org.apache.commons.beanutils

Class MethodUtils


public class MethodUtils
extends java.lang.Object

Utility reflection methods focussed on methods in general rather than properties in particular.

Known Limitations

Accessing Public Methods In A Default Access Superclass

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

MethodUtils contains a workaround for this situation. It will attempt to call setAccessible on this method. If this call succeeds, then the method can be invoked as normal. This call will only succeed when the application has sufficient security privilages. If this call fails then a warning will be logged and the method may fail.

Authors:
Craig R. McClanahan
Ralph Schaer
Chris Audley
Rey François
Gregor Raýman
Jan Sorensen
Robert Burrell Donkin

Nested Class Summary

private static class
MethodUtils.MethodDescriptor
Represents the key to looking up a Method by reflection.

Field Summary

private static Class[]
EMPTY_CLASS_PARAMETERS
An empty class array
private static Object[]
EMPTY_OBJECT_ARRAY
An empty object array
private static WeakHashMap
cache
Stores a cache of MethodDescriptor -> Method in a WeakHashMap.
private static boolean
loggedAccessibleWarning
Only log warning about accessibility work around once.

Method Summary

static Method
getAccessibleMethod(Class clazz, String methodName, Class parameterType)
Return an accessible method (that is, one that can be invoked via reflection) with given name and a single parameter.
static Method
getAccessibleMethod(Class clazz, String methodName, Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) with given name and parameters.
static Method
getAccessibleMethod(Method method)
Return an accessible method (that is, one that can be invoked via reflection) that implements the specified Method.
private static Method
getAccessibleMethodFromInterfaceNest(Class clazz, String methodName, Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) that implements the specified method, by scanning through all implemented interfaces and subinterfaces.
private static Method
getAccessibleMethodFromSuperclass(Class clazz, String methodName, Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) by scanning through the superclasses.
static Method
getMatchingAccessibleMethod(Class clazz, String methodName, Class[] parameterTypes)
Find an accessible method that matches the given name and has compatible parameters.
private static float
getObjectTransformationCost(Class srcClass, Class destClass)
Gets the number of steps required needed to turn the source class into the destination class.
static Class
getPrimitiveType(Class wrapperType)
Gets the class for the primitive type corresponding to the primitive wrapper class given.
static Class
getPrimitiveWrapper(Class primitiveType)
Gets the wrapper object class for the given primitive type class.
private static float
getTotalTransformationCost(Class[] srcArgs, Class[] destArgs)
Returns the sum of the object transformation cost for each class in the source argument list.
static Object
invokeExactMethod(Object object, String methodName, Object arg)
Invoke a method whose parameter type matches exactly the object type.
static Object
invokeExactMethod(Object object, String methodName, Object[] args)
Invoke a method whose parameter types match exactly the object types.
static Object
invokeExactMethod(Object object, String methodName, Object[] args, Class[] parameterTypes)
Invoke a method whose parameter types match exactly the parameter types given.
static Object
invokeExactStaticMethod(Class objectClass, String methodName, Object arg)
Invoke a static method whose parameter type matches exactly the object type.
static Object
invokeExactStaticMethod(Class objectClass, String methodName, Object[] args)
Invoke a static method whose parameter types match exactly the object types.
static Object
invokeExactStaticMethod(Class objectClass, String methodName, Object[] args, Class[] parameterTypes)
Invoke a static method whose parameter types match exactly the parameter types given.
static Object
invokeMethod(Object object, String methodName, Object arg)
Invoke a named method whose parameter type matches the object type.
static Object
invokeMethod(Object object, String methodName, Object[] args)
Invoke a named method whose parameter type matches the object type.
static Object
invokeMethod(Object object, String methodName, Object[] args, Class[] parameterTypes)
Invoke a named method whose parameter type matches the object type.
static Object
invokeStaticMethod(Class objectClass, String methodName, Object arg)
Invoke a named static method whose parameter type matches the object type.
static Object
invokeStaticMethod(Class objectClass, String methodName, Object[] args)
Invoke a named static method whose parameter type matches the object type.
static Object
invokeStaticMethod(Class objectClass, String methodName, Object[] args, Class[] parameterTypes)
Invoke a named static method whose parameter type matches the object type.
static boolean
isAssignmentCompatible(Class parameterType, Class parameterization)
Determine whether a type can be used as a parameter in a method invocation.
static Class
toNonPrimitiveClass(Class clazz)
Find a non primitive representation for given primitive class.

