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Refactor -> StringUtils replace Optimization #33665

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Refactor -> StringUtils replace Optimization #33665

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10 changes: 6 additions & 4 deletions spring-core/src/main/java/org/springframework/util/StringUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -450,17 +450,19 @@ public static String replace(String inString, String oldPattern, @Nullable Strin
}

int capacity = inString.length();
if (newPattern.length() > oldPattern.length()) {
capacity += 16;

int newPatternLen = newPattern.length();
int oldPatternLen = oldPattern.length();
if (newPatternLen > oldPatternLen) {
capacity += Math.min(Integer.MAX_VALUE, newPatternLen - oldPatternLen);
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Can you elaborate on why Math.min(Integer.MAX_VALUE, newPatternLen - oldPatternLen) is used here?

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@J-unStiN J-unStiN Oct 8, 2024 •
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I thought that there might be a case where the length of NewPattern is larger than integer.max_value.

In that case, the size of StringBuilder can become ridiculously large when initialized, so I set the size to integer.max_value as a minimum safety measure.

++ If the size of integer.max_value is too large, I think it would be fine to just make it 1024 or 2048.

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capacity += Math.max(16, newPatternLen - oldPatternLen);

I would like to modify the initial size to 16 as in the existing code,
but if the length of newPattern is larger, I would like to modify it to newPatternLen - oldPatternLen.
What do you think?

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I think this change is likely to make performance worse. This part is trying to extend the capacity of the builder if the new pattern is longer than the one to be replaced. Here, this change assumes that the pattern will be replaced only once. If the pattern is replaced multiple times, the builder will be expanded again.

I guess 16 is a simple heuristic given that we don't know in advance how many patterns will be replaced. If anything, we could consider expanding the builder by (newPatternLen - oldPatternLen) * 8 because we would guess the builder needs to grow several times the difference.

Looking at our usage pattern in Spring Framework, we're massively using this method for single chars replacements like StringUtils.replace(result, "\r", "\\r");.

In summary, I don't think we should merge this change.

}
StringBuilder sb = new StringBuilder(capacity);

int pos = 0; // our position in the old string
int patLen = oldPattern.length();
while (index >= 0) {
sb.append(inString, pos, index);
sb.append(newPattern);
pos = index + patLen;
pos = index + oldPatternLen;
index = inString.indexOf(oldPattern, pos);
}

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