Class ResolverUtil<T>

Type Parameters:
T - the generic type

public class ResolverUtil<T> extends Object

ResolverUtil is used to locate classes that are available in the/a class path and meet arbitrary conditions. The two most common conditions are that a class implements/extends another class, or that is it annotated with a specific annotation. However, through the use of the ResolverUtil.Test class it is possible to search using arbitrary conditions.

A ClassLoader is used to locate all locations (directories and jar files) in the class path that contain classes within certain packages, and then to load those classes and check them. By default the ClassLoader returned by Thread.currentThread().getContextClassLoader() is used, but this can be overridden by calling setClassLoader(ClassLoader) prior to invoking any of the find() methods.

General searches are initiated by calling the find(Test, String) and supplying a package name and a Test instance. This will cause the named package and all sub-packages to be scanned for classes that meet the test. There are also utility methods for the common use cases of scanning multiple packages for extensions of particular classes, or classes annotated with a specific annotation.

The standard usage pattern for the ResolverUtil class is as follows:

 ResolverUtil<ActionBean> resolver = new ResolverUtil<ActionBean>();
 resolver.findImplementation(ActionBean.class, pkg1, pkg2);
 resolver.find(new CustomTest(), pkg1);
 resolver.find(new CustomTest(), pkg2);
 Collection<ActionBean> beans = resolver.getClasses();
Tim Fennell
  • Constructor Details

    • ResolverUtil

      public ResolverUtil()
  • Method Details

    • getClasses

      public Set<Class<? extends T>> getClasses()
      Provides access to the classes discovered so far. If no calls have been made to any of the find() methods, this set will be empty.
      the set of classes that have been discovered.
    • getClassLoader

      public ClassLoader getClassLoader()
      Returns the classloader that will be used for scanning for classes. If no explicit ClassLoader has been set by the calling, the context class loader will be used.
      the ClassLoader that will be used to scan for classes
    • setClassLoader

      public void setClassLoader(ClassLoader classloader)
      Sets an explicit ClassLoader that should be used when scanning for classes. If none is set then the context classloader will be used.
      classloader - a ClassLoader to use when scanning for classes
    • findImplementations

      public ResolverUtil<T> findImplementations(Class<?> parent, String... packageNames)
      Attempts to discover classes that are assignable to the type provided. In the case that an interface is provided this method will collect implementations. In the case of a non-interface class, subclasses will be collected. Accumulated classes can be accessed by calling getClasses().
      parent - the class of interface to find subclasses or implementations of
      packageNames - one or more package names to scan (including subpackages) for classes
      the resolver util
    • findAnnotated

      public ResolverUtil<T> findAnnotated(Class<? extends Annotation> annotation, String... packageNames)
      Attempts to discover classes that are annotated with the annotation. Accumulated classes can be accessed by calling getClasses().
      annotation - the annotation that should be present on matching classes
      packageNames - one or more package names to scan (including subpackages) for classes
      the resolver util
    • find

      public ResolverUtil<T> find(ResolverUtil.Test test, String packageName)
      Scans for classes starting at the package provided and descending into subpackages. Each class is offered up to the Test as it is discovered, and if the Test returns true the class is retained. Accumulated classes can be fetched by calling getClasses().
      test - an instance of ResolverUtil.Test that will be used to filter classes
      packageName - the name of the package from which to start scanning for classes, e.g. net.sourceforge.stripes
      the resolver util
    • getPackagePath

      protected String getPackagePath(String packageName)
      Converts a Java package name to a path that can be looked up with a call to ClassLoader.getResources(String).
      packageName - The Java package name to convert to a path
      the package path
    • addIfMatching

      protected void addIfMatching(ResolverUtil.Test test, String fqn)
      Add the class designated by the fully qualified class name provided to the set of resolved classes if and only if it is approved by the Test supplied.
      test - the test used to determine if the class matches
      fqn - the fully qualified name of a class