The attribute @JsonDeserialize#as can be used to to deserialize to a specific subtype of declared type of a Java object.
When serializing, Jackson will by default use the specific runtime type, but during deserializing time Jackson cannot determined the actual intended runtime type of a super type without @JsonDeserialize#as .
Example
Java Object
In this example we will assign Number to BigDecimal before serialization.
package com.logicbig.example;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import java.math.BigDecimal;
public class CurrencyRate {
private String pair;
@JsonDeserialize(as = BigDecimal.class)
private Number rate;
.............
}
Main class
public class ExampleMain {
public static void main(String[] args) throws IOException {
System.out.println("-- Java object to JSON (serialization) --");
CurrencyRate cr = new CurrencyRate();
cr.setPair("USD/JPY");
cr.setRate(new BigDecimal(109.15).setScale(2, RoundingMode.CEILING));
System.out.println("Java object: " + cr);
ObjectMapper om = new ObjectMapper();
String s2 = om.writeValueAsString(cr);
System.out.println("JSON string: " + s2);
System.out.println("-- JSON to Java object (deserialization) --");
CurrencyRate cr2 = om.readValue(s2, CurrencyRate.class);
System.out.println("Java Object: " + cr2);
System.out.println("rate type: "+cr2.getRate().getClass());
}
} -- Java object to JSON (serialization) -- Java object: CurrencyRate{pair='USD/JPY', rate=109.16} JSON string: {"pair":"USD/JPY","rate":109.16} -- JSON to Java object (deserialization) -- Java Object: CurrencyRate{pair='USD/JPY', rate=109.16} rate type: class java.math.BigDecimal
Without @JsonDeserialize#as
If we don't use @JsonDeserialize(as = BigDecimal.class) i.e.
public class CurrencyRate {
private String pair;
private Number rate;
.....
}
then output will be:
-- Java object to JSON (serialization) --
Java object: CurrencyRate{pair='USD/JPY', rate=109.16}
JSON string: {"pair":"USD/JPY","rate":109.16}
-- JSON to Java object (deserialization) --
Java Object: CurrencyRate{pair='USD/JPY', rate=109.16}
rate type: class java.lang.Double
Example ProjectDependencies and Technologies Used: - jackson-databind 2.9.5: General data-binding functionality for Jackson: works on core streaming API.
- JDK 10
- Maven 3.3.9
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