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

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Aleksander Blomsk  ld s solution did not work for me for parameterized tests  RunWith Parameterized class  when using Maven  The tests were named correctly and also where found but not executed   ------------------------------------------------------- T E S T S ------------------------------------------------------- Running some properly named test run with maven SomeTest Tests run  0  Failures  0  Errors  0  Skipped  0  Time elapsed  0 123 sec   A similar issue has been reported here   In my case  Parameters is creating instances of each class in a package  The tests worked well when run locally in the IDE  However  when running Maven no classes where found with Aleksander Blomsk  ld s solution   I did make it work with the following snipped which was inspired by David P  rsson s comment on Aleksander Blomsk  ld s answer   Reflections reflections   new Reflections new ConfigurationBuilder                setScanners new SubTypesScanner false    don t exclude Object class      new ResourcesScanner                 addUrls ClasspathHelper forJavaClassPath                  filterInputsBy new FilterBuilder                include FilterBuilder prefix basePackage       Set lt Class lt   gt  gt  subTypesOf   reflections getSubTypesOf Object class

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I just wrote a util class  it include test methods  you can have a check    IteratePackageUtil java   package eric j2se reflect   import java util Set   import org reflections Reflections  import org reflections scanners ResourcesScanner  import org reflections scanners SubTypesScanner  import org reflections util ClasspathHelper  import org reflections util ConfigurationBuilder  import org reflections util FilterBuilder          an util to iterate class in a package          author eric     date Dec 10  2013 12 36 46 AM     public class IteratePackageUtil                   lt p gt         Get set of all class in a specified package recursively  this only support lib         lt  p gt          lt p gt         class of sub package will be included  inner class will be included          lt  p gt          lt p gt         could load class that use the same classloader of current class  can t load system packages          lt  p gt                  param pkg                   path of a package         return             public static Set lt Class lt   extends Object gt  gt  getClazzSet String pkg               prepare reflection  include direct subclass of Object class         Reflections reflections   new Reflections new ConfigurationBuilder   setScanners new SubTypesScanner false   new ResourcesScanner                     setUrls ClasspathHelper forClassLoader ClasspathHelper classLoaders new ClassLoader 0                      filterInputsBy new FilterBuilder   includePackage pkg              return reflections getSubTypesOf Object class              public static void test             String pkg    org apache tomcat util            Set lt Class lt   extends Object gt  gt  clazzSet   getClazzSet pkg           for  Class lt   extends Object gt  clazz   clazzSet                System out println clazz getName                          public static void main String   args            test

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Without using any extra libraries   package test   import java io DataInputStream  import java io InputStream  import java net URL  import java util ArrayList  import java util List   public class Test       public static void main String   args  throws Exception          List lt Class gt  classes   getClasses Test class getClassLoader    test            for Class c classes               System out println  Class    c                        public static List lt Class gt  getClasses ClassLoader cl String pack  throws Exception           String dottedPackage   pack replaceAll                      List lt Class gt  classes   new ArrayList lt Class gt             URL upackage   cl getResource pack            DataInputStream dis   new DataInputStream  InputStream  upackage getContent             String line   null          while   line   dis readLine       null                if line endsWith   class                     classes add Class forName dottedPackage     line substring 0 line lastIndexOf                                          return classes

