parameter-names

Jackson module that adds support for accessing parameter names; a feature added in JDK 8.

NOTE: only available for Jackson 2.x; functionality included in jackson-databind itself for Jackson 3.x.

Usage

Maven dependency

For maven dependency definition, click on the second badge in the previous, Status section.

Registering module

Like all standard Jackson modules (libraries that implement Module interface), registration is done as follows:

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new ParameterNamesModule());

after which functionality is available for all normal Jackson operations.

Delegating creator

By default, Jackson uses single argument constructors for mapping whole JSON value into value of the argument.

To override this behavior use the ParameterNamesModule constructor with JsonCreator.Mode parameter. For example, to use same behavior as for constructors with multiple parameters:

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new ParameterNamesModule(JsonCreator.Mode.PROPERTIES));

Usage example

Java 8 API adds support for accessing parameter names at runtime in order to enable clients to abandon the JavaBeans standard if they want to without forcing them to use annotations (such as JsonProperty).

So, after registering the module as described above, you will be able to use data binding with a class like

class Person {

    // mandatory fields
    private final String name;
    private final String surname;
    
    // optional fields
    private String nickname;

    // no annotations are required if preconditions are met (details below)
    public Person(String name, String surname) {

        this.name = name;
        this.surname = surname;
    }

    public String getName() {
        return name;
    }

    public String getSurname() {
        return surname;
    }

    public String getNickname() {
        return nickname;
    }

    public void setNickname(String nickname) {
        this.nickname = nickname;
    }
}

Preconditions:

• class Person must be compiled with Java 8 compliant compiler with option to store formal parameter names turned on (-parameters option). For more information about Java 8 API for accessing parameter names at runtime see this
• if there are multiple visible constructors and there is no default constructor, @JsonCreator is required to select constructor for deserialization
• if used with jackson-databind lower than 2.6.0, @JsonCreator is required. In practice, @JsonCreator is also often required with 2.6.0+ due to issues with constructor discovery that will be resolved in 2.7.
• if class Person has a single argument constructor, its argument needs to be annotated with @JsonProperty("propertyName"). This is to preserve legacy behavior, see FasterXML/jackson-databind/#1498

More

See Wiki for more information (javadocs, downloads).