Android反射机制:什么是反射机制？ JAVA反射机制是在运行状态中，对于任意一个类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意一个方法和属性；这种动态获取的信息以及动态调用对象的方法的功能称为java语言的反射机制（注意关键词：运行状态）换句话说，Java程序可以加载一个运行时才得知名称的class，获悉其完整构造（但不包括methods定义），并生成其对象实体、或对其fields设值、或唤起其methods
反射机制主要提供的功能在运行时判断任意一个对象所属的类；在运行时构造任意一个类的对象；在运行时判断任意一个类所具有的成员变量和方法；在运行时调用任意一个对象的方法；java Reflection API简介Class类：代表一个类，位于java.lang包下Field类：代表类的成员变量（成员变量也称为类的属性）Method类：代表类的方法Constructor类：代表类的构造方法Array类：提供了动态创建数组，以及访问数组的元素的静态方法java中的Class介绍 Class 类十分特殊，它没有共有的构造方法，被jvm调用的（简单的理解：new对象或者被类加载器加载的时候），在Java中，每个class都有一个相应的Class对象。也就是说，当我们编写一个类，编译完成后，在生成的.class文件中，就会产生一个Class对象，用于表示这个类的类型信息。
java中的Class三种获取方式利用对象调用getClass()方法获取该对象的Class实例；使用Class类的静态方法forName()，用类的名字获取一个Class实例 ；运用.class的方式来获取Class实例，对于基本数据类型的封装类，还可以采用.TYPE来获取相对应的基本数据类型的Class实例； 说明：在运行期间，如果我们要产生某个类的对象，Java虚拟机(JVM)会检查该类型的Class对象是否已被加载。如果没有被加载，JVM会根据类的名称找到.class文件并加载它。一旦某个类型的Class对象已被加载到内存，就可以用它来产生该类型的所有对象。
代码语言：javascript复制 //方式一
Person person = new Person();
Class personClazz01 = person.getClass();
//方式二
try {
Class personClazz02 = Class.forName("Person");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
//方式三
Class personClazz03 = Person.class;
java中的Class中一些重要的方法 public Annotation[] getAnnotations () 获取这个类中所有注解
getClassLoader() 获取加载这个类的类加载器
getDeclaredMethods() 获取这个类中的所有方法
getReturnType() 获取方法的返回类型
getParameterTypes() 获取方法的传入参数类型
isAnnotation() 测试这类是否是一个注解类
getDeclaredConstructors() 获取所有的构造方法
getDeclaredMethod(String name, Class… parameterTypes) 获取指定的构造方法（参数：参数类型.class）
getSuperclass() 获取这个类的父类
getInterfaces() 获取这个类实现的所有接口
getFields() 获取这个类中所有被public修饰的成员变量
getField(String name) 获取指定名字的被public修饰的成员变量
newInstance() 返回此Class所表示的类，通过调用默认的（即无参数）构造函数创建的一个新实例
等等方法
代码语言：javascript复制invokeMethod ：运行方法。下面是一个反射ReflectionUtils 反射工具类
代码语言：javascript复制package com.itep.mt.common.util;
/**
* Created by hx on 2019/7/12.
*/
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 java.util.regex.Pattern;
/**
* Simple utility class for working with the reflection API and handling
* reflection exceptions.
*
*
Only intended for internal use.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @author Rod Johnson
* @author Costin Leau
* @author Sam Brannen
* @author Chris Beams
* @since 1.2.2
*/
public abstract class ReflectionUtils {
/**
* Pattern for detecting CGLIB-renamed methods.
* @see #isCglibRenamedMethod
*/
private static final Pattern CGLIB_RENAMED_METHOD_PATTERN = Pattern.compile("CGLIB\\$(.+)\\$\\d+");
/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied {@code name}. 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} 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} 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} if type is specified)
* @param type the type of the field (may be {@code null} if name is specified)
* @return the corresponding Field object, or {@code null} if not found
*/
public static Field findField(Class clazz, String name, Class type) {
//Assert.notNull(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;
}
/**
* Set the field represented by the supplied {@link Field field object} on the
* specified {@link Object target object} to the specified {@code value}.
* In accordance with {@link Field#set(Object, Object)} semantics, the new value
* is automatically unwrapped if the underlying field has a primitive type.
*
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}
*/
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.
*
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 {
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}.
*
Returns {@code null} 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} if none found
*/
public static Method findMethod(Class clazz, String name) {
return findMethod(clazz, name, new Class[0]);
}
/**
* Attempt to find a {@link Method} on the supplied class with the supplied name
* and parameter types. Searches all superclasses up to {@code Object}.
*
Returns {@code null} 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} to indicate any signature)
* @return the Method object, or {@code null} if none found
*/
public static Method findMethod(Class clazz, String name, Class... paramTypes) {
//Assert.notNull(clazz, "Class must not be null");
//Assert.notNull(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} when invoking a static {@link Method}.
*
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(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} when invoking a
* static {@link Method}.
*
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})
* @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(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})
* @return the invocation result, if any
* @throws SQLException the JDBC API SQLException to rethrow (if any)
* @see #invokeMethod(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.
*
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.
*
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
* target exception of an {@link InvocationTargetException}. Should
* only be called if no checked exception is expected to be thrown by the
* target method.
*
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
* target exception of an {@link InvocationTargetException}. Should
* only be called if no checked exception is expected to be thrown by the
* target method.
*
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} if the exception can be thrown as-is;
* {@code false} if it needs to be wrapped
*/
public static boolean declaresException(Method method, Class exceptionType) {
//Assert.notNull(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 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 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 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 Object}.
*/
public static boolean isObjectMethod(Method method) {
if (method == null) {
return false;
}
try {
Object.class.getDeclaredMethod(method.getName(), method.getParameterTypes());
return true;
}
catch (Exception ex) {
return false;
}
}
/**
* Determine whether the given method is a CGLIB 'renamed' method,
* following the pattern "CGLIB$methodName$0".
* @param renamedMethod the method to check
* @see //org.springframework.cglib.proxy.Enhancer#rename
*/
public static boolean isCglibRenamedMethod(Method renamedMethod) {
return CGLIB_RENAMED_METHOD_PATTERN.matcher(renamedMethod.getName()).matches();
}
/**
* Make the given field accessible, explicitly setting it accessible if
* necessary. The {@code setAccessible(true)} 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 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)} 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 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)} 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 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.
*
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).
*
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
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
doWithMethods(leafClass, new MethodCallback() {
public void doWith(Method method) {
boolean knownSignature = false;
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;
}
else {
knownSignature = true;
}
break;
}
}
if (methodBeingOverriddenWithCovariantReturnType != null) {
methods.remove(methodBeingOverriddenWithCovariantReturnType);
}
if (!knownSignature && !isCglibRenamedMethod(method)) {
methods.add(method);
}
}
});
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}.
*/
public static MethodFilter USER_DECLARED_METHODS = new MethodFilter() {
public boolean matches(Method method) {
return (!method.isBridge() && method.getDeclaringClass() != Object.class);
}
};
}