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Yeah using few API s you can  here is how I like doing it  faced this problem which I was using hibernate core  amp  had to find classes which where annotated with a certain annotation   Make these an custom annotation using which you will mark which classes you want to be picked up   import java lang annotation ElementType  import java lang annotation Retention  import java lang annotation RetentionPolicy  import java lang annotation Target    Retention RetentionPolicy RUNTIME   Target ElementType TYPE  public  interface EntityToBeScanned        Then mark your class with it like   EntityToBeScanned  public MyClass       Make this utility class which has the following method  public class ClassScanner        public static Set lt Class lt   gt  gt  allFoundClassesAnnotatedWithEntityToBeScanned            Reflections reflections   new Reflections                Set lt Class lt   gt  gt  annotated   reflections getTypesAnnotatedWith EntityToBeScanned class           return annotated             Call the allFoundClassesAnnotatedWithEntityToBeScanned   method to get a Set of Classes found   You will need libs given below   lt  -- https   mvnrepository com artifact com google guava guava -- gt       lt dependency gt           lt groupId gt com google guava lt  groupId gt           lt artifactId gt guava lt  artifactId gt           lt version gt 21 0 lt  version gt       lt  dependency gt   lt  -- https   mvnrepository com artifact org javassist javassist -- gt   lt dependency gt       lt groupId gt org javassist lt  groupId gt       lt artifactId gt javassist lt  artifactId gt       lt version gt 3 22 0-CR1 lt  version gt   lt  dependency gt   lt  -- https   mvnrepository com artifact org reflections reflections -- gt   lt dependency gt       lt groupId gt org reflections lt  groupId gt       lt artifactId gt reflections lt  artifactId gt       lt version gt 0 9 10 lt  version gt   lt  dependency gt

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In general class loaders do not allow for scanning through all the classes on the classpath  But usually the only used class loader is UrlClassLoader from which we can retrieve the list of directories and jar files  see getURLs  and open them one by one to list available classes  This approach  called class path scanning  is implemented in Scannotation and Reflections   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      package-info java  IndexSubclasses package my package      your code Iterable lt Class gt  classes   ClassIndex getPackageClasses  my package      Notice that no additional setup is needed as the scanning is fully automated thanks to Java compiler automatically discovering any processors found on the classpath

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It is very possible  but without additional libraries like Reflections it is hard    It is hard because you haven t full instrument for get class name  And  I take the code of my ClassFinder class   package play util   import java io File  import java io IOException  import java util ArrayList  import java util Enumeration  import java util List  import java util jar JarEntry  import java util jar JarFile          Created by LINKOR on 26 05 2017 in 15 12     Date  2017 05 26     public class FileClassFinder   private JarFile file  private boolean trouble  public FileClassFinder String filePath        try           file   new JarFile filePath         catch  IOException e            trouble   true           public List lt String gt  findClasses String pkg        ArrayList lt String gt  classes   new ArrayList lt  gt         Enumeration lt JarEntry gt  entries   file entries        while  entries hasMoreElements              JarEntry cls   entries nextElement            if   cls isDirectory                  String fileName   cls getName                String className   fileName replaceAll                   replaceAll File pathSeparator       substring 0  fileName lastIndexOf                    if  className startsWith pkg   classes add className substring pkg length     1                        return classes

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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 lt BeanDefinition gt  classes   provider findCandidateComponents  my package name        this is how you can load the class type from BeanDefinition instance for  BeanDefinition bean  classes        Class lt   gt  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 lt   gt  clazz   info load           do something with your clazz

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Provided you are not using any dynamic class loaders you can search the classpath and for each entry search the directory or JAR file

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You should probably take a look at the open source Reflections library  With it you can easily achieve what you want   First  setup the reflections index  it s a bit messy since searching for all classes is disabled by default    List lt ClassLoader gt  classLoadersList   new LinkedList lt ClassLoader gt     classLoadersList add ClasspathHelper contextClassLoader     classLoadersList add ClasspathHelper staticClassLoader      Reflections reflections   new Reflections new ConfigurationBuilder        setScanners new SubTypesScanner false    don t exclude Object class      new ResourcesScanner         setUrls ClasspathHelper forClassLoader classLoadersList toArray new ClassLoader 0          filterInputsBy new FilterBuilder   include FilterBuilder prefix  org your package         Then you can query for all objects in a given package   Set lt Class lt   gt  gt  classes   reflections getSubTypesOf Object class

