在Java中如何通过反射找到一个变量，这个变量的类型是指定的类型

1. 说明以下的代码是我从Spring中抓出来的，然后加了一些我认为对自己有用的方法。

2. 直接上代码，看不懂的请留言。

3. 如何解决标题中提到的问题呢？请查找findAllField方法。

ReflectionUtils.java

package test.util;

/*
* Copyright 2002-2013 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
*
*      http://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.
*/

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.UndeclaredThrowableException;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.eclipse.core.runtime.Assert;

/**
* Simple utility class for working with the reflection API and handling
* reflection exceptions.
*
* <p>Only intended for internal use.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @author Rod Johnson
* @author Costin Leau
* @author Sam Brannen
* @author Chris Beams
* @author Roy Clarkson
* @author jialiang
* @since 1.1
*/
public abstract class ReflectionUtils {

/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied <code>name</code>. Searches all superclasses up to {@link Object}.
* @param clazz the class to introspect
* @param name the name of the field
* @return the corresponding Field object, or <code>null</code> if not found
*/
public static Field findField(Class<?> clazz, String name) {
return findField(clazz, name, null);
}

/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied <code>name</code> and/or {@link Class type}. Searches all superclasses
* up to {@link Object}.
* @param clazz the class to introspect
* @param name the name of the field (may be <code>null</code> if type is specified)
* @param type the type of the field (may be <code>null</code> if name is specified)
* @return the corresponding Field object, or <code>null</code> if not found
*/
public static Field findField(Class<?> clazz, String name, Class<?> type) {
Assert.isNotNull(clazz, "Class must not be null");
Assert.isTrue(name != null || type != null, "Either name or type of the field must be specified");
Class<?> searchType = clazz;
while (!Object.class.equals(searchType) && searchType != null) {
Field[] fields = searchType.getDeclaredFields();
for (Field field : fields) {
if ((name == null || name.equals(field.getName())) && (type == null || type.equals(field.getType()))) {
return field;
}
}
searchType = searchType.getSuperclass();
}
return null;
}

/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied <code>name</code> and/or {@link Class type}. Searches all superclasses
* up to {@link Object}.
* @param clazz the class to introspect
* @param name the name of the field (may be <code>null</code> if type is specified)
* @param type the type of the field, must not be <code>null</code>
* @return the corresponding Field object, or <code>null</code> if not found
*/
public static List<Field> findAllField(Class<?> clazz, String name, Class<?> type) {
Assert.isNotNull(clazz, "Class must not be null");
Assert.isNotNull(type, "The type of filed must not be null");

List<Field> list = new ArrayList<Field>();
Class<?> searchType = clazz;

while (!Object.class.equals(searchType) && searchType != null) {
Field[] fields = searchType.getDeclaredFields();
for (Field field : fields) {
if ((name == null || name.equals(field.getName())) && type.equals(field.getType())) {
list.add(field);
}
}
searchType = searchType.getSuperclass();
}
return list;
}

public static List<Field> findAllField(Class<?> clazz, Class<?> type) {
return findAllField(clazz, null, type);
}

/**
* Set the field represented by the supplied {@link Field field object} on the
* specified {@link Object target object} to the specified <code>value</code>.
* In accordance with {@link Field#set(Object, Object)} semantics, the new value
* is automatically unwrapped if the underlying field has a primitive type.
* <p>Thrown exceptions are handled via a call to {@link #handleReflectionException(Exception)}.
* @param field the field to set
* @param target the target object on which to set the field
* @param value the value to set; may be <code>null</code>
*/
public static void setField(Field field, Object target, Object value) {
try {
field.set(target, value);
}
catch (IllegalAccessException ex) {
handleReflectionException(ex);
throw new IllegalStateException("Unexpected reflection exception - " + ex.getClass().getName() + ": "
+ ex.getMessage());
}
}

/**
* Get the field represented by the supplied {@link Field field object} on the
* specified {@link Object target object}. In accordance with {@link Field#get(Object)}
* semantics, the returned value is automatically wrapped if the underlying field
* has a primitive type.
* <p>Thrown exceptions are handled via a call to {@link #handleReflectionException(Exception)}.
* @param field the field to get
* @param target the target object from which to get the field
* @return the field's current value
*/
public static Object getField(Field field, Object target) {
try {
field.setAccessible(true);
return field.get(target);
}
catch (IllegalAccessException ex) {
handleReflectionException(ex);
throw new IllegalStateException(
"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
}
}

public static Object getField(String fieldName, Object target) {
Field field = findField(target.getClass(), fieldName);
if(field == null) {
return null;
}

try {
field.setAccessible(true);
return field.get(target);
}
catch (IllegalAccessException ex) {
handleReflectionException(ex);
throw new IllegalStateException(
"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
}
}

