pjfanning opened a new pull request, #1399:
URL: https://github.com/apache/poi/pull/1399
`String.replaceAll` and `String.replaceFirst` compile their regex on every
call. Several of these calls run once per formatted cell.
## Changes
- `DataFormatter`
- The E-notation fix-up `replaceFirst("E(\\d)", "E+$1")` runs for every
formatted number; it now uses a static `Pattern`.
- The other per-call regexes use static `Pattern`s too: the fraction chunk
spaces, the `E` → `E+` fix-up in `formatRawCellContents`, and trimming trailing
commas (which now reuses the existing `endsWithCommas` pattern).
- `ExcelStyleDateFormatter`
- `format()` runs for every date cell. The `MMMMM` truncation regex is now
a static `Pattern`.
- The eight elapsed-time and millisecond placeholder replacements now use
`String.replace`. They replace a single private-use character with digits, so
no regex was needed.
- The `s.000`, `s.00` and `s.0` rewrites in `processFormatPattern` are now
static `Pattern`s. They keep their regex semantics, where `.` matches any
character, so behaviour is unchanged.
- `DateUtil.parseDateTime`: uses a static whitespace `Pattern`.
## Thread safety
`Pattern` is immutable and safe to share between threads. Each call still
creates its own `Matcher`, and no `Matcher` is cached or shared.
`ExcelStyleDateFormatter` does have an existing problem: its static
`DecimalFormat` fields (`format1digit` and the others) are shared across all
instances, and `DecimalFormat` is not thread-safe. This PR doesn't change that.
## Tests
`TestDataFormatter`, `TestExcelStyleDateFormatter`, `TestDateUtil` and
`TestHSSFDataFormatter` pass locally.
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