Jackson: How to edit existing property to the JSON without modifying the POJO?

问题

I need to edit the name of "existing field" in POJO instead of adding "extra_field". Is it possible with the approach referenced link below?

Please note I do not want to use @JsonProperty annotation.

Requirement is, I have a POJO and want to use different field name every time without change in POJO. For example I have a field c_id in POJO and some times it need to write as cust_id and another time it would be my_id.

Also note I cannot change implementation of POJO as it is already used in several modules and have generic implementation.

POJO Example:

class MyPojo {
    String id; 
    // getter and setters
}

Expected output can be the following: (name of field can be changed)

{"cust_id": "123"}
{"my_id": "123"}

回答1:

Mixins

The easiest way to modify the output of Jackson without adding annotations to the original POJO is using mixins.

Just define a mixin-class with the necessary annotations and indicate to Jackson that you want to use the mixin when serializing the original object.

private static class MyPojoMixin {
    @JsonProperty("cust_id")
    private String id;
}

public String serializeWithMixin(MyPojo p) throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    mapper.addMixIn(MyPojo.class, MyPojoMixin.class);

    return mapper.writeValueAsString(p);
}

Custom property naming strategy

If you need to programmatically change the field-name, you might not be able to use the mixin solution. You could then use a custom PropertyNamingStrategy:

public class IdRenamingStrategy extends PropertyNamingStrategy {
    private final PropertyNamingStrategy inner;
    private final String newIdPropertyName;

    public IdRenamingStrategy(String newIdPropertyName) {
        this(PropertyNamingStrategy.LOWER_CAMEL_CASE, newIdPropertyName);
    }

    public IdRenamingStrategy(PropertyNamingStrategy inner, String newIdPropertyName) {
        this.inner = inner;
        this.newIdPropertyName = newIdPropertyName;
    }

    private String translate(String propertyName) {
        if ("id".equals(propertyName)) {
            return newIdPropertyName;
        } else {
            return propertyName;
        }
    }

    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
        return inner.nameForField(config, field, translate(defaultName));
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return inner.nameForGetterMethod(config, method, translate(defaultName));
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return inner.nameForSetterMethod(config, method, translate(defaultName));
    }

    @Override
    public String nameForConstructorParameter(MapperConfig<?> config, AnnotatedParameter ctorParam, String defaultName) {
        return inner.nameForConstructorParameter(config, ctorParam, translate(defaultName));
    }
}

This can be used like this:

public String serializeWithPropertyNamingStrategy(MyPojo p) throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    mapper.setPropertyNamingStrategy(new IdRenamingStrategy("cust_id"));

    return mapper.writeValueAsString(p));
}

来源：https://stackoverflow.com/questions/62065614/jackson-how-to-edit-existing-property-to-the-json-without-modifying-the-pojo

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