com.fasterxml.jackson.annotation.JsonCreator Maven / Gradle / Ivy
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package com.fasterxml.jackson.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Marker annotation that can be used to define constructors and factory
* methods as one to use for instantiating new instances of the associated
* class.
*
* NOTE: when annotating creator methods (constructors, factory methods),
* method must either be:
*
* - Single-argument constructor/factory method without {@link JsonProperty}
* annotation for the argument: if so, this is so-called "delegate creator",
* in which case Jackson first binds JSON into type of the argument, and
* then calls creator. This is often used in conjunction with {@link JsonValue}
* (used for serialization).
*
* - Constructor/factory method where every argument is annotated with
* either {@link JsonProperty} or {@link JacksonInject}, to indicate name
* of property to bind to
*
*
* Also note that all {@link JsonProperty} annotations must specify actual name
* (NOT empty String for "default") unless you use one of extension modules
* that can detect parameter name; this because default JDK versions before 8
* have not been able to store and/or retrieve parameter names from bytecode.
* But with JDK 8 (or using helper libraries such as Paranamer, or other JVM
* languages like Scala or Kotlin), specifying name is optional.
*
* One common use case is to use a delegating Creator to construct instances from
* scalar values (like java.lang.String) during deserialization,
* and serialize values using {@link JsonValue}.
*
* NOTE: As of Jackson 2.6, use of {@link JsonProperty#required()} is supported
* for Creator methods (but not necessarily for regular setters or fields!).
*
* @see JsonCreator
*/
@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD, ElementType.CONSTRUCTOR})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonCreator
{
/**
* Property that is used to indicate how argument(s) is/are bound for creator,
* in cases there may be multiple alternatives. Currently the one case is that
* of a single-argument creator method, for which both so-called "delegating" and
* "property-based" bindings are possible: since
* delegating mode can not be used for multi-argument creators, the only choice
* there is "property-based" mode.
* Check {@link Mode} for more complete explanation of possible choices.
*
* Default value of {@link Mode#DEFAULT} means that caller is to use standard
* heuristics for choosing mode to use.
*
* @since 2.5
*/
public Mode mode() default Mode.DEFAULT;
/**
* @since 2.5
*/
public enum Mode {
/**
* Pseudo-mode that indicates that caller is to use default heuristics for
* choosing mode to use. This typically favors use of delegating mode for
* single-argument creators that take structured types.
*/
DEFAULT,
/**
* Mode that indicates that if creator takes a single argument, the whole incoming
* data value is to be bound into declared type of that argument; this "delegate"
* value is then passed as the argument to creator.
*/
DELEGATING,
/**
* Mode that indicates that the argument(s) for creator are to be bound from matching
* properties of incoming Object value, using creator argument names (explicit or implicit)
* to match incoming Object properties to arguments.
*
* Note that this mode is currently (2.5) always used for multiple-argument creators;
* the only ambiguous case is that of a single-argument creator.
*/
PROPERTIES,
/**
* Pseudo-mode that indicates that creator is not to be used. This can be used as a result
* value for explicit disabling, usually either by custom annotation introspector,
* or by annotation mix-ins (for example when choosing different creator).
*/
DISABLED
}
}