Field Details

EMPTY_CLASS_PARAMETERS

private static final Class[] EMPTY_CLASS_PARAMETERS
An empty class array

EMPTY_OBJECT_ARRAY

private static final Object[] EMPTY_OBJECT_ARRAY
An empty object array

cache

private static WeakHashMap cache
Stores a cache of MethodDescriptor -> Method in a WeakHashMap.

The keys into this map only ever exist as temporary variables within methods of this class, and are never exposed to users of this class. This means that the WeakHashMap is used only as a mechanism for limiting the size of the cache, ie a way to tell the garbage collector that the contents of the cache can be completely garbage-collected whenever it needs the memory. Whether this is a good approach to this problem is doubtful; something like the commons-collections LRUMap may be more appropriate (though of course selecting an appropriate size is an issue).

This static variable is safe even when this code is deployed via a shared classloader because it is keyed via a MethodDescriptor object which has a Class as one of its members and that member is used in the MethodDescriptor.equals method. So two components that load the same class via different classloaders will generate non-equal MethodDescriptor objects and hence end up with different entries in the map.


loggedAccessibleWarning

private static boolean loggedAccessibleWarning
Only log warning about accessibility work around once.

Note that this is broken when this class is deployed via a shared classloader in a container, as the warning message will be emitted only once, not once per webapp. However making the warning appear once per webapp means having a map keyed by context classloader which introduces nasty memory-leak problems. As this warning is really optional we can ignore this problem; only one of the webapps will get the warning in its logs but that should be good enough.

Method Details

getAccessibleMethod

public static Method getAccessibleMethod(Class clazz,
                                         String methodName,
                                         Class parameterType)
Return an accessible method (that is, one that can be invoked via reflection) with given name and a single parameter. If no such method can be found, return null. Basically, a convenience wrapper that constructs a Class array for you.
Parameters:
clazz - get method from this class
methodName - get method with this name
parameterType - taking this type of parameter
Returns:
The accessible method

getAccessibleMethod

public static Method getAccessibleMethod(Class clazz,
                                         String methodName,
                                         Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) with given name and parameters. If no such method can be found, return null. This is just a convenient wrapper for getAccessibleMethod(Method method).
Parameters:
clazz - get method from this class
methodName - get method with this name
parameterTypes - with these parameters types
Returns:
The accessible method

getAccessibleMethod

public static Method getAccessibleMethod(Method method)
Return an accessible method (that is, one that can be invoked via reflection) that implements the specified Method. If no such method can be found, return null.
Parameters:
method - The method that we wish to call
Returns:
The accessible method

getAccessibleMethodFromInterfaceNest

private static Method getAccessibleMethodFromInterfaceNest(Class clazz,
                                                           String methodName,
                                                           Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) that implements the specified method, by scanning through all implemented interfaces and subinterfaces. If no such method can be found, return null.

There isn't any good reason why this method must be private. It is because there doesn't seem any reason why other classes should call this rather than the higher level methods.

Parameters:
clazz - Parent class for the interfaces to be checked
methodName - Method name of the method we wish to call
parameterTypes - The parameter type signatures

getAccessibleMethodFromSuperclass

private static Method getAccessibleMethodFromSuperclass(Class clazz,
                                                        String methodName,
                                                        Class[] parameterTypes)
Return an accessible method (that is, one that can be invoked via reflection) by scanning through the superclasses. If no such method can be found, return null.
Parameters:
clazz - Class to be checked
methodName - Method name of the method we wish to call
parameterTypes - The parameter type signatures

getMatchingAccessibleMethod

public static Method getMatchingAccessibleMethod(Class clazz,
                                                 String methodName,
                                                 Class[] parameterTypes)
Find an accessible method that matches the given name and has compatible parameters. Compatible parameters mean that every method parameter is assignable from the given parameters. In other words, it finds a method with the given name that will take the parameters given.

