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Polish "Optimize allocation in StringUtils#cleanPath"

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This commit also introduces JMH benchmarks related to the code
optimizations.

Closes gh-2631
This commit is contained in:
Brian Clozel
2021-08-30 17:58:12 +02:00
parent 8d3e8ca3a2
commit cc026fcb8a
2 changed files with 123 additions and 33 deletions
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40
spring-core/src/main/java/org/springframework/util/StringUtils.java
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@@ -735,42 +735,11 @@ public abstract class StringUtils {
pathElements.addFirst(CURRENT_PATH);
}
final String joined = joinStrings(pathElements, FOLDER_SEPARATOR);
final String joined = collectionToDelimitedString(pathElements, FOLDER_SEPARATOR);
// avoid string concatenation with empty prefix
return prefix.isEmpty() ? joined : prefix + joined;
}
/**
* Convert a {@link Collection Collection<String>} to a delimited {@code String} (e.g. CSV).
* <p>This is an optimized variant of {@link #collectionToDelimitedString(Collection, String)}, which does not
* require dynamic resizing of the StringBuilder's backing array.
* @param coll the {@code Collection Collection&lt;String&gt;} to convert (potentially {@code null} or empty)
* @param delim the delimiter to use (typically a ",")
* @return the delimited {@code String}
*/
private static String joinStrings(@Nullable Collection<String> coll, String delim) {
if (CollectionUtils.isEmpty(coll)) {
return "";
}
// precompute total length of resulting string
int totalLength = (coll.size() - 1) * delim.length();
for (String str : coll) {
totalLength += str.length();
}
StringBuilder sb = new StringBuilder(totalLength);
Iterator<?> it = coll.iterator();
while (it.hasNext()) {
sb.append(it.next());
if (it.hasNext()) {
sb.append(delim);
}
}
return sb.toString();
}
/**
* Compare two paths after normalization of them.
* @param path1 first path for comparison
@@ -1330,7 +1299,12 @@ public abstract class StringUtils {
return "";
}
StringBuilder sb = new StringBuilder();
int totalLength = coll.size() * (prefix.length() + suffix.length()) + (coll.size() - 1) * delim.length();
for (Object element : coll) {
totalLength += element.toString().length();
}
StringBuilder sb = new StringBuilder(totalLength);
Iterator<?> it = coll.iterator();
while (it.hasNext()) {
sb.append(prefix).append(it.next()).append(suffix);