Android 14 新特性代码 UUID.fromString Matcher.matches 的细节改动（扒源码）

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前言

Android 14 已经出来好久好久了…

今天其他的暂且不论，单纯的讲一下 OpenJDK 17 更新的两点变更（扒源代码）~

• 对正则表达式的更改
• UUID 处理

首先，正则表达式的更改：现在，为了更严格地遵循 OpenJDK 的语义，不允许无效的组引用。您可能会看到 java.util.regex.Matcher 类抛出 IllegalArgumentException 的新情况，因此请务必测试应用中使用正则表达式的情形。如需在测试期间启用或停用此变更，请使用兼容性框架工具切换 DISALLOW_INVALID_GROUP_REFERENCE 标志。

其次，UUID 处理：现在，验证输入参数时，java.util.UUID.fromString() 方法会执行更严格的检查，因此您可能会在反序列化期间看到 IllegalArgumentException。如需在测试期间启用或停用此变更，请使用兼容性框架工具切换 ENABLE_STRICT_VALIDATION 标志。

巴拉巴拉，以上是官网的言论，诸君可以看官方的描述地址

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UUID 处理的更改

原有代码逻辑~

 /*** Creates a {@code UUID} from the string standard representation as* described in the {@link #toString} method.** @param  name*         A string that specifies a {@code UUID}** @return  A {@code UUID} with the specified value** @throws  IllegalArgumentException*          If name does not conform to the string representation as*          described in {@link #toString}**/public static UUID fromString(String name) {String[] components = name.split("-");if (components.length != 5)//仅会判断以-分割的数组长度是否等于5来抛出异常throw new IllegalArgumentException("Invalid UUID string: "+name);for (int i=0; i<5; i++)components[i] = "0x"+components[i];long mostSigBits = Long.decode(components[0]).longValue();mostSigBits <<= 16;mostSigBits |= Long.decode(components[1]).longValue();mostSigBits <<= 16;mostSigBits |= Long.decode(components[2]).longValue();long leastSigBits = Long.decode(components[3]).longValue();leastSigBits <<= 48;leastSigBits |= Long.decode(components[4]).longValue();return new UUID(mostSigBits, leastSigBits);}

新代码逻辑~

/*** Creates a {@code UUID} from the string standard representation as* described in the {@link #toString} method.** @param  name*         A string that specifies a {@code UUID}** @return  A {@code UUID} with the specified value** @throws  IllegalArgumentException*          If name does not conform to the string representation as*          described in {@link #toString}**/public static UUID fromString(String name) {// BEGIN Android-changed: Java 8 behaviour is more lenient and the new implementation// might break apps (b/254278943).// Using old implementation for apps targeting Android older than U.// 取反！ 如果设备的sdk版本，大于等于  UPSIDE_DOWN_CAKE（34）的话，且启用严格验证if (!(VMRuntime.getSdkVersion() >= VersionCodes.UPSIDE_DOWN_CAKE&& Compatibility.isChangeEnabled(ENABLE_STRICT_VALIDATION))) {return fromStringJava8(name);}//如果小于或者没开启严格验证，则执行其他的验证 return fromStringCurrentJava(name);// END Android-changed: Java 8 behaviour is more lenient and the new implementation// might break apps (b/254278943).}

如下是java8 的判断方式（跟原来一致）

  /*** Extracted for testing purposes only.* @hide*/public static UUID fromStringJava8(String name) {String[] components = name.split("-");if (components.length != 5)throw new IllegalArgumentException("Invalid UUID string: "+ name);for (int i=0; i<5; i++)components[i] = "0x"+components[i];long mostSigBits = Long.decode(components[0]).longValue();mostSigBits <<= 16;mostSigBits |= Long.decode(components[1]).longValue();mostSigBits <<= 16;mostSigBits |= Long.decode(components[2]).longValue();long leastSigBits = Long.decode(components[3]).longValue();leastSigBits <<= 48;leastSigBits |= Long.decode(components[4]).longValue();return new UUID(mostSigBits, leastSigBits);}

