在Java NetBeans中解析JSON字符串

Question

Can anyone please tell me how to get the values of og:description , og:title , book:release_date , book:author , and book:isbn from every metatags? (please see the JSON content below) Eventually these values will be displayed in a table so I need them as Java objects (Strings)..

So far, I have tried using many external libs but this is my first project using JSON, so I didn't understand how they worked..

For your information, I am using NetBeans and am making a restful web service.

I have managed to convert these into a JSON string using this code:

    JSONObject obj = new JSONObject(builder.toString());
    String theJsonString = obj.toString();

but when I tried to do this:

    ObjectMapper mapper = new ObjectMapper();
                  Map<String,Object> data = mapper.readValue(theJsonString.getBytes(), Map.class);
                  Map items = (Map) data.get("items");
                  Map pagemap = (Map) items.get("pagemap");
                  Map metatags = (Map) pagemap.get("metatags");
                  String b_title = (String) metatags.get("og:title");

     System.out.println(b_title);

I get this error:

java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map at API.GCustSearchAPI.main(GCustSearchAPI.java:77)

line 77 is this:

Map items = (Map) data.get("items");

here is the json content:

{
"items": [
{
"pagemap": {
"metatags": [
 {
  "og:description": "A boxed set, including the titles 'Harry Potter and the Philosopher's Stone', 'Harry Potter and the Chamber of Secrets', 'Harry Potter and the Prisoner of Azkaban', 'Harry Potter and the Goblet of Fire', 'Harry Potter and the Order of the Phoenix', 'Harry Potter and the Half-Blood Prince' and 'Harry Potter and the Deathly Hallows'.",
  "og:title": "Harry Potter Adult Paperback Boxed Set: Adult Edition (Paperback)",
  "book:release_date": "2008-10-06",
  "book:author": "J. K. Rowling",
  "book:isbn": "9780747595847"
 }
]
}
},
 {
"pagemap": {
"metatags": [
 {
  "og:description": "Offers an in-depth look at the craftsmanship, artistry, technology, and more than ten-year journey that took the world's bestselling fiction from page to screen. From elaborate sets and luxurious costumes to advanced special effects and film making techniques, this title chronicles all eight films.",
  "og:title": "Harry Potter: Page to Screen (Hardback)",
  "book:release_date": "2011-10-25",
  "book:author": "Bob McCabe",
  "book:isbn": "9780857687753"
 }
 ]
}
 }
 ]
}

Any input will be appreciated. Please tell me in an easy way because I am a beginner (just touched NetBeans for 2 months). Many thanks!!!

Answer 1

If you look at the json items is an array, the corresponding java representaion is a List. So you need to fetch items as a List

List items = (List ) data.get("items");

The same logic is applied to metatags also

List metatags = (List) pagemap.get("metatags");

With the above mentioned changes, try this

ObjectMapper mapper = new ObjectMapper();
Map<String, Object> data = mapper.readValue(file, Map.class);
List<Map<String, Object>> items = (List) data.get("items");
for (Map<String, Object> item : items) {
    Map pagemap = (Map) item.get("pagemap");
    List<Map<String, Object>> metatags = (List) pagemap.get("metatags");
    for (Map<String, Object> tag : metatags) {
        String b_title = (String) tag.get("og:title");
        System.out.println(b_title);
    }

}

Answer 2

create a java class ie item.java and write the line

Item item= mapper.readValue(new File(theJsonString.getBytes()), Item .class);

then read the json