使用Jackson进行不对称序列化和反序列化

问题描述

我正在使用Jackson为RESTful API序列化和反序列化数据。我想要一个REST资源（ / comments ），它允许POST注释以及获取注释列表。

以下是发布到 / comments 的内容的简化示例。

  {text：Text，author：Paul，email：[email protected]} 
  

以下是 GET / comments 的结果应如下所示：

  [{text：Text，author：Paul，emailHash：76w0kjKP9HpsdhBjx895Sg ==}] 
  

由于电子邮件地址不应该对任何人可见，我决定只返回响应中电子邮件地址的MD5哈希。 / p>

我创建了一个简单的POJO类 Comment ，其中包含带有文本的getter和setter的字段， author ， email ， emailHash 。

现在，当我序列化结果时，得到的结果如下：

  [{ text：Text，author：Paul，email：null，emailHash：76w0kjKP9HpsdhBjx895Sg ==}] 
  

但我真的不喜欢将电子邮件作为 null 这里。它根本不应该被包括在内。

在该字段上使用注释 @JsonIgnore 也将忽略它关于反序列化。我是否必须使用超类注释创建两个类，例如 CreationComment 和 ResultComment 分享公共字段还是有办法避免创建其他类？

解决方案

你不要必须创建2个类。使用Jackson，您可以在序列化和反序列化期间使用注释完全控制属性的行为，在getter中使用 @JsonIgnore 可以防止在Json响应中序列化属性在setter中使用 @JsonProperty 注释，在反序列化期间将设置该属性。代码如下所示：

  import com.fasterxml.jackson.annotation.JsonIgnore; 
 import com.fasterxml.jackson.annotation.JsonProperty; 
 import com.fasterxml.jackson.databind.ObjectMapper; 
 
公共类评论{
 
 private String author; 
 
 private String email; 
 
 @JsonIgnore 
 public String getEmail（）{
 return email; 
} 
 
 @JsonProperty 
 public void setEmail（String email）{
 this.email = email; 
} 
 
 public String getAuthor（）{
 return author; 
} 
 
 public void setAuthor（String author）{
 this.author = author; 
} 
 
 public static void main（String [] args）{
 ObjectMapper objectMapper = new ObjectMapper（）; 
 
评论comment = new评论（）; 
 comment.setAuthor（anAuthor）; 
 comment.setEmail（[email protected]）; 
 
 try {
 System.out.println（objectMapper.writeValueAsString（comment））; 
 
 String json ={\author \：\anAuthor\，\email \：\[email protected]\} ; 
来自于Json = objectMapper.readValue（json，Comment.class）的评论; 
 
 System.out.println（来自Json的结果：author =+ fromJson.getAuthor（）+，email =+ fromJson.getEmail（））; 
 
} catch（例外e）{
 e.printStackTrace（）; 
} 
 
} 
} 
  

输出在运行 main（）方法来测试解决方案后：

{author ：anAuthor}

Json的结果：author = anAuthor，email = [email protected]

希望有所帮助，

Jose Luis

I am using Jackson to serialize and deserialize data for a RESTful API. I'd like to have a REST resource (/comments) that allows to POST comments as well as to GET a list of comments.

Here's a (simplified) example of what gets posted to /comments.

{"text":"Text","author":"Paul","email":"[email protected]"}

Here's what the result of GET /comments should look like:

[{"text":"Text","author":"Paul","emailHash":"76w0kjKP9HpsdhBjx895Sg=="}]

Since email addresses shouldn't be visible to anyone, I decided to return only a MD5 hash of the email addresses in the response.

I have created a simple POJO class Comment that has fields with getters and setters for text, author, email, and emailHash.

Now, when I serialize the result, what I get is the following:

[{"text":"Text","author":"Paul","email":null,"emailHash":"76w0kjKP9HpsdhBjx895Sg=="}]

But I really don't like email to be returned as null here. It rather shouldn't be included at all.

Using the annotation @JsonIgnore on that field will also ignore it on deserialization. Do I have to create two classes, say CreationComment and ResultComment with a super-class Comment that shares common fields or is there a way that avoids creating additional classes?

解决方案

You don't have to create 2 classes at all. With Jackson you have full control of the behavior of a property during serialization and deserialization using annotations, with @JsonIgnorein the getter you prevent the property from being serialized in your Json response and using @JsonProperty annotation in the setter the property will be set during deserialization. The code will look like this:

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Comment {

    private String author;

    private String email;

    @JsonIgnore
    public String getEmail() {
        return email;
    }

    @JsonProperty
    public void setEmail(String email) {
        this.email = email;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();

        Comment comment = new Comment();
        comment.setAuthor("anAuthor");
        comment.setEmail("[email protected]");

        try {
            System.out.println(objectMapper.writeValueAsString(comment));

            String json = "{\"author\":\"anAuthor\",\"email\":\"[email protected]\"}";
            Comment fromJson = objectMapper.readValue(json, Comment.class);

            System.out.println("Result from Json: author= " + fromJson.getAuthor() + ", email= " + fromJson.getEmail());

        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

The output after running the main() method to test the solution:

{"author":"anAuthor"}

Result from Json: author= anAuthor, email= [email protected]

Hope it helps,

Jose Luis

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