雖然apache認為JakartaORO是一個更完 備的正則表達式處理包，但regexp的應用也是非常廣泛，大概是因為它的簡單吧。下面 是regexp的學習筆記。
1、下載安裝
下載源碼
cvs -d :pserver:anoncvs@cvs.apache.org:/home/cvspublic login
password: anoncvs
cvs -d :pserver:anoncvs@cvs.apache.org:/home/cvspublic checkout jakarta-regexp
或下載編譯好的包
wget http://apache.linuxforum.net/dist/jakarta/regexp/binaries/jakarta-regexp-1.3.tar.gz
2、基本情況
1)Regexp是一個由100%純java正則式處理包，是
Jonathan Locke捐給Apache軟件基金會的。 他最初開發這個軟件是在1996年，在時間的考驗面前RegExp表達非常堅 挺:)。 它包括完整的Javadoc文檔，以及一個簡單的Applet來做可視化調試和兼容性測試.
2)RE類regexp包中非常重要的一個類，它是一個高效的、輕量級的正則式計算器/匹配器的類，RE是regular expression的縮寫。正則式是能夠進行復雜的字符串匹配的模板，而且當一個字符串能匹配某個模板時，你可 以抽取出那些匹配的部分，這在進行文本解析時非常有用。下面討論一下正則式的語法。
為了編譯一個正則式，你需要簡單地以模板為參數構造一個RE匹配器對象來完成，然后就可調用任一個 RE.match方法來對一個字符串進行匹配檢查，如果匹配成功/失敗，則返回真/假值。例如：
RE r = new RE("a*b");
boolean matched = r.match("aaaab");
RE.getParen可以取回匹配的字符序列，或者匹配的字符序列的某一部分（如果模板中有相應的括號的 話），以及它們的位置、長度等屬性。如：
RE r = new RE("(a*)b"); // Compile expression
boolean matched = r.match("xaaaab"); // Match against "xaaaab"
String wholeExpr = r.getParen(0); // wholeExpr will be 'aaaab'
String insideParens = r.getParen(1); // insideParens will be 'aaaa'
int startWholeExpr = r.getParenStart(0); // startWholeExpr will be index 1
int endWholeExpr = r.getParenEnd(0); // endWholeExpr will be index 6
int lenWholeExpr = r.getParenLength(0); // lenWholeExpr will be 5
int startInside = r.getParenStart(1); // startInside will be index 1
int endInside = r.getParenEnd(1); // endInside will be index 5
int lenInside = r.getParenLength(1); // lenInside will be 4
RE支持正則式的后向引用，如：
([0-9]+)=\1
匹配 n=n (象 0=0 or 2=2)這樣的字符串
3)RE支持的正則式的語法如下：
字符
| unicodeChar |
Matches any identical unicode character |
| \ |
Used to quote a meta-character (like '*') |
| \\ |
Matches a single '\' character |
| \0nnn |
Matches a given octal character |
| \xhh |
Matches a given 8-bit hexadecimal character |
| \\uhhhh |
Matches a given 16-bit hexadecimal character |
| \t |
Matches an ASCII tab character |
| \n |
Matches an ASCII newline character |
| \r |
Matches an ASCII return character |
| \f |
Matches an ASCII form feed character |
字符集
| [abc] |
簡單字符集 |
| [a-zA-Z] |
帶區間的 字符集 |
| [^abc] |
字符集的否定 |
標準POSIX 字符集
| [:alnum:] |
Alphanumeric characters. |
| [:alpha:] |
Alphabetic characters. |
| [:blank:] |
Space and tab characters. |
| [:cntrl:] |
Control characters. |
| [:digit:] |
Numeric characters. |
| [:graph:] |
Characters that are printable and are also visible.(A space is printable, but not visible, while an `a' is both.) |
| [:lower:] |
Lower-case alphabetic characters. |
| [:print:] |
Printable characters (characters that are not control characters.) |
| [:punct:] |
Punctuation characters (characters that are not letter,digits, control characters, or space characters). |
| [:space:] |
Space characters (such as space, tab, and formfeed, to name a few). |
| [:upper:] |
Upper-case alphabetic characters. |
| [:xdigit:] |
Characters that are hexadecimal digits. |
