如何使用Jackson排除超类属性

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英文:

How to exclude super class properties using Jackson

问题

我有一个类:

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

    //getters and setters
}

我想要通过Jackson映射器排除Body类的属性,因为我遇到了一个错误。

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

我如何将对象转换为JSON,排除所有继承或实现的类?我只需要转换User类,不需要Body类。

我的父类有很多像这样的公共方法:

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

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

I have a class:

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

    //getters and setters
}

I want to exclude Body class properties with Jackson mapper because I get an error.

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

How I can convert object to JSON with excluding all extended or implementation class? I need convert only User class without Body

My super class has many public method like this:

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

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

答案1

得分: 4

1. 使用 @JsonView 注解

Jackson 库有一个 @JsonView 注解,它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,就像这样:

public class Views {
    public interface Base {}  // 基类属性的视图
    public interface Child {} // 子类属性的视图(如 User)
}

然后,在基类 Body 的字段/获取器上标记 @JsonView(Views.Base.class)

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

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

    // 其他获取器/设置器
}

User 类可以在类级别上进行标记:

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

    // 获取器/设置器
}

当使用 ObjectMapper 进行序列化时,您可以设置其 writer 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("自定义视图:" + json);  
System.out.println("完整视图:" + mapper.writeValueAsString(user));

输出:

自定义视图:{"userId":1,"userName":"Jack","email":"jack@company.com"}
完整视图:{"foo":0,"userId":1,"userName":"Jack","email":"jack@company.com","bar":"bar"}

2. 使用 @JsonIgnoreProperties 注解

还可以通过忽略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 userName;
    private String email;
}

然后,无需配置 writer 的 ObjectMapper 实例:

System.out.println("忽略基类字段:" + mapper.writeValueAsString(user));

输出:

忽略基类字段:{"userId":1,"userName":"Jack","email":"jack@company.com"}

3. 配置 ObjectMapper 设置自定义的 JacksonAnnotationIntrospector

还可以配置 ObjectMapper 实例以设置自定义的注解内省器,以完全忽略属于父类 Body 的属性:

// 导入用于 Jackson v.2.x 的类
// import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
// import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;
// 导入用于 Jackson v.1.9 的类
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 并将 User 序列化,无需更改 BodyUser 的任何代码:

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

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

System.out.println("没有基类字段:" + mapper.writeValueAsString(user));

输出:

没有基类字段:{"userId":3,"userName":"Nobody","email":"nobody@company.com"}
英文:

1. Using @JsonView annotation

Jackson library has @JsonView annotation which allows to provide different views of the serialized class.

You need to create a class describing different views like this:

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

Then you mark up the fields/getters in the base Body class with @JsonView(Views.Base.class):

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

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

    // other getters/setters
}

The User class can be marked at class level:

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

    // getters/setters
}

And when serializing with ObjectMapper you set its writer up to use specific view 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));

Output:

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. Using @JsonIgnoreProperties annotation

It is also possible to customize the view of the child class by ignoring its parent class' properties:

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

Then there's no need to configure the writer ObjectMapper instance:

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

Output:

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

3. Configure ObjectMapper to set custom JacksonAnnotationIntrospector

It is also possible to configure the ObjectMapper instance to set a custom annotation introspector to completely ignore properties belonging to the parent Body class:

// 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);
    }
}

Configure ObjectMapper and serialize User without any code changes to Body and User:

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));

Output:

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

huangapple
  • 本文由 发表于 2020年9月28日 16:54:05
  • 转载请务必保留本文链接:https://go.coder-hub.com/64098919.html
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