java.lang.NumberFormatException：对于输入字符串：“2019-11-27”

Question

In my app I am getting date from an API server as String value and I want to parse it to int but I get this error:

Caused by: java.lang.NumberFormatException: For input string: "2019-11-27"
at java.lang.Integer.parseInt(Integer.java: 521)
at java.lang.Integer.parseInt(Integer.java: 556)

I am trying to parse into an int . I want to pass it to BarEntry class constructor and it takes only int value or float new BarEntry(int or float values,float). I need it for showing Chart.

My Activity

try {
    Response response = client.newCall(request).execute();
    Log.d("Response", response.toString());
    JSONObject object = new JSONObject(Objects.requireNonNull(response.body()).string());
    JSONObject rates = object.getJSONObject("rates");
    Iterator < String > iterator = rates.keys();
    while (iterator.hasNext()) {
        String keyDate = iterator.next(); // this date which i want to parse to int value
        String cad = rates.getJSONObject(keyDate).getString("CAD");
        @SuppressLint("DefaultLocale") String value = String.format("%.4s", cad);
        float value1 = Float.parseFloat(value);
        int date = Integer.parseInt(keyDate);
        Log.d("TAG", date + "");
        //Log.d("TAG", value1 + "");

        //barEntries.add(new BarEntry(keyDate, value1));

    }
} catch (IOException | JSONException e) {
    e.printStackTrace();
    Log.d("ChartActivity", e.toString());
}

Answer 1

LocalDate and ThreeTenABP

    String dateString = "2019-11-27";
    LocalDate date = LocalDate.parse(dateString);
    int epochDay = (int) date.toEpochDay();

    System.out.println(epochDay);

This snippet outputs:

18227

The documentation explains:

The Epoch Day count is a simple incrementing count of days where day 0 is 1970-01-01 (ISO).

So my suggestion is that this number is fine for feeding into your BarEntry constructor.

toEpochDay() returns a long . If your constructor doesn't accept a long , convert to int . In the code above I did a simple cast. The risk is that we will get a very wrong result in case of int overflow for dates in the far future or the far past. I prefer to do a range check to avoid that:

    long epochDayLong = date.toEpochDay();
    if (epochDayLong < Integer.MIN_VALUE || epochDayLong > Integer.MAX_VALUE) {
        throw new IllegalStateException("Date " + date + " is out of range");
    }
    int epochDay = (int) epochDayLong;

The result is the same as before. This check is the same check that the Math.toIntExact method I mentioned in a comment does (available from Android API level 24).

I had converted this value 18227 to normal date and it gives date of this year 1970/01/01 and in JSON it's 2019-11-27 why? and how should i correct it?

Let me guess, you effectively did new Date(18227) . My suggestion is that you avoid the Date class completely and stick to java.time, the modern Java date and time API. Why you got 1970 is: 18227 is a count of days since the epoch, and Date counts milliseconds (since 00:00 UTC on the epoch day). So you got 00:00:18.227 UTC on that day. We already have a LocalDate in the above code, so just use that.

    System.out.println(date);

2019-11-27

Should you need to convert the opposite way, it's easy when you know how:

    LocalDate convertedBack = LocalDate.ofEpochDay(epochDay);

The result is a LocalDate with the same value.

Question: Doesn't java.time require Android API level 26?

java.time works nicely on both older and newer Android devices. It just requires at least Java 6 .

• In Java 8 and later and on newer Android devices (from API level 26) the modern API comes built-in.
• In non-Android Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310; see the links at the bottom).
• On (older) Android use the Android edition of ThreeTen Backport. It's called ThreeTenABP. And make sure you import the date and time classes from org.threeten.bp with subpackages.

Links

• Documentation of LocalDate.toEpochDay()
• Oracle tutorial: Date Time explaining how to use java.time.
• Java Specification Request (JSR) 310 , where java.time was first described.
• ThreeTen Backport project , the backport of java.time to Java 6 and 7 (ThreeTen for JSR-310).
• ThreeTenABP , Android edition of ThreeTen Backport
• Question: How to use ThreeTenABP in Android Project , with a very thorough explanation.