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Based on  Staale s answer  and in an attempt not to rely on third party libraries  I would implement the File System approach by inspecting first package physical location with   import java io File  import java io FileFilter  import java util ArrayList      Class lt   gt    foundClasses   new Class lt   gt  0   final ArrayList lt Class lt   gt  gt  foundClassesDyn   new ArrayList lt Class lt   gt  gt      new java io File      klass getResource                curPackage replace                   getFile     listFiles      new java io FileFilter             public boolean accept java io File file                final String classExtension     class                if   file isFile                    amp  amp  file getName   endsWith classExtension                     avoid inner classes                  amp  amp    file getName   contains                                      try                       String className   file getName                        className   className substring 0  className length   - classExtension length                         foundClassesDyn add  Class forName  curPackage         className                        catch  ClassNotFoundException e                        e printStackTrace System out                                                return false                      foundClasses   foundClassesDyn toArray foundClasses

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I couldn t find a short working snipped for something so simple  So here it is  I made it myself after screwing around for a while       Reflections reflections           new Reflections new ConfigurationBuilder                    filterInputsBy new FilterBuilder   includePackage packagePath                    setUrls ClasspathHelper forPackage packagePath                    setScanners new SubTypesScanner false          Set lt String gt  typeList   reflections getAllTypes

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Almost all the answers either uses Reflections or reads class files from file system  If you try to read classes from file system  you may get errors when you package your application as JAR or other  Also you may not want to use a separate library for that purpose    Here is another approach which is pure java and not depends on file system    import javax tools JavaFileObject  import javax tools StandardJavaFileManager  import javax tools StandardLocation  import javax tools ToolProvider  import java io File  import java util ArrayList  import java util Collection  import java util Collections  import java util regex Pattern  import java util stream Collectors  import java util stream StreamSupport   public class PackageUtil        public static Collection lt Class gt  getClasses final String pack  throws Exception           final StandardJavaFileManager fileManager   ToolProvider getSystemJavaCompiler   getStandardFileManager null  null  null           return StreamSupport stream fileManager list StandardLocation CLASS PATH  pack  Collections singleton JavaFileObject Kind CLASS   false  spliterator    false                   map javaFileObject - gt                        try                           final String   split   javaFileObject getName                                    replace   class                                        replace                                           split Pattern quote File separator                             final String fullClassName   pack         split split length - 1                           return Class forName fullClassName                         catch  ClassNotFoundException e                            throw new RuntimeException e                                                              collect Collectors toCollection ArrayList  new              Java 8 is not a must  You can use for loops instead of streams  And you can test it like this  public static void main String   args  throws Exception       final String pack    java nio file      Or any other package     PackageUtil getClasses pack  stream   forEach System out  println

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Due to the dynamic nature of class loaders  this is not possible  Class loaders are not required to tell the VM which classes it can provide  instead they are just handed requests for classes  and have to return a class or throw an exception   However  if you write your own class loaders  or examine the classpaths and it s jars  it s possible to find this information  This will be via filesystem operations though  and not reflection  There might even be libraries that can help you do this   If there are classes that get generated  or delivered remotely  you will not be able to discover those classes   The normal method is instead to somewhere register the classes you need access to in a file  or reference them in a different class  Or just use convention when it comes to naming   Addendum  The Reflections Library will allow you to look up classes in the current classpath  It can be used to get all classes in a package    Reflections reflections   new Reflections  my project prefix      Set lt Class lt   extends Object gt  gt  allClasses         reflections getSubTypesOf Object class

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If you re in Spring-land you can use PathMatchingResourcePatternResolver     PathMatchingResourcePatternResolver resolver   new PathMatchingResourcePatternResolver      Resource   resources   resolver getResources  classpath  some package name   class         Arrays asList resources  forEach r- gt

