Trying to Validate JSON using Jackson through Spring Boot Rest

Question

Am trying to create a RESTful Web Service using Spring Boot which will take in a JSON and validate it using Jackson.

Here's the RESTful Web Service:

import java.util.Map;

import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParser;
import com.google.gson.Gson;

@RestController
@RequestMapping("/myservice")
public class ValidationService {    

    @RequestMapping(value="/validate", method = RequestMethod.POST)
    public void validate(@RequestBody Map<String, Object> payload) throws Exception {
        Gson gson = new Gson();
        String json = gson.toJson(payload); 
        System.out.println(json);
        boolean retValue = false;

        try {
            retValue = Validator.isValid(json);
        } 
        catch(Throwable t) {
            t.printStackTrace();
        }
        System.out.println(retValue);

    }
}

Here's the code to the Validator:

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Validator {

    public static boolean isValid(String json) {
        boolean retValue = false;
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.enable(DeserializationFeature.FAIL_ON_READING_DUP_TREE_KEY);
            JsonParser parser = objectMapper.getFactory().createParser(json);
            while (parser.nextToken() != null) {}
            retValue = true;
            objectMapper.readTree(json);
        }catch(JsonParseException jpe) {
            jpe.printStackTrace();
        }
        catch(IOException ioe) {

        }
        return retValue;
    }
}

So, when I use a curl to send a valid JSON:

curl -H "Accept: application/json" -H "Content-type: application/json" \ 
-X POST -d '{"name":"value"}' http://localhost:8080/myservice/validate

I receive the following to stdout:

{"name":"value"}
true

But when use the following curl command for invalid JSON (deliberately removed the closing curly brace):

curl -H "Accept: application/json" -H "Content-type: application/json" \
 -X POST -d '{"name":"value"' http://localhost:8080/myservice/validate

I receive the following inside stdout:

{"timestamp":1427698779063,
 "status":400,"error":
 "Bad Request",
 "exception":"org.springframework.http.converter.HttpMessageNotReadableException",
 "message":"Could not read JSON: 
 Unexpected end-of-input: expected close marker for OBJECT 
 (from [Source: java.io.PushbackInputStream@1edeb3e; line: 1, column: 0])\n
 at [Source: java.io.PushbackInputStream@1edeb3e; line: 1, column: 31]; 
 nested exception is
 com.fasterxml.jackson.core.JsonParseException: 
 Unexpected end-of-input: expected close marker for OBJECT 
 (from [Source: java.io.PushbackInputStream@1edeb3e; line: 1, column: 0])\n 
 at [Source: java.io.PushbackInputStream@1edeb3e; line: 1, column: 31]",
 "path":"/myservice/validate"

Is there a way to ensure exception is handled on the server side but not thrown in stdout and then just have my code respond with:

false

Thanks for taking the time to read this...

Solution 1

Figured it out!

Added the following changes:

Inside the @RequestMapping code section:

consumes = "text/plain",
produces = "application/json"

Changed @RequestBody from Map to String payload.

ValidationService class:

@RequestMapping(value="/validate", 
                method = RequestMethod.POST, 
                consumes="text/plain", 
                produces="application/json")
public ValidationResponse process(@RequestBody String payload) throws JsonParseException,
                                                                      IOException {
    ValidationResponse response = new ValidationResponse();
    boolean retValue = false;
    retValue = Validator.isValid(payload);
    System.out.println(retValue);
    if (retValue == false) {
        response.setMessage("Invalid JSON");
    }
    else {
        response.setMessage("Valid JSON");
    }
    return response;
}

Validator class:

import java.io.IOException;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Validator {

    public static boolean isValid(String json) {
        boolean retValue = true;
        try {
            ObjectMapper mapper = new ObjectMapper();
            mapper.enable(DeserializationFeature.FAIL_ON_READING_DUP_TREE_KEY);
            JsonFactory factory = mapper.getFactory();
            JsonParser parser = factory.createParser(json);
            JsonNode jsonObj = mapper.readTree(parser);
            System.out.println(jsonObj.toString());
        }
        catch(JsonParseException jpe) {
            retValue = false;   
        }
        catch(IOException ioe) {
            retValue = false;
        }
        return retValue;
    }
}

ValidationResponse:

public class ValidationResponse {

    public String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

Using 'text/plain' for Content-type:

curl -H "Accept: application/json" -H "Content-type: text/plain" -X POST -d \ 
 '{"name":"value"}' http://localhost:8080/myservice/validate

Now, everything works! This rocks!

Solution 2

After spring 3.2 you can use org.springframework.web.bind.annotation.ControllerAdvice to handle these kind of globally thrown exceptions. read more

Example code

@ExceptionHandler(HttpMessageNotReadableException.class)
public ResponseEntity<?> handleHttpMessageNotReadable(HttpMessageNotReadableException ex,
        MultipleReadHttpRequest request) {

    Map<String, String> errorResponse = new HashMap<>();
    errorResponse.put("error", ex.getMessage());
    errorResponse.put("code", "01");

    return new ResponseEntity<>(errorResponse, HttpStatus.BAD_REQUEST);
}

If there is a JSON format invalid error this method will be executed. You can customize your response.