Jackson jr is a compact alternative to full Jackson Databind component. It implements a subset of functionality, for example for cases where:
In addition to basic datatypes (core JDK types like List
s, Map
s, wrapper types),
package supports reading and writing of standard Java Beans (implementation that mimics standard
JDK Bean Introspection): that is,
subset of POJOs that define setters/getters (starting with Jackson-jr 2.8
)
you can alternatively use public
fields).
Jackson jr also adds composer
implementation that can be used to
construct JSON output with builder-style API, but without necessarily having
to build an in-memory representation: instead, it can directly use streaming-api
for direct output. It is also possible to build actual in-memory
JSON String
or byte[]
representation, if that is preferable.
Jackson jr artifact itself is currently about 95 kB in size, and only depends on Jackson Streaming API package. Combined size, for "all" jar, is about 400 kB (of which streaming API is about 300 kB), for use cases where a single jar is preferred over more modular approach. Finally, use of jar minimizers like ProGuard can bring the jar size down even further, by renaming and removing debug information.
Good old Apache License.
Project is composed of multiple Maven sub-modules, each corresponding to a jar:
jackson-core
for low-level reading/writingTreeCodec
implementation, with which it is possible to read JSON as TreeNode
s (see more below)jackson-jr
- based handlers for Retrofit 2 library
jackson-jr
and Retrofit
API jars, and indirectly on jackson-core
jr-objects
classes as-is, without relocatingjr-stree
classes as-is, without relocatingjackson-core
) contents relocated ("shaded"), for private use by jackson-jr
jr-retrofit2
or jr-annotation-support
componentsIf you are not sure which package to use, the answer is usually jr-objects
, and build system (maven, gradle) will fetch the dependency needed. jr-all
jar is only used if the single-jar deployment (self-contained, no external dependencies) is needed.
Functionality of this package is contained in Java package com.fasterxml.jackson.jr.ob
.
All functionality is accessed through main JSON
Object; you can either used singleton JSON.std
,
or construct individual objects -- either way, JSON
instances are ALWAYS immutable and hence thread-safe.
We can start by reading JSON
String INPUT = "{\"a\":[1,2,{\"b\":true},3],\"c\":3}";
Object ob = JSON.std.anyFrom(INPUT);
// or
Map<String,Object> map = JSON.std.mapFrom(INPUT);
// or
MyBean bean = JSON.std.beanFrom(MyBean.class, INPUT);
from any of the usual input sources (InputStream
, Reader
, String
or byte[]
that contains JSON, URL
,
JsonParser
); and can write same Objects as JSON:
String json = JSON.std.asString(map);
JSON.std.write(ob, new File("/tmp/stuff.json");
// and with indentation; but skip writing of null properties
byte[] bytes = JSON.std
.with(Feature.PRETTY_PRINT_OUTPUT)
.without(Feature.WRITE_NULL_PROPERTIES)
.asBytes(bean);
and may also read List
s and arrays of simple and Bean types:
List<MyType> beans = JSON.std.listOfFrom(MyType.class, INPUT);
(writing of List
s and arrays works without addition effort: just pass List/array as-is)
Version 2.10 added ability to read Streaming JSON content. See "Jackson 2.10 features" for an example.
[TO BE WRITTEN]
An alternative method exists for writing: "fluent" style output can be used as follows:
String json = JSON.std
.with(JSON.Feature.PRETTY_PRINT_OUTPUT)
.composeString()
.startObject()
.put("a", 1)
.startArrayField("arr")
.add(1).add(2).add(3)
.end()
.startObjectField("ob")
.put("x", 3)
.put("y", 4)
.startArrayField("args").add("none").end()
.end()
.put("last", true)
.end()
.finish();
would produce (since pretty-printing is enabled)
{
"a" : 1,
"arr" : [1,2,3],
"ob" : {
"x" : 3,
"y" : 4,
"args" : ["none"]
},
"last" : true
}
Jackson jr allows pluggable "tree models", and also provides one implementation, jr-stree
.
Usage for jr-stree
is by configuring JSON
with codec, and then using treeFrom
and write
methods
like so:
JSON json = JSON.std.with(new JacksonJrsTreeCodec());
TreeNode root = json.treeFrom("{\"value\" : [1, 2, 3]}");
assertTrue(root.isObject());
TreeNode array = root.get("value");
assertTrue(array.isArray());
JrsNumber n = (JrsNumber) array.get(1);
assertEquals(2, n.getValue().intValue());
String json = json.asString(root);
Note that jr-stree
implementation is a small minimalistic implementation with immutable
nodes. It is most useful for simple reading use cases.
It is however possible to write your own TreeCodec
implementations that integrate seamlessly,
and in future other tree models may be offered as part of jackson-jr, or via other libraries.
To support readability and writability of your own types, your Java objects must either:
long
or Long
argument)Note that although getters and setters need to be public (since JDK Bean Introspection does not find any other methods),
constructors may have any access right, including private
.
Also: starting with version 2.8, public
fields may also be used (although their
discovery may be disabled using JSON.Feature.USE_FIELDS
) as an alternative:
this is useful when limiting number of otherwise useless "getter" and "setter"
methods.
There are many customizable features you can use with JSON
object; see Full List of Features for details. But usage itself is via fluent methods like so:
String json = JSON.std
.with(JSON.Feature.PRETTY_PRINT_OUTPUT)
.without(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS)
.asString(...);
Version 2.10 added ability to add custom ValueReader
s and ValueWriter
s, to
allow pluggable support for types beyond basic JDK types and Beans.
You can check this unit test
jr-objects/src/test/java/com/fasterxml/jackson/jr/ob/impl/CustomValueReadersTest.java
for an example.
[TO BE COMPLETED]
You can use Maven dependency like:
<dependency>
<groupId>com.fasterxml.jackson.jr</groupId>
<artifactId>jackson-jr-objects</artifactId>
<version>2.9.0</version>
</dependency>
and then you can also download jars via Central Maven repository.
Or you can also clone the project and build it locally with mvn clean install
.
Alternatively if you want a single jar deployment, you can use jackson-jr-all
jar which embeds jackson-core
(repackaged using Shade plug-in, so as not to conflict with "vanilla" jackson-core
):
http://repo1.maven.org/maven2/com/fasterxml/jackson/jr/jackson-jr-all/
Initial performance testing using JVM Serializers benchmark suggests that it is almost as fast as full Jackson databind -- additional overhead for tests is 5-10% for both serialization and deserialization. So performance is practically identical.
In fact, when only handling List
s and Map
s style content, speed jackson-jr
speed fully matches jackson-databind
performance (Bean/POJO case is where full databinding's extensive optimizations help more).
So performance should be adequate, and choice should be more based on functionality, convenience and
deployment factors.
About the only thing missing is that there is no equivalent to Afterburner, which can further speed up databind by 20-30%, for most performance-sensitive systems.