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You could use this method1 that uses the ClassLoader          Scans all classes accessible from the context class loader which belong to the given package and subpackages         param packageName The base package     return The classes     throws ClassNotFoundException     throws IOException     private static Class   getClasses String packageName          throws ClassNotFoundException  IOException       ClassLoader classLoader   Thread currentThread   getContextClassLoader        assert classLoader    null      String path   packageName replace                Enumeration lt URL gt  resources   classLoader getResources path       List lt File gt  dirs   new ArrayList lt File gt         while  resources hasMoreElements              URL resource   resources nextElement            dirs add new File resource getFile                ArrayList lt Class gt  classes   new ArrayList lt Class gt         for  File directory   dirs            classes addAll findClasses directory  packageName              return classes toArray new Class classes size                Recursive method used to find all classes in a given directory and subdirs         param directory   The base directory     param packageName The package name for classes found inside the base directory     return The classes     throws ClassNotFoundException     private static List lt Class gt  findClasses File directory  String packageName  throws ClassNotFoundException       List lt Class gt  classes   new ArrayList lt Class gt         if   directory exists              return classes            File   files   directory listFiles        for  File file   files            if  file isDirectory                  assert  file getName   contains                   classes addAll findClasses file  packageName         file getName                else if  file getName   endsWith   class                  classes add Class forName packageName         file getName   substring 0  file getName   length   - 6                         return classes                 1 This method was taken originally from http   snippets dzone com posts show 4831  which was archived by the Internet Archive  as linked to now  The snippet is also available at https   dzone com articles get-all-classes-within-package

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It is not possible  since all classes in the package might not be loaded  while you always  knows package of a class

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plain java  FindAllClassesUsingPlainJavaReflectionTest java   Slf4j class FindAllClassesUsingPlainJavaReflectionTest      private static final Function lt Throwable  RuntimeException gt  asRuntimeException   throwable - gt        log error throwable getLocalizedMessage         return new RuntimeException throwable           private static final Function lt String  Collection lt Class lt   gt  gt  gt  findAllPackageClasses   basePackageName - gt         Locale locale   Locale getDefault        Charset charset   StandardCharsets UTF 8      val fileManager   ToolProvider getSystemJavaCompiler                                      getStandardFileManager    diagnosticListener    null  locale  charset        StandardLocation location   StandardLocation CLASS PATH      JavaFileObject Kind kind   JavaFileObject Kind CLASS      Set lt JavaFileObject Kind gt  kinds   Collections singleton kind       val javaFileObjects   Try of    - gt  fileManager list location  basePackageName  kinds     recurse    true                                 getOrElseThrow asRuntimeException        String pathToPackageAndClass   basePackageName replace      File separator       Function lt String  String gt  mapToClassName   s - gt          String prefix   Arrays stream s split pathToPackageAndClass                                findFirst                                orElse            return s replaceFirst prefix                     replaceAll File separator                    return StreamSupport stream javaFileObjects spliterator       parallel    true                           filter javaFileObject - gt  javaFileObject getKind   equals kind                            map FileObject  getName                           map fileObjectName - gt  fileObjectName replace   class                                 map mapToClassName                           map className - gt  Try of    - gt  Class forName className                                                 getOrElseThrow asRuntimeException                            collect Collectors toList              Test    DisplayName  should get classes recursively in given package     void test         Collection lt Class lt   gt  gt  classes   findAllPackageClasses apply getClass   getPackage   getName         assertThat classes  hasSizeGreaterThan 4       classes stream   map String  valueOf  forEach log  info           PS  to simplify boilerplates for handling errors  etc  I m using here vavr and lombok libraries  other implementations could be found in my GitHub daggerok java-reflection-find-annotated-classes-or-methods repo

