Java 获取泛型的类型实例详解

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Class lstUClazz = List<User>.class

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List<User> listUser = new ArrayList<User>();

Type genType = listUser.getClass().getClass().getGenericSuperclass();

Class templatClazz = null;

if(ParameterizedType.class.isInstance(genType)

{

  //无法获取到User类，或者可能获取到错误的类型，如果有同名且不带包名的泛型存在

  ParameterizedType parameterizedType = (ParameterizedType) genType;

 templatClazz = (Class) parameterizedType.getActualTypeArguments()[0];

}

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public abstract class JdbcDaoSupport<T> {

  protected JdbcDaoSupport() {

  }

   public Class getTempalteType()

  {

     Class<T> clazz = (Class<T>) ((ParameterizedType) getClass()

        .getGenericSuperclass()).getActualTypeArguments()[0];

     return clazz;                   

  }

}

public class UserDao extends JdbcDaoSupport<User> {

}

public class Test{

    public static void main(String[] args)

    {

      UserDao dao = new UserDao();

      Class clazz = dao.getTemplateType();

      System.out.println(clazz.getName()); //输出 xxx.xxx.User

    }

}

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public class Test extends ClassA<String> {

  private List<String> list;

  private Map<String, Object> map;

  /***

   * 获取List中的泛型

   */

  public static void testList() throws NoSuchFieldException, SecurityException {

    Type t = Test.class.getDeclaredField("list").getGenericType();

    if (ParameterizedType.class.isAssignableFrom(t.getClass())) {

      for (Type t1 : ((ParameterizedType) t).getActualTypeArguments()) {

        System.out.print(t1 + ",");

      }

      System.out.println();

    }

  }

  /***

   * 获取Map中的泛型

   */

  public static void testMap() throws NoSuchFieldException, SecurityException {

    Type t = Test.class.getDeclaredField("map").getGenericType();

    if (ParameterizedType.class.isAssignableFrom(t.getClass())) {

      for (Type t1 : ((ParameterizedType) t).getActualTypeArguments()) {

        System.out.print(t1 + ",");

      }

      System.out.println();

    }

  }

  public static void main(String args[]) throws Exception {

    System.out.println(">>>>>>>>>>>testList>>>>>>>>>>>");

    testList();

    System.out.println("<<<<<<<<<<<testList<<<<<<<<<<<\n");

    System.out.println(">>>>>>>>>>>testMap>>>>>>>>>>>");

    testMap();

    System.out.println("<<<<<<<<<<<testMap<<<<<<<<<<<\n");

    System.out.println(">>>>>>>>>>>testClassA>>>>>>>>>>>");

    new Test().testClassA();

    System.out.println("<<<<<<<<<<<testClassA<<<<<<<<<<<");

  }

}

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List<User> lst = new ArrayList<User>(){};

Type genType = listUser.getClass().getClass().getGenericSuperclass();

Class templatClazz = null;

if(ParameterizedType.class.isInstance(genType)

{

  ParameterizedType parameterizedType = (ParameterizedType) genType;

 templatClazz = (Class) parameterizedType.getActualTypeArguments()[0];

}

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Class clz = new ArrayList<User>(){}.getClass();

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class JsonToObjectUtil {

 public static <T> T jsonToObject(Class<T> clz,List<String> jsonList){

 Type genType = clz.getClass().getGenericSuperclass();

 Class templatClazz = null;

 if(ParameterizedType.class.isInstance(genType));

 {

  ParameterizedType parameterizedType = (ParameterizedType) genType;

  templatClazz = (Class) parameterizedType.getActualTypeArguments()[0];

 }

 List<Object> lst = new ArrayList<Object>();

 /*****/

 if(templatClazz!=null && jsonList!=null)

 {

  for (String str : jsonList) {

  Gson gson = new Gson();

  Object fromJson = gson.fromJson(str, templatClazz);

  lst.add(fromJson);

  }

 }

 /*****/

 return (T) lst;

 }

 public static void main(String[] args) {

 List<String> jsonList = null;

 //略去一部分填充jsonList的逻辑

 Class superClazz = new ArrayList<User>(){}.getClass();

 List jsonToObject = JsonToObjectUtil.jsonToObject(superClazz, jsonList);

 }

}