虽然apache认为JakartaORO是一个更完 备的正则表达式处理包，但regexp的应用也是非常广泛，大概是因为它的简单吧。下面 是regexp的学习笔记。
1、下载安装
下载源码
cvs -d :pserver:anoncvs@cvs.apache.org:/home/cvspublic login
password: anoncvs
cvs -d :pserver:anoncvs@cvs.apache.org:/home/cvspublic checkout jakarta-regexp
或下载编译好的包
wget http://apache.linuxforum.net/dist/jakarta/regexp/binaries/jakarta-regexp-1.3.tar.gz
2、基本情况
1)Regexp是一个由100%纯java正则式处理包，是
Jonathan Locke捐给Apache软件基金会的。 他最初开发这个软件是在1996年，在时间的考验面前RegExp表达非常坚 挺:)。 它包括完整的Javadoc文档，以及一个简单的Applet来做可视化调试和兼容性测试.
2)RE类regexp包中非常重要的一个类，它是一个高效的、轻量级的正则式计算器/匹配器的类，RE是regular expression的缩写。正则式是能够进行复杂的字符串匹配的模板，而且当一个字符串能匹配某个模板时，你可 以抽取出那些匹配的部分，这在进行文本解析时非常有用。下面讨论一下正则式的语法。
为了编译一个正则式，你需要简单地以模板为参数构造一个RE匹配器对象来完成，然后就可调用任一个 RE.match方法来对一个字符串进行匹配检查，如果匹配成功/失败，则返回真/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（如果模板中有相应的括号的 话），以及它们的位置、长度等属性。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支持正则式的后向引用，如：
([0-9]+)=\1
匹配 n=n (象 0=0 or 2=2)这样的字符串
3)RE支持的正则式的语法如下：
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] |
简单字符集 |
| [a-zA-Z] |
带区间的 字符集 |
| [^abc] |
字符集的否定 |
标准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. |
非标准的 POSIX样式的字符集
| [:javastart:] |
Start of a Java identifier |
| [:javapart:] |
Part of a Java identifier |
预定义的字符集
| . |
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 |
边界匹配符
| ^ |
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 |
贪婪匹配限定符
| 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) |
非贪婪匹配限定符
| A*? |
Matches A 0 or more times (reluctant) |
| A+? |
Matches A 1 or more times (reluctant) |
| A?? |
Matches A 0 or 1 times (reluctant) |
逻辑运算符
| 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运行的程序先经过RECompiler类的编译. 由于效率的原因，RE匹配器没有包括正则式的编译类. 实际上， 如果要预编译1个或多个正则式，可以通过命令行运行'recompile'类,如
java org.apache.regexp.recompile a*b
则产生类似下面的编译输出（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);
通过利用预编译的req来构建RE匹配器对象，可以避免运行时进行编译的成本。 如果需要动态的构造正 则式，则可以创建单独一个RECompiler对象，并利用它来编译每个正则式。注意，RE 和 RECompiler 都不是 threadsafe的（出于效率的原因）, 因此当多线程运行时，你需要为每个线程分别创建编译器和匹配器。
3、例程
1)regexp包中带有一个applet写的小程序，运行如下:
java org.apache.regexp.REDemo
2)Jeffer Hunter写了一个例程，可以
下载。
3)regexp自带的测试例程，也很有参考价值。它把所有正则式及相关的字符串以及结果都放在一个单独的文件 里，在$REGEXPHOME/docs/RETest.txt中。当然，这个例程的运行也要在$REGEXPHOME目录下。
cd $REGEXPHOME
java org.apache.regexp.RETest
参考资料
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
来 源：http://hedong.3322.org/