Java 通过反射获取泛型的类型

由于 Java 的泛型在运行时会被擦除，不能够直接获取泛型的类型，但是其实在 class 字节码中还是保存着泛型的信息，可以通过特殊的方式获取到泛型的类型

• 获取父类中的泛型类型

/*** 定义一个抽象的父类* 获取父类中的泛型类型 T*/
public abstract class SuperClass<T> {// 泛型类型private Class<T> clazz;public SuperClass() {super();// 根据实现类反射获取包含泛型的父类，然后获取泛型的类型this.clazz = (Class<T>)((ParameterizedType)getClass().getGenericSuperclass()).getActualTypeArguments()[0];}public Class<T> getClazz() {return this.clazz;}public static void main(String[] args) {// 构造匿名子类SuperClass<String> superClassString = new SuperClass<String>(){};System.out.println(superClassString.getClazz()); // class java.lang.String// 构造匿名子类SuperClass<Entity> superClassEntity = new SuperClass<Entity>(){};System.out.println(superClassEntity.getClazz()); // class Entity}}

• 获取父接口中的泛型类型

public interface SuperInterface<T> {@SuppressWarnings("unchecked")default Class<T> getEntityClass() {Type[] types = getClass().getGenericInterfaces();for (Type type : types) {if (type.getTypeName().startsWith(SuperInterface.class.getName())) {ParameterizedType pt = (ParameterizedType) type;return (Class<T>)pt.getActualTypeArguments()[0];}}return null;}}public class Children implements SuperInterface<Entity> {public static void main() {Children children = new Children();System.out.println(children.getEntityClass()); // class Entity}}

• 获取父类或接口中的指定位置的泛型类型

public class SystemUtils {/*** 根据子类获取父接口指定的泛型类型，未找到指定泛型时将返回空* * @param subClass 子类类型* @param targetInterfaceClass 父接口类型* @param genericIndex 泛型下标* @return 泛型类型*/public static Class<?> getInterfaceGenericClass(Class<?> subClass, Class<?> targetInterfaceClass, int genericIndex) {if (subClass == null || targetInterfaceClass == null || genericIndex < 0) {return null;}Class<?> clazz = subClass;while (clazz != null && clazz != Object.class) {Type[] types = clazz.getGenericInterfaces();for (Type type : types) {if (type.getTypeName().contains(targetInterfaceClass.getName())) {Type[] typeArguments = ((ParameterizedType) type).getActualTypeArguments();if (genericIndex >= typeArguments.length) {return null;}Type typeArgument = typeArguments[genericIndex];if (typeArgument instanceof Class) {return (Class<?>) typeArgument;}return null;}}Class<?>[] interfaces = clazz.getInterfaces();if (interfaces != null) {for (Class<?> inter : interfaces) {Class<?> result = getInterfaceGenericClass(inter, targetInterfaceClass, genericIndex);if (result != null) {return result;}}}clazz = clazz.getSuperclass();}return null;}public static void main(String[] args) {System.out.println(SystemUtils.getInterfaceGenericClass(Children.class, SuperInterface.class, 0)); // class Entity}}

• Entity 对象

/*** 简单 Java 对象 POJO*/
@Getter
@Setter
class Entity {private int id;private String name;}