This method is slightly undeterminstic since it loops through methods names and return the first matching method.

This method is used by invokeMethod(Object object,String methodName,Object [] args,Class[] parameterTypes).

This method can match primitive parameter by passing in wrapper classes. For example, a Boolean will match a primitive boolean parameter.

Parameters:
clazz - find method in this class
methodName - find method with this name
parameterTypes - find method with compatible parameters
Returns:
The accessible method

getObjectTransformationCost

private static float getObjectTransformationCost(Class srcClass,
                                                 Class destClass)
Gets the number of steps required needed to turn the source class into the destination class. This represents the number of steps in the object hierarchy graph.
Parameters:
srcClass - The source class
destClass - The destination class
Returns:
The cost of transforming an object

getPrimitiveType

public static Class getPrimitiveType(Class wrapperType)
Gets the class for the primitive type corresponding to the primitive wrapper class given. For example, an instance of Boolean.class returns a boolean.class.
Parameters:
wrapperType - the
Returns:
the primitive type class corresponding to the given wrapper class, null if no match is found

getPrimitiveWrapper

public static Class getPrimitiveWrapper(Class primitiveType)
Gets the wrapper object class for the given primitive type class. For example, passing boolean.class returns Boolean.class
Parameters:
primitiveType - the primitive type class for which a match is to be found
Returns:
the wrapper type associated with the given primitive or null if no match is found

getTotalTransformationCost

private static float getTotalTransformationCost(Class[] srcArgs,
                                                Class[] destArgs)
Returns the sum of the object transformation cost for each class in the source argument list.
Parameters:
srcArgs - The source arguments
destArgs - The destination arguments
Returns:
The total transformation cost

invokeExactMethod

public static Object invokeExactMethod(Object object,
                                       String methodName,
                                       Object arg)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a method whose parameter type matches exactly the object type.

This is a convenient wrapper for invokeExactMethod(Object object,String methodName,Object [] args).

Parameters:
object - invoke method on this object
methodName - get method with this name
arg - use this argument
Returns:
The value returned by the invoked method

invokeExactMethod

public static Object invokeExactMethod(Object object,
                                       String methodName,
                                       Object[] args)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a method whose parameter types match exactly the object types.

This uses reflection to invoke the method obtained from a call to getAccessibleMethod().

Parameters:
object - invoke method on this object
methodName - get method with this name
args - use these arguments - treat null as empty array
Returns:
The value returned by the invoked method

invokeExactMethod

public static Object invokeExactMethod(Object object,
                                       String methodName,
                                       Object[] args,
                                       Class[] parameterTypes)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a method whose parameter types match exactly the parameter types given.

This uses reflection to invoke the method obtained from a call to getAccessibleMethod().

Parameters:
object - invoke method on this object
methodName - get method with this name
args - use these arguments - treat null as empty array
parameterTypes - match these parameters - treat null as empty array
Returns:
The value returned by the invoked method

invokeExactStaticMethod

public static Object invokeExactStaticMethod(Class objectClass,
                                             String methodName,
                                             Object arg)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a static method whose parameter type matches exactly the object type.

This is a convenient wrapper for invokeExactStaticMethod(Class objectClass,String methodName,Object [] args).

Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
arg - use this argument
Returns:
The value returned by the invoked method

invokeExactStaticMethod

public static Object invokeExactStaticMethod(Class objectClass,
                                             String methodName,
                                             Object[] args)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
args - use these arguments - treat null as empty array
Returns:
The value returned by the invoked method

invokeExactStaticMethod

public static Object invokeExactStaticMethod(Class objectClass,
                                             String methodName,
                                             Object[] args,
                                             Class[] parameterTypes)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
args - use these arguments - treat null as empty array
parameterTypes - match these parameters - treat null as empty array
Returns:
The value returned by the invoked method

invokeMethod

public static Object invokeMethod(Object object,
                                  String methodName,
                                  Object arg)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactMethod(). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

This is a convenient wrapper for invokeMethod(Object object,String methodName,Object [] args).

Parameters:
object - invoke method on this object
methodName - get method with this name
arg - use this argument
Returns:
The value returned by the invoked method

invokeMethod

public static Object invokeMethod(Object object,
                                  String methodName,
                                  Object[] args)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactMethod(Object object,String methodName,Object [] args). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

This is a convenient wrapper for invokeMethod(Object object,String methodName,Object [] args,Class[] parameterTypes).

Parameters:
object - invoke method on this object
methodName - get method with this name
args - use these arguments - treat null as empty array
Returns:
The value returned by the invoked method

invokeMethod

public static Object invokeMethod(Object object,
                                  String methodName,
                                  Object[] args,
                                  Class[] parameterTypes)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactMethod(Object object,String methodName,Object [] args,Class[] parameterTypes). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

Parameters:
object - invoke method on this object
methodName - get method with this name
args - use these arguments - treat null as empty array
parameterTypes - match these parameters - treat null as empty array
Returns:
The value returned by the invoked method

invokeStaticMethod

public static Object invokeStaticMethod(Class objectClass,
                                        String methodName,
                                        Object arg)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named static method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactMethod(Object,String,Object[],Class[]). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

This is a convenient wrapper for invokeStaticMethod(Class objectClass,String methodName,Object [] args).

Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
arg - use this argument
Returns:
The value returned by the invoked method

invokeStaticMethod

public static Object invokeStaticMethod(Class objectClass,
                                        String methodName,
                                        Object[] args)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named static method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactMethod(Object object,String methodName,Object [] args). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

This is a convenient wrapper for invokeStaticMethod(Class objectClass,String methodName,Object [] args,Class[] parameterTypes).

Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
args - use these arguments - treat null as empty array
Returns:
The value returned by the invoked method

invokeStaticMethod

public static Object invokeStaticMethod(Class objectClass,
                                        String methodName,
                                        Object[] args,
                                        Class[] parameterTypes)
            throws NoSuchMethodException,
                   IllegalAccessException,
                   InvocationTargetException
Invoke a named static method whose parameter type matches the object type.

The behaviour of this method is less deterministic than invokeExactStaticMethod(Class objectClass,String methodName,Object [] args,Class[] parameterTypes). It loops through all methods with names that match and then executes the first it finds with compatable parameters.

This method supports calls to methods taking primitive parameters via passing in wrapping classes. So, for example, a Boolean class would match a boolean primitive.

Parameters:
objectClass - invoke static method on this class
methodName - get method with this name
args - use these arguments - treat null as empty array
parameterTypes - match these parameters - treat null as empty array
Returns:
The value returned by the invoked method

isAssignmentCompatible

public static final boolean isAssignmentCompatible(Class parameterType,
                                                   Class parameterization)
Determine whether a type can be used as a parameter in a method invocation. This method handles primitive conversions correctly.

In order words, it will match a Boolean to a boolean, a Long to a long, a Float to a float, a Integer to a int, and a Double to a double. Now logic widening matches are allowed. For example, a Long will not match a int.

Parameters:
parameterType - the type of parameter accepted by the method
parameterization - the type of parameter being tested
Returns:
true if the assignement is compatible.

toNonPrimitiveClass

public static Class toNonPrimitiveClass(Class clazz)
Find a non primitive representation for given primitive class.
Parameters:
clazz - the class to find a representation for, not null
Returns:
the original class if it not a primitive. Otherwise the wrapper class. Not null

Copyright (c) 2001-2007 - Apache Software Foundation