Find where java class is loaded from

Question

Does anyone know how to programmaticly find out where the java classloader actually loads the class from     I often work on large projects where the classpath gets very long and manual searching is not really an option   I recently had a problem where the classloader was loading an incorrect version of a class because it was on the classpath in two different places   So how can I get the classloader to tell me where on disk the actual class file is coming from   Edit  What about if the classloader actually fails to load the class due to a version mismatch  or something else    is there anyway we could find out what file its trying to read before it reads it

User · Accepted Answer

Here s an example   package foo   public class Test       public static void main String   args                ClassLoader loader   Test class getClassLoader            System out println loader getResource  foo Test class               This printed out   file  C  Users Jon Test foo Test class

User · Answer

Assuming that you re working with a class named MyClass  the following should work   MyClass class getClassLoader      Whether or not you can get the on-disk location of the  class file is dependent on the classloader itself   For example  if you re using something like BCEL  a certain class may not even have an on-disk representation

User · Answer

Simple way      System out println java lang String class getResource String class getSimpleName     class       Out Example      jar file  D  Java jdk1 8 jre lib rt jar  java lang String class   Or     String obj    simple test     System out println obj getClass   getResource obj getClass   getSimpleName     class       Out Example      jar file  D  Java jdk1 8 jre lib rt jar  java lang String class

User · Answer

Take a look at this similar question   Tool to discover same class    I think the most relevant obstacle is if you have a custom classloader   loading  from a db or ldap

User · Answer

This is what we use   public static String getClassResource Class lt   gt  klass      return klass getClassLoader   getResource       klass getName   replace               class   toString        This will work depending on the ClassLoader implementation   getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

Typically  we don t what to use hardcoding  We can get className first  and then use ClassLoader to get the class URL           String className   MyClass class getName   replace             class           URL classUrl    MyClass class getClassLoader   getResource className           String fullPath   classUrl  null   null   classUrl getPath

User · Answer

Edit just 1st line  Main class  Class lt   gt  c   Main class  String path   c getResource c getSimpleName       class   getPath   replace c getSimpleName       class         System out println path     Output     C  Users Test bin    Maybe bad style but works fine

User · Answer

Simple way      System out println java lang String class getResource String class getSimpleName     class       Out Example      jar file  D  Java jdk1 8 jre lib rt jar  java lang String class   Or     String obj    simple test     System out println obj getClass   getResource obj getClass   getSimpleName     class       Out Example      jar file  D  Java jdk1 8 jre lib rt jar  java lang String class

User · Answer

This approach works for both files and jars   Class clazz   Class forName nameOfClassYouWant    URL resourceUrl   clazz getResource       clazz getCanonicalName   replace               class    InputStream classStream   resourceUrl openStream       load the bytecode  if you wish

User · Answer

Take a look at this similar question   Tool to discover same class    I think the most relevant obstacle is if you have a custom classloader   loading  from a db or ldap

User · Answer

Edit just 1st line  Main class  Class lt   gt  c   Main class  String path   c getResource c getSimpleName       class   getPath   replace c getSimpleName       class         System out println path     Output     C  Users Test bin    Maybe bad style but works fine

User · Answer

This is what we use   public static String getClassResource Class lt   gt  klass      return klass getClassLoader   getResource       klass getName   replace               class   toString        This will work depending on the ClassLoader implementation   getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

This approach works for both files and jars   Class clazz   Class forName nameOfClassYouWant    URL resourceUrl   clazz getResource       clazz getCanonicalName   replace               class    InputStream classStream   resourceUrl openStream       load the bytecode  if you wish

User · Answer

Assuming that you re working with a class named MyClass  the following should work   MyClass class getClassLoader      Whether or not you can get the on-disk location of the  class file is dependent on the classloader itself   For example  if you re using something like BCEL  a certain class may not even have an on-disk representation

User · Answer

This is what we use   public static String getClassResource Class lt   gt  klass      return klass getClassLoader   getResource       klass getName   replace               class   toString        This will work depending on the ClassLoader implementation   getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

Assuming that you re working with a class named MyClass  the following should work   MyClass class getClassLoader      Whether or not you can get the on-disk location of the  class file is dependent on the classloader itself   For example  if you re using something like BCEL  a certain class may not even have an on-disk representation

User · Answer

This is what we use   public static String getClassResource Class lt   gt  klass      return klass getClassLoader   getResource       klass getName   replace               class   toString        This will work depending on the ClassLoader implementation   getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

Take a look at this similar question   Tool to discover same class    I think the most relevant obstacle is if you have a custom classloader   loading  from a db or ldap

User · Answer

Assuming that you re working with a class named MyClass  the following should work   MyClass class getClassLoader      Whether or not you can get the on-disk location of the  class file is dependent on the classloader itself   For example  if you re using something like BCEL  a certain class may not even have an on-disk representation

User · Answer

getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

Another way to find out where a class is loaded from  without manipulating the source  is to start the Java VM with the option  -verbose class

User · Answer

getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

getClass   getProtectionDomain   getCodeSource   getLocation

User · Answer

Typically  we don t what to use hardcoding  We can get className first  and then use ClassLoader to get the class URL           String className   MyClass class getName   replace             class           URL classUrl    MyClass class getClassLoader   getResource className           String fullPath   classUrl  null   null   classUrl getPath

User · Answer

Another way to find out where a class is loaded from  without manipulating the source  is to start the Java VM with the option  -verbose class

User · Answer

Jon s version fails when the object s ClassLoader is registered as null which seems to imply that it was loaded by the Boot ClassLoader   This method deals with that issue   public static String whereFrom Object o      if   o    null         return null        Class lt   gt  c   o getClass      ClassLoader loader   c getClassLoader      if   loader    null            Try the bootstrap classloader - obtained from the ultimate parent of the System Class Loader      loader   ClassLoader getSystemClassLoader        while   loader    null  amp  amp  loader getParent      null           loader   loader getParent                if  loader    null        String name   c getCanonicalName        URL resource   loader getResource name replace               class        if   resource    null           return resource toString                return  Unknown

User · Answer

Another way to find out where a class is loaded from  without manipulating the source  is to start the Java VM with the option  -verbose class

User · Answer

Take a look at this similar question   Tool to discover same class    I think the most relevant obstacle is if you have a custom classloader   loading  from a db or ldap

User · Answer

Another way to find out where a class is loaded from  without manipulating the source  is to start the Java VM with the option  -verbose class

User · Answer

Jon s version fails when the object s ClassLoader is registered as null which seems to imply that it was loaded by the Boot ClassLoader   This method deals with that issue   public static String whereFrom Object o      if   o    null         return null        Class lt   gt  c   o getClass      ClassLoader loader   c getClassLoader      if   loader    null            Try the bootstrap classloader - obtained from the ultimate parent of the System Class Loader      loader   ClassLoader getSystemClassLoader        while   loader    null  amp  amp  loader getParent      null           loader   loader getParent                if  loader    null        String name   c getCanonicalName        URL resource   loader getResource name replace               class        if   resource    null           return resource toString                return  Unknown

[java] Find where java class is loaded from

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