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