如何使用jackson庫從JSON字符串獲取值？

Question

我想從一個JSON字符串獲取值，但我得到一個空值，而不是。

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(); 

    } 
} 

調試後，我發現遠處值保持爲空。 任何想法？

Answer 1

您的根節點沒有customerSessionId，它有HotelListResponse。先得到。

//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); 
} 

這將打印

customerSessionId is:0ABAAA7A-90C9-7491-3FF2-7E2C37496CA2