cor3000 opened a new pull request #215:
URL: https://github.com/apache/poi/pull/215
improves parseDouble performance by about 85%-90%
100000 invocations
before ~230ms
after ~28ms (using a precompiled regex)
I am not sure how to add a meaningful performance unit test for this in this
project.
Here my local test printing comparing the two different method
implementations:
```
import org.junit.Test;
import java.util.regex.Pattern;
public class TestParseDoublePerformance {
private static final String fpRegex =
"[\\x00-\\x20]*[+-]?(((((\\p{Digit}+)(\\.)?((\\p{Digit}+)?)([eE][+-]?(\\p{Digit}+))?)|(\\.((\\p{Digit}+))([eE][+-]?(\\p{Digit}+))?))))[\\x00-\\x20]*";
private static final Pattern fpPattern = Pattern.compile(fpRegex);
@Test
public void testPerformance() {
long start;
for (int j = 0; j < 10; j++) {
start = System.nanoTime();
for(int i = 0; i < 100000; i++) {
parseDouble(1000 + ".1234" + i);
}
System.out.println("100000 x Pattern.matches(fpRegex,
pText) : " + ((System.nanoTime() - start) / 1000000.0) + "ms");
start = System.nanoTime();
for(int i = 0; i < 100000; i++) {
parseDouble2(1000 + ".1234" + i);
}
System.out.println("100000 x
fpPattern.matcher(pText).matches(): " + ((System.nanoTime() - start) /
1000000.0) + "ms");
}
}
public static Double parseDouble(String pText) {
if (Pattern.matches(fpRegex, pText)) {
try {
return Double.parseDouble(pText);
} catch (NumberFormatException var2) {
return null;
}
} else {
return null;
}
}
public static Double parseDouble2(String pText) {
if (fpPattern.matcher(pText).matches()) {
try {
return Double.parseDouble(pText);
} catch (NumberFormatException var2) {
return null;
}
} else {
return null;
}
}
}
```
Output (using jdk 11)
```
100000 x Pattern.matches(fpRegex, pText) : 528.583911ms
100000 x fpPattern.matcher(pText).matches(): 36.131033ms
100000 x Pattern.matches(fpRegex, pText) : 247.689554ms
100000 x fpPattern.matcher(pText).matches(): 28.203332ms
100000 x Pattern.matches(fpRegex, pText) : 230.243142ms
100000 x fpPattern.matcher(pText).matches(): 28.258646ms
100000 x Pattern.matches(fpRegex, pText) : 246.361356ms
100000 x fpPattern.matcher(pText).matches(): 28.530509ms
100000 x Pattern.matches(fpRegex, pText) : 232.466833ms
100000 x fpPattern.matcher(pText).matches(): 29.992254ms
100000 x Pattern.matches(fpRegex, pText) : 232.972345ms
100000 x fpPattern.matcher(pText).matches(): 27.680976ms
100000 x Pattern.matches(fpRegex, pText) : 227.946587ms
100000 x fpPattern.matcher(pText).matches(): 28.363269ms
100000 x Pattern.matches(fpRegex, pText) : 235.331679ms
100000 x fpPattern.matcher(pText).matches(): 27.830178ms
100000 x Pattern.matches(fpRegex, pText) : 233.785736ms
100000 x fpPattern.matcher(pText).matches(): 29.759473ms
100000 x Pattern.matches(fpRegex, pText) : 231.619982ms
100000 x fpPattern.matcher(pText).matches(): 28.545904ms
```
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