com.opensymphony.xwork2.util
Class ResolverUtil<T>

java.lang.Object
  extended by com.opensymphony.xwork2.util.ResolverUtil<T>

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(com.opensymphony.xwork2.util.ResolverUtil.Test, String...) ()} method 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();

This class was copied from Stripes - http://stripes.mc4j.org/confluence/display/stripes/Home

Author:
Tim Fennell

Nested Class Summary
static class ResolverUtil.AnnotatedWith
          A Test that checks to see if each class is annotated with a specific annotation.
static class ResolverUtil.IsA
          A Test that checks to see if each class is assignable to the provided class.
static class ResolverUtil.NameEndsWith
          A Test that checks to see if each class name ends with the provided suffix.
static interface ResolverUtil.Test
          A simple interface that specifies how to test classes to determine if they are to be included in the results produced by the ResolverUtil.
 
Field Summary
private  ClassLoader classloader
          The ClassLoader to use when looking for classes.
private static Log log
          An instance of Log to use for logging in this class.
private  Set<Class<? extends T>> matches
          The set of matches being accumulated.
 
Constructor Summary
ResolverUtil()
           
 
Method Summary
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.
 void find(ResolverUtil.Test test, String... packageNames)
          Attempts to discover classes that pass the test.
 void findAnnotated(Class<? extends Annotation> annotation, String... packageNames)
          Attempts to discover classes that are annotated with to the annotation.
 void findImplementations(Class parent, String... packageNames)
          Attempts to discover classes that are assignable to the type provided.
 void findInPackage(ResolverUtil.Test test, String packageName)
          Scans for classes starting at the package provided and descending into subpackages.
 void findSuffix(String suffix, String... packageNames)
          Attempts to discover classes who's name ends with the provided suffix.
 Set<Class<? extends T>> getClasses()
          Provides access to the classes discovered so far.
 ClassLoader getClassLoader()
          Returns the classloader that will be used for scanning for classes.
private  void loadImplementationsInDirectory(ResolverUtil.Test test, String parent, File location)
          Finds matches in a physical directory on a filesystem.
private  void loadImplementationsInJar(ResolverUtil.Test test, String parent, File jarfile)
          Finds matching classes within a jar files that contains a folder structure matching the package structure.
 void setClassLoader(ClassLoader classloader)
          Sets an explicit ClassLoader that should be used when scanning for classes.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

log

private static final Log log
An instance of Log to use for logging in this class.


matches

private Set<Class<? extends T>> matches
The set of matches being accumulated.


classloader

private ClassLoader classloader
The ClassLoader to use when looking for classes. If null then the ClassLoader returned by Thread.currentThread().getContextClassLoader() will be used.

Constructor Detail

ResolverUtil

public ResolverUtil()
Method Detail

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.

Returns:
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.

Returns:
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.

Parameters:
classloader - a ClassLoader to use when scanning for classes

findImplementations

public void 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().

Parameters:
parent - the class of interface to find subclasses or implementations of
packageNames - one or more package names to scan (including subpackages) for classes

findSuffix

public void findSuffix(String suffix,
                       String... packageNames)
Attempts to discover classes who's name ends with the provided suffix. Accumulated classes can be accessed by calling getClasses().

Parameters:
suffix - The class name suffix to match
packageNames - one or more package names to scan (including subpackages) for classes

findAnnotated

public void findAnnotated(Class<? extends Annotation> annotation,
                          String... packageNames)
Attempts to discover classes that are annotated with to the annotation. Accumulated classes can be accessed by calling getClasses().

Parameters:
annotation - the annotation that should be present on matching classes
packageNames - one or more package names to scan (including subpackages) for classes

find

public void find(ResolverUtil.Test test,
                 String... packageNames)
Attempts to discover classes that pass the test. Accumulated classes can be accessed by calling getClasses().

Parameters:
test - the test to determine matching classes
packageNames - one or more package names to scan (including subpackages) for classes

findInPackage

public void findInPackage(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().

Parameters:
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

loadImplementationsInDirectory

private void loadImplementationsInDirectory(ResolverUtil.Test test,
                                            String parent,
                                            File location)
Finds matches in a physical directory on a filesystem. Examines all files within a directory - if the File object is not a directory, and ends with .class the file is loaded and tested to see if it is acceptable according to the Test. Operates recursively to find classes within a folder structure matching the package structure.

Parameters:
test - a Test used to filter the classes that are discovered
parent - the package name up to this directory in the package hierarchy. E.g. if /classes is in the classpath and we wish to examine files in /classes/org/apache then the values of parent would be org/apache
location - a File object representing a directory

loadImplementationsInJar

private void loadImplementationsInJar(ResolverUtil.Test test,
                                      String parent,
                                      File jarfile)
Finds matching classes within a jar files that contains a folder structure matching the package structure. If the File is not a JarFile or does not exist a warning will be logged, but no error will be raised.

Parameters:
test - a Test used to filter the classes that are discovered
parent - the parent package under which classes must be in order to be considered
jarfile - the jar file to be examined for classes

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.

Parameters:
test - the test used to determine if the class matches
fqn - the fully qualified name of a class


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