工具類:
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
/**
* 泛型工具類,用於獲取類對象綁定的泛型參數
* @author skyfalling
* @version 1.0.0
*/
public class Generics {
/**
* 查找類對象clazz綁定的genericClass聲明的泛型參數
*
* @param clazz 綁定泛型參數的類
* @param genericClass 聲明泛型的類
* @param index 泛型在聲明類中的索引位置
* @return 如果綁定了泛型參數, 則返回泛型類型, 否則返回null
*/
public static Class find(Class clazz, Class genericClass, int index) {
if (!genericClass.isAssignableFrom(clazz)) {
return null;
}
List<Type> types = getGenericTypes(clazz);
for (Type type : types) {
Class genericType = find(type, genericClass, index);
if (genericType != null) {
return genericType;
}
}
return null;
}
/**
* 查找類type上綁定的genericClass聲明的泛型類型
*
* @param type 泛型對象
* @param genericClass 聲明泛型的類
* @param index 泛型在聲明類中的索引位置
* @return
*/
private static Class find(Type type, Class genericClass, int index) {
if (type instanceof Class) {
return find((Class) type, genericClass, index);
}
if (type instanceof ParameterizedType) {
ParameterizedType pType = (ParameterizedType) type;
Type rawType = pType.getRawType();
if (rawType instanceof Class) {
Class rawClass = (Class) rawType;
if (rawClass == genericClass) {
Type realType = pType.getActualTypeArguments()[index];
if (realType instanceof Class) {
return (Class) realType;
} else if (realType instanceof ParameterizedType) {
//這裏是泛型的泛型
return (Class) ((ParameterizedType) realType).getRawType();
}
} else if (genericClass.isAssignableFrom(rawClass)) {
Map<String, Type> map = combine(pType.getActualTypeArguments(), rawClass);
return find(rawClass, genericClass, index, map);
}
}
}
return null;
}
/**
* 查找類currentClass上綁定的genericClass聲明的泛型類型
*
* @param currentClass 綁定泛型參數的類
* @param genericClass 聲明泛型的類
* @param index 泛型在聲明類中的索引位置
* @param typeMap 已綁定的泛型類型映射表
* @return
*/
private static Class find(Class currentClass, Class genericClass, int index, Map<String, Type> typeMap) {
List<Type> types = getGenericTypes(currentClass);
for (Type type : types) {
if (type instanceof ParameterizedType) {
ParameterizedType pType = (ParameterizedType) type;
Type rawType = pType.getRawType();
if (rawType instanceof Class) {
Class rawClass = (Class) rawType;
Map<String, Type> map = transfer(pType, typeMap);
Type[] typeArray = map.values().toArray(new Type[0]);
if (rawClass == genericClass) {
Type realType = typeArray[index];
if (realType instanceof Class) {
return (Class) realType;
} else if (realType instanceof ParameterizedType) {
//這裏是泛型的泛型
return (Class) ((ParameterizedType) realType).getRawType();
}
} else if (genericClass.isAssignableFrom(rawClass)) {
return find(rawClass, genericClass, index, combine(typeArray, rawClass));
}
}
}
}
return null;
}
/**
* 獲取當前類繼承的父類和實現接口的泛型列表
*
* @param clazz
* @return
*/
private static List<Type> getGenericTypes(Class clazz) {
if (clazz == Object.class) {
return Collections.EMPTY_LIST;
}
List<Type> list = new ArrayList<>();
Type[] types = clazz.getGenericInterfaces();
for (Type type : types) {
list.add(type);
}
list.add(clazz.getGenericSuperclass());
return list;
}
/**
* 構建泛型映射表
*
* @param typeArguments 泛型參數
* @param rawClass 聲明泛型的類
* @return
*/
private static Map<String, Type> combine(Type[] typeArguments, Class rawClass) {
Map<String, Type> map = new LinkedHashMap<>(typeArguments.length);
TypeVariable[] typeParameters = rawClass.getTypeParameters();
for (int i = 0; i < typeParameters.length; i++) {
map.put(typeParameters[i].getName(), typeArguments[i]);
}
return map;
}
/**
* 轉換泛型映射表
*
* @param parameterizedType 綁定參數類型的泛型對象
* @param typeMap 已綁定的泛型類型映射表
* @return
*/
private static Map<String, Type> transfer(ParameterizedType parameterizedType, Map<String, Type> typeMap) {
Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
TypeVariable[] typeParameters = ((Class) parameterizedType.getRawType()).getTypeParameters();
Map<String, Type> map = new LinkedHashMap<>();
for (int i = 0; i < actualTypeArguments.length; i++) {
Type type = actualTypeArguments[i];
if (type instanceof TypeVariable) {
String variableName = ((TypeVariable) type).getName();
map.put(variableName, typeMap.get(variableName));
} else {
map.put(typeParameters[i].getName(), type);
}
}
return map;
}
}
使用方式:
定義泛型接口:
public interface Node<T, R> {
R execute(T param);
default Class<T> paramType() {
return Generics.find(this.getClass(), Node.class, 0);
}
}
定義泛型類:
public class MyNode implements Node<String, User> {
@Override
public User execute(String param) {
Class<String> stringClass = paramType();
System.out.println(stringClass);
return null;
}
public static void main(String[] args) {
MyNode myNode=new MyNode();
myNode.execute("123");
}