JSON schema validation in Java

Sometimes it is required to validate JSON objects before the processing as it helps in catching error early and to make sure valid data is received by application. You can validate a JSON object by providing JSON schema definition and then using it in Java.

In this example we will show how to validate a JSON object using Java. We will use org.everit.json.schema library to validate JSON object. You can check list of JSON types that can be used by JSON schema here

JSON Schema types

First you need to download below dependencies

<dependency>
    <groupId>org.everit.json</groupId>
    <artifactId>org.everit.json.schema</artifactId>
    <version>1.11.1</version>
</dependency>

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20160810</version>
</dependency>

Below is the JSON data & schema to validate the JSON

{
    "id":12345, 
    "name":"Huge Grant",
    "age":35,
    "profession":"Actor"
}

{
    "$schema": "http://json-schema.org/draft-07/schema",
    "title" : "Person",
    "type": "object",
    "properties": {
        "id": {"type": "integer", "minLength": 4, "maxLength": 64},
        "name": {"type": "string"},
        "age": {"type": "integer", "minimum": 18},
        "profession": {"type": "string", "enum": ["Actor","Professor"]}
    },
    "required": ["id", "name"]
}

$schema keyword describes specification version 7
$title keyword describes json
$type means its a JSON object
$properties defined that array of properties in JSON
$required means these proeprties are mandatory in JSON

Validating JSON in Java

Below example shows how to validate a JSON object in Java

package json;

import org.everit.json.schema.Schema;
import org.everit.json.schema.ValidationException;
import org.everit.json.schema.loader.SchemaLoader;
import org.json.JSONObject;
import org.json.JSONTokener;

public class JsonValidator {

    public static void main(String[] args) {
        JSONObject jsonSchema = new JSONObject(new JSONTokener(
            JsonValidator.class.getResourceAsStream("/schema.json")));
        JSONObject jsonData = new JSONObject(new JSONTokener(
            JsonValidator.class.getResourceAsStream("/data.json")));

        Schema schema = SchemaLoader.load(jsonSchema);
        try {
            schema.validate(jsonData);
        } catch (ValidationException e) {
            System.out.println("schema validation failed");
            e.printStackTrace();
        }
        System.out.println("schema validated successfully");
        
    }

}

Console Output :

schema validated successfully

Suppose you pass invalid value in json data "profession":"Actors" instead of "profession":"Actor", code will throw below Exception

schema validation failed
org.everit.json.schema.ValidationException: #/profession: Actors is not a valid enum value
at org.everit.json.schema.ValidationException.prepend (ValidationException.java:333)
at org.everit.json.schema.ValidationException.prepend (ValidationException.java:312)