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 {@Overridepublic 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 Body 和 User 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 propertiespublic 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.1.9import org.codehaus.jackson.map.introspect.AnnotatedMember;import org.codehaus.jackson.map.introspect.JacksonAnnotationIntrospector;class IgnoreBodyClassIntrospector extends JacksonAnnotationIntrospector {@Overridepublic 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"}
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