Using json.Number avoids parsing errors and preserves the original data format. When processing JSON data in Go, json.Unmarshal parses all numbers to float64 by default, which may cause integers to become floating point problems; by defining the field type as json.Number, such as type MyStruct struct { ID json.Number json:"id" }, the original numerical value can be maintained in the form of a string (such as "123" or "123.45"); the .Int64() or .Float64() method can be used when converting. If you are not sure of the type, it is recommended to check whether the string contains decimal points to distinguish integers and floating point numbers first; in addition, it is necessary to note that too large values ??may cause .Int64() to overflow, and illegal values ??will cause conversion errors; you can also combine custom UnmarshalJSON The method implements more flexible verification logic, such as limiting scope or mandatory type, thereby adding control rules during the parsing stage.
json.Number
is an easily overlooked but useful type when processing JSON data in Go. When you are not sure whether a JSON numeric field is an integer or a floating point number, using json.Number
can avoid parsing errors and preserve the original data format.

Use json.Number instead of float64
By default, Go's json.Unmarshal
parses all numbers into float64
, regardless of whether it is an integer or a floating point form. This can cause problems, such as if you were originally expecting an integer, but you end up with a decimal value.

To avoid this, you can use the json.Number
type to preserve the original numeric value:
type MyStruct struct { ID json.Number `json:"id"` }
This way, the ID
field can maintain the string representation in the original JSON, such as "123"
or "123.45"
without automatically converting to float64
.

Convert json.Number to the type you need
After getting json.Number
, you usually need to convert it to a specific type, such as int
, int64
or float64
. You can use its .Int64()
and .Float64()
methods:
-
.Int64()
: If the value is actually an integer, return the correspondingint64
-
.Float64()
:float64
will be returned regardless of whether it is an integer or not.
If you are not sure about the type, it is recommended to check the string representation first:
numStr := myStruct.ID.String() if strings.Contains(numStr, ".") { // Process floating point numbers} else { // Process integers}
Notice:
- If the value is too large,
.Int64()
may overflow - If the numbers in the original JSON are not legal values, an error will be reported during conversion
For more flexible processing with custom UnmarshalJSON
Sometimes you need to do additional verification or unified processing of numeric values, and you can implement the UnmarshalJSON
method to customize logic:
type MyNumber struct { json.Number } func (n *MyNumber) UnmarshalJSON(b []byte) error { var num json.Number if err := json.Unmarshal(b, &num); err != nil { return err } n.Number = num return nil }
This allows you to add your own rules during the parsing stage, such as limiting ranges, forcing integers, etc.
Basically that's it. The key is to understand that json.Number
is a string-wrapped number type, which can help you retain the original format and then type conversion when you really need it. As long as you pay attention to the boundary situation and potential error handling, it is not complicated to use but it is easy to ignore details.
The above is the detailed content of How to handle json.Number when unmarshaling in golang. For more information, please follow other related articles on the PHP Chinese website!

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