How do I read all classes from a Java package in the classpath

Question

I need to read classes contained in a Java package  Those classes are in classpath  I need to do this task from a Java program directly  Do you know a simple way to do   List lt Class gt  classes   readClassesFrom  my package

User · Answer

I use this one  it works with files or jar archives  public static ArrayList lt String gt getClassNamesFromPackage String packageName  throws IOException      ClassLoader classLoader   Thread currentThread   getContextClassLoader        URL packageURL      ArrayList lt String gt  names   new ArrayList lt String gt           packageName   packageName replace                packageURL   classLoader getResource packageName        if packageURL getProtocol   equals  jar             String jarFileName          JarFile jf           Enumeration lt JarEntry gt  jarEntries          String entryName              build jar file name  then loop through zipped entries         jarFileName   URLDecoder decode packageURL getFile     UTF-8            jarFileName   jarFileName substring 5 jarFileName indexOf                System out println   gt   jarFileName           jf   new JarFile jarFileName           jarEntries   jf entries            while jarEntries hasMoreElements                 entryName   jarEntries nextElement   getName                if entryName startsWith packageName   amp  amp  entryName length   gt packageName length   5                   entryName   entryName substring packageName length   entryName lastIndexOf                        names add entryName                                   loop through files in classpath      else      URI uri   new URI packageURL toString         File folder   new File uri getPath                won t work with path which contains blank   20             File folder   new File packageURL getFile              File   contenuti   folder listFiles            String entryName          for File actual  contenuti               entryName   actual getName                entryName   entryName substring 0  entryName lastIndexOf                    names add entryName                       return names

User · Answer

The most robust mechanism for listing all classes in a given package is currently ClassGraph  because it handles the widest possible array of classpath specification mechanisms  including the new JPMS module system   I am the author    List lt String gt  classNames  try  ScanResult scanResult   new ClassGraph   whitelistPackages  my package            enableClassInfo   scan          classNames   scanResult getAllClasses   getNames

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You could use the Reflections Project described here  It s quite complete and easy to use   Brief description from the above website      Reflections scans your classpath  indexes the metadata  allows you to   query it on runtime and may save and collect that information for many   modules within your project    Example   Reflections reflections   new Reflections      new ConfigurationBuilder            setUrls ClasspathHelper forJavaClassPath       Set lt Class lt   gt  gt  types   reflections getTypesAnnotatedWith Scannable class

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Here is another option  slight modification to another answer in above below   Reflections reflections   new Reflections  com example project package        new SubTypesScanner false    Set lt Class lt   extends Object gt  gt  allClasses        reflections getSubTypesOf Object class

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Brent - the reason the association is one way has to do with the fact that any class on any component of your CLASSPATH can declare itself in any package  except for java javax   Thus there just is no mapping of ALL the classes in a given  package  because nobody knows nor can know  You could update a jar file tomorrow and remove or add classes  It s like trying to get a list of all people named John Jon Johan in all the countries of the world - none of us is omniscient therefore none of us will ever have the correct answer

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Back when applets were common place  one might have a URL on the classpath   When the classloader required a class  it would search all the locations on the classpath  including http resources   Because you can have things like URLs and directories on the classpath  there is no easy way to get a definitive list of the classes   However  you can get pretty close   Some of the Spring libraries are doing this now   You can get all the jar s on the classpath  and open them up like files   You can then take this list of files  and create a data structure containing your classes

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Spring has implemented an excellent classpath search function in the PathMatchingResourcePatternResolver   If you use the classpath   prefix  you can find all the resources  including classes in a given hierarchy  and even filter them if you want   Then you can use the children of AbstractTypeHierarchyTraversingFilter  AnnotationTypeFilter and AssignableTypeFilter to filter those resources either on class level annotations or on interfaces they implement

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eXtcos looks promising  Imagine you want to find all the classes that    Extend from class  Component   and store them Are annotated with  MyComponent   and Are in the    common    package     With eXtcos this is as simple as  ClasspathScanner scanner   new ClasspathScanner    final Set lt Class gt  classStore   new ArraySet lt Class gt      Set lt Class gt  classes   scanner getClasses new ClassQuery         protected void query             select            from    common              andStore thoseExtending Component class  into classStore            returning allAnnotatedWith MyComponent class

