[GitHub] [druid] suneet-s commented on a change in pull request #9215: [0.17.0] Speed up String first/last aggregators when folding isn't needed. (#9181)

[GitBox <gi...@apache.org>]

suneet-s commented on a change in pull request #9215: [0.17.0] Speed up String first/last aggregators when folding isn't needed. (#9181)
URL: https://github.com/apache/druid/pull/9215#discussion_r368190414
 
 

 ##########
 File path: core/src/main/java/org/apache/druid/java/util/common/StringUtils.java
 ##########
 @@ -546,4 +546,39 @@ public static String rpad(String base, Integer len, String pad)
     return new String(data);
   }
 
+  /**
+   * Returns the string truncated to maxBytes.
+   * If given string input is shorter than maxBytes, then it remains the same.
+   *
+   * @param s        The input string to possibly be truncated
+   * @param maxBytes The max bytes that string input will be truncated to
+   *
+   * @return the string after truncated to maxBytes
+   */
+  @Nullable
+  public static String chop(@Nullable final String s, final int maxBytes)
+  {
+    if (s == null) {
+      return null;
+    } else {
+      // Shorten firstValue to what could fit in maxBytes as UTF-8.
+      final byte[] bytes = new byte[maxBytes];
+      final int len = StringUtils.toUtf8WithLimit(s, ByteBuffer.wrap(bytes));
+      return new String(bytes, 0, len, StandardCharsets.UTF_8);
+    }
+  }
+
+  /**
+   * Shorten "s" to "maxBytes" chars. Fast and loose because these are *chars* not *bytes*. Use
+   * {@link #chop(String, int)} for slower, but accurate chopping.
+   */
+  @Nullable
+  public static String fastLooseChop(@Nullable final String s, final int maxBytes)
+  {
+    if (s == null || s.length() <= maxBytes) {
+      return s;
+    } else {
+      return s.substring(0, maxBytes);
+    }
 
 Review comment:
   To resolve I moved chop and fastLooseChop to StringUtils since this has tests with them and renamed references in StringFirst/Last aggs

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