String propsFile = "log4j";
    String propsPath = this.getClass().getClassLoader().getResource(".").getPath();
    File f = new File(propsPath, propsFile + ".properties");
    if(!f.exists()){
        System.out.println("File not found!!!!");
        System.exit(-1);
    }
    bundle = ResourceBundle.getBundle(propsFile);
    System.out.println(bundle.getString("log4j.rootLogger"));
}

public static void main(String[] args) {
     new PropertiesExist();         
}

This will look for the logging file, log4.properties, if not found program will exit