/**
* Attempt to find a {@link Method} on the supplied class with the supplied name
* and no parameters. Searches all superclasses up to <code>Object</code>.
* <p>Returns <code>null</code> if no {@link Method} can be found.
* @param clazz the class to introspect
* @param name the name of the method
* @return the Method object, or <code>null</code> if none found
*/
public static Method findMethod(Class<?> clazz, String name) {
return findMethod(clazz, name, new Class[0]);
}

public static Object invokeMethod(Object target, String name) {
Assert.isNotNull(target, "target must not be null");
Assert.isNotNull(name, "Method name must not be null");

Method m = findMethod(target.getClass(), name);
if(m == null) {
return null;
}

makeAccessible(m);

return invokeMethod(m, target);
}

public static Object invokeMethod(Object target, String name,  Object... args) {
Assert.isNotNull(target, "target must not be null");
Assert.isNotNull(name, "Method name must not be null");

Method m = findMethod(target.getClass(), name);
if(m == null) {
return null;
}

return invokeMethod(m, target, args);
}

/**
* Attempt to find a {@link Method} on the supplied class with the supplied name
* and parameter types. Searches all superclasses up to <code>Object</code>.
* <p>Returns <code>null</code> if no {@link Method} can be found.
* @param clazz the class to introspect
* @param name the name of the method
* @param paramTypes the parameter types of the method
* (may be <code>null</code> to indicate any signature)
* @return the Method object, or <code>null</code> if none found
*/
public static Method findMethod(Class<?> clazz, String name, Class<?>... paramTypes) {
Assert.isNotNull(clazz, "Class must not be null");
Assert.isNotNull(name, "Method name must not be null");
Class<?> searchType = clazz;
while (searchType != null) {
Method[] methods = (searchType.isInterface() ? searchType.getMethods() : searchType.getDeclaredMethods());
for (Method method : methods) {
if (name.equals(method.getName())
&& (paramTypes == null || Arrays.equals(paramTypes, method.getParameterTypes()))) {
return method;
}
}
searchType = searchType.getSuperclass();
}
return null;
}

/**
* Invoke the specified {@link Method} against the supplied target object with no arguments.
* The target object can be <code>null</code> when invoking a static {@link Method}.
* <p>Thrown exceptions are handled via a call to {@link #handleReflectionException}.
* @param method the method to invoke
* @param target the target object to invoke the method on
* @return the invocation result, if any
* @see #invokeMethod(java.lang.reflect.Method, Object, Object[])
*/
public static Object invokeMethod(Method method, Object target) {
return invokeMethod(method, target, new Object[0]);
}

/**
* Invoke the specified {@link Method} against the supplied target object with the
* supplied arguments. The target object can be <code>null</code> when invoking a
* static {@link Method}.
* <p>Thrown exceptions are handled via a call to {@link #handleReflectionException}.
* @param method the method to invoke
* @param target the target object to invoke the method on
* @param args the invocation arguments (may be <code>null</code>)
* @return the invocation result, if any
*/
public static Object invokeMethod(Method method, Object target, Object... args) {
try {
return method.invoke(target, args);
}
catch (Exception ex) {
handleReflectionException(ex);
}
throw new IllegalStateException("Should never get here");
}

/**
* Invoke the specified JDBC API {@link Method} against the supplied target
* object with no arguments.
* @param method the method to invoke
* @param target the target object to invoke the method on
* @return the invocation result, if any
* @throws SQLException the JDBC API SQLException to rethrow (if any)
* @see #invokeJdbcMethod(java.lang.reflect.Method, Object, Object[])
*/
public static Object invokeJdbcMethod(Method method, Object target) throws SQLException {
return invokeJdbcMethod(method, target, new Object[0]);
}

/**
* Invoke the specified JDBC API {@link Method} against the supplied target
* object with the supplied arguments.
* @param method the method to invoke
* @param target the target object to invoke the method on
* @param args the invocation arguments (may be <code>null</code>)
* @return the invocation result, if any
* @throws SQLException the JDBC API SQLException to rethrow (if any)
* @see #invokeMethod(java.lang.reflect.Method, Object, Object[])
*/
public static Object invokeJdbcMethod(Method method, Object target, Object... args) throws SQLException {
try {
return method.invoke(target, args);
}
catch (IllegalAccessException ex) {
handleReflectionException(ex);
}
catch (InvocationTargetException ex) {
if (ex.getTargetException() instanceof SQLException) {
throw (SQLException) ex.getTargetException();
}
handleInvocationTargetException(ex);
}
throw new IllegalStateException("Should never get here");
}

