使用 JSON-Simple (Java) 在 JSON 数据中解析十进制数字，其中一些缺少小数分隔符

Question

I am trying to use the JSON-Simple JSON processor library.

When parsing JSON fragment such as:

"speed":1.13

…I call get and cast as a Double . No problem.

Double speed = ( Double ) wind.get( "speed" );

But then I encounter a value without a decimal fraction. Ex: 1 rather than 1.0 .

"speed":1

Granted, the publisher of this data should have written "speed":1.0 . But they did not.

My get with casting throws an exception:

Exception in thread "main" java.lang.ClassCastException: class java.lang.Long cannot be cast to class java.lang.Double (java.lang.Long and java.lang.Double are in module java.base of loader 'bootstrap')

Apparently JSON-Simple insisted on parsing the JSON value of 1 as a Long . So I need a workaround, a way to tell JSON-Simple how to parse this particular element.

➥ Is there a way to tell JSON-Simple to parse the string inputs as Double regardless of whether a decimal separator (a decimal point) is present?

➥ Even better, can I tell JSON-Simple to parse the string input for a particular JSON element as BigDecimal to bypass the inaccuracy of floating-point ? (that is, going from String to BigDecimal without involving floating-point along the way)

Answer 1

Instead of casting try

Double.parseDouble(wind.get( "speed" ).toString())

Answer 2

Use later version

You are using the original JSON-Simple library led by Fang Yidong. Later versions 2 and 3 were developed as a fork at this Clifton Labs page on GitHub, led by Davin Loegering.

The original does not support BigDecimal . The fork does supports BigDecimal . See the getBigDecimal method.

The fork has changed the original library quite a bit. See the History section of that Clifton Labs page .