如下是执行34或者开启严格验证的方法：

/*** Extracted for testing purposes only.* @hide*/public static UUID fromStringCurrentJava(String name) {if (name.length() == 36) {char ch1 = name.charAt(8);char ch2 = name.charAt(13);char ch3 = name.charAt(18);char ch4 = name.charAt(23);if (ch1 == '-' && ch2 == '-' && ch3 == '-' && ch4 == '-') {long msb1 = parse4Nibbles(name, 0);long msb2 = parse4Nibbles(name, 4);long msb3 = parse4Nibbles(name, 9);long msb4 = parse4Nibbles(name, 14);long lsb1 = parse4Nibbles(name, 19);long lsb2 = parse4Nibbles(name, 24);long lsb3 = parse4Nibbles(name, 28);long lsb4 = parse4Nibbles(name, 32);if ((msb1 | msb2 | msb3 | msb4 | lsb1 | lsb2 | lsb3 | lsb4) >= 0) {return new UUID(msb1 << 48 | msb2 << 32 | msb3 << 16 | msb4,lsb1 << 48 | lsb2 << 32 | lsb3 << 16 | lsb4);}}}return fromString1(name);}private static UUID fromString1(String name) {int len = name.length();if (len > 36) {throw new IllegalArgumentException("UUID string too large");}int dash1 = name.indexOf('-', 0);int dash2 = name.indexOf('-', dash1 + 1);int dash3 = name.indexOf('-', dash2 + 1);int dash4 = name.indexOf('-', dash3 + 1);int dash5 = name.indexOf('-', dash4 + 1);// For any valid input, dash1 through dash4 will be positive and dash5// negative, but it's enough to check dash4 and dash5:// - if dash1 is -1, dash4 will be -1// - if dash1 is positive but dash2 is -1, dash4 will be -1// - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be//   positive, but so will dash5if (dash4 < 0 || dash5 >= 0) {throw new IllegalArgumentException("Invalid UUID string: " + name);}long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;mostSigBits <<= 16;mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;mostSigBits <<= 16;mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;leastSigBits <<= 48;leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;return new UUID(mostSigBits, leastSigBits);}

解析：
从代码的角度看起来是多了好多验证，梳理一下：

1. 判断是否34（sdk版本），且未开启严格验证的情况下，还是按照原有代码执行，仅仅判断 以-分割的数组长度是否等于5，若不等于5，则主动抛出异常；2. 如果sdk版本大于等于34，且开启了严格验证，则会执行fromStringCurrentJava（）& fromString1（）方法，fromStringCurrentJava方法中没有主动抛出异常的代码，判断长度是否=36，不等于则执行 fromString1，若等于则继续执行，获取字符串下标8、13、18、23的值，若这四个值不等于 - ，则执行 fromString1；
在fromString1； 方法中，传递的字符串长度不得大于36，若超出则主动抛异常；继续判断；对于任何有效输入，dash1 到 dash4 将为正数，dash5 将为正数，负数，但检查 dash4 和 dash5 就足够了：
若是dash4小于0，dash5大于等于0，则主动抛出异常；

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正则表达式的更改

原有代码逻辑~

/*** Attempts to match the entire region against the pattern.** <p> If the match succeeds then more information can be obtained via the* <tt>start</tt>, <tt>end</tt>, and <tt>group</tt> methods.  </p>** @return  <tt>true</tt> if, and only if, the entire region sequence*          matches this matcher's pattern*/public boolean matches() {synchronized (this) {matchFound = nativeMatcher.matches(groups);}return matchFound;

新代码逻辑~

 /*** Attempts to match the entire region against the pattern.** <p> If the match succeeds then more information can be obtained via the* {@code start}, {@code end}, and {@code group} methods.  </p>** @return  {@code true} if, and only if, the entire region sequence*          matches this matcher's pattern*/public boolean matches() {synchronized (this) {matchFound = nativeMatcher.matches(groups);}//主要增加一个这个modCount++;return matchFound;}

modCount的描述 ：记录该匹配器状态被修改的次数

/*** Number of times this matcher's state has been modified*/int modCount;

结束

不是我说哈，你都是系统代码了，还起个 fromString1 这样的方法名称，丢人不~
就这，有问题私聊我~
再会~

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