使用freemarker中的小數點處理的一點心得！

阿新 • • 發佈：2019-01-13

在開發中很容易忽視一點，輸入一個值(可能是小數)，輸出時如果不做處理，就很容易出現

隱形的BUG。比如，如果從資料庫取出一個0.22的數值，一般的輸出${x?if_exists?html},

這時是顯示0，而不是0.22。

應該寫成${x?if_exists?string.number} 或者 ${x?if_exists.toString()?html}

下面就是關於數字的具體介紹：

Built-ins for numbers

Related FAQs: Do you have things like 1,000,000 or 1 000 000 instead of 1000000, or something like 3.14 instead of 3,14 or vice versa? See this and this FAQ entry, also note the c built-in above.

c
Note

This built-in exists since FreeMarker 2.3.3.

This built-in converts a number to string for ``computer audience'' as opposed to human audience. That is, it formats with the rules that programming languages used to use, which is independent of all the locale and number format settings of FreeMarker. It always uses dot as decimal separator, and it never uses grouping separators (like 3,000,000), nor exponential form (like 5E20), nor superfluous leading or trailing 0-s (like 03 or 1.0), nor + sign (like +1). It will print at most 16 digits after the decimal dot, and thus numbers whose absolute value is less than 1E-16 will be shown as 0. This built-in is crucial because be default (like with ${x}) numbers are converted to strings with the locale (language, country) specific number formatting, which is for human readers (like 300000 is possibly printed as 3,000,000). When the number is printed not for human audience (e.g., for a database record ID used as the part of an URL, or as invisible field value in a HTML form, or for printing CSS/JavaScript numerical literals) this built-in must be used to print the number (i.e., use ${x?c} instead of ${x}), or else the output will be possibly broken depending on the current number formatting settings and locale (like the decimal point is not dot, but comma in many countries) and the value of the number (like big numbers are possibly ``damaged'' by grouping separators).

string (when used with a numerical value)

Converts a number to a string. It uses the default format that the programmer has specified. You can also specify a number format explicitly with this built-in, as it will be shown later.

There are three predefined number formats: number, currency, and percent. The exact meaning of these is locale (nationality) specific, and is controlled by the Java platform installation, rather than by FreeMarker. You can use these predefined formats like this:

<#assign x=42>
${x}
${x?string} <#-- the same as ${x} -->
${x?string.number}
${x?string.currency}
${x?string.percent}

If your locale is US English, this will certainly produce:

42
42
42
$42.00
4,200%

The output of first three expressions is identical because the first two expressions use the default format, which is "number" here. You can change this default using a setting:

<#setting number_format="currency">
<#assign x=42>
${x}
${x?string} <#-- the same as ${x} -->
${x?string.number}
${x?string.currency}
${x?string.percent}

Will now output:

$42.00
$42.00
42
$42.00
4,200%

since the default number format was set to "currency".

Beside the three predefined formats, you can use arbitrary number format patterns written in Java decimal number format syntax:

<#assign x = 1.234>
${x?string("0")}
${x?string("0.#")}
${x?string("0.##")}
${x?string("0.###")}
${x?string("0.####")}

${1?string("000.00")}
${12.1?string("000.00")}
${123.456?string("000.00")}

${1.2?string("0")}
${1.8?string("0")}
${1.5?string("0")} <-- 1.5, rounded towards even neighbor
${2.5?string("0")} <-- 2.5, rounded towards even neighbor

${12345?string("0.##E0")}

outputs this:

1
1.2
1.23
1.234
1.234

001.00
012.10
123.46

1
2
2 <-- 1.5, rounded towards even neighbor
2 <-- 2.5, rounded towards even neighbor

1.23E4

Following the financial and statistics practice, the rounding goes according the so called half-even rule, which means rounding towards the nearest ``neighbor'', unless both neighbors are equidistant, in which case, it rounds towards the even neighbor. This was visible in the above example if you look at the rounding of 1.5 and of 2.5, as both were rounded to 2, since 2 is even, but 1 and 3 are odds.

Appart from the Java decimal syntax patterns, you can also write ${aNumber?string("currency")} and like, that will do the same as ${aNumber?string.currency} and like.

As it was shown for the predefined formats earlier, the default formatting of the numbers can be set in the template:

<#setting number_format="0.##">
${1.234}

outputs this:

1.23

Note that the number formatting is locale sensitive:

<#setting locale="en_US">
US people write:        ${12345678?string(",##0.00")}
<#setting locale="hu">
Hungarian people write: ${12345678?string(",##0.00")}

outputs this:

US people write:        12,345,678.00
Hungarian people write: 12 345 678,00

You can find information about the formatting of dates here.
round, floor, ceiling
Note

The rounding built-ins exist since FreeMarker 2.3.13.

Converts a number to a whole number using the specified rounding rule:

    *

      round: Rounds to the nearest whole number. If the number ends with .5, then it rounds upwards (i.e., towards positive infinity)
    *

      floor: Rounds the number downwards (i.e., towards neagative infinity)
    *

      ceiling: Rounds the number upwards (i.e., towards positive infinity)

Example:

<#assign testlist=[
0, 1, -1, 0.5, 1.5, -0.5,
-1.5, 0.25, -0.25, 1.75, -1.75]>
<#list testlist as result>
    ${result} ?floor=${result?floor} ?ceiling=${result?ceiling} ?round=${result?round}
</#list>

Prints:

    0 ?floor=0 ?ceiling=0 ?round=0
    1 ?floor=1 ?ceiling=1 ?round=1
    -1 ?floor=-1 ?ceiling=-1 ?round=-1
    0.5 ?floor=0 ?ceiling=1 ?round=1
    1.5 ?floor=1 ?ceiling=2 ?round=2
    -0.5 ?floor=-1 ?ceiling=0 ?round=0
    -1.5 ?floor=-2 ?ceiling=-1 ?round=-1
    0.25 ?floor=0 ?ceiling=1 ?round=0
    -0.25 ?floor=-1 ?ceiling=0 ?round=0
    1.75 ?floor=1 ?ceiling=2 ?round=2
    -1.75 ?floor=-2 ?ceiling=-1 ?round=-2

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使用freemarker中的小數點處理的一點心得！

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