Android反射机制简单理解，ReflectionUtils  反射工具类

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。

1.     //方式一

2.     Person person = new Person();

3.     Class personClazz02 = Class.forName("Person");

4.     } catch (ClassNotFoundException e) {

5.         e.printStackTrace();

6.     }

7.  

8.     //方式三

9.     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 methods = new ArrayList(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 methods = new ArrayList(32); 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); } }; }