[LANG-1588] performance refine for StringUtils.center

src/main/java/org/apache/commons/lang3/StringUtils.java

@@ -621,9 +621,11 @@ public static String center(String str, final int size, final char padChar) {
         if (pads <= 0) {
             return str;
         }
-        str = leftPad(str, strLen + pads / 2, padChar);
-        str = rightPad(str, size, padChar);
-        return str;
+        StringBuilder stringBuilder = new StringBuilder(size);
+        repeat(stringBuilder, padChar, pads / 2);
+        stringBuilder.append(str);
+        repeat(stringBuilder, padChar, size - (strLen + pads / 2));
+        return stringBuilder.toString();
     }
 
     /**
@@ -6253,6 +6255,23 @@ public static String repeat(final char ch, final int repeat) {
         return new String(buf);
     }
 
+    /**
+     * <p>Make the padding using the specified delimiter repeated
+     * to a given length, and fill the result to a StringBuilder</p>
+     *
+     * This function works like {@code stringBuilder.append(repeat(ch,repeat))}, but runs faster.
+     *
+     * @param stringBuilder  stringBuilder to fill
+     * @param ch  character to repeat
+     * @param repeat  number of times to repeat char, negative treated as zero
+     * @see #repeat(char, int)
+     */
+    static void repeat(StringBuilder stringBuilder, final char ch, final int repeat) {
+        for (int i = repeat - 1; i >= 0; i--) {
+            stringBuilder.append(ch);
+        }
+    }
+
     /**
      * <p>Repeat a String {@code repeat} times to form a
      * new String.</p>

src/test/java/org/apache/commons/lang3/StringUtilCenterTest.java

@@ -0,0 +1,137 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.lang3;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+
+import java.util.concurrent.TimeUnit;
+
+import static org.apache.commons.lang3.StringUtils.leftPad;
+import static org.apache.commons.lang3.StringUtils.repeat;
+import static org.apache.commons.lang3.StringUtils.rightPad;
+
+/**
+ * Test to show whether using BitSet for removeAll() methods is faster than using HashSet.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Thread)
+public class StringUtilCenterTest {
+
+    @Benchmark
+    public void test0Old() {
+        centerOld("a", 20, 'a');
+    }
+
+    @Benchmark
+    public void test0New() {
+        centerNew("a", 20, 'a');
+    }
+
+    @Benchmark
+    public void test1Old() {
+        centerOld("a", 10000000, ' ');
+    }
+
+    @Benchmark
+    public void test1New() {
+        centerNew("a", 10000000, ' ');
+    }
+
+    /**
+     * <p>Centers a String in a larger String of size {@code size}.
+     * Uses a supplied character as the value to pad the String with.</p>
+     *
+     * <p>If the size is less than the String length, the String is returned.
+     * A {@code null} String returns {@code null}.
+     * A negative size is treated as zero.</p>
+     *
+     * <pre>
+     * StringUtils.center(null, *, *)     = null
+     * StringUtils.center("", 4, ' ')     = "    "
+     * StringUtils.center("ab", -1, ' ')  = "ab"
+     * StringUtils.center("ab", 4, ' ')   = " ab "
+     * StringUtils.center("abcd", 2, ' ') = "abcd"
+     * StringUtils.center("a", 4, ' ')    = " a  "
+     * StringUtils.center("a", 4, 'y')    = "yayy"
+     * </pre>
+     *
+     * @param str  the String to center, may be null
+     * @param size  the int size of new String, negative treated as zero
+     * @param padChar  the character to pad the new String with
+     * @return centered String, {@code null} if null String input
+     * @since 2.0
+     */
+    public static String centerNew(String str, final int size, final char padChar) {
+        if (str == null || size <= 0) {
+            return str;
+        }
+        final int strLen = str.length();
+        final int pads = size - strLen;
+        if (pads <= 0) {
+            return str;
+        }
+        StringBuilder stringBuilder = new StringBuilder(size);
+        repeat(stringBuilder, padChar, pads / 2);
+        stringBuilder.append(str);
+        repeat(stringBuilder, padChar, size - (strLen + pads / 2));
+        return stringBuilder.toString();
+    }
+
+    /**
+     * <p>Centers a String in a larger String of size {@code size}.
+     * Uses a supplied character as the value to pad the String with.</p>
+     *
+     * <p>If the size is less than the String length, the String is returned.
+     * A {@code null} String returns {@code null}.
+     * A negative size is treated as zero.</p>
+     *
+     * <pre>
+     * StringUtils.center(null, *, *)     = null
+     * StringUtils.center("", 4, ' ')     = "    "
+     * StringUtils.center("ab", -1, ' ')  = "ab"
+     * StringUtils.center("ab", 4, ' ')   = " ab "
+     * StringUtils.center("abcd", 2, ' ') = "abcd"
+     * StringUtils.center("a", 4, ' ')    = " a  "
+     * StringUtils.center("a", 4, 'y')    = "yayy"
+     * </pre>
+     *
+     * @param str  the String to center, may be null
+     * @param size  the int size of new String, negative treated as zero
+     * @param padChar  the character to pad the new String with
+     * @return centered String, {@code null} if null String input
+     * @since 2.0
+     */
+    public static String centerOld(String str, final int size, final char padChar) {
+        if (str == null || size <= 0) {
+            return str;
+        }
+        final int strLen = str.length();
+        final int pads = size - strLen;
+        if (pads <= 0) {
+            return str;
+        }
+        str = leftPad(str, strLen + pads / 2, padChar);
+        str = rightPad(str, size, padChar);
+        return str;
+    }
+}