Class ConstructorUtils

java.lang.Object
org.apache.commons.lang3.reflect.ConstructorUtils

public class ConstructorUtils extends Object
Utility reflection methods focused on constructors, modeled after MethodUtils.

Known Limitations

Accessing Public Constructors In A Default Access Superclass

There is an issue when invoking public constructors contained in a default access superclass. Reflection correctly locates these constructors and assigns them as public. However, an IllegalAccessException is thrown if the constructor is invoked.

ConstructorUtils contains a workaround for this situation: it will attempt to call AccessibleObject.setAccessible(boolean) on this constructor. If this call succeeds, then the method can be invoked as normal. This call will only succeed when the application has sufficient security privileges. If this call fails then a warning will be logged and the method may fail.

Since:
2.5
  • Constructor Details

    • ConstructorUtils

      @Deprecated public ConstructorUtils()
      Deprecated.
      TODO Make private in 4.0.
      ConstructorUtils instances should NOT be constructed in standard programming. Instead, the class should be used as ConstructorUtils.invokeConstructor(cls, args).

      This constructor is public to permit tools that require a JavaBean instance to operate.

  • Method Details

    • getAccessibleConstructor

      public static <T> Constructor<T> getAccessibleConstructor(Class<T> cls, Class<?>... parameterTypes)
      Finds a constructor given a class and signature, checking accessibility.

      This finds the constructor and ensures that it is accessible. The constructor signature must match the parameter types exactly.

      Type Parameters:
      T - the constructor type
      Parameters:
      cls - the class to find a constructor for, not null
      parameterTypes - the array of parameter types, null treated as empty
      Returns:
      the constructor, null if no matching accessible constructor found
      Throws:
      NullPointerException - if cls is null
      See Also:
    • getAccessibleConstructor

      public static <T> Constructor<T> getAccessibleConstructor(Constructor<T> ctor)
      Checks if the specified constructor is accessible.

      This simply ensures that the constructor is accessible.

      Type Parameters:
      T - the constructor type
      Parameters:
      ctor - the prototype constructor object, not null
      Returns:
      the constructor, null if no matching accessible constructor found
      Throws:
      NullPointerException - if ctor is null
      See Also:
    • getMatchingAccessibleConstructor

      public static <T> Constructor<T> getMatchingAccessibleConstructor(Class<T> cls, Class<?>... parameterTypes)
      Finds an accessible constructor with compatible parameters.

      This checks all the constructor and finds one with compatible parameters This requires that every parameter is assignable from the given parameter types. This is a more flexible search than the normal exact matching algorithm.

      First it checks if there is a constructor matching the exact signature. If not then all the constructors of the class are checked to see if their signatures are assignment-compatible with the parameter types. The first assignment-compatible matching constructor is returned.

      Type Parameters:
      T - the constructor type
      Parameters:
      cls - the class to find a constructor for, not null
      parameterTypes - find method with compatible parameters
      Returns:
      the constructor, null if no matching accessible constructor found
      Throws:
      NullPointerException - if cls is null
    • invokeConstructor

      public static <T> T invokeConstructor(Class<T> cls, Object... args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException
      Returns a new instance of the specified class inferring the right constructor from the types of the arguments.

      This locates and calls a constructor. The constructor signature must match the argument types by assignment compatibility.

      Type Parameters:
      T - the type to be constructed
      Parameters:
      cls - the class to be constructed, not null
      args - the array of arguments, null treated as empty
      Returns:
      new instance of cls, not null
      Throws:
      NullPointerException - if cls is null
      NoSuchMethodException - if a matching constructor cannot be found
      IllegalAccessException - if invocation is not permitted by security
      InvocationTargetException - if an error occurs on invocation
      InstantiationException - if an error occurs on instantiation
      See Also:
    • invokeConstructor

      public static <T> T invokeConstructor(Class<T> cls, Object[] args, Class<?>[] parameterTypes) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException
      Returns a new instance of the specified class choosing the right constructor from the list of parameter types.

      This locates and calls a constructor. The constructor signature must match the parameter types by assignment compatibility.

      Type Parameters:
      T - the type to be constructed
      Parameters:
      cls - the class to be constructed, not null
      args - the array of arguments, null treated as empty
      parameterTypes - the array of parameter types, null treated as empty
      Returns:
      new instance of cls, not null
      Throws:
      NullPointerException - if cls is null
      NoSuchMethodException - if a matching constructor cannot be found
      IllegalAccessException - if invocation is not permitted by security
      InvocationTargetException - if an error occurs on invocation
      InstantiationException - if an error occurs on instantiation
      See Also:
    • invokeExactConstructor

      public static <T> T invokeExactConstructor(Class<T> cls, Object... args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException
      Returns a new instance of the specified class inferring the right constructor from the types of the arguments.

      This locates and calls a constructor. The constructor signature must match the argument types exactly.

      Type Parameters:
      T - the type to be constructed
      Parameters:
      cls - the class to be constructed, not null
      args - the array of arguments, null treated as empty
      Returns:
      new instance of cls, not null
      Throws:
      NullPointerException - if cls is null
      NoSuchMethodException - if a matching constructor cannot be found
      IllegalAccessException - if invocation is not permitted by security
      InvocationTargetException - if an error occurs on invocation
      InstantiationException - if an error occurs on instantiation
      See Also:
    • invokeExactConstructor

      public static <T> T invokeExactConstructor(Class<T> cls, Object[] args, Class<?>[] parameterTypes) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException
      Returns a new instance of the specified class choosing the right constructor from the list of parameter types.

      This locates and calls a constructor. The constructor signature must match the parameter types exactly.

      Type Parameters:
      T - the type to be constructed
      Parameters:
      cls - the class to be constructed, not null
      args - the array of arguments, null treated as empty
      parameterTypes - the array of parameter types, null treated as empty
      Returns:
      new instance of cls, not null
      Throws:
      NullPointerException - if cls is null
      NoSuchMethodException - if a matching constructor cannot be found
      IllegalAccessException - if invocation is not permitted by security
      InvocationTargetException - if an error occurs on invocation
      InstantiationException - if an error occurs on instantiation
      See Also:
    • isAccessible

      private static boolean isAccessible(Class<?> type)
      Tests whether the specified class is generally accessible, i.e. is declared in an entirely public manner.
      Parameters:
      type - to check
      Returns:
      true if type and any enclosing classes are public.