ig-json-parser

Fast JSON parser for java projects.

Getting started

The easiest way to get started is to look at maven-example. For more comprehensive examples, check out the unit tests or the demo.

Gradle

For Java projects, to use this library, add this to your build.gradle file:

allprojects {
  repositories {
    maven { url 'https://jitpack.io' }
  }
}

...

dependencies {
  implementation 'com.github.instagram.ig-json-parser:runtime:master-SNAPSHOT' // the runtime
  implementation 'com.github.instagram.ig-json-parser:processor:master-SNAPSHOT' // the annotation processor
}

For Android projects using Android Studio 3.0+ or Gradle 4.0+, you can enable the annotation processor as following:

allprojects {
  repositories {
    maven { url 'https://jitpack.io' }
  }
}

...

dependencies {
  annotationProcessor 'com.github.instagram.ig-json-parser:processor:master-SNAPSHOT'
  implementation 'com.github.instagram.ig-json-parser:runtime:master-SNAPSHOT'
}

If you are using older gradle versions, you can use old apt plugin to integrate the annotation processor:

allprojects {
  repositories {
    maven { url 'https://jitpack.io' }
  }
}

...

apply plugin: 'com.neenbedankt.android-apt'

dependencies {
  apt 'com.github.instagram.ig-json-parser:processor:master-SNAPSHOT'
  implementation 'com.github.instagram.ig-json-parser:runtime:master-SNAPSHOT'
}

If you are using other build systems, please find instructions here

Requirements for model classes

There should be a package-visible no-argument constructor for each of your model classes. The fields also need to be package-visible.

Each class that needs a serializer/deserializer generated should be annotated with @JsonType. Each field that needs to be mapped to/from JSON should be annotated with @JsonField. The @JsonField annotation has one mandatory argument, which is the fieldname for the field in the JSON.

The following is an example of a very simple model class:

@JsonType
class Dessert {
  @JsonField(fieldName="type")
  String type;

  @JsonField(fieldName="rating")
  float rating;
}

Serializer/deserializer

Compiling your model classes with the annotations will automatically generate the serializer and deserializer. They will be in a generated class with the same name as your class, except with the suffix __JsonHelper. For example, to deserialize the Dessert class above, simply run the code:

Dessert parsed = Dessert__JsonHelper.parseFromJson(inputJsonString);

To serialize a class, run:

String serialized = Dessert__JsonHelper.serializeToJson(dessertObject);

Supported data types

The following scalar types are supported:

String
boolean/Boolean
int/Integer
long/Long
float/Float
double/Double

The following collection types are supported:

List/ArrayList
Queue/ArrayDeque
Map/HashMap
Set/HashSet

If a json field is another dictionary, it can be represented by another model class. That model class must also have the @JsonType annotation.

Proguard

Add the following lines to your proguard-rules file:

-dontwarn sun.misc.Unsafe
-dontwarn javax.annotation.**

Advanced features

Postprocessing

If you need to process your JSON after a first pass, you can change your @JsonType annotation to be @JsonType(postprocess = true) and add a method to your code and add a method YourClass postprocess() which will be called after the JSON is processed (see: QuestionableDesignChoice in the example below)

  @JsonType
  public class Example {
    @JsonField(fieldName = "container")
    Container mContainer;

    @JsonType
    public static class Container {
        @JsonField(fieldName = "questionable_design_choice")
        List<QuestionableDesignChoice> mQuestionableDesignChoice;
    }

    @JsonType(postprocessingEnabled = true)
    public static class QuestionableDesignChoice {
        @JsonField(fieldName = "property")
        String mProperty;

        QuestionableDesignChoice postprocess() {
          // post-process things here...
          return this;
        }
    }
}

Customized parsing code

Parsing the supported data types is straightforward. For enums or built-in Java classes, you will need to add customized parsing.

Value extract formatters override how we extract the value from the JsonParser object, while serialize code formatters override how we serialize a java field back to json. We use the serde for PointF in the example below, where a point is represented as an array in json.

  @JsonField(
      fieldName = "position",
      valueExtractFormatter =
          "com.instagram.common.json.android.JsonTypeHelper.deserializePointF(${parser_object})",
      serializeCodeFormatter =
          "com.instagram.common.json.android.JsonTypeHelper.serializePointF("
              + "${generator_object}, \"${json_fieldname}\", ${object_varname}.${field_varname})")
  @Nullable
  protected PointF mPosition;

Optional serializer generation

To save generating serializer code if you only need deserialization, serializer generation can be disabled or enabled globally and per-class. The default is to generate serializers for all classes. To disable generation globally, pass

-AgenerateSerializer=false

to the command-line arguments of javac. To override the default generation option for a single class, see JsonType.generateSerializer().

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