How to parse JSON placed in resource folder in SpringBoot

Question

Hi I am trying to parse a JSON that I have saved in a resource folder and test it. So I took these steps for now.

DataLoader.java

@Service
public class DataLoader {

private static ObjectMapper  objectMapper = defaultObjectMapper();

  private static ObjectMapper defaultObjectMapper(){
    ObjectMapper  defaultObjectMapper = new ObjectMapper();
    //defaultObjectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    return defaultObjectMapper;
  }

  public static JsonNode parse(String str) throws IOException {
    return objectMapper.readTree(str);
  }

  public static <A> A fromJason(JsonNode node, Class<A> clazz) throws JsonProcessingException {
    return objectMapper.treeToValue(node, clazz);
  }

}

DataLoaderTest.java

public class DataLoaderTest {

    @Value("classpath:data/novo.json")
    Resource jsonSource;

    //private String jsonSource = "{\"title\":\"new book\"}";

    @Test
    public void parse() throws IOException {
        JsonNode node = DataLoader.parse(jsonSource);
        assertEquals(node.get("title").asText(), "new book");
    }

    @Test
    public void fromJson() throws IOException {
        JsonNode node = DataLoader.parse(jsonSource);
        Fruit pojo = DataLoader.fromJason(node, Fruit.class);
        System.out.println("Pojo title " + pojo.title);
    }

}

So when I test it with //private String jsonSource = "{\"title\":\"new book\"}";everything is working fine.

When I try to load JSON file from resources folder I am getting error:

error: incompatible types: Resource cannot be converted to String JsonNode node = ApxDataLoader.parse(jsonSource);

Any help highly appreciated.

Answer 1

The Resource object is not a string. To parse it to the appropriate JSON structure, you would have to read the Resource . See: https://www.baeldung.com/spring-load-resource-as-string

Here's: The relevant part copied from the article.

public static String asString(Resource resource) {
        try (Reader reader = new InputStreamReader(resource.getInputStream(), UTF_8)) {
            return FileCopyUtils.copyToString(reader);
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }

Which should give you the string read from the Resource .

Another option you have is to use the InputStream from the resource and pass it to the overloaded readTree() method that can take an input stream.

See: https://fasterxml.github.io/jackson-databind/javadoc/2.7/com/fasterxml/jackson/databind/ObjectMapper.html#readTree(java.io.InputStream)

I would recommend the second approach instead of reading the whole file as a String and then passing it to the ObjectMapper.

Answer 2

with Spring-boot, the easy way to load a json in the classpath (for example in the resources folder) would be:

File jsonFile = new ClassPathResource("data.json").getFile();
// or
File jsonFile = jsonResource.getFile();

JsonNode node = objectMapper.readTree(jsonFile);

No need to deal with InputStream, Spring takes care of that for you. and Jackson can read a File directly, so no need for a String neither.

No need to deal with JsonNode neither: You can also even further optimize the readability of the code by doing all the parsing/mapping at the same time:

Fruit myFruit = objectMapper.readValue(jsonFile, Fruit.class);

If you still need the contents of the file as a String for some reason:

String jsonString = Files.readString(jsonFile.toPath()); // default charset of readString is UTF8 

DataLoader could have only one method:

public class DataLoader {

  // ... objectmapper stuff ...

  public static <A> A fromJason(Resource jsonResource, Class<A> clazz) throws JsonProcessingException {
    return objectMapper.readValue(jsonResource.getFile(), clazz);
  }