非標準的 POSIX樣式的字符集
| [:javastart:] |
Start of a Java identifier |
| [:javapart:] |
Part of a Java identifier |
預定義的字符集
| . |
Matches any character other than newline |
| \w |
Matches a "word" character (alphanumeric plus "_") |
| \W |
Matches a non-word character |
| \s |
Matches a whitespace character |
| \S |
Matches a non-whitespace character |
| \d |
Matches a digit character |
| \D |
Matches a non-digit character |
邊界匹配符
| ^ |
Matches only at the beginning of a line |
| $ |
Matches only at the end of a line |
| \b |
Matches only at a word boundary |
| \B |
Matches only at a non-word boundary |
貪婪匹配限定符
| A* |
Matches A 0 or more times (greedy) |
| A+ |
Matches A 1 or more times (greedy) |
| A? |
Matches A 1 or 0 times (greedy) |
| A{n} |
Matches A exactly n times (greedy) |
| A{n,} |
Matches A at least n times (greedy) |
非貪婪匹配限定符
| A*? |
Matches A 0 or more times (reluctant) |
| A+? |
Matches A 1 or more times (reluctant) |
| A?? |
Matches A 0 or 1 times (reluctant) |
邏輯運算符
| AB |
Matches A followed by B |
| A|B |
Matches either A or B |
| (A) |
Used for subexpression grouping |
| (?:A) |
Used for subexpression clustering (just like grouping but no backrefs) |
后向引用符
| \1 |
Backreference to 1st parenthesized subexpression |
| \2 |
Backreference to 2nd parenthesized subexpression |
| \3 |
Backreference to 3rd parenthesized subexpression |
| \4 |
Backreference to 4th parenthesized subexpression |
| \5 |
Backreference to 5th parenthesized subexpression |
| \6 |
Backreference to 6th parenthesized subexpression |
| \7 |
Backreference to 7th parenthesized subexpression |
| \8 |
Backreference to 8th parenthesized subexpression |
| \9 |
Backreference to 9th parenthesized subexpression |
RE運行的程序先經過RECompiler類的編譯. 由于效率的原因，RE匹配器沒有包括正則式的編譯類. 實際上， 如果要預編譯1個或多個正則式，可以通過命令行運行'recompile'類,如
java org.apache.regexp.recompile a*b
則產生類似下面的編譯輸出（最后一行不是）：
// Pre-compiled regular expression "a*b"
char[] re1Instructions =
{
0x007c, 0x0000, 0x001a, 0x007c, 0x0000, 0x000d, 0x0041,
0x0001, 0x0004, 0x0061, 0x007c, 0x0000, 0x0003, 0x0047,
0x0000, 0xfff6, 0x007c, 0x0000, 0x0003, 0x004e, 0x0000,
0x0003, 0x0041, 0x0001, 0x0004, 0x0062, 0x0045, 0x0000,
0x0000,
};
REProgram re1 = new REProgram(re1Instructions);
RE r = new RE(re1);
通過利用預編譯的req來構建RE匹配器對象，可以避免運行時進行編譯的成本。 如果需要動態的構造正 則式，則可以創建單獨一個RECompiler對象，并利用它來編譯每個正則式。注意，RE 和 RECompiler 都不是 threadsafe的（出于效率的原因）, 因此當多線程運行時，你需要為每個線程分別創建編譯器和匹配器。
3、例程
1)regexp包中帶有一個applet寫的小程序，運行如下:
java org.apache.regexp.REDemo
2)Jeffer Hunter寫了一個例程，可以
下載。
3)regexp自帶的測試例程，也很有參考價值。它把所有正則式及相關的字符串以及結果都放在一個單獨的文件 里，在$REGEXPHOME/docs/RETest.txt中。當然，這個例程的運行也要在$REGEXPHOME目錄下。
cd $REGEXPHOME
java org.apache.regexp.RETest
參考資料
1、 Jeffrey Hunter's README_regular_expressions.txt |
http://www.idevelopment.info/topics/topics.cgi?LEVEL=programming
2、The Jakarta Site – CVS Repository
http://jakarta.apache.org/site/cvsindex.html
原作者：Hilton
來 源：http://hedong.3322.org/