1.获取反射Class类的方式
Class.forName("全类名")；
类名.class//需要在JVM已加载的前提下
对象.getClass
2.java对javabean进行操作的四种方式
public class Descriptor {
public static void main(String[] args) throws Exception {
// 方式1
PropertyDescriptor descriptor = new PropertyDescriptor("x", TestDemo1.class);
Method readMethod = descriptor.getReadMethod();
TestDemo1 testDemo1 = new TestDemo1();
Object invoke = readMethod.invoke(testDemo1);
if (invoke instanceof String) {
System.out.println((String) invoke);
}
// 方式2 这个方法只能得到所有的方法
BeanInfo beanInfo = Introspector.getBeanInfo(TestDemo1.class);
PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();
for (PropertyDescriptor propertyDescriptor : descriptors) {
if (propertyDescriptor.getName().equals("x")) {
System.out.println(propertyDescriptor.getName());
}
}
// 方式3
Class testClass = TestDemo1.class;
Object newInstance = testClass.newInstance();
if (newInstance instanceof TestDemo1) {
System.out.println(((TestDemo1) newInstance).getX());
}
// 方式4
Class testClass1 = Class.forName("cn.reflect.collection.TestDemo1");
Field declaredField = testClass1.getDeclaredField("x");
if (!declaredField.isAccessible()) {
//类似与上判断是否是公有的属性
// if(!Modifier.isPublic(declaredField.getModifiers())){
declaredField.setAccessible(true);
}
System.out.println(declaredField.get(testDemo1));
}
}
class TestDemo1 {
private String x = "qwe";
public String getX() {
return x;
}
public void setX(String x) {
this.x = x;
}
}
3.利用反射获取注解
//RetentionPolicy 枚举 RetentionPolicy.RUNTIME 运行时起作用,必须使用运行时才能够反射
@Retention(RetentionPolicy.RUNTIME)//元注解
// ElementType 枚举 ElementType.TYPE 修饰于类，接口，枚举，注解
@Target(ElementType.TYPE)
@interface ReflectAnnotationdemo1 {
// value可以省略 value= ,省略的前提是只有
String value();
}
@ReflectAnnotationdemo1("111")
class AnnotationDemo1 {
}
public class AnnotationDemo {
public static void main(String[] args) {
AnnotationDemo1 annotationDemo1 = new AnnotationDemo1();
Class<? extends AnnotationDemo1> class1 = annotationDemo1.getClass();
if (class1.isAnnotationPresent(ReflectAnnotationdemo1.class)) {
ReflectAnnotationdemo1 annotation = class1.getAnnotation(ReflectAnnotationdemo1.class);
System.out.println(annotation.value());
}
}
}
4.对泛型的反射
public class ReflectGenericity {
private static final String ParameterizedType = null;
public static void main(String[] args) throws NoSuchMethodException, SecurityException {
//获取父类的参数化类型
Type genericSuperclass = ReflectGenericityTest1.class.getGenericSuperclass();
if (genericSuperclass instanceof ParameterizedType) {
Type[] actualTypeArguments = ((ParameterizedType) genericSuperclass).getActualTypeArguments();
System.out.println(actualTypeArguments[0]);
}
//获取类型
Method[] methods = ReflectGenericityTest.class.getMethods();
for (int i = 0; i < methods.length; i++) {
if(methods[i].getName().equals("test1")){
Parameter[] parameters = methods[i].getParameters();
System.out.println(parameters[0]);
break;
}
}
//获取参数化类型
Method method = ReflectGenericityTest.class.getMethod("test2", Vector.class);
Type[] genericParameterTypes = method.getGenericParameterTypes();
System.out.println(genericParameterTypes[0]);
}
}
class ReflectGenericityTest<T> {
public static <E> E test1(E e) {
return e;
}
public static void test2(Vector<String> e) {
}
}
class ReflectGenericityTest1<T> extends ReflectGenericityTest<T> {
}
5.反射的工具类
public class ReflectUtils {
public static Class getSuperClass(Class clazz, int index) {
Type gentype = clazz.getGenericSuperclass();
if (!(gentype instanceof ParameterizedType)) {
return Object.class;
}
Type[] params = ((ParameterizedType) gentype).getActualTypeArguments();
if (index >= params.length || index < 0) {
return Object.class;
}
if (!(params[index] instanceof Class)) {
return Object.class;
}
return (Class) params[index];
}
public static <T> Class<T> getSupergType(Class clazz) {
return getSuperClass(clazz, 0);
}
public static Method getDecaredMethod(Object obj, String methoname, Class<?>[] paraterty) {
for (Class clazz = obj.getClass(); clazz != Object.class; clazz.getSuperclass()) {
try {
return clazz.getDeclaredMethod(methoname, paraterty);
} catch (Exception e) {
}
}
return null;
}
public static void makeAccsible(Field field) {
// getmodifys获取各种权限的叠加整型
if (Modifier.isPublic(field.getModifiers())) {
field.setAccessible(true);
}
}
public static Field getDecaredMethod(Object obj, String fieldname) {
for (Class clazz = obj.getClass(); clazz != Object.class; clazz.getSuperclass()) {
try {
return clazz.getDeclaredField(fieldname);
} catch (Exception e) {
}
}
// ArrayList<Object> arrayList = new ArrayList<String>();
return null;
}
public static Object invokeMethod(Object obj, String methoname, Class<?>[] paraterty, Object[] parame) {
Method method = getDecaredMethod(obj, methoname, paraterty);
if (method == null) {
throw new IllegalAccessError();
}
if (Modifier.isPublic(method.getModifiers())) {
method.setAccessible(true);
}
try {
method.invoke(obj, parame);
} catch (Exception e) {
}
return null;
}
public static void setFieldValue(Object obj, String fieldname, Object param) {
Field field = getDecaredMethod(obj, fieldname);
if (field == null) {
throw new IllegalAccessError();
}
makeAccsible(field);
try {
field.set(obj, param);
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
public static Object geyFieldValue(Object object, String name) {
Field field = getDecaredMethod(object, name);
if (field == null) {
throw new IllegalArgumentException("not find field!");
}
try {
field.get(object);
} catch (IllegalAccessException e) {
}
return null;
}
}
6.多态反射获取的字节码是对象自身的字节码文件，也可以这么认为多态的字节码是对象本身
public class ReflectPoly implements ReflectPolyFather { public static void main(String[] args) { ReflectPolyFather reflectPoly = new ReflectPoly(); // 获得class文件是其对象的class文件 System.out.println(reflectPoly.getClass().getName());// cn.reflect.demo.ReflectPoly } @Override public void test() { System.err.println("test"); } } interface ReflectPolyFather { public abstract void test(); }