使用未知属性反序列化 JSON Jackson

17 Mar 2025 | 4 分钟阅读

在本节中，我们将使用 Jackson 的 "2.x" 版本来介绍最重要的解组过程。目前，JSON 已被广泛用于表示数据。当我们处理具有未知属性的 JSON 数据并对其进行解组时，它将抛出 Unknown Property 异常。

让我们通过一个例子来了解如何使用附加/未知字段解组 JSON 数据。

使用附加或未知字段反序列化 JSON

在解组 JSON 时，JSON 数据的形状和大小可以是任意的。当我们将它映射到具有一组字段的预定义 Java 对象时，它可能会导致异常。当它在 Java 对象中找不到匹配的字段时，可能会发生异常。为了处理此异常，我们需要忽略无法映射到现有 Java 字段的 JSON 属性。

JSON 数据

{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\",\"expire\":\"10-11-2022\"}

Java 对象

class Product {  
//Creating properties of Product class  
    	private String proId;    
    	private String proName;    
    	private String price;
}

当我们将 JSON 反序列化为 Product 对象时，它将导致 com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.

DeserializeJSONWithUnknownFields1.java

//import required classes and package   
import java.io.IOException;    
import com.fasterxml.jackson.databind.ObjectMapper;    

//create class DeserializeJSONWithUnknownFields1 
public class DeserializeJSONWithUnknownFields1 {     
	//main() method start   
	public static void main(String args[]){  
		
		//create instance of ObjectMapper class   
		ObjectMapper mapper = new ObjectMapper();    
		try{   
            //deserialize JsonString   
			String jsonString = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\",\"expire\":\"10-11-2022\"}";    
            System.out.println(jsonString);    
              
            Product pro = mapper.readerFor(Product.class).readValue(jsonString);  
            System.out.println("Product Id: "+pro.getProId());  
            System.out.println("Product Name: "+pro.getName());  
            System.out.println("Product Price: "+pro.getPrice());  
	              
        } catch (IOException e) {    
            e.printStackTrace();    
        }   
    }   
}
class Product {  

//Creating properties of Product class  
    private String proId;    
    private String proName;    
    private String price;
    
    //Getter and Setters
    public String getProId() {  
        return proId;  
    }  
    public void setProId(String proId) {  
        this.proId = proId;  
    }  
    public String getName() {  
        return proName;  
    }  
    public void setProName(String name) {  
        this.proName = name;  
    }  
    public String getPrice() {  
        return price;  
    }  
    public void setPrice(String price) {  
        this.price = price;  
    }
    @Override    
    public String toString() {    
        // TODO Auto-generated method stub    
        return "\"Product [ProductId "+ proId + ", ProductName = " + proName + ", ProductPrice = " + price + "]";    
    }  
} 

输出

Deserializing JSON with Unknown Properties Jackson

现在，为了处理未知字段，我们将配置完整的 ObjectMapper 类以忽略 JSON 中的未知属性。我们按以下方式配置 ObjectMapper 类

new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)

现在，我们只需配置 ObjectMapper 类并将其添加到上述代码中即可。

DeserializeJSONWithUnknownFields2.java

//import required classes and package   
import java.io.IOException;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;    

//create class DeserializeJSONWithUnknownFields2 
public class DeserializeJSONWithUnknownFields2 {     
	//main() method start   
	public static void main(String args[]){  
		
		//create instance of ObjectMapper class   
		ObjectMapper mapper = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		
		try{   
			//deserialize JsonString   
			String jsonString = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\",\"expire\":\"10-11-2022\"}";    
			System.out.println(jsonString);    
            
			Product pro = mapper.readerFor(Product.class).readValue(jsonString);  
			System.out.println("Product Id: "+pro.getProId());  
			System.out.println("Product Name: "+pro.getName());  
			System.out.println("Product Price: "+pro.getPrice());  
	              
		} catch (IOException e) {    
			e.printStackTrace();    
		}   
	}   
}
class Product {  

	//Creating properties of Product class  
	private String proId;    
	private String proName;    
	private String price;
  
	//Getter and Setters
	public String getProId() {  
		return proId;  
	}  
	public void setProId(String proId) {  
		this.proId = proId;  
	}  
	public String getName() {  
		return proName;  
	}  
	public void setProName(String name) {  
		this.proName = name;  
	}  
	public String getPrice() {  
		return price;  
	}  
	public void setPrice(String price) {  
		this.price = price;  
	}
	@Override    
	public String toString() {    
		// TODO Auto-generated method stub    
		return "\"Product [ProductId "+ proId + ", ProductName = " + proName + ", ProductPrice = " + price + "]";    
	}  
}  

输出

还有另一种处理未知属性的方法，即通过在类级别使用 @JsonIgnoreProperties(ignoreUnknown = true) 注释，如下所示

@JsonIgnoreProperties(ignoreUnknown = true)
public class Product { ... }

当我们在类级别使用注释时，无需配置 ObjectMapper 类来忽略 JSON 属性。

DeserializeJSONWithUnknownFields3.java

//import required classes and package   
import java.io.IOException;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.databind.ObjectMapper;    

//create class DeserializeJSONWithUnknownFields3 
public class DeserializeJSONWithUnknownFields3 {     
	//main() method start   
	public static void main(String args[]){  
		
		//create instance of ObjectMapper class   
		ObjectMapper mapper = new ObjectMapper();
		
		try{   
			//deserialize JsonString   
			String jsonString = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\",\"expire\":\"10-11-2022\"}";    
			System.out.println(jsonString);    
          
			Product pro = mapper.readerFor(Product.class).readValue(jsonString);  
			System.out.println("Product Id: "+pro.getProId());  
			System.out.println("Product Name: "+pro.getName());  
			System.out.println("Product Price: "+pro.getPrice());  
	              
		} catch (IOException e) {    
			e.printStackTrace();    
		}   
	}   
}

// create class Product by using @JsonIgnoreProperties annotation 
@JsonIgnoreProperties(ignoreUnknown = true)
class Product {  

	//Creating properties of Product class  
	private String proId;    
	private String proName;    
	private String price;

	//Getter and Setters
	public String getProId() {  
		return proId;  
	}  
	public void setProId(String proId) {  
		this.proId = proId;  
	}  
	public String getName() {  
		return proName;  
	}  
	public void setProName(String name) {  
		this.proName = name;  
	}  
	public String getPrice() {  
		return price;  
	}  
	public void setPrice(String price) {  
		this.price = price;  
	}
	@Override    
	public String toString() {    
		// TODO Auto-generated method stub    
		return "\"Product [ProductId "+ proId + ", ProductName = " + proName + ", ProductPrice = " + price + "]";    
	}  
}  

输出