/**
* Handle the given reflection exception. Should only be called if no
* checked exception is expected to be thrown by the target method.
* <p>Throws the underlying RuntimeException or Error in case of an
* InvocationTargetException with such a root cause. Throws an
* IllegalStateException with an appropriate message else.
* @param ex the reflection exception to handle
*/
public static void handleReflectionException(Exception ex) {
if (ex instanceof NoSuchMethodException) {
throw new IllegalStateException("Method not found: " + ex.getMessage());
}
if (ex instanceof IllegalAccessException) {
throw new IllegalStateException("Could not access method: " + ex.getMessage());
}
if (ex instanceof InvocationTargetException) {
handleInvocationTargetException((InvocationTargetException) ex);
}
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
throw new UndeclaredThrowableException(ex);
}

/**
* Handle the given invocation target exception. Should only be called if no
* checked exception is expected to be thrown by the target method.
* <p>Throws the underlying RuntimeException or Error in case of such a root
* cause. Throws an IllegalStateException else.
* @param ex the invocation target exception to handle
*/
public static void handleInvocationTargetException(InvocationTargetException ex) {
rethrowRuntimeException(ex.getTargetException());
}

/**
* Rethrow the given {@link Throwable exception}, which is presumably the
* <em>target exception</em> of an {@link InvocationTargetException}. Should
* only be called if no checked exception is expected to be thrown by the
* target method.
* <p>Rethrows the underlying exception cast to an {@link RuntimeException} or
* {@link Error} if appropriate; otherwise, throws an
* {@link IllegalStateException}.
* @param ex the exception to rethrow
* @throws RuntimeException the rethrown exception
*/
public static void rethrowRuntimeException(Throwable ex) {
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
if (ex instanceof Error) {
throw (Error) ex;
}
throw new UndeclaredThrowableException(ex);
}

/**
* Rethrow the given {@link Throwable exception}, which is presumably the
* <em>target exception</em> of an {@link InvocationTargetException}. Should
* only be called if no checked exception is expected to be thrown by the
* target method.
* <p>Rethrows the underlying exception cast to an {@link Exception} or
* {@link Error} if appropriate; otherwise, throws an
* {@link IllegalStateException}.
* @param ex the exception to rethrow
* @throws Exception the rethrown exception (in case of a checked exception)
*/
public static void rethrowException(Throwable ex) throws Exception {
if (ex instanceof Exception) {
throw (Exception) ex;
}
if (ex instanceof Error) {
throw (Error) ex;
}
throw new UndeclaredThrowableException(ex);
}

/**
* Determine whether the given method explicitly declares the given
* exception or one of its superclasses, which means that an exception of
* that type can be propagated as-is within a reflective invocation.
* @param method the declaring method
* @param exceptionType the exception to throw
* @return <code>true</code> if the exception can be thrown as-is;
* <code>false</code> if it needs to be wrapped
*/
public static boolean declaresException(Method method, Class<?> exceptionType) {
Assert.isNotNull(method, "Method must not be null");
Class<?>[] declaredExceptions = method.getExceptionTypes();
for (Class<?> declaredException : declaredExceptions) {
if (declaredException.isAssignableFrom(exceptionType)) {
return true;
}
}
return false;
}

/**
* Determine whether the given field is a "public static final" constant.
* @param field the field to check
*/
public static boolean isPublicStaticFinal(Field field) {
int modifiers = field.getModifiers();
return (Modifier.isPublic(modifiers) && Modifier.isStatic(modifiers) && Modifier.isFinal(modifiers));
}

/**
* Determine whether the given method is an "equals" method.
* @see java.lang.Object#equals(Object)
*/
public static boolean isEqualsMethod(Method method) {
if (method == null || !method.getName().equals("equals")) {
return false;
}
Class<?>[] paramTypes = method.getParameterTypes();
return (paramTypes.length == 1 && paramTypes[0] == Object.class);
}

/**
* Determine whether the given method is a "hashCode" method.
* @see java.lang.Object#hashCode()
*/
public static boolean isHashCodeMethod(Method method) {
return (method != null && method.getName().equals("hashCode") && method.getParameterTypes().length == 0);
}

/**
* Determine whether the given method is a "toString" method.
* @see java.lang.Object#toString()
*/
public static boolean isToStringMethod(Method method) {
return (method != null && method.getName().equals("toString") && method.getParameterTypes().length == 0);
}

