关于TypeReference的使用

在项目中,有遇到TypeReference的使用,其主要在字符串转对象过程中,对于序列化和反序列化中也有效果,将字符串转换成自定义对象.

1 说明

以常见为例,在com.alibaba.fastjson包下面的TypeReference类,是指Type的Reference，表示某类型的一个指向或者引用.

    protected TypeReference() {
        // 当前类父类的类型
        Type superClass = this.getClass().getGenericSuperclass();
        Type type = ((ParameterizedType)superClass).getActualTypeArguments()[0];
        Type cachedType = (Type)classTypeCache.get(type);
        if (cachedType == null) {
            classTypeCache.putIfAbsent(type, type);
            cachedType = (Type)classTypeCache.get(type);
        }

        this.type = cachedType;
    }

	// 返回类型
	public Type getType()

2 使用

1 常见字符串转对象

实体类

@Data
public class Student {

    @ExcelProperty("姓名")
    private String name;

    @ExcelProperty("描述")
    private  String des;
}

通用类

@Data
public class Generic<T> {
    private String id;
    private T t;
}

测试类

    public static void main(String[] args)  {
        // 创建对象设置值
        Generic<List<Student>> objectGeneric = new Generic<>();
        objectGeneric.setId("0001");
        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student("李白","唐"));
        studentList.add(new Student("王维","唐"));
        objectGeneric.setT(studentList);

        // 字符串
        String string1 = JSON.toJSONString(objectGeneric);
        System.out.println(string1);

        // 不指定类型
        JSONObject jsonObject = JSON.parseObject(string1);
        System.out.println(jsonObject);

        // 指定类型
        Generic<List<Student>> listGeneric = JSON.parseObject(string1, new com.alibaba.fastjson.TypeReference<Generic<List<Student>>>() {
        });
        System.out.println(listGeneric);

/*
运行结果:
{"id":"0001","t":[{"creatTime":1701172903084,"des":"唐","name":"李白"},{"creatTime":1701172903084,"des":"唐","name":"王维"}]}

{"t":[{"des":"唐","creatTime":1701172903084,"name":"李白"},{"des":"唐","creatTime":1701172903084,"name":"王维"}],"id":"0001"}

Generic(id=0001, t=[Student{name='李白', des='唐', creatTime=Tue Nov 28 20:01:43 CST 2023}, Student{name='王维', des='唐', creatTime=Tue Nov 28 20:01:43 CST 2023}])
*/
}

2 常见序列化和反序列化

此处TypeReference类是com.fasterxml.jackson.core.type包下面的.

模拟参数同上.

测试类

    public static void main(String[] args) throws JsonProcessingException {
        // 创建对象设置值
        Generic<List<Student>> objectGeneric = new Generic<>();
        objectGeneric.setId("0001");
        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student("李白","唐"));
        studentList.add(new Student("王维","唐"));
        objectGeneric.setT(studentList);

        ObjectMapper objectMapper = new ObjectMapper();
        // 序列化
        String string = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(objectGeneric);
        System.out.println(string);

        // 反序列化
        // 使用TypeReference
        Generic generic = objectMapper.readValue(string, new TypeReference<Generic<List<Student>>>() {
        });
        System.out.println("使用TypeReference" + generic);
        // 不使用TypeReference
        Generic generic2 = objectMapper.readValue(string, Generic.class);
        System.out.println("不使用TypeReference" + generic2);

/*
运行结果:

 {
  "id" : "0001",
  "t" : [ {
    "name" : "李白",
    "des" : "唐",
    "creatTime" : 1701173940428
  }, {
    "name" : "王维",
    "des" : "唐",
    "creatTime" : 1701173940428
  } ]
}

使用TypeReferenceGeneric(id=0001, t=[Student{name='李白', des='唐', creatTime=Tue Nov 28 20:19:00 CST 2023}, Student{name='王维', des='唐', creatTime=Tue Nov 28 20:19:00 CST 2023}])

不使用TypeReferenceGeneric(id=0001, t=[{name=李白, des=唐, creatTime=1701173940428}, {name=王维, des=唐, creatTime=1701173940428}])
*/

}

在JSON字符串转自定义对象过程中, 和对象序列化与反序列化中, 都可以使用TypeReference来指定或引用给某一对象.