java - 如何使用Java循环输入Json？

Question

我有一个 Json 数组文件，它有多个数据。正如您在下面的数据中看到的，您会多次注意到 timeLastUpdate 。当我用Java编译时，我得到的输出只是JSON中的第一次LastUpdate。我想要 Java 中显示的所有 timeLastUpdate。我该怎么做？

数据示例:

 [
      {
        "mmsi": "253336000",
        "status": "RESTRICTED_MANEUVERABILITY",
        "courseOverGround": 7.9,
        "timeLastUpdate": 1464545149000,
        "
      },
      {
        "mmsi": "253336000",    
        "timeLastUpdate": 1464545209000,
        "destination": "ZEEBRUGGE",
          },
]

Java 代码:

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.DeserializationFeature;
import java.io.File;
import java.net.URL;
import java.io.IOException;

public class ShipMain {

    public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {

             File jsonFile2 = new File("shiphistory.json");

             ShipData shiphistory  = null; 

             ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally

             mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

                shiphistory = mapper.readValue(jsonFile2, ShipData.class);
                System.out.println("______________ History_________");
                System.out.println("Ship Name : " + shiphistory.getName());
                System.out.println("Ship MMSI : " + shiphistory.getMmsi());
                System.out.println("Ship Type : " + shiphistory.getShipType());
                System.out.println("Ship Departure : " + shiphistory.getTimeLastUpdate());


        }

    }

Answer 1

要使用 ObjectMapper 解析 JSON 数组，您可以查看所选答案 here 。基本上，您的代码应该如下所示:

ObjectMapper mapper = new ObjectMapper(); 
ShipData[] shipDataArray  = mapper.readValue(jsonFile2, ShipData[].class);
//then you can look through the array
System.out.println("______________ History_________");
for(int x=0; x < shipDataArray.length(); x++){
     shiphistory = shipDataArray[x];
     System.out.println("Ship Name : " + shiphistory.getName());
     System.out.println("Ship MMSI : " + shiphistory.getMmsi());
     System.out.println("Ship Type : " + shiphistory.getShipType());
     System.out.println("Ship Departure : " + shiphistory.getTimeLastUpdate());
    //just a separating line (not necessary - just to separate the shipdata items
    System.out.println("-----------------------------------------------------");
}

尝试一下，如果这对您有帮助，请告诉我们。