jackson反序列化json到java-objects [英] jackson deserialization json to java-objects

问题描述

这是我的Java代码，用于反序列化，
我试图将json字符串转换为java对象。在这样做时，我使用了以下代码：

Here is my Java code which is used for the de-serialization, i am trying to convert json string into java object. In doing so i have used the following code:

package ex1jackson;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
public class Ex1jackson {
public static void main(String[] args) {
   ObjectMapper mapper = new ObjectMapper();
try {
        String userDataJSON = "[{\"id\":\"value11\",\"name\": \"value12\",\"qty\":\"value13\"},"
                              + "{\"id\": \"value21\",\"name\":\"value22\",\"qty\": \"value23\"}]";
        product userFromJSON = mapper.readValue(userDataJSON, product.class);
        System.out.println(userFromJSON);
    } catch (JsonGenerationException e) {
        System.out.println(e);
        } catch (JsonMappingException e) {
       System.out.println(e);
    } catch (IOException e) {
    System.out.println(e);
    } 
}
}

和我的product.java类

and my product.java class

package ex1jackson;
public class product 
{
private String id;
private String name; 
private String qty; 

@Override
public String toString() {
    return "Product [id=" + id+ ", name= " + name+",qty="+qty+"]";
}
}

我收到以下错误。

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: 
Unrecognized field "id" (class ex1jackson.product), not marked as ignorable (0 known properties: ]) at 
[Source: java.io.StringReader@16f76a8; line: 1, column: 8] (through reference chain: ex1jackson.product["id"]) 
BUILD SUCCESSFUL (total time: 0 seconds)

帮我解决这个问题，

推荐答案

看起来你好像是尝试从JSON中读取实际描述数组的对象。 Java对象使用大括号 {} 映射到JSON对象，但是您的JSON实际上以方括号 [] 开头指定数组。

It looks like you are trying to read an object from JSON that actually describes an array. Java objects are mapped to JSON objects with curly braces {} but your JSON actually starts with square brackets [] designating an array.

实际拥有的是 List< product> 描述泛型类型，因为Java的类型擦除，您必须使用 TypeReference 。您的反序列化可以是： myProduct = objectMapper.readValue（productJson，new TypeReference< List< product>>（）{}）;

What you actually have is a List<product> To describe generic types, due to Java's type erasure, you must use a TypeReference. Your deserialization could read: myProduct = objectMapper.readValue(productJson, new TypeReference<List<product>>() {});

其他一些注释：你的课程应该始终是CamelCased。你的main方法可以只是 public static void main（String [] args）抛出异常这可以节省你所有无用的 catch 块。

A couple of other notes: your classes should always be CamelCased. Your main method can just be public static void main(String[] args) throws Exception which saves you all the useless catch blocks.

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