Java中的消息格式以及如何在Golang中复制消息格式

Question

Here's the Java code:

AtomicInteger obIndex = new AtomicInteger(0);
MessageFormat.format("{0,number,#},{1},{2},{3},\"{4}\"",
    obIndex.getAndIncrement(),
    "5bb2b35c67525f9e845648df370652b8",
    "Vm:vm-289",
    "1.1.1.1:113",
    "ABC-Testvm-1");

Output:

0,5bb2b35c67525f9e845648df370652b8,Vm:vm-289,1.1.1.1:113,"ABC-Testvm-1"

I tried this in Go:

value := fmt.Sprintf("%d,%s,%s,%s,%s",
    0,
    "5bb2b35c67525f9e845648df370652b8",
    "Vm:vm-289",
    "1.1.1.1:113", "ABC-Testvm-1")
fmt.Println(value)

Which outputs:

0,5bb2b35c67525f9e845648df370652b8,Vm:vm-289,1.1.1.1:113,ABC-Testvm-1

What is the significance of {0,number,#} and how can I get the same in Go?

Answer 1

This is detailed at java.text.MessageFormat. The string you pass to MessageFormat.format() is a pattern. A pattern consists of format elements. The form of a format element is:

 FormatElement:
         { ArgumentIndex }
         { ArgumentIndex , FormatType }
         { ArgumentIndex , FormatType , FormatStyle }

So in the first format element:

{0,number,#}

0 is the argument index whose value to format.

number is a format type, and # is a format style, more specifically a subformat pattern. This means the argument will be formatted using a subformat of:

new DecimalFormat(subformatPattern, DecimalFormatSymbols.getInstance(getLocale()))

The # subformat is described at java.text.DecimalFormat. It simply means to not use fraction digits, only display it as an integer, and if it is not an integer, it will be rounded (using the RoundingMode.HALF_EVEN mode).

In Go to format an integer number, you may simply use the %d verb as you did, which will yield the same output format for integer numbers. If the number is a floating point number, this won't work (%d can only be used for integers). If the number is a floating point number, use the %f verb, more specifically %.0f to tell it to round to an integer, or the shortest form %.f.

Also your Java version puts the last argument in double quotes, so you should do the same in Go.

value := fmt.Sprintf("%d,%s,%s,%s,\"%s\"",
    0,
    "5bb2b35c67525f9e845648df370652b8",
    "Vm:vm-289",
    "1.1.1.1:113", "ABC-Testvm-1")

fmt.Println(value)

This will output (try it on the Go Playground):

0,5bb2b35c67525f9e845648df370652b8,Vm:vm-289,1.1.1.1:113,"ABC-Testvm-1"