How to Read JSON file from classpath in Spring-Boot

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Springboot

In this tutorial we will see a simple method to read a JSON file from classpath in Java and Spring-Boot. This will work even when JSON file is packaged and deployed as a spring-boot app or as a Java application.

Get Started:

First you will have to create a Spring-boot project as seen in my previous post using CLI. Then create a REST API which will return a JSON response by reading a JSON file as seen below:

@RestController
public class UserProfileRestService {  

    @GetMapping(value = RestConstants.REQUEST_URL,
      produces = MediaType.APPLICATION_JSON_VALUE)
    public String getUser(@PathVariable String userId) {
      return readFromJson(FileConstants.USER_JSON_FILE_NAME);
    }
  }

Now create a function that reads the JSON file from the classpath:

public class JsonUtil { 

private static final Logger LOG = LoggerFactory.getLogger(JsonUtil.class);

/**
   * Function returns the JSON String for a give json file.
   * 
   * @param filename fileName
   * @return String jsonString
   */
public static String readFromJson(String filename) {
    LOG.info("In readFromJson() fileName : " + filename);
    try {
      ClassPathResource cpr = new ClassPathResource(filename);
      byte[] bdata = FileCopyUtils.copyToByteArray(cpr.getInputStream());
      return new String(bdata, StandardCharsets.UTF_8);
    } catch (FileNotFoundException e) {
      LOG.error("Exception in : readFromJson(): File Not Found!!!: " + filename);
    } catch (IOException e) {
      LOG.error("Exception in : readFromJson(): IOException!!!: " + e.getMessage());
    }
    return null;
  }
}

Run it as a Java application to display the contents of the json file as seen below:

public class JsonReaderExample {

  private static final Logger LOG = LoggerFactory.getLogger(JsonReaderExample.class);

  public static void main(String[] args) {

    JsonUtil util = new JsonUtil();
    String jsonOutput = util.readFromJson(FileConstants.USER_JSON_FILE_NAME);
    LOG.info("JSON Response: {}", jsonOutput);
  }
}

OUTPUT:

{
  "userId": 1,
  "id": 1,
  "name": "John",
  "email": john@techknowbase.com
}

Therefore readFromJson() method read a JSON file from classpath under src/main/resources/user.json. That’s all folks. I hope it helps.