当返回类型是标记接口时使用Jackson的多态序列化

我有一个返回标记接口的休息服务,这个接口有多个实现,并且在实现中没有任何公共属性.

    @RequestMapping(value = "/users/{userName}", method = RequestMethod.GET)
    public User getUser(@PathVariable("userName") String userName) {
        return userService.getUser(userName);
    }

用户及其实现.注意:用户是标记界面.

public interface User {}

public AdminUser implements User { // some properties & its setters & getters } 

public SupportUser implements User { // some properties & its setters & getters } 

我使用Jackson 1.9.1来序列化和反序列化.

当我达到以上服务时,我的回答低于响应

{}

当我调试它时,我看到用户实现对象已准备好并发送回Jackson进行序列化.但杰克逊正在向浏览器发送空响应.任何人都建议如何在返回类型为标记接口时使用序列化.

使用@JsonTypeInfo和@JsonSubTypes反序列化多态类型,在序列化java对象时维护子类型信息并重新创建确切的子类型.

让我们举一个例子,动物是一个接口,它可以是老虎或狮子,它们都扩展了动物界面.在反序列化时,我们想要创建精确的动物类型并演示@JsonTypeInfo和@JsonSubTypes注释的使用.

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME,
        include=JsonTypeInfo.As.PROPERTY,
        property="name")
@JsonSubTypes({
        @JsonSubTypes.Type(value=Lion.class, name="lion"),
        @JsonSubTypes.Type(value=Tiger.class, name="tiger"),
})
public interface Animal {

}

@JsonTypeName("lion")
public class Lion implements Animal {

    private String name;
    private String roar;

//constructor & setters & getters
}

@JsonTypeName("tiger")
public class Tiger implements Animal {

    private String name;
    private String purr;

//constructor & setters & getters
}

主要方法:

List animal = new ArrayList();
animal.add(new Lion("lion", "roar"));
animal.add(new Tiger("tiger", "purr"));
animal.add(new Tiger("tiger", "purrrrrrrrr"));

URL url = JacksonPolymorphicSerialization.class.getClassLoader().getResource("animals.json");
File file = new File(url.getPath());

// de-serailization sub types
new ObjectMapper().writeValue(file, animal);

// serailization animals and its subtype
List animals = new ObjectMapper().readValue(file, List.class);
System.out.println(animals);


output : [{name=lion, roar=roar}, {name=tiger, purr=purr}, {name=tiger, purr=purrrrrrrr}]

希望这有助于您了解使用Jackson对多态类型进行序列化和反序列化.