Jakarta JSON Processing is the 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 a JSON Pointer to get a specific value from a JSON message very easily.

Let's get our dependency:

<dependencies>
    <dependency>
        <groupId>org.eclipse</groupId>
        <artifactId>yasson</artifactId>
        <version>1.0.3</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish</groupId>
        <artifactId>javax.json</artifactId>
        <version>1.1.4</version>
    </dependency>
    <dependency>
        <groupId>jakarta.platform</groupId>
        <artifactId>jakarta.jakartaee-api</artifactId>
        <version>8.0.0</version>
        <scope>runtime</runtime>
    </dependency>
</dependencies>

You need to perform the following steps to try this recipe:

1. First, we define a JSON message to represent the 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);
        }
    }
}

3. 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 if and else instances and things like that.

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

• 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.