如何使用杰克逊排除超类属性

Question

我有一堂课：

public class User extends Body {
    private Integer userId;
    private String userName;
    private String emailId;

    //getters and setters
}

我想用 Jackson 映射器排除 Body 类属性，因为我收到一个错误。

ObjectMapper mapper = new ObjectMapper();
User user = new User;
String jsonString = mapper.writeValueAsString(user);

如何在排除所有扩展类或实现类的情况下将对象转换为 JSON？我只需要转换 User 类而不需要 Body

我的超类有很多这样的公共方法：

public final Enumeration method(String email) {
    throw new RuntimeException("Error");
}

public final Object method(String name) {
    throw new RuntimeException("Error");
}

Answer 1

1.使用@JsonView注解

Jackson 库有 @JsonView 注释，允许提供序列化类的不同视图。

您需要创建一个描述不同视图的类，如下所示：

public class Views {
    public interface Base {}  // view of Base class properties
    public interface Child {} // view of Child class properties (i.e. User)
}

然后你用@JsonView(Views.Base.class)标记基类Body中的字段/getter：

public class Body {
    @JsonView(Views.Base.class)
    private int foo;

    @JsonView(Views.Base.class)
    public String getBar() {
        return "bar";
    }

    // other getters/setters
}

User 类可以在类级别标记：

@JsonView(Views.Child.class)
public class User extends Body {
    private Integer userId;
    private String userName;
    private String email;

    // getters/setters
}

当使用ObjectMapper 进行序列化时，您将其编写器设置为使用特定视图writerWithView：

ObjectMapper mapper = new ObjectMapper();//

User user = new User(1, "Jack", "jack@company.com");

String json = mapper.writerWithView(Views.Child.class).writeValueAsString(user);

System.out.println("custom view: " + json);  
System.out.println("full   view: " + mapper.writeValueAsString(user));

输出：

custom view: {"userId":1,"name":"Jack","email":"jack@company.com"}
full   view: {"foo":0,"userId":1,"name":"Jack","email":"jack@company.com","bar":"bar"}

---

2。使用@JsonIgnoreProperties注解

也可以通过忽略其父类的属性来自定义子类的视图：

@JsonIgnoreProperties({"foo", "bar"})
public class User extends Body {
    private Integer userId;
    private String name;
    private String email;
}

那么就不用配置作者ObjectMapper实例了：

System.out.println("base class fields ignored: " + mapper.writeValueAsString(user));

输出：

base class fields ignored: {"userId":1,"name":"Jack","email":"jack@company.com"}

---

3。配置ObjectMapper 设置自定义JacksonAnnotationIntrospector

还可以配置ObjectMapper 实例以设置自定义注解内省器以完全忽略属于父Body 类的属性：

// imports for Jackson v.2.x
// import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
// import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;
// imports for Jackson v.1.9
import org.codehaus.jackson.map.introspect.AnnotatedMember;
import org.codehaus.jackson.map.introspect.JacksonAnnotationIntrospector;

class IgnoreBodyClassIntrospector extends JacksonAnnotationIntrospector {
    @Override
    public boolean hasIgnoreMarker(final AnnotatedMember member) {
        return member.getDeclaringClass() == Body.class || super.hasIgnoreMarker(member);
    }
}

配置ObjectMapper并序列化User，无需对Body和User进行任何代码更改：

ObjectMapper mapper = new ObjectMapper()
        .setAnnotationIntrospector(new IgnoreBodyClassIntrospector());

User user = new User(3, "Nobody", "nobody@company.com");

System.out.println("no base class fields: " + mapper.writeValueAsString(user));

输出：

no base class fields: {"userId":3,"name":"Nobody","email":"nobody@company.com"}