JSON-Pointer is the Java API for JSON processing. By processing, we mean generating, transforming, parsing, and querying JSON strings and/or objects.

In this recipe, you will learn how to use JSON Pointer to get a specific value from a JSON message in a very easy way.

Let's get our dependency:

<dependency>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>8.0</version>
            <scope>provided</scope>
        </dependency>
</dependency>

1. First, we define a JSON message to represent a User object:

{
  "user": {
    "email": "[email protected]",
    "name": "Elder",
    "profile": [
      {
        "id": 1
      },
      {
        "id": 2
      },
      {
        "id": 3
      }
    ]
  }
}

2. Now, we create a method to read it and print the values we want:

public class JPointer {

    public static void main(String[] args) throws IOException{
        try (InputStream is = 
        JPointer.class.getClassLoader().getResourceAsStream("user.json");
                JsonReader jr = Json.createReader(is)) {

            JsonStructure js = jr.read();
            JsonPointer jp = Json.createPointer("/user/profile");
            JsonValue jv = jp.getValue(js);
            System.out.println("profile: " + jv);
        }
    }
}

The execution of this code prints the following:

profile: [{"id":1},{"id":2},{"id":3}]

The JSON Pointer is a standard defined by the Internet Engineering Task Force (IETF) under Request for Comments (RFC) 6901. The standard basically says that a JSON Pointer is a string that identifies a specific value in a JSON document.

Without a JSON Pointer, you would need to parse the whole message and iterate through it until you find the desired value; probably lots of ifs, elses, and things like that.

So, JSON Pointer helps you to decrease the written code dramatically by doing this kind of operation in a very elegant way.

• You can stay tuned with everything related to JSON-P at https://javaee.github.io/jsonp/
• The source code of this recipe is at https://github.com/eldermoraes/javaee8-cookbook/tree/master/chapter01/ch01-jsonp