在simple.json Java中解码浮点数

Question

I am trying to read and parse a json file using simple.json in Java. However, on floating point numbers I get error. How should I parse floating point numbers?

The JSON File is like:

[
  {
    "region":"NF",
    "destination":"d1",
    "source":"s1",
    "time":2003,
    "value":0.1
  },
  {
    "region":"NF",
    "destination":"d2",
    "source":"s2",
    "time":2004,
    "value":0.002
  },
]

My code to parse it is:

JSONArray jsonArray = (JSONArray)obj;
Iterator<JSONObject> iterator = jsonArray.iterator();

while(iterator.hasNext()){
    JSONObject jsonObject = iterator.next();
    String region = (String) jsonObject.get("region");
    String src = (String) jsonObject.get("source");
    String dst = (String) jsonObject.get("destination");
    long time = (long) jsonObject.get("time");
    long val = (long) jsonObject.get("value");
}

Answer 1

If you want to store a floating point number, then you need a variable of that type, ie, a double.

double val = ((Number)jsonObject.get("value")).doubleValue();

In this case, the get() method should return an instance of java.lang.Number . Then you can call the doubleValue() method to store the floating point value.

Answer 2

I would guess that this library (I'm guessing it's json-simple from your tag) returns numeric types as type double .

Double value = (Double) jsonObject.get("value");

For example (tested and working with json-simple-1.1.1):

String jsonString = "{\"foo\":1.23}";
JSONObject obj = (JSONObject) JSONValue.parse(jsonString);
Double d = (Double) obj.get("foo"); // => 1.23

Answer 3

In Java EE 7, use jsonObject.getJsonNumber("key").doubleValue() to get the double value.

See: https://docs.oracle.com/javaee/7/api/javax/json/JsonNumber.html