Can you find all classes in a package using reflection?

Question

Is it possible to find all classes or interfaces in a given package? (Quickly looking at e.g. Package, it would seem like no.)

Answer 1

Spring

This example is for Spring 4, but you can find the classpath scanner in earlier versions as well.

// create scanner and disable default filters (that is the 'false' argument)
final ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false);
// add include filters which matches all the classes (or use your own)
provider.addIncludeFilter(new RegexPatternTypeFilter(Pattern.compile(".*")));

// get matching classes defined in the package
final Set classes = provider.findCandidateComponents("my.package.name");

// this is how you can load the class type from BeanDefinition instance
for (BeanDefinition bean: classes) {
    Class clazz = Class.forName(bean.getBeanClassName());
    // ... do your magic with the class ...
}

Google Guava

Note: In version 14, the API is still marked as @Beta, so beware in production code.

final ClassLoader loader = Thread.currentThread().getContextClassLoader();

for (final ClassPath.ClassInfo info : ClassPath.from(loader).getTopLevelClasses()) {
  if (info.getName().startsWith("my.package.")) {
    final Class clazz = info.load();
    // do something with your clazz
  }
}