Java - Get a list of all Classes loaded in the JVM

Question

I would like to get a list of all the classes belonging to a certain package as well as all of their children   The classes may or may not be already loaded in the JVM

User · Answer

One way if you already know the package top level path is to use OpenPojo

final List<PojoClass> pojoClasses = PojoClassFactory.getPojoClassesRecursively("my.package.path", null);

Then you can go over the list and perform any functionality you desire.

User · Answer

using the Reflections library  it s easy as   Reflections reflections   new Reflections  my pkg   new SubTypesScanner false      That would scan all classes in the url s that contains my pkg package     the false parameter means - don t exclude the Object class  which is excluded by default   in some scenarios  different containers  you might pass the classLoader as well as a parameter     So  getting all classes is effectively getting all subtypes of Object  transitively   Set lt String gt  allClasses        reflections getStore   getSubTypesOf Object class getName        The ordinary way reflections getSubTypesOf Object class  would cause loading all classes into PermGen and would probably throw OutOfMemoryError  you don t want to do it      If you want to get all direct subtypes of Object  or any other type   without getting its transitive subtypes all in once  use this   Collection lt String gt  directSubtypes        reflections getStore   get SubTypesScanner class  get Object class getName

User · Answer

Well  what I did was simply listing all the files in the classpath   It may not be a glorious solution  but it works reliably and gives me everything I want  and more

User · Answer

It s not a programmatic solution but you can run   java -verbose class        and the JVM will dump out what it s loading  and from where    Opened  usr java j2sdk1 4 1 jre lib rt jar   Opened  usr java j2sdk1 4 1 jre lib sunrsasign jar   Opened  usr java j2sdk1 4 1 jre lib jsse jar   Opened  usr java j2sdk1 4 1 jre lib jce jar   Opened  usr java j2sdk1 4 1 jre lib charsets jar   Loaded java lang Object from  usr java j2sdk1 4 1 jre lib rt jar   Loaded java io Serializable from  usr java j2sdk1 4 1 jre lib rt jar   Loaded java lang Comparable from  usr java j2sdk1 4 1 jre lib rt jar   Loaded java lang CharSequence from  usr java j2sdk1 4 1 jre lib rt jar   Loaded java lang String from  usr java j2sdk1 4 1 jre lib rt jar    See here for more details

User · Answer

An alternative approach to those described above would be to create an external agent using java lang instrument to find out what classes are loaded and run your program with the -javaagent switch   import java lang instrument ClassFileTransformer  import java lang instrument IllegalClassFormatException  import java security ProtectionDomain   public class SimpleTransformer implements ClassFileTransformer        public SimpleTransformer             super               public byte   transform ClassLoader loader  String className  Class redefiningClass  ProtectionDomain domain  byte   bytes  throws IllegalClassFormatException           System out println  Loading class      className           return bytes            This approach has the added benefit of providing you with information about which ClassLoader loaded a given class

User · Answer

There are multiple answers to this question  partly due to ambiguous question - the title is talking about classes loaded by the JVM  whereas the contents of the question says  may or may not be loaded by the JVM    Assuming that OP needs classes that are loaded by the JVM by a given classloader  and only those classes - my need as well - there is a solution  elaborated here  that goes like this   import java net URL  import java util Enumeration  import java util Iterator  import java util Vector   public class CPTest        private static Iterator list ClassLoader CL          throws NoSuchFieldException  SecurityException          IllegalArgumentException  IllegalAccessException           Class CL class   CL getClass            while  CL class    java lang ClassLoader class                CL class   CL class getSuperclass                      java lang reflect Field ClassLoader classes field   CL class                  getDeclaredField  classes            ClassLoader classes field setAccessible true           Vector classes    Vector  ClassLoader classes field get CL           return classes iterator               public static void main String args    throws Exception           ClassLoader myCL   Thread currentThread   getContextClassLoader            while  myCL    null                System out println  ClassLoader      myCL               for  Iterator iter   list myCL   iter hasNext                       System out println   t    iter next                               myCL   myCL getParent                         One of the neat things about it is that you can choose an arbitrary classloader you want to check  It is however likely to break should internals of classloader class change  so it is to be used as one-off diagnostic tool

User · Answer

This program will prints all the classes with its physical path  use can simply copy this to any JSP if you need to analyse the class loading from any web application server   import java lang reflect Field  import java util Vector   public class TestMain        public static void main String   args            Field f          try               f   ClassLoader class getDeclaredField  classes                f setAccessible true               ClassLoader classLoader   Thread currentThread   getContextClassLoader                Vector lt Class gt  classes     Vector lt Class gt   f get classLoader                for Class cls   classes                   java net URL location   cls getResource       cls getName   replace                               class                    System out println   lt p gt   location    lt p  gt                             catch  Exception e                 e printStackTrace

User · Answer

You might be able to get a list of classes that are loaded through the classloader but this would not include classes you haven t loaded yet but are on your classpath   To get ALL classes on your classpath you have to do something like your second solution   If you really want classes that are currently  Loaded   in other words  classes you have already referenced  accessed or instantiated  then you should refine your question to indicate this

User · Answer

Run your code under a JRockit JVM  then use JRCMD  lt PID gt  print class summary  This will output all loaded classes  one on each line

User · Answer

From Oracle doc you can use -Xlog option that has a possibility to write into file   java -Xlog class load info classloaded txt

User · Answer

I d also suggest you write a -javagent agent  but use the getAllLoadedClasses method instead of transforming any classes   To synchronize with your client code  Normal Java code   create a socket and communicate with the agent through it   Then you can trigger a  list all classes  method whenever you need

[java] Java - Get a list of all Classes loaded in the JVM

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