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I put together a simple github project that solves this problem   https   github com ddopson java-class-enumerator  It should work for BOTH file-based classpaths AND for jar files   If you run  make  after checking out the project it will print this out    Cleaning    rm -rf build   Building    javac -d build classes src pro ddopson ClassEnumerator java src test ClassIShouldFindOne java src test ClassIShouldFindTwo java src test subpkg ClassIShouldFindThree java src test TestClassEnumeration java  Making JAR Files    jar cf build ClassEnumerator test jar -C build classes     jar cf build ClassEnumerator jar -C build classes  pro  Running Filesystem Classpath Test    java -classpath build classes test TestClassEnumeration ClassDiscovery  Package   test  becomes Resource   file  Users Dopson work other java-class-enumeration build classes test  ClassDiscovery  Reading Directory   Users Dopson work other java-class-enumeration build classes test  ClassDiscovery  FileName  ClassIShouldFindOne class       class  test ClassIShouldFindOne  ClassDiscovery  FileName  ClassIShouldFindTwo class       class  test ClassIShouldFindTwo  ClassDiscovery  FileName  subpkg       class  null  ClassDiscovery  Reading Directory   Users Dopson work other java-class-enumeration build classes test subpkg  ClassDiscovery  FileName  ClassIShouldFindThree class       class  test subpkg ClassIShouldFindThree  ClassDiscovery  FileName  TestClassEnumeration class       class  test TestClassEnumeration   Running JAR Classpath Test    java -classpath build ClassEnumerator test jar  test TestClassEnumeration ClassDiscovery  Package   test  becomes Resource   jar file  Users Dopson work other java-class-enumeration build ClassEnumerator test jar  test  ClassDiscovery  Reading JAR file    Users Dopson work other java-class-enumeration build ClassEnumerator test jar  ClassDiscovery  JarEntry  META-INF        class  null  ClassDiscovery  JarEntry  META-INF MANIFEST MF       class  null  ClassDiscovery  JarEntry  pro        class  null  ClassDiscovery  JarEntry  pro ddopson        class  null  ClassDiscovery  JarEntry  pro ddopson ClassEnumerator class       class  null  ClassDiscovery  JarEntry  test        class  null  ClassDiscovery  JarEntry  test ClassIShouldFindOne class       class  test ClassIShouldFindOne  ClassDiscovery  JarEntry  test ClassIShouldFindTwo class       class  test ClassIShouldFindTwo  ClassDiscovery  JarEntry  test subpkg        class  null  ClassDiscovery  JarEntry  test subpkg ClassIShouldFindThree class       class  test subpkg ClassIShouldFindThree  ClassDiscovery  JarEntry  test TestClassEnumeration class       class  test TestClassEnumeration   Tests Passed     See also my other answer

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Here s how I do it  I scan all the subfolders  sub-packages  and I don t try to load anonymous classes               Attempts to list all the classes in the specified package as determined      by the context class loader  recursively  avoiding anonymous classes             param pckgname                 the package name to search       return a list of classes that exist within that package       throws ClassNotFoundException                  if something went wrong         private static List lt Class gt  getClassesForPackage String pckgname  throws ClassNotFoundException            This will hold a list of directories matching the pckgname  There may be more than one if a package is split over multiple jars paths       ArrayList lt File gt  directories   new ArrayList lt File gt           String packageToPath   pckgname replace                  try             ClassLoader cld   Thread currentThread   getContextClassLoader              if  cld    null                  throw new ClassNotFoundException  Can t get class loader                               Ask for all resources for the packageToPath           Enumeration lt URL gt  resources   cld getResources packageToPath             while  resources hasMoreElements                    directories add new File URLDecoder decode resources nextElement   getPath     UTF-8                          catch  NullPointerException x              throw new ClassNotFoundException pckgname     does not appear to be a valid package  Null pointer exception             catch  UnsupportedEncodingException encex              throw new ClassNotFoundException pckgname     does not appear to be a valid package  Unsupported encoding             catch  IOException ioex              throw new ClassNotFoundException  IOException was thrown when trying to get all resources for     pckgname                  ArrayList lt Class gt  classes   new ArrayList lt Class gt              For every directoryFile identified capture all the  class files       while   directories isEmpty               File directoryFile    directories remove 0                          if  directoryFile exists                       Get the list of the files contained in the package               File   files   directoryFile listFiles                   for  File file   files                         we are only interested in  class files                   if   file getName   endsWith   class     amp  amp    file getName   contains                                   removes the  class extension                       int index   directoryFile getPath   indexOf packageToPath                         String packagePrefix   directoryFile getPath   substring index  replace                                                           try                                           String className   packagePrefix         file getName   substring 0  file getName   length   - 6                                                     classes add Class forName className                                                          catch  NoClassDefFoundError e                                                 do nothing  this class hasn t been found by the loader  and we don t care                                            else if  file isDirectory        If we got to a subdirectory                       directories add new File file getPath                                                                                else                 throw new ClassNotFoundException pckgname          directoryFile getPath        does not appear to be a valid package                              return classes

