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Jackson Release 2.7

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Tatu Saloranta edited this page Jul 5, 2016 · 83 revisions

Version 2.7 development started in August 2015; and the first official release happened on January 10, 2016.

New Modules, status changes

  • New datatype module: jackson-datatype-pcollections
  • Kotlin module become official with 2.7.2, as that is the first version based on the official Kotlin 1.0

Patches

Beyond initial 2.7.0 (described here), following patch releases have been made or are planned:

Changes: compatibility

Starting with 2.7, JDK baseline will be Java 7 / JDK 7, with following exceptions:

  • jackson-annotations and jackson-core (streaming) will remain Java 6
  • No new language features are yet used (diamond pattern, try-with-resources); only JDK types
  • All JDK 7 types are accessed dynamically
    • Deserializer for java.nio.file.Path
    • Handling of new annotations under java.beans: @ConstructorProperties, @Transient via JacksonAnnotationIntrospector, but

So it should still be possible to use Jackson 2.7 on Java 6, but not compile, build.

With Jackson 2.8, Java 7 languages features will be allowed

Implemented major features

Add support for dataformat-specific features

With Jackson 2.6, ObjectReader allows passing of JsonParser.Feature overrides, and ObjectWriter similarly JsonGenerator.Feature overrides. But there are some format-specific features for formats like CSV which were not being passed before 2.7.

Since ObjectReader and ObjectWriter are not easy to sub-class (an attempt to do so pointed out a few inconvenient quirks Java typing would impose), it would be most convenient to be able to pass opaque bitflags to actual parser/generator implementation, and this is what has been added.

Fix (generic) type resolution mechanism

While Jackson has the best support for generic types of all Java JSON libraries, there are certain tricky edge cases that do not work. Specifically, type variable aliasing (case where variable name like T binds to different types at different points in hierarchy) is not correctly resolved, as variable binding is constructed globally and not hierarchically.

java-classmate library which was built based on my experiences with Jackson does handle all these cases correctly (to my knowledge), and could be used as a blueprint for improved system. It can not necessarily be used directly because Jackson's type system is more complicated and adds semantics that classmate does not use (like Map and Collection types being special), but should help as an example.

Revert back expansion of NON_EMPTY handling

Although the intent has always been that Include.NON_EMPTY would apply not just to empty arrays, Collections , Maps and Strings, to include things like numbers with default values (0 for int, for example). But since many JsonSerializers did NOT properly check for these conditions, before Jackson 2.6 NON_EMPTY exclusion did not work as extensively as intended, and many users came to depend on this specific behavior.

With 2.6 serializers were improved to handle "emptiness" as originally envisioned. This confused some of users, leading to confusion and frustration on what seemed like arbitrary changes.

After lengthy discussions over this issue, it seems that instead of using extended definition of what is empty, it makes more sense to use another value, NON_DEFAULT for such concept, and keep NON_EMPTY to strictly ONLY exclude:

  • Anything that is null (that is, a superset of NON_NULL)
  • Anything that is "absent" (for Optionals and other "Reference Types" -- superset of NON_ABSENT)
  • Empty container types with no elements:
    • java.util.Collection
    • java.util.Map
    • Java arrays
  • Empty Strings

With that, NON_DEFAULT will have two modes:

  • When applied on containing class, it will try to compare actual defaults values of the POJO for given properties
  • Otherwise (when NON_DEFAULT is either default global or per-type value; or used as per-property override), use per-type criteria, where:
    • anything that would be considered "empty" is excluded, but also
    • default values for primitives (like 0 for int) and their wrappers (Integer.valueOf(0) for Integer) are also excluded

Changes, core

Annotations

  • #37: Add @JsonClassDescription
  • #77: Add a new ObjectIdGenerator, StringIdGenerator, to allow arbitrary String Object Id usage
  • Major rewrite of merging of JsonFormat.Value and JsonInclude.Value, to allow for better multi-level defaults (global, per-type, property)

Streaming

  • #37: JsonParser.getTokenLocation() doesn't update after field names
  • #198: Add back-references to JsonParser / JsonGenerator for low-level parsing issues (via JsonParseException, JsonGenerationException)
  • #211: Fix typo of function name com.fasterxml.jackson.core.Version.isUknownVersion() (add isUnknownVersion(), deprecated misspelled variant)
  • #229: Array element and field token spans include previous comma.