/**
* Determine whether the given method is originally declared by {@link java.lang.Object}.
*/
public static boolean isObjectMethod(Method method) {
try {
Object.class.getDeclaredMethod(method.getName(), method.getParameterTypes());
return true;
} catch (SecurityException ex) {
return false;
} catch (NoSuchMethodException ex) {
return false;
}
}

/**
* Make the given field accessible, explicitly setting it accessible if
* necessary. The <code>setAccessible(true)</code> method is only called
* when actually necessary, to avoid unnecessary conflicts with a JVM
* SecurityManager (if active).
* @param field the field to make accessible
* @see java.lang.reflect.Field#setAccessible
*/
public static void makeAccessible(Field field) {
if ((!Modifier.isPublic(field.getModifiers()) || !Modifier.isPublic(field.getDeclaringClass().getModifiers()) ||
Modifier.isFinal(field.getModifiers())) && !field.isAccessible()) {
field.setAccessible(true);
}
}

/**
* Make the given method accessible, explicitly setting it accessible if
* necessary. The <code>setAccessible(true)</code> method is only called
* when actually necessary, to avoid unnecessary conflicts with a JVM
* SecurityManager (if active).
* @param method the method to make accessible
* @see java.lang.reflect.Method#setAccessible
*/
public static void makeAccessible(Method method) {
if ((!Modifier.isPublic(method.getModifiers()) || !Modifier.isPublic(method.getDeclaringClass().getModifiers()))
&& !method.isAccessible()) {
method.setAccessible(true);
}
}

/**
* Make the given constructor accessible, explicitly setting it accessible
* if necessary. The <code>setAccessible(true)</code> method is only called
* when actually necessary, to avoid unnecessary conflicts with a JVM
* SecurityManager (if active).
* @param ctor the constructor to make accessible
* @see java.lang.reflect.Constructor#setAccessible
*/
public static void makeAccessible(Constructor<?> ctor) {
if ((!Modifier.isPublic(ctor.getModifiers()) || !Modifier.isPublic(ctor.getDeclaringClass().getModifiers()))
&& !ctor.isAccessible()) {
ctor.setAccessible(true);
}
}

/**
* Perform the given callback operation on all matching methods of the given
* class and superclasses.
* <p>The same named method occurring on subclass and superclass will appear
* twice, unless excluded by a {@link MethodFilter}.
* @param clazz class to start looking at
* @param mc the callback to invoke for each method
* @see #doWithMethods(Class, MethodCallback, MethodFilter)
*/
public static void doWithMethods(Class<?> clazz, MethodCallback mc) throws IllegalArgumentException {
doWithMethods(clazz, mc, null);
}

/**
* Perform the given callback operation on all matching methods of the given
* class and superclasses (or given interface and super-interfaces).
* <p>The same named method occurring on subclass and superclass will appear
* twice, unless excluded by the specified {@link MethodFilter}.
* @param clazz class to start looking at
* @param mc the callback to invoke for each method
* @param mf the filter that determines the methods to apply the callback to
*/
public static void doWithMethods(Class<?> clazz, MethodCallback mc, MethodFilter mf)
throws IllegalArgumentException {

// Keep backing up the inheritance hierarchy.
Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
if (mf != null && !mf.matches(method)) {
continue;
}
try {
mc.doWith(method);
}
catch (IllegalAccessException ex) {
throw new IllegalStateException("Shouldn't be illegal to access method '" + method.getName()
+ "': " + ex);
}
}
if (clazz.getSuperclass() != null) {
doWithMethods(clazz.getSuperclass(), mc, mf);
}
else if (clazz.isInterface()) {
for (Class<?> superIfc : clazz.getInterfaces()) {
doWithMethods(superIfc, mc, mf);
}
}
}

/**
* Get all declared methods on the leaf class and all superclasses. Leaf
* class methods are included first.
*/
public static Method[] getAllDeclaredMethods(Class<?> leafClass) throws IllegalArgumentException {
final List<Method> methods = new ArrayList<Method>(32);
doWithMethods(leafClass, new MethodCallback() {
public void doWith(Method method) {
methods.add(method);
}
});
return methods.toArray(new Method[methods.size()]);
}

