Java Jackson XML Custom Deserializer

1. Introduction

While Jackson provides out-of-the-box capabilities to deserialize XML into Java objects, sometimes the default behavior may not suit the needs of a particular application. In such cases, you can create a custom deserializer to instruct Jackson on how to process the XML data. In this tutorial, we will demonstrate how to create a custom deserializer for XML content using Jackson.

2. Example Steps

1. Add the required Jackson XML library dependencies to your project.

2. Create a Java class (POJO) representing the structure of your XML data.

3. Implement a custom deserializer by extending StdDeserializer.

4. Annotate the target field in the POJO with @JsonDeserialize to use the custom deserializer.

5. Utilize XmlMapper to convert the XML string into a Java object.

6. Display the deserialized object to verify the custom deserialization.

3. Java Jackson XML Custom Deserializer

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

public class JacksonXmlCustomDeserializerExample {

    public static void main(String[] args) {
        try {
            // Sample XML content
            String xmlString = "<product><name>Laptop</name><price value=\"1200.5\"/></product>";

            // Instantiate XmlMapper
            XmlMapper xmlMapper = new XmlMapper();

            // Deserialize XML string to Product object
            Product product = xmlMapper.readValue(xmlString, Product.class);

            System.out.println("Deserialized Product: " + product);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    static class Product {
        private String name;
        @JsonDeserialize(using = PriceDeserializer.class)
        private double price;

        // Getters, setters, and toString method...
    }

    static class PriceDeserializer extends StdDeserializer<Double> {

        public PriceDeserializer() {
            super(Double.class);
        }

        @Override
        public Double deserialize(JsonParser parser, DeserializationContext context) throws IOException {
            // Extract the value attribute from the <price> XML tag
            return Double.parseDouble(parser.getAttributes().getValue("value"));
        }
    }
}

Output:

Deserialized Product: Product [name=Laptop, price=1200.5]

4. Step By Step Explanation

1. The Product class represents the structure of our XML data. The class has two fields, name and price. We intend to customize the deserialization for the price field.

2. The PriceDeserializer class is our custom deserializer. It extends StdDeserializer and overrides the deserialize method. Inside this method, we extract the value attribute from the <price> XML tag to obtain the price value.

3. The @JsonDeserialize annotation in the Product class informs Jackson to use our custom PriceDeserializer for deserializing the price field.

4. Using the XmlMapper, we deserialize the XML string into the Product object.

5. The deserialized object's details are then printed, and we can see that the custom deserialization was applied correctly.

This approach enables you to handle complex XML structures and convert them into Java objects using custom logic. It's a powerful way to deal with non-standard XML formats or when the XML representation doesn't map directly to the Java object structure.