Databind

  • 76: Problem handling datatypes Recursive type parameters
  • 819: Add support for setting FormatFeature via ObjectReader, ObjectWriter
  • 905: Add support for @ConstructorProperties
  • 909: Rename PropertyNamingStrategy CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES as SNAKE_CASE, PASCAL_CASE_TO_CAMEL_CASE as UPPER_CAMEL_CASE
  • 918: Add MapperFeature.ALLOW_EXPLICIT_PROPERTY_RENAMING
  • 948: Support leap seconds, any number of millisecond digits for ISO-8601 Dates.
  • 952: Revert non-empty handling of primitive numbers wrt NON_EMPTY; make NON_DEFAULT use extended criteria
  • 957: Merge datatype-jdk7 stuff in (java.nio.file.Path handling)
  • 959: Schema generation: consider active view, discard non-included properties
  • 963: Add PropertyNameStrategy KEBAB_CASE
  • 997: Add MapperFeature.OVERRIDE_PUBLIC_ACCESS_MODIFIERS
  • 998: Allow use of NON_DEFAULT for POJOs without default constructor
  • 1000: Add new mapping exception type for enums and UUIDs
  • 1010: Support for array delegator
  • 1044: Add AnnotationIntrospector.resolveSetterConflict(...) to allow custom setter conflict resolution

Changes, Data formats

Avro

  • #21: Add AVRO_BUFFERING feature for AvroParser, AvroGenerator (enabled by default, same as existing pre-2.7 behavior)

CSV

  • #81: Add alternative way to configure 'wrap-as-array', as CsvParser feature
  • #89: Allow choice of using header-line declaration to reorder columns of explicit schema, with CsvSchema.setReorderColumns
  • #92: Allow multi-character separator values
  • #94: Change schema/mapping related JsonParseExceptions to proper JsonMappingExceptions
  • #95: Add CsvParser.Feature.IGNORE_TRAILING_UNMAPPABLE to allow skipping of all extra, unmappable columns
  • #97: Verify CSV headers are in the order as expected (added strictHeaders property in CsvSchema)
  • #103: JsonGenerator.Feature.IGNORE_UNKNOWN does not prevent error when writing structured values
  • #106: Null fields are always ignored when serializing list of
  • #109: Allow specifying (via CsvSchema) a way to map "extra" columns into specific key (to use via any setter)

Protobuf

  • #11: dd Support for Generating Protobuf Schema From POJO Definition

XML

  • #156: Add XmlMapper.setDefaultUseWrapper() for convenience.
  • #167: Exception on deserializing empty element with an xsi attribute
  • #169: Fail to deserialize "empty" polymorphic classes
  • #180: Problem with deserialization of nested non-wrapped lists, with empty inner list

YAML

  • 38: Add MINIMIZE_QUOTES generator feature
  • 50: Lack of SnakeYAML Resolver leaves some missing features

Changes, Datatypes

Guava

  • #79: New configuration for Guava Range default bound type.

Java8 Date/time

  • #54: LocalDateTimeSerializer default constructor should use the same formatter as LocalDateTimeDeserializer

Changes, JAX-RS

Changes, other modules

JAXB Annotations

  • #52: Add a feature in JaxbAnnotationIntrospector to define meaning of nillable=false as "JsonInclude.NON_EMPTY"

JSON Schema

  • #80: Support NumberFormat#multipleOf
  • #81: Deserialize ArrayItems and JsonValueFormat correctly
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