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/*
* Copyright 2002-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.util;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import org.springframework.lang.Nullable;
/**
* 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.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 19.02.2004
* @see #prepare
* @see #invoke
*/
public class MethodInvoker {
private static final Object[] EMPTY_ARGUMENTS = new Object[0];
@Nullable
protected Class targetClass;
@Nullable
private Object targetObject;
@Nullable
private String targetMethod;
@Nullable
private String staticMethod;
@Nullable
private Object[] arguments;
/** The method we will call. */
@Nullable
private Method methodObject;
/**
* 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 #setTargetObject
* @see #setTargetMethod
*/
public void setTargetClass(@Nullable Class targetClass) {
this.targetClass = targetClass;
}
/**
* Return the target class on which to call the target method.
*/
@Nullable
public Class getTargetClass() {
return this.targetClass;
}
/**
* 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 #setTargetClass
* @see #setTargetMethod
*/
public void setTargetObject(@Nullable Object targetObject) {
this.targetObject = targetObject;
if (targetObject != null) {
this.targetClass = targetObject.getClass();
}
}
/**
* Return the target object on which to call the target method.
*/
@Nullable
public Object getTargetObject() {
return this.targetObject;
}
/**
* 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 #setTargetClass
* @see #setTargetObject
*/
public void setTargetMethod(@Nullable String targetMethod) {
this.targetMethod = targetMethod;
}
/**
* Return the name of the method to be invoked.
*/
@Nullable
public String getTargetMethod() {
return this.targetMethod;
}
/**
* Set a fully qualified static method name to invoke,
* e.g. "example.MyExampleClass.myExampleMethod".
* Convenient alternative to specifying targetClass and targetMethod.
* @see #setTargetClass
* @see #setTargetMethod
*/
public void setStaticMethod(String staticMethod) {
this.staticMethod = staticMethod;
}
/**
* 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.
*/
public void setArguments(Object... arguments) {
this.arguments = arguments;
}
/**
* Return the arguments for the method invocation.
*/
public Object[] getArguments() {
return (this.arguments != null ? this.arguments : EMPTY_ARGUMENTS);
}
/**
* Prepare the specified method.
* The method can be invoked any number of times afterwards.
* @see #getPreparedMethod
* @see #invoke
*/
public void prepare() throws ClassNotFoundException, NoSuchMethodException {
if (this.staticMethod != null) {
int lastDotIndex = this.staticMethod.lastIndexOf('.');
if (lastDotIndex == -1 || lastDotIndex == this.staticMethod.length()) {
throw new IllegalArgumentException(
"staticMethod must be a fully qualified class plus method name: " +
"e.g. 'example.MyExampleClass.myExampleMethod'");
}
String className = this.staticMethod.substring(0, lastDotIndex);
String methodName = this.staticMethod.substring(lastDotIndex + 1);
this.targetClass = resolveClassName(className);
this.targetMethod = methodName;
}
Class targetClass = getTargetClass();
String targetMethod = getTargetMethod();
Assert.notNull(targetClass, "Either 'targetClass' or 'targetObject' is required");
Assert.notNull(targetMethod, "Property 'targetMethod' is required");
Object[] arguments = getArguments();
Class[] argTypes = new Class[arguments.length];
for (int i = 0; i < arguments.length; ++i) {
argTypes[i] = (arguments[i] != null ? arguments[i].getClass() : Object.class);
}
// Try to get the exact method first.
try {
this.methodObject = targetClass.getMethod(targetMethod, argTypes);
}
catch (NoSuchMethodException ex) {
// Just rethrow exception if we can't get any match.
this.methodObject = findMatchingMethod();
if (this.methodObject == null) {
throw ex;
}
}
}
/**
* Resolve the given class name into a Class.
*
The default implementations uses {@code ClassUtils.forName},
* using the thread context class loader.
* @param className the class name to resolve
* @return the resolved Class
* @throws ClassNotFoundException if the class name was invalid
*/
protected Class resolveClassName(String className) throws ClassNotFoundException {
return ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
}
/**
* Find a matching method with the specified name for the specified arguments.
* @return a matching method, or {@code null} if none
* @see #getTargetClass()
* @see #getTargetMethod()
* @see #getArguments()
*/
@Nullable
protected Method findMatchingMethod() {
String targetMethod = getTargetMethod();
Object[] arguments = getArguments();
int argCount = arguments.length;
Class targetClass = getTargetClass();
Assert.state(targetClass != null, "No target class set");
Method[] candidates = ReflectionUtils.getAllDeclaredMethods(targetClass);
int minTypeDiffWeight = Integer.MAX_VALUE;
Method matchingMethod = null;
for (Method candidate : candidates) {
if (candidate.getName().equals(targetMethod)) {
if (candidate.getParameterCount() == argCount) {
Class[] paramTypes = candidate.getParameterTypes();
int typeDiffWeight = getTypeDifferenceWeight(paramTypes, arguments);
if (typeDiffWeight < minTypeDiffWeight) {
minTypeDiffWeight = typeDiffWeight;
matchingMethod = candidate;
}
}
}
}
return matchingMethod;
}
/**
* Return the prepared Method object that will be invoked.
*
Can for example be used to determine the return type.
* @return the prepared Method object (never {@code null})
* @throws IllegalStateException if the invoker hasn't been prepared yet
* @see #prepare
* @see #invoke
*/
public Method getPreparedMethod() throws IllegalStateException {
if (this.methodObject == null) {
throw new IllegalStateException("prepare() must be called prior to invoke() on MethodInvoker");
}
return this.methodObject;
}
/**
* Return whether this invoker has been prepared already,
* i.e. whether it allows access to {@link #getPreparedMethod()} already.
*/
public boolean isPrepared() {
return (this.methodObject != null);
}
/**
* Invoke the specified method.
*
The invoker needs to have been prepared before.
* @return the object (possibly null) returned by the method invocation,
* or {@code null} if the method has a void return type
* @throws InvocationTargetException if the target method threw an exception
* @throws IllegalAccessException if the target method couldn't be accessed
* @see #prepare
*/
@Nullable
public Object invoke() throws InvocationTargetException, IllegalAccessException {
// In the static case, target will simply be {@code null}.
Object targetObject = getTargetObject();
Method preparedMethod = getPreparedMethod();
if (targetObject == null && !Modifier.isStatic(preparedMethod.getModifiers())) {
throw new IllegalArgumentException("Target method must not be non-static without a target");
}
ReflectionUtils.makeAccessible(preparedMethod);
return preparedMethod.invoke(targetObject, getArguments());
}
/**
* 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).
* @param paramTypes the parameter types to match
* @param args the arguments to match
* @return the accumulated weight for all arguments
*/
public static int getTypeDifferenceWeight(Class[] paramTypes, Object[] args) {
int result = 0;
for (int i = 0; i < paramTypes.length; i++) {
if (!ClassUtils.isAssignableValue(paramTypes[i], args[i])) {
return Integer.MAX_VALUE;
}
if (args[i] != null) {
Class paramType = paramTypes[i];
Class superClass = args[i].getClass().getSuperclass();
while (superClass != null) {
if (paramType.equals(superClass)) {
result = result + 2;
superClass = null;
}
else if (ClassUtils.isAssignable(paramType, superClass)) {
result = result + 2;
superClass = superClass.getSuperclass();
}
else {
superClass = null;
}
}
if (paramType.isInterface()) {
result = result + 1;
}
}
}
return result;
}
}