Ian Robertson在这篇文章中描述的技巧对我很有用。

简单粗暴的例子:

 public abstract class AbstractDAO<T extends EntityInterface, U extends QueryCriteria, V>
 {
    /**
     * Method returns class implementing EntityInterface which was used in class
     * extending AbstractDAO
     *
     * @return Class<T extends EntityInterface>
     */
    public Class<T> returnedClass()
    {
        return (Class<T>) getTypeArguments(AbstractDAO.class, getClass()).get(0);
    }

    /**
     * Get the underlying class for a type, or null if the type is a variable
     * type.
     *
     * @param type the type
     * @return the underlying class
     */
    public static Class<?> getClass(Type type)
    {
        if (type instanceof Class) {
            return (Class) type;
        } else if (type instanceof ParameterizedType) {
            return getClass(((ParameterizedType) type).getRawType());
        } else if (type instanceof GenericArrayType) {
            Type componentType = ((GenericArrayType) type).getGenericComponentType();
            Class<?> componentClass = getClass(componentType);
            if (componentClass != null) {
                return Array.newInstance(componentClass, 0).getClass();
            } else {
                return null;
            }
        } else {
            return null;
        }
    }

    /**
     * Get the actual type arguments a child class has used to extend a generic
     * base class.
     *
     * @param baseClass the base class
     * @param childClass the child class
     * @return a list of the raw classes for the actual type arguments.
     */
    public static <T> List<Class<?>> getTypeArguments(
            Class<T> baseClass, Class<? extends T> childClass)
    {
        Map<Type, Type> resolvedTypes = new HashMap<Type, Type>();
        Type type = childClass;
        // start walking up the inheritance hierarchy until we hit baseClass
        while (!getClass(type).equals(baseClass)) {
            if (type instanceof Class) {
                // there is no useful information for us in raw types, so just keep going.
                type = ((Class) type).getGenericSuperclass();
            } else {
                ParameterizedType parameterizedType = (ParameterizedType) type;
                Class<?> rawType = (Class) parameterizedType.getRawType();

                Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
                TypeVariable<?>[] typeParameters = rawType.getTypeParameters();
                for (int i = 0; i < actualTypeArguments.length; i++) {
                    resolvedTypes.put(typeParameters[i], actualTypeArguments[i]);
                }

                if (!rawType.equals(baseClass)) {
                    type = rawType.getGenericSuperclass();
                }
            }
        }

        // finally, for each actual type argument provided to baseClass, determine (if possible)
        // the raw class for that type argument.
        Type[] actualTypeArguments;
        if (type instanceof Class) {
            actualTypeArguments = ((Class) type).getTypeParameters();
        } else {
            actualTypeArguments = ((ParameterizedType) type).getActualTypeArguments();
        }
        List<Class<?>> typeArgumentsAsClasses = new ArrayList<Class<?>>();
        // resolve types by chasing down type variables.
        for (Type baseType : actualTypeArguments) {
            while (resolvedTypes.containsKey(baseType)) {
                baseType = resolvedTypes.get(baseType);
            }
            typeArgumentsAsClasses.add(getClass(baseType));
        }
        return typeArgumentsAsClasses;
    }
  }

我不认为你可以，Java在编译时使用类型擦除，这样你的代码就可以与在泛型之前创建的应用程序和库兼容。

来自Oracle文档:

Type Erasure Generics were introduced to the Java language to provide tighter type checks at compile time and to support generic programming. To implement generics, the Java compiler applies type erasure to: Replace all type parameters in generic types with their bounds or Object if the type parameters are unbounded. The produced bytecode, therefore, contains only ordinary classes, interfaces, and methods. Insert type casts if necessary to preserve type safety. Generate bridge methods to preserve polymorphism in extended generic types. Type erasure ensures that no new classes are created for parameterized types; consequently, generics incur no runtime overhead.

http://docs.oracle.com/javase/tutorial/java/generics/erasure.html

你不能。如果向类中添加类型为T的成员变量(甚至不需要初始化它)，则可以使用它来恢复类型。

我发现这是一个简单易懂且容易解释的解决方案

public class GenericClass<T> {

    private Class classForT(T...t) {
        return t.getClass().getComponentType();
    }

    public static void main(String[] args) {
        GenericClass<String> g = new GenericClass<String>();

        System.out.println(g.classForT());
        System.out.println(String.class);
    }
}

这是受到Pablo和CoolMind的回答的启发。 我偶尔也会使用kayz1的答案中的技巧(在许多其他答案中也有表达)，我相信这是一种完成OP要求的体面而可靠的方法。

我选择首先将其定义为一个接口(类似于PJWeisberg)，因为我有可以从该功能中受益的现有类型，特别是异构泛型联合类型:

public interface IGenericType<T>
{
    Class<T> getGenericTypeParameterType();
}

我在一个通用匿名接口实现中的简单实现如下所示:

//Passed into the generic value generator function: toStore
//This value name is a field in the enclosing class.
//IUnionTypeValue<T> is a generic interface that extends IGenericType<T>
value = new IUnionTypeValue<T>() {
    ...
    private T storedValue = toStore;
    ...
    
    @SuppressWarnings("unchecked")
    @Override
    public Class<T> getGenericTypeParameterType()
    {
        return (Class<T>) storedValue.getClass();
    }
}

我想这也可以通过用类定义对象作为源来实现，这只是一个单独的用例。 我认为关键在于，正如许多其他答案所述，以某种方式，您需要在运行时获得类型信息，以便在运行时可用;对象本身保持其类型，但是擦除(也如其他人所说，使用适当的引用)会导致任何封闭/容器类型丢失该类型信息。

public abstract class AbstractDao<T>
{
    private final Class<T> persistentClass;

    public AbstractDao()
    {
        this.persistentClass = (Class<T>) ((ParameterizedType) this.getClass().getGenericSuperclass())
                .getActualTypeArguments()[0];
    }
}