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如何在映射到Java对象时忽略几个JSON元素

spring-boot spring json java

user08152017 · 技术社区 · 5 年前

我的Spring引导服务处理一个JSON,如下所示

"Books":[
  {
   "Title": "Title1",
   "Author": "Author1"
  },
  {
   "Title": "Title2",
   "Author": "Author2"
  },
  {
   "Title": "IGNORE",
   "Author": "IGNORE"
  }
]

我有一本书

public class Book{
  @JsonProperty("Title")
  private String title;
  @JsonProperty("Author")
  private String author;

  public setters & Getters
  ....
}

这些书被映射到MyFavBooks.java

public class MyFavBooks{
  @JsonProperty("Books")
  private Book[] books;
  ....
}

我试图不映射以下元素(基于标题)。有没有办法做到这一点?

{
   "Title": "IGNORE",
   "Author": "IGNORE"
}

2 回复 | 直到 5 年前

ILya Cyclone 5 年前

您可以尝试使用自定义序列化程序 @JsonSerialize . 大概是这样的:

public class Book{
  @JsonProperty("Title")
  @JsonSerialize(using = IgnoreSerializer.class)
  private String title;

  @JsonProperty("Author")
  @JsonSerialize(using = IgnoreSerializer.class)
  private String author;

  public setters & Getters
  ....
}

public class IgnoreSerializer extends JsonSerializer<String> {

    @Override
    public void serialize(String s, 
                          JsonGenerator jsonGenerator, 
                          SerializerProvider serializerProvider) 
                          throws IOException, JsonProcessingException {
        if(!s.equals("IGNORE")) {
            jsonGenerator.writeObject(s);
        }
    }
}

或者,如果需要基于标题值跳过整个项目,请使用相同的方法定义自定义序列化程序在你的书本课上。

@JsonSerialize(using = IgnoreByTitleSerializer.class)
public class Book{ ... }

class IgnoreByTitleSerializer extends StdSerializer<Book> {
...
@Override
    public void serialize(
      Book book, JsonGenerator jgen, SerializerProvider provider) 
      throws IOException, JsonProcessingException {
        if(!book.getTitle().equals("IGNORE") {
            ...
        }
    }
}

看见 https://www.baeldung.com/jackson-custom-serialization 例如

upd
正如Dmitry Bogdanovich公正地提到的,这个问题涉及反序列化,所以我相信您可以使用类似的方法 @JsonDeserialize .

Jeff I 5 年前

例子:

import java.io.IOException;

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.gson.Gson;

public class Book {
    private String title;
    private String author;

    @JsonIgnore
    private transient String isbn;


    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    public String getIsbn() {
        return isbn;
    }
    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    private static void printGson(Book book) {
        System.out.println("Gson: " + new Gson().toJson(book));
    }

    private static void printJackson(Book book) {
        ObjectMapper objectMapper = new ObjectMapper();

        try {
            System.out.print("Jackson: ");
            objectMapper.writeValue(System.out, book);
        } catch (JsonGenerationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        Book book = new Book();
        book.setAuthor("Me");
        book.setTitle("Cool");
        book.setIsbn("123");
        printGson(book);
        printJackson(book);
    }
}

输出:

Gson: {"title":"Cool","author":"Me"}
Jackson: {"title":"Cool","author":"Me"}