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在频繁调用场景#xff0c;如方法体内或者循环语句中#xff0c;新定义Pattern会导致重复预编译正则表达式#xff0c;降低程序执行效率。另外#xff0c;在 JDK 中部分 入参为正则表达式格式的 API#xff0c;如 String.replaceAll, String.split 等#xff0c;也…背景
在频繁调用场景如方法体内或者循环语句中新定义Pattern会导致重复预编译正则表达式降低程序执行效率。另外在 JDK 中部分 入参为正则表达式格式的 API如 String.replaceAll, String.split 等也需要关注性能问题。
验证
正例
将 Pattern 对象预编译并在常量中声明。 private static final String IP_V4 ^(((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))\\.){3}((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))$;// Pattern 常量private static final Pattern IP_V4_PATTERN Pattern.compile(IP_V4);public static boolean isValidIpv4V2(String input) {if (input null) {return false;}return IP_V4_PATTERN.matcher(input).matches();}反例
每次调用时才声明 Pattern。 private static final String IP_V4 ^(((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))\\.){3}((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))$;public static boolean isValidIpv4V1(String input) {if (input null) {return false;}Pattern pattern Pattern.compile(IP_V4);return pattern.matcher(input).matches();}测试代码
package com.ysx.utils.pattern.performance;import org.junit.jupiter.api.Test;import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.regex.Pattern;/*** author youngbear* email youngbearaliyun.com* date 2023-09-17 8:31* blog a hrefhttps://blog.csdn.net/next_second.../a* github a hrefhttps://github.com/YoungBear.../a* description 正则表达式性能测试*/
public class PrecompilePerformanceTest {private static final String IP_V4 ^(((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))\\.){3}((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))$;// Pattern 常量private static final Pattern IP_V4_PATTERN Pattern.compile(IP_V4);// 缓存private static final MapString, Pattern cacheCompilePatternMap new ConcurrentHashMap();public static boolean isValidIpv4V1(String input) {if (input null) {return false;}Pattern pattern Pattern.compile(IP_V4);return pattern.matcher(input).matches();}public static boolean isValidIpv4V2(String input) {if (input null) {return false;}return IP_V4_PATTERN.matcher(input).matches();}public static boolean isValidIpv4V3(String input) {if (input null) {return false;}if (!cacheCompilePatternMap.containsKey(IP_V4)) {cacheCompilePatternMap.put(IP_V4, Pattern.compile(IP_V4));}Pattern pattern cacheCompilePatternMap.get(IP_V4);return pattern.matcher(input).matches();}Testpublic void performanceTest() {String input1 192.168.12.13;long start System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V1(input1);}long stop System.currentTimeMillis();System.out.println(isValidIpv4V1, input1, consume: (stop - start) ms);String input2 192.168.12.13;long start2 System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V1(input2);}long stop2 System.currentTimeMillis();System.out.println(isValidIpv4V1, input2, consume: (stop2 - start2) ms);}Testpublic void performanceV2Test() {String input1 192.168.12.13;long start System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V2(input1);}long stop System.currentTimeMillis();System.out.println(isValidIpv4V2, input1, consume: (stop - start) ms);String input2 192.168.12.13;long start2 System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V2(input2);}long stop2 System.currentTimeMillis();System.out.println(isValidIpv4V2, input2, consume: (stop2 - start2) ms);}Testpublic void performanceV3Test() {String input1 192.168.12.13;long start System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V3(input1);}long stop System.currentTimeMillis();System.out.println(isValidIpv4V3, input1, consume: (stop - start) ms);String input2 192.168.12.13;long start2 System.currentTimeMillis();for (int i 0; i 10000; i) {isValidIpv4V3(input2);}long stop2 System.currentTimeMillis();System.out.println(isValidIpv4V3, input2, consume: (stop2 - start2) ms);}}
执行结果
isValidIpv4V1, input1, consume: 232ms
isValidIpv4V1, input2, consume: 74ms
isValidIpv4V2, input1, consume: 24ms
isValidIpv4V2, input2, consume: 19ms
isValidIpv4V3, input1, consume: 20ms
isValidIpv4V3, input2, consume: 12ms根据执行结果可以明显看到预编译正则表达式可以提升性能。
总结
通常情况下正则表达式为常量所以可以将其作为常量量在类编译时预编译。 private static final Pattern xxx_PATTERN Pattern.compile(xxx);对于动态的正则表达式可以将其缓存即缓存其 Pattern 结果。参考 isValidIpv4V3 )。另外对于外部收入的正则表达式一定要校验其安全性防止 ReDos 攻击。
