Any way to Invoke a private method

Question

I have a class that uses XML and reflection to return Objects to another class   Normally these objects are sub fields of an external object  but occasionally it s something I want to generate on the fly  I ve tried something like this but to no avail  I believe that s because Java won t allow you to access private methods for reflection   Element node   outerNode item 0   String methodName   node getAttribute  method    String objectName   node getAttribute  object     if   SomeObject  equals objectName       object   someObject  else     object   this   method   object getClass   getMethod methodName   Class    null     If the method provided is private  it fails with a NoSuchMethodException  I could solve it by making the method public  or making another class to derive it from   Long story short  I was just wondering if there was a way to access a private method via reflection

User · Answer

Use getDeclaredMethod   to get a private Method object and then use method setAccessible   to allow to actually call it

User · Answer

you can do this using ReflectionTestUtils of Spring  org springframework test util ReflectionTestUtils   ReflectionTestUtils invokeMethod instantiatedObject  methodName  argument     Example   if you have a class with a private method square int x   Calculator calculator   new Calculator    ReflectionTestUtils invokeMethod calculator  square  10

User · Answer

If the method accepts non-primitive data type then the following method can be used to invoke a private method of any class   public static Object genericInvokeMethod Object obj  String methodName              Object    params            int paramCount   params length          Method method          Object requiredObj   null          Class lt   gt    classArray   new Class lt   gt  paramCount           for  int i   0  i  lt  paramCount  i                  classArray i    params i  getClass                      try               method   obj getClass   getDeclaredMethod methodName  classArray               method setAccessible true               requiredObj   method invoke obj  params             catch  NoSuchMethodException e                e printStackTrace              catch  IllegalArgumentException e                e printStackTrace              catch  IllegalAccessException e                e printStackTrace              catch  InvocationTargetException e                e printStackTrace                       return requiredObj          The Parameter accepted are obj  methodName and the parameters  For example   public class Test   private String concatString String a  String b        return  a b         Method concatString can be invoked as   Test t   new Test        String str    String  genericInvokeMethod t   concatString    Hello    Mr x

User · Answer

You can use Manifold s  Jailbreak for direct  type-safe Java reflection    Jailbreak Foo foo   new Foo    foo callMe     public class Foo       private void callMe         Jailbreak unlocks the foo local variable in the compiler for direct access to all the members in Foo s hierarchy   Similarly you can use the jailbreak   extension method for one-off use   foo jailbreak   callMe      Through the jailbreak   method you can access any member in Foo s hierarchy   In both cases the compiler resolves the method call for you type-safely  as if a public method  while Manifold generates efficient reflection code for you under the hood   Alternatively  if the type is not known statically  you can use Structural Typing to define an interface a type can satisfy without having to declare its implementation   This strategy maintains type-safety and avoids performance and identity issues associated with reflection and proxy code   Discover more about Manifold

User · Answer

One more variant is using very powerfull JOOR library https   github com jOOQ jOOR  MyObject myObject   new MyObject   on myObject  get  privateField        It allows to modify any fields like final static constants and call yne protected methods without specifying concrete class in the inheritance hierarhy    lt  -- https   mvnrepository com artifact org jooq joor-java-8 -- gt   lt dependency gt        lt groupId gt org jooq lt  groupId gt        lt artifactId gt joor-java-8 lt  artifactId gt        lt version gt 0 9 7 lt  version gt   lt  dependency gt

User · Answer

Let me provide complete code for execution protected methods via reflection  It supports any types of params including  generics  autoboxed params and null values   SuppressWarnings  unchecked   public static  lt T gt  T executeSuperMethod Object instance  String methodName  Object    params  throws Exception       return executeMethod instance getClass   getSuperclass    instance  methodName  params      public static  lt T gt  T executeMethod Object instance  String methodName  Object    params  throws Exception       return executeMethod instance getClass    instance  methodName  params       SuppressWarnings  unchecked   public static  lt T gt  T executeMethod Class clazz  Object instance  String methodName  Object    params  throws Exception        Method   allMethods   clazz getDeclaredMethods         if  allMethods    null  amp  amp  allMethods length  gt  0             Class   paramClasses   Arrays stream params  map p - gt  p    null   p getClass     null  toArray Class    new            for  Method method   allMethods                String currentMethodName   method getName                if   currentMethodName equals methodName                     continue                            Type   pTypes   method getParameterTypes                if  pTypes length    paramClasses length                    boolean goodMethod   true                  int i   0                  for  Type pType   pTypes                        if   ClassUtils isAssignable paramClasses i      Class lt   gt   pType                             goodMethod   false                          break                                                          if  goodMethod                        method setAccessible true                       return  T  method invoke instance  params                                                      throw new MethodNotFoundException  There are no methods found with name     methodName     and params                 Arrays toString paramClasses               throw new MethodNotFoundException  There are no methods found with name     methodName       Method uses apache ClassUtils for checking compatibility of autoboxed params

User · Answer

You can invoke private method with reflection  Modifying the last bit of the posted code   Method method   object getClass   getDeclaredMethod methodName   method setAccessible true   Object r   method invoke object     There are a couple of caveats  First  getDeclaredMethod will only find method declared in the current Class  not inherited from supertypes  So  traverse up the concrete class hierarchy if necessary  Second  a SecurityManager can prevent use of the setAccessible method  So  it may need to run as a PrivilegedAction  using AccessController or Subject

[java] Any way to Invoke a private method?

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