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Hello  I always have had some issues with the solutions above  and on other sites   I  as a developer  am programming a addon for a API  The API prevents the use of any external libraries or 3rd party tools  The setup also consists of a mixture of code in jar or zip files and class files located directly in some directories  So my code had to be able to work arround every setup  After a lot of research I have come up with a method that will work in at least 95  of all possible setups   The following code is basically the overkill method that will always work   The code   This code scans a given package for all classes that are included in it  It will only work for all classes in the current ClassLoader          Private helper method         param directory               The directory to start with     param pckgname               The package name to search for  Will be needed for getting the               Class object      param classes               if a file isn t loaded but still is in the directory     throws ClassNotFoundException     private static void checkDirectory File directory  String pckgname          ArrayList lt Class lt   gt  gt  classes  throws ClassNotFoundException       File tmpDirectory       if  directory exists    amp  amp  directory isDirectory              final String   files   directory list             for  final String file   files                if  file endsWith   class                      try                       classes add Class forName pckgname                                     file substring 0  file length   - 6                       catch  final NoClassDefFoundError e                           do nothing  this class hasn t been found by the                        loader  and we don t care                                  else if   tmpDirectory   new File directory  file                        isDirectory                      checkDirectory tmpDirectory  pckgname         file  classes                                           Private helper method          param connection               the connection to the jar     param pckgname               the package name to search for     param classes               the current ArrayList of all classes  This method will simply               add new classes      throws ClassNotFoundException                if a file isn t loaded but still is in the jar file     throws IOException                if it can t correctly read from the jar file      private static void checkJarFile JarURLConnection connection          String pckgname  ArrayList lt Class lt   gt  gt  classes          throws ClassNotFoundException  IOException       final JarFile jarFile   connection getJarFile        final Enumeration lt JarEntry gt  entries   jarFile entries        String name       for  JarEntry jarEntry   null  entries hasMoreElements                amp  amp    jarEntry   entries nextElement       null              name   jarEntry getName             if  name contains   class                  name   name substring 0  name length   - 6  replace                         if  name contains pckgname                     classes add Class forName name                                            Attempts to list all the classes in the specified package as determined    by the context class loader         param pckgname               the package name to search     return a list of classes that exist within that package     throws ClassNotFoundException                if something went wrong     public static ArrayList lt Class lt   gt  gt  getClassesForPackage String pckgname          throws ClassNotFoundException       final ArrayList lt Class lt   gt  gt  classes   new ArrayList lt Class lt   gt  gt          try           final ClassLoader cld   Thread currentThread                    getContextClassLoader             if  cld    null              throw new ClassNotFoundException  Can t get class loader              final Enumeration lt URL gt  resources   cld getResources pckgname                  replace                     URLConnection connection           for  URL url   null  resources hasMoreElements                    amp  amp    url   resources nextElement       null                  try                   connection   url openConnection                     if  connection instanceof JarURLConnection                        checkJarFile  JarURLConnection  connection  pckgname                              classes                     else if  connection instanceof FileURLConnection                        try                           checkDirectory                                  new File URLDecoder decode url getPath                                             UTF-8     pckgname  classes                         catch  final UnsupportedEncodingException ex                            throw new ClassNotFoundException                                  pckgname                                             does not appear to be a valid package  Unsupported encoding                                    ex                                           else                     throw new ClassNotFoundException pckgname                                      url getPath                                    does not appear to be a valid package                  catch  final IOException ioex                    throw new ClassNotFoundException                           IOException was thrown when trying to get all resources for                                     pckgname  ioex                                 catch  final NullPointerException ex            throw new ClassNotFoundException                  pckgname                             does not appear to be a valid package  Null pointer exception                    ex         catch  final IOException ioex            throw new ClassNotFoundException                   IOException was thrown when trying to get all resources for                             pckgname  ioex              return classes      These three methods provide you with the ability to find all classes in a given package  You use it like this   getClassesForPackage  package your classes are in      The explanation   The method first gets the current ClassLoader  It then fetches all resources that contain said package and iterates of these URLs  It then creates a URLConnection and determines what type of URl we have  It can either be a directory  FileURLConnection  or a directory inside a jar or zip file  JarURLConnection   Depending on what type of connection we have two different methods will be called   First lets see what happens if it is a FileURLConnection  It first checks if the passed File exists and is a directory  If that s the case it checks if it is a class file  If so a Class object will be created and put in the ArrayList  If it is not a class file but is a directory  we simply iterate into it and do the same thing  All other cases files will be ignored   If the URLConnection is a JarURLConnection the other private helper method will be called  This method iterates over all Entries in the zip jar archive  If one entry is a class file and is inside of the package a Class object will be created and stored in the ArrayList   After all resources have been parsed it  the main method  returns the ArrayList containig all classes in the given package  that the current ClassLoader knows about   If the process fails at any point a ClassNotFoundException will be thrown containg detailed information about the exact cause