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Java 1 6 0 24   public static File   getPackageContent String packageName  throws IOException      ArrayList lt File gt  list   new ArrayList lt File gt         Enumeration lt URL gt  urls   Thread currentThread   getContextClassLoader                                getResources packageName       while  urls hasMoreElements              URL url   urls nextElement            File dir   new File url getFile             for  File f   dir listFiles                  list add f                       return list toArray new File           This solution was tested within the EJB environment

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Bill Burke has written a  nice article about class scanning   and then he wrote Scannotation  Hibernate has this already written    org hibernate ejb packaging Scanner org hibernate ejb packaging NativeScanner  CDI might solve this  but don t know - haven t investigated fully yet        Inject Instance lt  MyClass gt  x      x iterator      Also for annotations   abstract class MyAnnotationQualifier extends AnnotationLiteral lt Entity gt  implements Entity

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That functionality is still suspiciously missing from the Java reflection API as far as I know   You can get a package object by just doing this   Package packageObj   Package getPackage  my package      But as you probably noticed  that won t let you list the classes in that package   As of right now  you have to take sort of a more filesystem-oriented approach   I found some sample implementations in this post    I m not 100  sure these methods will work when your classes are buried in JAR files  but I hope one of those does it for you   I agree with  skaffman   if you have another way of going about this  I d recommend doing that instead

User · Answer

I happen to have implemented it  and it works in most cases  Since it is long  I put it in a file here   The idea is to find the location of the class source file which is available in most cases  a known exception are JVM class files -- as far as I ve tested   If the code is in a directory  scan through all files and only spot class files  If the code is in a JAR file  scan all entries   This method can only be used when    You have a class that is in the same package you want to discover  This class is called a SeedClass  For example  if you want to list all classes in  java io   the seed class may be java io File  Your classes are in a directory or in a JAR file it has source file information  not source code file  but just source file   As far as I ve tried  it work almost 100  except the JVM class  those classes come with the JVM   Your program must have permission to access ProtectionDomain of those classes  If your program is loaded locally  there should be no problem    I ve tested the program only for my regular usage  so it may still have problem   I hope this helps

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If you have Spring in you classpath then the following will do it   Find all classes in a package that are annotated with XmlRootElement   private List lt Class gt  findMyTypes String basePackage  throws IOException  ClassNotFoundException       ResourcePatternResolver resourcePatternResolver   new PathMatchingResourcePatternResolver        MetadataReaderFactory metadataReaderFactory   new CachingMetadataReaderFactory resourcePatternResolver        List lt Class gt  candidates   new ArrayList lt Class gt         String packageSearchPath   ResourcePatternResolver CLASSPATH ALL URL PREFIX                                  resolveBasePackage basePackage                class       Resource   resources   resourcePatternResolver getResources packageSearchPath       for  Resource resource   resources            if  resource isReadable                  MetadataReader metadataReader   metadataReaderFactory getMetadataReader resource               if  isCandidate metadataReader                     candidates add Class forName metadataReader getClassMetadata   getClassName                                        return candidates     private String resolveBasePackage String basePackage        return ClassUtils convertClassNameToResourcePath SystemPropertyUtils resolvePlaceholders basePackage       private boolean isCandidate MetadataReader metadataReader  throws ClassNotFoundException       try           Class c   Class forName metadataReader getClassMetadata   getClassName             if  c getAnnotation XmlRootElement class     null                return true                      catch Throwable e             return false

User · Answer

Scannotation and Reflections use class path scanning approach   Reflections reflections   new Reflections  my package    Set lt Class lt   extends Object gt  gt  classes   reflections getSubTypesOf Object class     Another approach is to use Java Pluggable Annotation Processing API to write annotation processor which will collect all annotated classes at compile time and build the index file for runtime use  This mechanism is implemented in ClassIndex library   Iterable lt Class gt  classes   ClassIndex getPackageClasses  my package

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use dependency maven    groupId  net sf extcos artifactId  extcos version  0 4b   then use this code     ComponentScanner scanner   new ComponentScanner            Set classes   scanner getClasses new ComponentQuery                  Override             protected void query                     select   from  com leyton   returning allExtending DynamicForm class

[java] How do I read all classes from a Java package in the classpath?

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