JAVA中如何高效的实现SQL的like语法?

/** SQL {@code LIKE} function. */public static boolean like(String s,String pattern){    final String regex = Like.sqlToRegexLike(pattern, null);    return Pattern.matches(regex, s);}

/** Translates a SQL LIKE pattern to Java regex pattern.*/static String sqlToRegexLike(String sqlPattern,char escapeChar) {    int i;    final int len = sqlPattern.length();    final StringBuilder javaPattern = new StringBuilder(len + len);    for (i = ; i < len; i++) {      char c = sqlPattern.charAt(i);      if (JAVA_REGEX_SPECIALS.indexOf(c) >= ) {        javaPattern.append('\\');      }      if (c == escapeChar) {        if (i == (sqlPattern.length() - 1)) {          throw invalidEscapeSequence(sqlPattern, i);        }        char nextChar = sqlPattern.charAt(i + 1);        if ((nextChar == '_')            || (nextChar == '%')            || (nextChar == escapeChar)) {          javaPattern.append(nextChar);          i++;        } else {          throw invalidEscapeSequence(sqlPattern, i);        }      } else if (c == '_') {        javaPattern.append('.');      } else if (c == '%') {        javaPattern.append("(?s:.*)");      } else {        javaPattern.append(c);      }    }    return javaPattern.toString();}

...try {    Pattern pattern = patterns.get(buildKey(right, escTmp), new Callable<Pattern>() {        @Override        public Pattern call() throws Exception {            return Pattern.compile(buildPattern(right, escTmp), Pattern.CASE_INSENSITIVE);        }    });    Matcher m = pattern.matcher(left);    return m.matches() ? 1l : 0l;} catch (ExecutionException e) {    throw new FunctionException(e.getCause());}...

到此，综上来看，不少项目是基于正则表达式来完成的，接下来我整理了下我近实现的几种方式：

public static boolean like(final String dest, final String pattern) {    String regex = regexParse(pattern);    regex = regex.replace("_",".").replace("%",".*?");    Pattern p = Pattern.compile(regex,Pattern.CASE_INSENSITIVE | Pattern.DOTALL);    return p.matcher(dest).matches();}

这种方式在代码层面简单明了，但是性能非常差，多次replace的使用就已经进行了多次遍历，这里有个可以优化的点，对于单个字符做替换可以选择用replaceChars(str, searchChar, replaceChar)这个方案。

public static boolean like(final String dest, final String pattern) {    int destPointer = , patternPointer = ;    int destRecall = -1, patternRecall = -1;    final int patternLen = pattern.length();    final int destLen = dest.length();    while( destPointer < destLen) {        ......        ......    }    while(patternPointer < patternLen && pattern.chatAt(patternPointer) == '%') {        patternPointer++;    }    return patternPointer == patternLen;}    

有个场景我们不得不去考虑，那就是回溯的情况，举个例子：

public void compile(final String pattern) {    ...    LikeStateMachine machine = LikeStateMachine.build(pattern);    ...}

构建的过程就是我们把pattern解析加载的过程，我采用的方式是构建链表的方式。实现就是遍历构建的过程，compile时间复杂度O(n)

public LikeParserResult compile(final String pattern) {    return parseLikeExpress(pattern);}
....public boolean match(final String dest, LikeParserResult likeParserResult) {    switch (likeParserResult.getMatchResult()) {        case LikeMatchResult.TYPE.ALLMATCH:            return true;        case LikeMatchResult.TYPE.EQUALS:            return doEquals(dest, likeParserResult.getFinalPattern());        case LikeMatchResult.TYPE.STARTSWITH:            return doStartsWith(dest, likeParserResult.getFinalPattern());        case LikeMatchResult.TYPE.ENDSWITH:            return doEndsWith(dest, likeParserResult.getFinalPattern());        case LikeMatchResult.TYPE.CONTAINS:            return doContain(dest, likeParserResult.getFinalPattern());        default:            //或者别的实现            return likeParserResult.getLikeStateMachine().match(dest);    }}

上面给出的代码是为了清楚的看到里面运行，终根据自己擅长的代码风格（函数式Function，接口等），还可以进一步优化和精简。

...public LikeParserResult compile(final String pattern) {        return parseLikeExpress(pattern);}

public boolean match(final String dest, LikeParserResult likeParserResult) {        return likeParserResult.getMatcher().match(dest);}

...
public class StartsWithMatcher implements Matcher {    ...        @Override    public Boolean match(String dest) {        return dest.startsWith(this.pattern);    }}...

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