com.fasterxml.jackson.annotation.JsonTypeInfo Maven / Gradle / Ivy
package com.fasterxml.jackson.annotation;
import java.lang.annotation.*;
/**
* Annotation used for configuring details of if and how type information is
* used with JSON serialization and deserialization, to preserve information
* about actual class of Object instances. This is necessarily for polymorphic
* types, and may also be needed to link abstract declared types and matching
* concrete implementation.
*
* Some examples of typical annotations:
*
* // Include Java class name ("com.myempl.ImplClass") as JSON property "class"
* @JsonTypeInfo(use=Id.CLASS, include=As.PROPERTY, property="class")
*
* // Include logical type name (defined in impl classes) as wrapper; 2 annotations
* @JsonTypeInfo(use=Id.NAME, include=As.WRAPPER_OBJECT)
* @JsonSubTypes({com.myemp.Impl1.class, com.myempl.Impl2.class})
*
* Alternatively you can also define fully customized type handling by using
* @JsonTypeResolver annotation (from databind package).
*
* This annotation can be used both for types (classes) and properties.
* If both exist, annotation on property has precedence, as it is
* considered more specific.
*
* When used for properties (fields, methods), this annotation applies
* to values: so when applied to structure types
* (like {@link java.util.Collection}, {@link java.util.Map}, arrays),
* will apply to contained values, not the container;
* for non-structured types there is no difference.
* This is identical to how JAXB handles type information
* annotations; and is chosen since it is the dominant use case.
* There is no per-property way to force type information to be included
* for type of container (structured type); for container types one has
* to use annotation for type declaration.
*
* Note on visibility of type identifier: by default, deserialization
* (use during reading of JSON) of type identifier
* is completely handled by Jackson, and is not passed to
* deserializers. However, if so desired,
* it is possible to define property visible = true
* in which case property will be passed as-is to deserializers
* (and set via setter or field) on deserialization.
*
* On serialization side, Jackson will generate type id by itself,
* except if there is a property with name that matches
* {@link #property()}, in which case value of that property is
* used instead.
*
* NOTE: use of type id of "class name" with very general base type
* (such as {@link java.lang.Object} or {@link java.io.Serializable})
* can potentially open up security holes if deserializing content
* generated by untrusted sources. If content can not be trusted,
* it is necessary to either use "type name" as type id, or to
* limit possible types using other means.
*/
@Target({ElementType.ANNOTATION_TYPE, ElementType.TYPE,
ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonTypeInfo
{
/*
/**********************************************************
/* Value enumerations used for properties
/**********************************************************
*/
/**
* Definition of different type identifiers that can be included in JSON
* during serialization, and used for deserialization.
*/
public enum Id {
/**
* This means that no explicit type metadata is included, and typing is
* purely done using contextual information possibly augmented with other
* annotations.
*/
NONE(null),
/**
* Means that fully-qualified Java class name is used as the type identifier.
*/
CLASS("@class"),
/**
* Means that Java class name with minimal path is used as the type identifier.
* Minimal means that only the class name, and that part of preceding Java
* package name is included that is needed to construct fully-qualified name
* given fully-qualified name of the declared supertype; additionally a single
* leading dot ('.') must be used to indicate that partial class name is used.
* For example, for supertype "com.foobar.Base", and concrete type
* "com.foo.Impl", only ".Impl" would be included; and for "com.foo.impl.Impl2"
* only ".impl.Impl2" would be included.
*
* NOTE: leading dot ('.') MUST be used to denote partial (minimal) name;
* if it is missing, value is assumed to be fully-qualified name. Fully-qualified
* name is used in cases where subtypes are not in same package (or sub-package
* thereof) as base class.
*
* If all related classes are in the same Java package, this option can reduce
* amount of type information overhead, especially for small types.
* However, please note that using this alternative is inherently risky since it
* assumes that the
* supertype can be reliably detected. Given that it is based on declared type
* (since ultimate supertype, java.lang.Object would not be very
* useful reference point), this may not always work as expected.
*/
MINIMAL_CLASS("@c"),
/**
* Means that logical type name is used as type information; name will then need
* to be separately resolved to actual concrete type (Class).
*/
NAME("@type"),
/**
* Means that typing mechanism uses customized handling, with possibly
* custom configuration. This means that semantics of other properties is
* not defined by Jackson package, but by the custom implementation.
*/
CUSTOM(null)
;
private final String _defaultPropertyName;
private Id(String defProp) {
_defaultPropertyName = defProp;
}
public String getDefaultPropertyName() { return _defaultPropertyName; }
}
/**
* Definition of standard type inclusion mechanisms for type metadata.
* Used for standard metadata types, except for {@link Id#NONE}.
* May or may not be used for custom types ({@link Id#CUSTOM}).
*/
public enum As {
/**
* Inclusion mechanism that uses a single configurable property, included
* along with actual data (POJO properties) as a separate meta-property.
*
* Default choice for inclusion.
