GSON /如何解析数字

Question

I want to parse JSON-documents with GSON. However, I have a problem with numbers.

My pattern is simply iterating over all tokens... that is first peeking and then doing stuff based on the TokenType in a switch-statement. The reader in the following code snippet is a JsonReader .

while (reader.hasNext() && !endReached) {
  final var nextToken = reader.peek();

  switch (nextToken) {
    case NUMBER:
      // reader.nextInt(), reader.nextLong(), reader.nextDouble()
      break;
    ...
  }
}

How do I know if it's an Integer/Long or a decimal value, maybe only fitting into a BigDecimal? Just calling nextString() and then try to parse the String with BigDecimal and so on?

Answer 1

In JSON , numbers are always floating-point numbers of the form
['-'] digits [ '.' digits ] [ 'e' sign digits ]

So basically a double , except NaN and ±Infinity .

For generic code use nextDouble() , unless you expect very large numbers, where BigDecimal needs to be used.

The nextInt() and nextLong() method are helper methods for when you know the number is supposed to be an integer value.