How do I validate incoming JSON data inside a REST service?

I searched for the best practice to enforce validation for incoming json data into a RESTful service. My suggestion is to use a MessageBodyReader which performs the validation inside the readFrom method. Below there is an message-body-reader example which is non-generic for the sake of simplicity.

I also was interesed in finding the best framework for doing json data validation. Because I use the jackson framework (version 1.8.5) for marshaling and unmarshaling between json and java, it would have been nice if this framework would provide a json data validation functionality. Unfortunately I couldn’t find any possibility to do this with jackson. Finally I got it working with the json-schema-validator available at https://github.com. The version I use is 2.1.7

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

import javax.servlet.ServletContext;
import javax.ws.rs.Consumes;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.Provider;

import org.codehaus.jackson.map.ObjectMapper;

import at.fhj.ase.dao.data.Address;
import at.fhj.ase.xmlvalidation.msbreader.MessageBodyReaderValidationException;

import com.fasterxml.jackson.databind.JsonNode;
import com.github.fge.jackson.JsonLoader;
import com.github.fge.jsonschema.exceptions.ProcessingException;
import com.github.fge.jsonschema.main.JsonSchemaFactory;
import com.github.fge.jsonschema.main.JsonValidator;
import com.github.fge.jsonschema.report.ProcessingReport;

@Provider
@Consumes(MediaType.APPLICATION_JSON)
public class AddressJsonValidationReader implements MessageBodyReader<Address> {

    private final String jsonSchemaFileAsString;

    public AddressJsonValidationReader(@Context ServletContext servletContext) {
        this.jsonSchemaFileAsString = servletContext
                .getRealPath("/json/Address.json");
    }

    @Override
    public boolean isReadable(Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType) {
        if (type == Address.class) {
            return true;
        }
        return false;
    }

    @Override
    public Address readFrom(Class<Address> type, Type genericType,
            Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
            throws IOException, WebApplicationException {

        final String jsonData = getStringFromInputStream(entityStream);
        System.out.println(jsonData);

        InputStream isSchema = new FileInputStream(jsonSchemaFileAsString);
        String jsonSchema = getStringFromInputStream(isSchema);

        /*
         * Perform JSON data validation against schema
         */
        validateJsonData(jsonSchema, jsonData);

        /*
         * Convert stream to data entity
         */
        ObjectMapper m = new ObjectMapper();
        Address addr = m.readValue(stringToStream(jsonData), Address.class);

        return addr;
    }

    /**
     * Validate the given JSON data against the given JSON schema
     * 
     * @param jsonSchema
     *            as String
     * @param jsonData
     *            as String
     * @throws MessageBodyReaderValidationException
     *             in case of an error during validation process
     */
    private void validateJsonData(final String jsonSchema, final String jsonData)
            throws MessageBodyReaderValidationException {
        try {
            final JsonNode d = JsonLoader.fromString(jsonData);
            final JsonNode s = JsonLoader.fromString(jsonSchema);

            final JsonSchemaFactory factory = JsonSchemaFactory.byDefault();
            JsonValidator v = factory.getValidator();

            ProcessingReport report = v.validate(s, d);
            System.out.println(report);
            if (!report.toString().contains("success")) {
                throw new MessageBodyReaderValidationException(
                        report.toString());
            }

        } catch (IOException e) {
            throw new MessageBodyReaderValidationException(
                    "Failed to validate json data", e);
        } catch (ProcessingException e) {
            throw new MessageBodyReaderValidationException(
                    "Failed to validate json data", e);
        }
    }

    /**
     * Taken from <a href=
     * "http://www.mkyong.com/java/how-to-convert-inputstream-to-string-in-java/"
     * >www.mkyong.com</a>
     * 
     * @param is
     *            {@link InputStream}
     * @return Stream content as String
     */
    private String getStringFromInputStream(InputStream is) {
        BufferedReader br = null;
        StringBuilder sb = new StringBuilder();

        String line;
        try {

            br = new BufferedReader(new InputStreamReader(is));
            while ((line = br.readLine()) != null) {
                sb.append(line);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return sb.toString();
    }

    private InputStream stringToStream(final String str) throws UnsupportedEncodingException {
        return new ByteArrayInputStream(str.getBytes("UTF-8"));
    }

}