*/
PROPERTY,
/**
* Inclusion mechanism that wraps typed JSON value (POJO
* serialized as JSON) in
* a JSON Object that has a single entry,
* where field name is serialized type identifier,
* and value is the actual JSON value.
*
* Note: can only be used if type information can be serialized as
* String. This is true for standard type metadata types, but not
* necessarily for custom types.
*/
WRAPPER_OBJECT,
/**
* Inclusion mechanism that wraps typed JSON value (POJO
* serialized as JSON) in
* a 2-element JSON array: first element is the serialized
* type identifier, and second element the serialized POJO
* as JSON Object.
*/
WRAPPER_ARRAY,
/**
* Inclusion mechanism similar to PROPERTY, except that
* property is included one-level higher in hierarchy, i.e. as sibling
* property at same level as JSON Object to type.
* Note that this choice can only be used for properties, not
* for types (classes). Trying to use it for classes will result in
* inclusion strategy of basic PROPERTY instead.
*/
EXTERNAL_PROPERTY,
/**
* Inclusion mechanism similar to PROPERTY with respect
* to deserialization; but one that is produced by a "regular" accessible
* property during serialization. This means that TypeSerializer
* will do nothing, and expects a property with defined name to be output
* using some other mechanism (like default POJO property serialization, or
* custom serializer).
*
* Note that this behavior is quite similar to that of using {@link JsonTypeId}
* annotation;
* except that here TypeSerializer is basically suppressed;
* whereas with {@link JsonTypeId}, output of regular property is suppressed.
* This mostly matters with respect to output order; this choice is the only
* way to ensure specific placement of type id during serialization.
*
* @since 2.3.0 but databind only since 2.5.0.
*/
EXISTING_PROPERTY
;
}
/*
/**********************************************************
/* Annotation properties
/**********************************************************
*/
/**
* Specifies kind of type metadata to use when serializing
* type information for instances of annotated type
* and its subtypes; as well as what is expected during
* deserialization.
*/
public Id use();
/**
* Specifies mechanism to use for including type metadata (if any; for
* {@link Id#NONE} nothing is included); used when serializing,
* and expected when deserializing.
*
* Note that for type metadata type of {@link Id#CUSTOM},
* this setting may or may not have any effect.
*/
public As include() default As.PROPERTY;
/**
* Property names used when type inclusion method ({@link As#PROPERTY}) is used
* (or possibly when using type metadata of type {@link Id#CUSTOM}).
* If POJO itself has a property with same name, value of property
* will be set with type id metadata: if no such property exists, type id
* is only used for determining actual type.
*
* Default property name used if this property is not explicitly defined
* (or is set to empty String) is based on
* type metadata type ({@link #use}) used.
*/
public String property() default "";
/**
* Optional property that can be used to specify default implementation
* class to use for deserialization if type identifier is either not present,
* or can not be mapped to a registered type (which can occur for ids,
* but not when specifying explicit class to use).
* Property has no effect on choice of type id used for serialization;
* it is only used in deciding what to do for otherwise unmappable cases.
*
* Note that while this property allows specification of the default
* implementation to use, it does not help with structural issues that
* may arise if type information is missing. This means that most often
* this is used with type-name -based resolution, to cover cases
* where new sub-types are added, but base type is not changed to
* reference new sub-types.
*
* There are certain special values that indicate alternate behavior:
*
* - {@link java.lang.Void} means that objects with unmappable (or missing)
* type are to be mapped to null references.
* For backwards compatibility (2.5 and below), value of
*
com.fasterxml.jackson.databind.annotation.NoClass is also allowed
* for such usage.
*
* - Placeholder value of {@link JsonTypeInfo} (that is, this annotation type
* itself} means "there is no default implementation" (in which
* case an error results from unmappable type).
* For backwards compatibility with earlier versions (2.5 and below),
* value of {@link JsonTypeInfo.None} may also be used.
*
*
*/
public Class defaultImpl() default JsonTypeInfo.class;
/**
* Property that defines whether type identifier value will be passed
* as part of JSON stream to deserializer (true), or handled and
* removed by TypeDeserializer (false).
* Property has no effect on serialization.
*
* Default value is false, meaning that Jackson handles and removes
* the type identifier from JSON content that is passed to
* JsonDeserializer.
*
* @since 2.0
*/
public boolean visible() default false;
// 19-Dec-2014, tatu: Was hoping to implement for 2.5, but didn't quite make it.
// Hope for better luck with 2.8 or later
/**
* Property that defines whether type serializer is allowed to omit writing
* of type id, in case that value written has type same as {@link #defaultImpl()}.
* If true, omission is allowed (although writer may or may not be able to do that);
* if false, type id should always be written still.
*
* @since 2.5
public boolean skipWritingDefault() default false;
/*
/*
/**********************************************************
/* Helper classes
/**********************************************************
*/
/**
* This marker class that is only to be used with defaultImpl
* annotation property, to indicate that there is no default implementation
* specified.
*
* @deprecated Since 2.5, use any Annotation type (such as {@link JsonTypeInfo},
* if such behavior is needed; this is rarely necessary.
*/
@Deprecated
public abstract static class None { }
}