无法使用Jackson从JSON获取单个值

Question

我需要从JSON获取一个值，但是我将null作为值。

public class PlaceTest {
    public void sendRequest() throws Exception{
        URIBuilder builder = new URIBuilder("https://maps.googleapis.com/maps/api/place/findplacefromtext/json");
        builder.addParameter("key","mykey");
        builder.addParameter("input","London");
        builder.addParameter("inputtype","textquery");
        HttpGet getReq = new HttpGet(builder.build());

        HttpClient client = new DefaultHttpClient();
        HttpResponse httpResponse = client.execute(getReq);
        BufferedReader reader = new BufferedReader(new InputStreamReader(httpResponse.getEntity().getContent()));
        StringBuilder builders = new StringBuilder();
        String s;
        while ((s = reader.readLine())!=null){
        builders.append(s+"\n");
        }

        ObjectMapper mapper = new ObjectMapper();

        JsonNode node = mapper.readTree(builders.toString());
        JsonNode candidates = node.get("candidates");
        System.out.println(candidates.get("place_id"));

        //json
        System.out.println(builders.toString());
    }
}

JSON代码为：

{"candidates":[{"place_id" : "ChIJdd4hrwug2EcRmSrV3Vo6llI"}],"status" : "OK"}

Answer 1

在上述JSON candidates中，值是JsonArray

JsonNode node = mapper.readTree(builders.toString());
JsonNode candidates = node.get("candidates");

现在迭代JsonArray并获得place_id：

if (candidates.isArray()) {
    for (JsonNode objNode : arrNode) {
        System.out.println(objNode.get("place_id"));
    }
}