org.springframework.util

## Class MethodInvoker

- java.lang.Object
- - org.springframework.util.MethodInvoker

- Direct Known Subclasses:
    ArgumentConvertingMethodInvoker

      public class MethodInvoker
      extends Object

  Helper class that allows for specifying a method to invoke in a declarative fashion, be it static or non-static.

  Usage: Specify "targetClass"/"targetMethod" or "targetObject"/"targetMethod", optionally specify arguments, prepare the invoker. Afterwards, you may invoke the method any number of times, obtaining the invocation result.

  Since:
    19.02.2004
  Author:
    Colin Sampaleanu, Juergen Hoeller
  See Also:
    `prepare()`, `invoke()`

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `MethodInvoker()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected Method` | `findMatchingMethod()` Find a matching method with the specified name for the specified arguments.
    `Object[]` | `getArguments()` Return the arguments for the method invocation.
    `Method` | `getPreparedMethod()` Return the prepared Method object that will be invoked.
    `Class<?>` | `getTargetClass()` Return the target class on which to call the target method.
    `String` | `getTargetMethod()` Return the name of the method to be invoked.
    `Object` | `getTargetObject()` Return the target object on which to call the target method.
    `static int` | `getTypeDifferenceWeight(Class<?>[] paramTypes, Object[] args)` Algorithm that judges the match between the declared parameter types of a candidate method and a specific list of arguments that this method is supposed to be invoked with.
    `Object` | `invoke()` Invoke the specified method.
    `boolean` | `isPrepared()` Return whether this invoker has been prepared already, i.e.
    `void` | `prepare()` Prepare the specified method.
    `protected Class<?>` | `resolveClassName(String className)` Resolve the given class name into a Class.
    `void` | `setArguments(Object[] arguments)` Set arguments for the method invocation.
    `void` | `setStaticMethod(String staticMethod)` Set a fully qualified static method name to invoke, e.g.
    `void` | `setTargetClass(Class<?> targetClass)` Set the target class on which to call the target method.
    `void` | `setTargetMethod(String targetMethod)` Set the name of the method to be invoked.
    `void` | `setTargetObject(Object targetObject)` Set the target object on which to call the target method.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### MethodInvoker

          public MethodInvoker()

  - ### Method Detail

    - #### setTargetClass

          public void setTargetClass(Class<?> targetClass)

      Set the target class on which to call the target method. Only necessary when the target method is static; else, a target object needs to be specified anyway.
      See Also:
        `setTargetObject(java.lang.Object)`, `setTargetMethod(java.lang.String)`

    - #### getTargetClass

          public Class<?> getTargetClass()

      Return the target class on which to call the target method.

    - #### setTargetObject

          public void setTargetObject(Object targetObject)

      Set the target object on which to call the target method. Only necessary when the target method is not static; else, a target class is sufficient.
      See Also:
        `setTargetClass(java.lang.Class<?>)`, `setTargetMethod(java.lang.String)`

    - #### getTargetObject

          public Object getTargetObject()

      Return the target object on which to call the target method.

    - #### setTargetMethod

          public void setTargetMethod(String targetMethod)

      Set the name of the method to be invoked. Refers to either a static method or a non-static method, depending on a target object being set.
      See Also:
        `setTargetClass(java.lang.Class<?>)`, `setTargetObject(java.lang.Object)`

    - #### getTargetMethod

          public String getTargetMethod()

      Return the name of the method to be invoked.

    - #### setStaticMethod

          public void setStaticMethod(String staticMethod)

      Set a fully qualified static method name to invoke, e.g. "example.MyExampleClass.myExampleMethod". Convenient alternative to specifying targetClass and targetMethod.
      See Also:
        `setTargetClass(java.lang.Class<?>)`, `setTargetMethod(java.lang.String)`

    - #### setArguments

          public void setArguments(Object[] arguments)

      Set arguments for the method invocation. If this property is not set, or the Object array is of length 0, a method with no arguments is assumed.

    - #### getArguments

          public Object[] getArguments()

      Return the arguments for the method invocation.

    - #### prepare

          public void prepare()
                       throws ClassNotFoundException,
                              NoSuchMethodException

      Prepare the specified method. The method can be invoked any number of times afterwards.
      Throws:
        `ClassNotFoundException`
        `NoSuchMethodException`
      See Also:
        `getPreparedMethod()`, `invoke()`

    - #### resolveClassName

          protected Class<?> resolveClassName(String className)
                                       throws ClassNotFoundException

      Resolve the given class name into a Class.

      The default implementations uses `ClassUtils.forName`, using the thread context class loader.

      Parameters:
        `className` - the class name to resolve
      Returns:
        the resolved Class
      Throws:
        `ClassNotFoundException` - if the class name was invalid

    - #### findMatchingMethod

          protected Method findMatchingMethod()

      Find a matching method with the specified name for the specified arguments.
      Returns:
        a matching method, or `null` if none
      See Also:
        `getTargetClass()`, `getTargetMethod()`, `getArguments()`

    - #### getPreparedMethod

          public Method getPreparedMethod()
                                   throws IllegalStateException

      Return the prepared Method object that will be invoked.

      Can for example be used to determine the return type.

      Returns:
        the prepared Method object (never `null`)
      Throws:
        `IllegalStateException` - if the invoker hasn't been prepared yet
      See Also:
        `prepare()`, `invoke()`

    - #### isPrepared

          public boolean isPrepared()

      Return whether this invoker has been prepared already, i.e. whether it allows access to `getPreparedMethod()` already.

    - #### invoke

          public Object invoke()
                        throws InvocationTargetException,
                               IllegalAccessException

      Invoke the specified method.

      The invoker needs to have been prepared before.

      Returns:
        the object (possibly null) returned by the method invocation, or `null` if the method has a void return type
      Throws:
        `InvocationTargetException` - if the target method threw an exception
        `IllegalAccessException` - if the target method couldn't be accessed
      See Also:
        `prepare()`

    - #### getTypeDifferenceWeight

          public static int getTypeDifferenceWeight(Class<?>[] paramTypes,
                                    Object[] args)

      Algorithm that judges the match between the declared parameter types of a candidate method and a specific list of arguments that this method is supposed to be invoked with.

      Determines a weight that represents the class hierarchy difference between types and arguments. A direct match, i.e. type Integer -> arg of class Integer, does not increase the result - all direct matches means weight 0. A match between type Object and arg of class Integer would increase the weight by 2, due to the superclass 2 steps up in the hierarchy (i.e. Object) being the last one that still matches the required type Object. Type Number and class Integer would increase the weight by 1 accordingly, due to the superclass 1 step up the hierarchy (i.e. Number) still matching the required type Number. Therefore, with an arg of type Integer, a constructor (Integer) would be preferred to a constructor (Number) which would in turn be preferred to a constructor (Object). All argument weights get accumulated.

      Note: This is the algorithm used by MethodInvoker itself and also the algorithm used for constructor and factory method selection in Spring's bean container (in case of lenient constructor resolution which is the default for regular bean definitions).

      Parameters:
        `paramTypes` - the parameter types to match
        `args` - the arguments to match
      Returns:
        the accumulated weight for all arguments