我有一个json字符串，我无法提取特定字段

Question

I Have a json String that looks like this:

{
   "results" : [
      {
         "address_components" : [
            {
               "long_name" : "Arad",
               "short_name" : "Arad",
               "types" : [ "locality", "political" ]
            },
            {
               "long_name" : "Arad",
               "short_name" : "Arad",
               "types" : [ "administrative_area_level_2", "political" ]
            },
            {
               "long_name" : "Arad County",
               "short_name" : "AR",
               "types" : [ "administrative_area_level_1", "political" ]
            },
            {
               "long_name" : "Romania",
               "short_name" : "RO",
               "types" : [ "country", "political" ]
            }
         ],
         "formatted_address" : "Arad, Romania",
         "geometry" : {
            "bounds" : {
               "northeast" : {
                  "lat" : 46.2217118,
                  "lng" : 21.3823449
               },
               "southwest" : {
                  "lat" : 46.1286902,
                  "lng" : 21.230371
               }
            },
            "location" : {
               "lat" : 46.1865606,
               "lng" : 21.3122677
            },
            "location_type" : "APPROXIMATE",
            "viewport" : {
               "northeast" : {
                  "lat" : 46.2217118,
                  "lng" : 21.3823449
               },
               "southwest" : {
                  "lat" : 46.1286902,
                  "lng" : 21.230371
               }
            }
         },
         "place_id" : "ChIJw1lco0uYRUcRkYRVPkoHcA8",
         "types" : [ "locality", "political" ]
      }
   ],
   "status" : "OK"
}

My java code:

jsonString = readUrl("https://maps.googleapis.com/")
rootNode = objectMapper.readTree(jsonString);
JsonNode resultsNode = rootNode.path("results");
        JsonNode addressNode = resultsNode.path("address_components");
        JsonNode geometryNode = addressNode.path("geometry");
        JsonNode locationNode = geometryNode.path("location");
        JsonNode latNode = locationNode.path("lat");
        JsonNode lngNode = locationNode.path("lng");
        System.out.println(latNode.asDouble());
        System.out.println(lngNode.asDouble());

The last 2 line print 0.0 and 0.0. How can I obtain lat and lng information from this json? ps I diden't post the full url link. Maybe the jsonNodes are not correct but I can't find the solution.

Answer 1

The problem is that results is not an object but an array of objects. You have to choose element by index. The proper solution is:

jsonString = readUrl("https://maps.googleapis.com/")
rootNode = objectMapper.readTree(jsonString);
JsonNode resultsNode = rootNode.path("results");
JsonNode addressNode = resultsNode.get(0); //selecting first json object from an array
JsonNode geometryNode = addressNode.path("geometry");
JsonNode locationNode = geometryNode.path("location");
JsonNode latNode = locationNode.path("lat");
JsonNode lngNode = locationNode.path("lng");
System.out.println(latNode.asDouble());
System.out.println(lngNode.asDouble());

You may also want to iterate all objects in results, in that case code, which will print coordinates of each object, should be:

jsonString = readUrl("https://maps.googleapis.com/")
rootNode = objectMapper.readTree(jsonString);
JsonNode resultsNode = rootNode.path("results");
Iterator<JsonNode> results = resultsNode.elements();
while(results.hasNext()){
    JsonNode addressNode = results.next();
    JsonNode geometryNode = addressNode.path("geometry");
    JsonNode locationNode = geometryNode.path("location");
    JsonNode latNode = locationNode.path("lat");
    JsonNode lngNode = locationNode.path("lng");
    System.out.println(latNode.asDouble());
    System.out.println(lngNode.asDouble());
}