[Enhancement] Report the first failure from write finish() instead of the last

[nkuprins]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

WriteContextImpl#finish(boolean) runs its steps one after another and collects failures into a single throwable. Each catch overwrites it, so when more than one step fails, the caller only sees the last failure (code). Shortened:

Throwable throwable = null;
...
try {
    workbook.write(outputStream);    // 1. fails
    workbook.close();
} catch (Throwable t) {
    throwable = t;                   //    recorded
}
...
try {
    outputStream.close();            // 2. fails too, because the stream is already broken
} catch (Throwable t) {
    throwable = t;                   //    overwrites 1.
}
...
if (throwable != null) {
    throw new ExcelGenerateException("Can not close IO.", throwable);   // cause = 2.
}

Solution

The first catch can't overwrite anything. In the five after it, keep the exception only if none has been recorded yet:

} catch (Throwable t) {
    if (throwable == null) {
        throwable = t;
    }
}

Alternatives

Attach later failures with addSuppressed. Nothing is lost, but each catch gets a helper call, and later failures are usually consequences of the first anyway.

Anything else?

For background: when this code was first written, each of these catch blocks threw straight away, so the first failure was the one reported. alibaba/easyexcel@2c8918be changed them to save the exception and carry on, so the later close steps would still run.

Are you willing to submit a PR?

• I'm willing to submit a PR!