JSON parsing in java from file

Question

I am doing my first steps with JSON programming. I have big json file with books archive from:

https://www.googleapis.com/books/v1/volumes?q=java&maxResults=30

I created POJO's with getters and setters. Now I want to find for example all books wrote by given author:

byte[] jsonData = Files.readAllBytes(Paths.get("archive.json"));
ObjectMapper objectMapper = new ObjectMapper();
JsonNode rootNode = objectMapper.readTree(jsonData);

JsonNode authorNode = rootNode.path("Gary Cornell");
Iterator<JsonNode> elements = authorNode.elements();
while(elements.hasNext()){
    JsonNode isbn = elements.next();
    System.out.println(isbn.textValue());
}

But saddly I am doing something wrong. My app just write whole json.

Answer 1

You need to access inner nodes to compare author values. You might want to do it like this:

byte[] jsonData = Files.readAllBytes(Paths.get("volumes.json"));
ObjectMapper objectMapper = new ObjectMapper();
JsonNode rootNode = objectMapper.readTree(jsonData);
String authorName = "Joshua Bloch"; // author name to find
JsonNode items = rootNode.path("items");
Iterator<JsonNode> elements = items.elements();

while(elements.hasNext()){
    JsonNode isbn = elements.next();
    if(isbn.has("volumeInfo")) {
        JsonNode volumeInfo = isbn.path("volumeInfo");
        if(volumeInfo.has("authors")) {
            JsonNode authors = volumeInfo.path("authors");
            if(authors.toString().contains(authorName)) {
                // Print complete book JSON value
                System.out.println(isbn.toString());
            }
        }

    }
}

Answer 2

Most of the jsonNode methods expect fieldNames not actual values.

If you`re looking for the ISBN you can do it like this (so this is probably not the best example)

    public static void main(String[] args) throws IOException {

        byte[] jsonData = Files.readAllBytes(Paths.get("archive.json"));
        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode rootNode = objectMapper.readTree(jsonData);

        List<JsonNode> volumeNodes = rootNode.findValues("volumeInfo");
        String authorName = "Gary Cornell";

        for (JsonNode volumeNode : volumeNodes) {

            JsonNode authors = volumeNode.path("authors");
            Iterator<JsonNode> authorIt = authors.elements();

            while(authorIt.hasNext()){

                JsonNode author = authorIt.next();

                if (authorName.equals(author.textValue())) {

                    System.out.println(author.textValue());

                    JsonNode isbn = volumeNode.path("industryIdentifiers");
                    Iterator<JsonNode> isbnIt = isbn.elements();

                    while(isbnIt.hasNext()) {
                        System.out.println(isbnIt.next());
                    }
                }
            }
        }
    }

Answer 3

谢谢大家，这正是我所需要的。