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What is JSON Processing (JSON-P API)?

JSON Processing

Introduction to JSON-P in Java EE

The Java API for JSON Processing 1.0 (JSR 353) is a low level, lightweight JSON parser, and generator that provides that capacity to manipulate JSON data at the property and value level.

The JSR 353 provides two JSON processing models: an object model and a streaming model. Both models can generate JSON data and output it to a stream such as a flat file, and both models can read data. However, the streaming model is especially efficient at processing high volumes of JSON data. This allows for the implementation of data import functionality and the transformation of such data on the fly.

However, the streaming model is especially efficient at processing high volumes of JSON data. This allows for the implementation of data import functionalities and the transformation of such data on the fly.

The JSON-P Object Model

The javax.json package provides the Object model API for processing JSON data. It includes classes that model the JSON structure and factories for JSON readers and writers.

The Object model represents the elements that form the JSON data structure, as objects. For example, a JSON array is represented by the javax.json.JsonArray class, and in turn, this class implements the List interface.

A JSON object is represented by the javax.json.JsonObject class which implements the Map interface.

The javax.json.Json class includes various factory methods that create JsonGenerator, JsonParser and JsonReader instances among others.

The following code snippet creates a JSONObject instance from a JSON document and then retrieves the data from its properties.

1: private String json = "{\"id\": 123456, \"title\": \"Fun with JSON-Processing\", \"published\": true}";

2: JsonReader jsonReader = Json.createReader(new StringReader(json));
3: JsonObject jsonObject = jsonReader.readObject();
4: jsonReader.close();
5: jsonObject.getInt("id")
6: jsonObject.getString("title")
7: jsonObject.getBoolean("published")

Line 1 is the JSON document I want to process. I create an instance of a StringReader object and pass it the JSON document, which I pass to the JsonReader via the createReader() static method.

I read the JSON document into a JsonObject instance on line 3 and close the reader on line 4.

Now that I have a JsonObject I can read the values of the JSON properties by passing the property name to the getString() method.

The code for this example is stored in the GitHub repository that accompanies this post.

The JSON-P Streaming Model

The javax.json.streaming package provides the Streaming model API that parses and generates JSON data. It includes factories for creating parsers and generators.

It is implemented quite differently and at a lower level. At its heart, there are two principle factories that generate and parse JSON data they are the JsonGeneratorFactory and the JsonParserFactory. These factories are orientated towards writing to and reading from streams of data.

The writing of JSON data is done by chaining methods that add data to the buffer, and then flushing it to the output stream by calling the flush or close methods.

JSON data is parsed in a streaming manner and is designed to be the most efficient way to read JSON data. Parsers are created from InputStream or Reader input sources.

The following code snippet creates a JSONObject instance by constructing it using builder methods on the JsonObjectBuilder and then it retrieves the data from the JsonObject.

1: JsonObject jsonObject = Json.createObjectBuilder()
        .add("id", 123456)
        .add("title", "Fun with JSON-Processing")
        .add("published", true)
        .build();

2: jsonObject.getInt("id")
3: jsonObject.getString("title")
4: jsonObject.getBoolean("published")

On line 1 the JsonObject is constructed. As you can see it calls the static createObjectBuilder() method from the Json class and I call the add method for as many properties as I want my JsonObject to have. In this case, I want three properties: id, title and published. The final method is the build() method that constructs the JsonObject.

Line 2 to 4 called the getter methods on the JsonObject build on line 1 and retrieves the properties values one by one just as I did in the previous example.

The code for this example is stored in the GitHub repository that accompanies this post.

What Next?

If you liked this article you will enjoy my new JSON Processing with Java EE course I recorded for Lynde.com. In this course, I go through the entire API looking in depth as the Object and Streaming models. I use plenty of code examples and set you challenges to help you improve you learn.

Further Reading

I often post on Java EE technologies so you might be interested in the following:

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