我正在尝试从JSON字符串中获取值，但我得到的是null值。
App2.java：
package JsonExample1;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.ObjectMapper;
import java.io.IOException;
import java.io.StringReader;
public class App2 {
private JsonNode rootNode;
public void setup() throws IOException {
String jsonString = "{\n" +
" \"HotelListResponse\" : {\n" +
" \"customerSessionId\" : \"0ABAAA7A-90C9-7491-3FF2-7E2C37496CA2\",\n" +
" \"numberOfRoomsRequested\" : 1,\n" +
" \"moreResultsAvailable\" : true,\n" +
" \"cacheKey\" : \"7790c974:13ff7e2c374:6ccd\",\n" +
" \"cacheLocation\" : \"10.186.170.122:7300\",\n" +
" \"HotelList\" : {\n" +
" \"@activePropertyCount\" : \"223\",\n" +
" \"@size\" : \"1\",\n" +
" \"HotelSummary\" : {\n" +
" \"@order\" : \"0\",\n" +
" \"hotelId\" : 125727,\n" +
" \"name\" : \"Red Lion Hotel on Fifth Avenue\",\n" +
" \"address1\" : \"1415 5th Ave\",\n" +
" \"city\" : \"Seattle\",\n" +
" \"stateProvinceCode\" : \"WA\",\n" +
" \"postalCode\" : 98101,\n" +
" \"countryCode\" : \"US\",\n" +
" \"airportCode\" : \"SEA\",\n" +
" \"supplierType\" : \"E\",\n" +
" \"hotelRating\" : 3.5,\n" +
" \"propertyCategory\" : 1,\n" +
" \"confidenceRating\" : 90,\n" +
" \"amenityMask\" : 7847938,\n" +
" \"tripAdvisorRating\" : 4,\n" +
" \"locationDescription\" : \"Near Pike Place Market\",\n" +
" \"shortDescription\" : \"<p><b>Location. </b> <br />Red Lion Hotel on Fifth Avenue is located close to 5th Avenue Theater, Pike Place Market, and Washington State Convention & Trade Center. Additional points of interest\",\n" +
" \"highRate\" : 149,\n" +
" \"lowRate\" : 126.65,\n" +
" \"rateCurrencyCode\" : \"USD\",\n" +
" \"latitude\" : 47.60985,\n" +
" \"longitude\" : -122.33475,\n" +
" \"proximityDistance\" : 11.168453,\n" +
" \"proximityUnit\" : \"MI\",\n" +
" \"hotelInDestination\" : true,\n" +
" \"thumbNailUrl\" : \"/hotels/1000000/60000/51000/50947/50947_180_t.jpg\",\n" +
" \"deepLink\" : \"http://travel.ian.com/index.jsp?pageName=hotAvail&cid=55505&hotelID=125727&mode=2&numberOfRooms=1&room-0-adult-total=2&room-0-child-total=0&arrivalMonth=8&arrivalDay=4&departureMonth=8&departureDay=5&showInfo=true&locale=en_US&currencyCode=USD\",\n" +
" \"RoomRateDetailsList\" : {\n" +
" \"RoomRateDetails\" : {\n" +
" \"roomTypeCode\" : 253461,\n" +
" \"rateCode\" : 201054304,\n" +
" \"maxRoomOccupancy\" : 2,\n" +
" \"quotedRoomOccupancy\" : 2,\n" +
" \"minGuestAge\" : 0,\n" +
" \"roomDescription\" : \"Classic Single Queen\",\n" +
" \"promoId\" : 202161947,\n" +
" \"promoDescription\" : \"Summer Sale! Save 15%\",\n" +
" \"currentAllotment\" : 0,\n" +
" \"propertyAvailable\" : true,\n" +
" \"propertyRestricted\" : false,\n" +
" \"expediaPropertyId\" : 50947,\n" +
" \"rateKey\" : \"0ABAAA7A-90C9-7491-3FF2-7E2C37496CCE\",\n" +
" \"RateInfo\" : {\n" +
" \"@rateChange\" : \"false\",\n" +
" \"@promo\" : \"true\",\n" +
" \"@priceBreakdown\" : \"true\",\n" +
" \"ChargeableRateInfo\" : {\n" +
" \"@total\" : \"151.23\",\n" +
" \"@surchargeTotal\" : \"24.58\",\n" +
" \"@nightlyRateTotal\" : \"126.65\",\n" +
" \"@maxNightlyRate\" : \"126.65\",\n" +
" \"@currencyCode\" : \"USD\",\n" +
" \"@commissionableUsdTotal\" : \"126.65\",\n" +
" \"@averageRate\" : \"126.65\",\n" +
" \"@averageBaseRate\" : \"149.0\",\n" +
" \"NightlyRatesPerRoom\" : {\n" +
" \"@size\" : \"1\",\n" +
" \"NightlyRate\" : {\n" +
" \"@promo\" : \"true\",\n" +
" \"@rate\" : \"126.65\",\n" +
" \"@baseRate\" : \"149.0\"\n" +
" }\n" +
" },\n" +
" \"Surcharges\" : {\n" +
" \"@size\" : \"1\",\n" +
" \"Surcharge\" : {\n" +
" \"@amount\" : \"24.58\",\n" +
" \"@type\" : \"TaxAndServiceFee\"\n" +
" }\n" +
" }\n" +
" }\n" +
" },\n" +
" \"ValueAdds\" : {\n" +
" \"@size\" : \"1\",\n" +
" \"ValueAdd\" : {\n" +
" \"@id\" : \"2048\",\n" +
" \"description\" : \"Free Wireless Internet\"\n" +
" }\n" +
" }\n" +
" }\n" +
" }\n" +
" }\n" +
" }\n" +
" }\n" +
" }";
rootNode = new ObjectMapper().readTree(new StringReader(jsonString));
}
//other methods
public void basicTreeModelRead()
{
//Just like DOM, our data is in a hierarchy of node (in this case, it is JsonNode)
JsonNode aField = rootNode.get("customerSessionId");
//the customerSessionId has a String value
String myString = aField.asText();
System.out.println("customerSessionId is:" + myString);
}
}
StartHere.java：
package JsonExample1;
import java.io.IOException;
public class StartHere {
public static void main(String[] args) {
App2 myApp = new App2();
try {
myApp.setup();
} catch (IOException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
myApp.basicTreeModelRead();
}
}
调试后，我发现aField值仍然为null。 有什么想法吗？
答案 0 :(得分：19)
您的根节点没有customerSessionId，它有HotelListResponse。首先得到它。
//other methods
public void basicTreeModelRead()
{
JsonNode innerNode = rootNode.get("HotelListResponse"); // Get the only element in the root node
// get an element in that node
JsonNode aField = innerNode.get("customerSessionId");
//the customerSessionId has a String value
String myString = aField.asText();
System.out.println("customerSessionId is:" + myString);
}
打印
customerSessionId is:0ABAAA7A-90C9-7491-3FF2-7E2C37496CA2
答案 1 :(得分：2)
使用.at（）方法获取内部元素的另一种方法：
rootNode.at("/HotelListResponse/customerSessionId")
答案 2 :(得分：0)
转换为地图
Map map = objectMapper.readValue(jsonString, Map.class);
在地图中导航的方法
private static <T> T get(Map map, Class<T> clazz, String... path) {
Map node = map;
for (int i = 0; i < path.length - 1; i++) {
node = (Map) node.get(path[i]);
}
return (T) node.get(path[path.length - 1]);
}
用法：
String value = get(map, String.class, "path", "to", "the", "node")