JSON Schema validator

Like XML, JSON also provides schema and the code has to validate the json instance with a schema.  In this post, let us see how we can validate the given instance with its JSON schema.

The validator I would recommend is 'json-schema-validator'.  The version I have used is 2.0.1, which  supports both v3 and v4 Json schemas.  You can take a look at the latest versions of the validator also.

Add the following in your pom.xml:

<dependency>

    <groupId>com.github.fge</groupId>
    <artifactId>json-schema-validator</artifactId>
    <version>2.0.1</version>
</dependency>

Then follow these steps:

1) If the schema or the instance are strings, transform them to JsonNode objects:

            ObjectMapper mapper = new ObjectMapper();
             //json instance object
            JsonNode instanceJsonObject = mapper.readTree(jsonInstance);
            //json schema string to json object.
            JsonNode schemaJsonObject = mapper.readTree(jsonSchema);

2) Next step is to get the json schema object:

             //The schema factory supports both Json's v3 and v4 schemas.  Most of the times, the default
             //factory is enough.
             JsonSchemaFactory schemaFactory = JsonSchemaFactory.byDefault();            
             JsonSchema schema = schemaFactory.getJsonSchema(schemaJsonObject );

3) Now the instance can be validated with the validate() of JsonSchema:

             ListProcessingReport report = (ListProcessingReport)schema.validate(instanceNode);

The ListProcessing contains the valiation messages, the missing required field(s) details.  To obtain those details, follow these steps:

            if(!report.isSuccess()){

                JsonNode reportRootNode = report.asJson();            

                if(rootNode.size() > 0){
                    JsonNode errorNode = rootNode.get(0);
                    JsonNode messageNode = errorNode.get("message");
                    if(messageNode != null){
                        logger.error(messageNode.asText());
                    }
                    JsonNode requiredNode = errorNode.get("required");
                    if(requiredNode != null) {
                        logger.error(requiredNode.toString());
                    }
                    JsonNode missingNode = errorNode.get("missing");
                    if(missingNode != null){
                        logger.error((missingNode.toString());
                    }

                }
            }

And...that's all folks.