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I ve been trying to use the Reflections library  but had some problems using it  and there were too many jars I should include just to simply obtain the classes on a package   I ll post a solution I ve found in this duplicate question  How to get all classes names in a package   The answer was written by sp00m  I ve added some corrections to make it work   import java io File  import java io IOException  import java net URL  import java util Enumeration  import java util LinkedList  import java util List   public final class ClassFinder        private final static char DOT            private final static char SLASH            private final static String CLASS SUFFIX     class       private final static String BAD PACKAGE ERROR    Unable to get resources from path   s   Are you sure the given   s  package exists         public final static List lt Class lt   gt  gt  find final String scannedPackage            final ClassLoader classLoader   Thread currentThread   getContextClassLoader            final String scannedPath   scannedPackage replace DOT  SLASH           final Enumeration lt URL gt  resources          try               resources   classLoader getResources scannedPath             catch  IOException e                throw new IllegalArgumentException String format BAD PACKAGE ERROR  scannedPath  scannedPackage   e                     final List lt Class lt   gt  gt  classes   new LinkedList lt Class lt   gt  gt             while  resources hasMoreElements                  final File file   new File resources nextElement   getFile                 classes addAll find file  scannedPackage                      return classes             private final static List lt Class lt   gt  gt  find final File file  final String scannedPackage            final List lt Class lt   gt  gt  classes   new LinkedList lt Class lt   gt  gt             if  file isDirectory                  for  File nestedFile   file listFiles                      classes addAll find nestedFile  scannedPackage                            File names with the  1   2 holds the anonymous inner classes  we are not interested on them             else if  file getName   endsWith CLASS SUFFIX   amp  amp   file getName   contains                      final int beginIndex   0              final int endIndex   file getName   length   - CLASS SUFFIX length                final String className   file getName   substring beginIndex  endIndex               try                   final String resource   scannedPackage   DOT   className                  classes add Class forName resource                  catch  ClassNotFoundException ignore                                    return classes             To use it just call the find method as sp00n mentioned in this example  I ve added the creation of instances of the classes if needed   List lt Class lt   gt  gt  classes   ClassFinder find  com package     ExcelReporting excelReporting  for  Class lt   gt  aClass   classes        Constructor constructor   aClass getConstructor          Create an object of the class type     constructor newInstance

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Worth mentioning  If you want to have a list of all classes under some package  you can use Reflection the following way   List lt Class gt  myTypes   new ArrayList lt  gt      Reflections reflections   new Reflections  com package    for  String s   reflections getStore   get SubTypesScanner class  values          myTypes add Class forName s        This will create a list of classes that later you can use them as you wish

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Google Guava 14 includes a new class ClassPath with three methods to scan for top level classes    getTopLevelClasses   getTopLevelClasses String packageName  getTopLevelClassesRecursive String packageName    See the ClassPath javadocs for more info

