Commons Lang StringUtils.replace性能vs String.replace

Question

当我比较Apache
StringUtils.replace()与vs的性能时，String.replace()我惊讶地发现前者的速度大约是后者的4倍。我使用Google的Caliper框架来衡量性能。这是我的测试

public class Performance extends SimpleBenchmark {
    String s = "111222111222";

    public int timeM1(int n) {
        int res = 0;
        for (int x = 0; x < n; x++) {
            res += s.replace("111", "333").length();
        }
        return res;
    }

    public int timeM2(int n) {
        int res = 0;
        for (int x = 0; x < n; x++) {
            res += StringUtils.replace(s, "111", "333", -1).length();
        }
        return res;
    }

    public static void main(String... args) {
        Runner.main(Performance.class, args);
    }
}

输出

 0% Scenario{vm=java, trial=0, benchmark=M1} 9820,93 ns; ?=1053,91 ns @ 10 trials
50% Scenario{vm=java, trial=0, benchmark=M2} 2594,67 ns; ?=58,12 ns @ 10 trials

benchmark   us linear runtime
       M1 9,82 ==============================
       M2 2,59 =======

这是为什么？两种方法似乎做同样的工作，StringUtils.replace()甚至更加灵活。

Answer 1

从1的源代码中：java.lang.String

public String replace(CharSequence target, CharSequence replacement) {
   return Pattern
            .compile(target.toString(), Pattern.LITERAL)
            .matcher(this )
            .replaceAll(
                    Matcher.quoteReplacement(replacement.toString()));
}

String.replace(CharSequence target, CharSequence replacement)与实施java.util.regex.Pattern，因此，它是不奇怪的是较慢的是2，这是与实现和。StringUtils.replace(String text, String searchString, String replacement)indexOf``StringBuffer

public static String replace(String text, String searchString, String replacement) {
    return replace(text, searchString, replacement, -1);
}

public static String replace(String text, String searchString, String replacement, int max) {
    if (isEmpty(text) || isEmpty(searchString) || replacement == null || max == 0) {
        return text;
    }
    int start = 0;
    int end = text.indexOf(searchString, start);
    if (end == -1) {
        return text;
    }
    int replLength = searchString.length();
    int increase = replacement.length() - replLength;
    increase = (increase < 0 ? 0 : increase);
    increase *= (max < 0 ? 16 : (max > 64 ? 64 : max));
    StringBuffer buf = new StringBuffer(text.length() + increase);
    while (end != -1) {
        buf.append(text.substring(start, end)).append(replacement);
        start = end + replLength;
        if (--max == 0) {
            break;
        }
        end = text.indexOf(searchString, start);
    }
    buf.append(text.substring(start));
    return buf.toString();
}

脚注

1我链接到并复制源代码的版本是JDK 7

2我链接到并从中复制源代码的版本是common-lang-2.5