/**
* Get the unique set of declared methods on the leaf class and all superclasses. Leaf
* class methods are included first and while traversing the superclass hierarchy any methods found
* with signatures matching a method already included are filtered out.
*/
public static Method[] getUniqueDeclaredMethods(Class<?> leafClass) throws IllegalArgumentException {
final List<Method> methods = new ArrayList<Method>(32);
doWithMethods(leafClass, new MethodCallback() {
public void doWith(Method method) {
Method methodBeingOverriddenWithCovariantReturnType = null;

for (Method existingMethod : methods) {
if (method.getName().equals(existingMethod.getName()) &&
Arrays.equals(method.getParameterTypes(), existingMethod.getParameterTypes())) {
// is this a covariant return type situation?
if (existingMethod.getReturnType() != method.getReturnType() &&
existingMethod.getReturnType().isAssignableFrom(method.getReturnType())) {
methodBeingOverriddenWithCovariantReturnType = existingMethod;
}
break;
}
}
if (methodBeingOverriddenWithCovariantReturnType != null) {
methods.remove(methodBeingOverriddenWithCovariantReturnType);
}
}
});
return methods.toArray(new Method[methods.size()]);
}

/**
* Invoke the given callback on all fields in the target class, going up the
* class hierarchy to get all declared fields.
* @param clazz the target class to analyze
* @param fc the callback to invoke for each field
*/
public static void doWithFields(Class<?> clazz, FieldCallback fc) throws IllegalArgumentException {
doWithFields(clazz, fc, null);
}

/**
* Invoke the given callback on all fields in the target class, going up the
* class hierarchy to get all declared fields.
* @param clazz the target class to analyze
* @param fc the callback to invoke for each field
* @param ff the filter that determines the fields to apply the callback to
*/
public static void doWithFields(Class<?> clazz, FieldCallback fc, FieldFilter ff)
throws IllegalArgumentException {

// Keep backing up the inheritance hierarchy.
Class<?> targetClass = clazz;
do {
Field[] fields = targetClass.getDeclaredFields();
for (Field field : fields) {
// Skip static and final fields.
if (ff != null && !ff.matches(field)) {
continue;
}
try {
fc.doWith(field);
}
catch (IllegalAccessException ex) {
throw new IllegalStateException(
"Shouldn't be illegal to access field '" + field.getName() + "': " + ex);
}
}
targetClass = targetClass.getSuperclass();
}
while (targetClass != null && targetClass != Object.class);
}

/**
* Given the source object and the destination, which must be the same class
* or a subclass, copy all fields, including inherited fields. Designed to
* work on objects with public no-arg constructors.
* @throws IllegalArgumentException if the arguments are incompatible
*/
public static void shallowCopyFieldState(final Object src, final Object dest) throws IllegalArgumentException {
if (src == null) {
throw new IllegalArgumentException("Source for field copy cannot be null");
}
if (dest == null) {
throw new IllegalArgumentException("Destination for field copy cannot be null");
}
if (!src.getClass().isAssignableFrom(dest.getClass())) {
throw new IllegalArgumentException("Destination class [" + dest.getClass().getName()
+ "] must be same or subclass as source class [" + src.getClass().getName() + "]");
}
doWithFields(src.getClass(), new FieldCallback() {
public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
makeAccessible(field);
Object srcValue = field.get(src);
field.set(dest, srcValue);
}
}, COPYABLE_FIELDS);
}

/**
* Action to take on each method.
*/
public interface MethodCallback {

/**
* Perform an operation using the given method.
* @param method the method to operate on
*/
void doWith(Method method) throws IllegalArgumentException, IllegalAccessException;
}

/**
* Callback optionally used to filter methods to be operated on by a method callback.
*/
public interface MethodFilter {

/**
* Determine whether the given method matches.
* @param method the method to check
*/
boolean matches(Method method);
}

/**
* Callback interface invoked on each field in the hierarchy.
*/
public interface FieldCallback {

/**
* Perform an operation using the given field.
* @param field the field to operate on
*/
void doWith(Field field) throws IllegalArgumentException, IllegalAccessException;
}

/**
* Callback optionally used to filter fields to be operated on by a field callback.
*/
public interface FieldFilter {

/**
* Determine whether the given field matches.
* @param field the field to check
*/
boolean matches(Field field);
}

/**
* Pre-built FieldFilter that matches all non-static, non-final fields.
*/
public static FieldFilter COPYABLE_FIELDS = new FieldFilter() {

public boolean matches(Field field) {
return !(Modifier.isStatic(field.getModifiers()) || Modifier.isFinal(field.getModifiers()));
}
};

/**
* Pre-built MethodFilter that matches all non-bridge methods.
*/
public static MethodFilter NON_BRIDGED_METHODS = new MethodFilter() {

public boolean matches(Method method) {
return !method.isBridge();
}
};

/**
* Pre-built MethodFilter that matches all non-bridge methods
* which are not declared on <code>java.lang.Object</code>.
*/
public static MethodFilter USER_DECLARED_METHODS = new MethodFilter() {

public boolean matches(Method method) {
return (!method.isBridge() && method.getDeclaringClass() != Object.class);
}
};

}