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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   new ArrayList lt  gt     try  ScanResult scanResult   new ClassGraph   acceptPackages  quot my package quot            enableClassInfo   scan          classNames addAll scanResult getAllClasses   getNames

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What about this   public static List lt Class lt   gt  gt  getClassesForPackage final String pkgName  throws IOException  URISyntaxException       final String pkgPath   pkgName replace                final URI pkg   Objects requireNonNull ClassLoader getSystemClassLoader   getResource pkgPath   toURI        final ArrayList lt Class lt   gt  gt  allClasses   new ArrayList lt Class lt   gt  gt          Path root      if  pkg toString   startsWith  jar               try               root   FileSystems getFileSystem pkg  getPath pkgPath             catch  final FileSystemNotFoundException e                root   FileSystems newFileSystem pkg  Collections emptyMap    getPath pkgPath                   else           root   Paths get pkg              final String extension     class       try  final Stream lt Path gt  allPaths   Files walk root             allPaths filter Files  isRegularFile  forEach file - gt                try                   final String path   file toString   replace                            final String name   path substring path indexOf pkgName   path length   - extension length                     allClasses add Class forName name                  catch  final ClassNotFoundException   StringIndexOutOfBoundsException ignored                                        return allClasses      You can then overload the function   public static List lt Class lt   gt  gt  getClassesForPackage final Package pkg  throws IOException  URISyntaxException       return getClassesForPackage pkg getName         If you need to test it   public static void main final String   argv  throws IOException  URISyntaxException       for  final Class lt   gt  cls   getClassesForPackage  my package              System out println cls             for  final Class lt   gt  cls   getClassesForPackage MyClass class getPackage               System out println cls             If your IDE does not have import helper   import java io IOException  import java net URI  import java net URISyntaxException  import java nio file FileSystemNotFoundException  import java nio file FileSystems  import java nio file Files  import java nio file Path  import java nio file Paths  import java util ArrayList  import java util Collections  import java util List  import java util Objects  import java util stream Stream    It works    from your IDE for a JAR file without external dependencies

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If you are merely looking to load a group of related classes  then Spring can help you   Spring can instantiate a list or map of all classes that implement a given interface in one line of code  The list or map will contain instances of all the classes that implement that interface   That being said  as an alternative to loading the list of classes out of the file system  instead just implement the same interface in all the classes you want to load  regardless of package and use Spring to provide you instances of all of them  That way  you can load  and instantiate  all the classes you desire regardless of what package they are in   On the other hand  if having them all in a package is what you want  then simply have all the classes in that package implement a given interface

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You need to look up every class loader entry in the class path       String pkg    org apache commons lang       ClassLoader cl   ClassLoader getSystemClassLoader        URL   urls     URLClassLoader  cl  getURLs        for  URL url   urls            System out println url getFile             File jar   new File url getFile                                If entry is directory  just look up in the right subdirectory    if  jar isDirectory          File subdir   new File jar  pkg       if   subdir exists            continue      File   files   subdir listFiles        for  File file   files            if   file isFile                continue          if  file getName   endsWith   class                System out println  Found class                          file getName   substring 0                              file getName   length   - 6                 If the entry is the file  and it s jar  inspect the ZIP entries of it    else          try to open as ZIP     try           ZipFile zip   new ZipFile jar           for  Enumeration lt   extends ZipEntry gt  entries   zip                  entries    entries hasMoreElements                   ZipEntry entry   entries nextElement                String name   entry getName                if   name startsWith pkg                   continue              name   name substring pkg length     1               if  name indexOf       lt  0  amp  amp  name endsWith   class                    System out println  Found class                              name substring 0  name length   - 6                    catch  ZipException e            System out println  Not a ZIP      e getMessage           catch  IOException e            System err println e getMessage               Now once you have all class names withing package  you can try loading them with reflection and analyze if they are classes or interfaces  etc

[java] Can you find all classes in a package using reflection?

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