1. 前言
项目中的TCP连接器需要解码终端设备上传的指令，绝大多数的指令数据字段字段基于","进行分隔，主要使用Java字符串的原生split方法。近期，在优化连接器性能的过程中，对于字符串分割的性能表现产生好奇。
因此基于网上给出的benchmark代码，测试不同编译器下，常见的字符串分割方法的性能表现（注意，基于单字符进行测试）。
2. 测试代码
原始Benchmark代码地址（本文对引用的代码主要进行了格式化调整）：
package org.example;
import java.util.*;
public class Main {
public static void main(String[] args) {
System.out.println("Java Version: " + System.getProperty("java.version"));
System.out.println("Java Vendor: " + System.getProperty("java.vendor") + "\n");
int n = 10000000;
long start;
start = System.currentTimeMillis();
for (int i = 0; i < n; i++) {
split_banthar(TEST_STR, ',');
}
System.out.println("split_banthar: " + (System.currentTimeMillis() - start));
start = System.currentTimeMillis();
for (int i = 0; i < n; i++) {
split_tskuzzy(TEST_STR, ',');
}
System.out.println("split_tskuzzy: " + (System.currentTimeMillis() - start));
start = System.currentTimeMillis();
for (int i = 0; i < n; i++) {
split_tskuzzy2(TEST_STR, ',');
}
System.out.println("split_tskuzzy2: " + (System.currentTimeMillis() - start));
start = System.currentTimeMillis();
for (int i = 0; i < n; i++) {
split_string_split(TEST_STR, ",");
}
System.out.println("string.split: " + (System.currentTimeMillis() - start));
start = System.currentTimeMillis();
for (int i = 0; i < n; i++) {
split_tokenizer(TEST_STR, ",");
}
System.out.println("StringTokenizer: " + (System.currentTimeMillis() - start));
}
private static final String TEST_STR = "a,b,c,d,e,f,g,h,i,j,asd,asdas,dasdjasodjoa,sjd,oajs,djoasjd,as,odj,jaowdj,oajw,odj,aojwd,oja,owjd,oja,wjdoja,wdj,awjdojaw,odj,oawjd,oja,wjdoawjdojaw,d,dff";
public static String[] split_tskuzzy(String s, char delimiter) {
char[] c = s.toCharArray();
List<String> ll = new ArrayList<>();
int index = 0;
for (int i = 0; i < c.length; i++) {
if (c[i] == delimiter) {
ll.add(s.substring(index, i));
index = i + 1;
}
}
return ll.toArray(new String[0]);
}
public static String[] split_tskuzzy2(String s, char delimiter) {
List<String> ll = new ArrayList<>();
int index = 0;
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == delimiter) {
ll.add(s.substring(index, i));
index = i + 1;
}
}
if (index != s.length()) {
ll.add(s.substring(index));
}
return ll.toArray(new String[0]);
}
public static String[] split_banthar(String s, char delimiter) {
int count = 1;
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == delimiter) {
count++;
}
}
String[] array = new String[count];
int a = -1;
int b = 0;
for (int i = 0; i < count; i++) {
while (b < s.length() && s.charAt(b) != delimiter) {
b++;
}
array[i] = s.substring(a + 1, b);
a = b;
b++;
}
return array;
}
private static String[] split_tokenizer(String s, String delimiter) {
List<String> ll = new ArrayList<>();
StringTokenizer tokenizer = new StringTokenizer(s, delimiter);
while (tokenizer.hasMoreElements()) {
ll.add((String) tokenizer.nextElement());
}
return ll.toArray(new String[0]);
}
private static String[] split_string_split(String s, String delimiter) {
return s.split(delimiter);
}
}3. 测试结果
3.1 Java 8
Java Version: 1.8.0_422
Java Vendor: Amazon.com Inc.
split_banthar: 4183
split_tskuzzy: 3870
split_tskuzzy2: 4158
string.split: 3847
StringTokenizer: 49233.2 Java 11
Java Version: 11.0.24
Java Vendor: Amazon.com Inc.
split_banthar: 4741
split_tskuzzy: 4117
split_tskuzzy2: 5739
string.split: 4237
StringTokenizer: 51323.3 Java 17
Java Version: 17.0.12
Java Vendor: Amazon.com Inc.
split_banthar: 4077
split_tskuzzy: 3924
split_tskuzzy2: 5539
string.split: 4057
StringTokenizer: 55193.4 Java 21
Java Version: 21.0.3
Java Vendor: Amazon.com Inc.
split_banthar: 4881
split_tskuzzy: 4256
split_tskuzzy2: 5737
string.split: 4394
StringTokenizer: 56274. 结论
基于以上的测试结果，可以放心的使用Java中String的原生方法spilt进行单字符分割。
实际上，Java String的spilt方法对单字符（非特殊正则表达式字符）进行了特例优化，满足性能要求，具体参考如下Java源码。
public String[] split(String regex, int limit) {
/* fastpath if the regex is a
(1)one-char String and this character is not one of the
RegEx's meta characters ".$|()[{^?*+\\", or
(2)two-char String and the first char is the backslash and
the second is not the ascii digit or ascii letter.
*/
char ch = 0;
if (((regex.length() == 1 &&
".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
(regex.length() == 2 &&
regex.charAt(0) == '\\' &&
(((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
((ch-'a')|('z'-ch)) < 0 &&
((ch-'A')|('Z'-ch)) < 0)) &&
(ch < Character.MIN_HIGH_SURROGATE ||
ch > Character.MAX_LOW_SURROGATE))
{
int off = 0;
int next = 0;
boolean limited = limit > 0;
ArrayList<String> list = new ArrayList<>();
while ((next = indexOf(ch, off)) != -1) {
if (!limited || list.size() < limit - 1) {
list.add(substring(off, next));
off = next + 1;
} else { // last one
//assert (list.size() == limit - 1);
int last = length();
list.add(substring(off, last));
off = last;
break;
}
}
// If no match was found, return this
if (off == 0)
return new String[]{this};
// Add remaining segment
if (!limited || list.size() < limit)
list.add(substring(off, length()));
// Construct result
int resultSize = list.size();
if (limit == 0) {
while (resultSize > 0 && list.get(resultSize - 1).isEmpty()) {
resultSize--;
}
}
String[] result = new String[resultSize];
return list.subList(0, resultSize).toArray(result);
}
return Pattern.compile(regex).split(this, limit);
}