最近深入看struts2的validation校验框架，看到底层的很多的实现都用到正则表达式来实现。其中用得比较多的是两个类，一个是
java.util.regex.Matcher和java.util.regex.Pattern
现在通过例子来说明：
1、要求查找一段字符串里面相关匹配的字符串，然后根据要求奇偶大小写替换。
1、1先从不考虑奇偶考虑
程序如下：
1
Pattern p = Pattern.compile("hello");
2 Matcher m = p.matcher("hello Hello HELLo HeLLo HelLoworld HellOWORLD dafdasfadsf");
3
4
while(m.find())
{
5
System.out.println(m.group());
6
}
7 System.out.println("----------------");
8 System.out.println(m.replaceAll("HELLO"));
输出如下：
hello
----------------
HELLO Hello HELLo HeLLo HelLoworld HellOWORLD dafdasfadsf
注：只有第一个hello是匹配的，所以打印出来只有一个hello
*在JDK文档中对Pattern的描述是：A compiled representation of a regular expression.
其中complie( )方法是把里面的字符串"hello"先编译
matcher( )方法就是把要校验的字符串加载进来：
matcher
public Matcher matcher(CharSequence input)
- Creates a matcher that will match the given input against this pattern.
-
-
- Parameters:
input - The character sequence to be matched
- Returns:
- A new matcher for this pattern
**Matcher在JDK文档里面描述是：
An engine that performs match operations on a Pattern.
A matcher is created from a pattern by invoking the pattern's matcher method. Once created, a matcher can be used to perform three different kinds of match operations:
注：（英文通俗易懂就不翻译了）
***其中replaceAll方法是替换字符串里面符合“hello”的字符串
源码为：
1public String replaceAll(String replacement) {
2 reset();
3 boolean result = find();
4
if (result) {
5 StringBuffer sb = new StringBuffer();
6 do {
7 appendReplacement(sb, replacement);
8 result = find();
9
} while (result);
10 appendTail(sb);
11 return sb.toString();
12 }
13 return text.toString();
14 }
--------------------------------------------------------------------------------------
1、2下面对1、1中实现所有替换所有符合的字符串程序进行重构
源码如下：
1Pattern p = Pattern.compile("hello",Pattern.CASE_INSENSITIVE);
2 Matcher m = p.matcher("hello Hello HELLo HeLLo HelLoworld HellOWORLD dafdasfadsf");
3 StringBuffer sb= new StringBuffer();
4 int i = 0;
5 while(m.find())
6 {
7 i++;
8 if(i%2 == 0)
9 {
10 m.appendReplacement(sb, "hello");
11 }else{
12 m.appendReplacement(sb, "HELLO");
13 }
14
15 }
16 m.appendTail(sb);
17 System.out.println(sb);
控制台输出：
HELLO hello HELLO hello HELLOworld helloWORLD dafdasfadsf
第1行中的Pattern.CASE_INSENSITIVE是忽略字母大小写
其中第5----13行加入就奇偶判断
appendReplacement就是把替换后的字符串放进StringBuffer的引用里面
源码为：
1public Matcher appendReplacement(StringBuffer sb, String replacement) {
2
3 // If no match, return error
4 if (first < 0)
5 throw new IllegalStateException("No match available");
6
7 // Process substitution string to replace group references with groups
8 int cursor = 0;
9 String s = replacement;
10 StringBuffer result = new StringBuffer();
11
12 while (cursor < replacement.length()) {
13 char nextChar = replacement.charAt(cursor);
14 if (nextChar == '\\') {
15 cursor++;
16 nextChar = replacement.charAt(cursor);
17 result.append(nextChar);
18 cursor++;
19 } else if (nextChar == '$') {
20 // Skip past $
21 cursor++;
22
23 // The first number is always a group
24 int refNum = (int)replacement.charAt(cursor) - '0';
25 if ((refNum < 0)||(refNum > 9))
26 throw new IllegalArgumentException(
27 "Illegal group reference");
28 cursor++;
29
30 // Capture the largest legal group string
31 boolean done = false;
32 while (!done) {
33 if (cursor >= replacement.length()) {
34 break;
35 }
36 int nextDigit = replacement.charAt(cursor) - '0';
37 if ((nextDigit < 0)||(nextDigit > 9)) { // not a number
38 break;
39 }
40 int newRefNum = (refNum * 10) + nextDigit;
41 if (groupCount() < newRefNum) {
42 done = true;
43 } else {
44 refNum = newRefNum;
45 cursor++;
46 }
47 }
48
49 // Append group
50 if (group(refNum) != null)
51 result.append(group(refNum));
52 } else {
53 result.append(nextChar);
54 cursor++;
55 }
56 }
57
58 // Append the intervening text
59 sb.append(getSubSequence(lastAppendPosition, first));
60 // Append the match substitution
61 sb.append(result.toString());
62
63 lastAppendPosition = last;
64 return this;
65 }
注：通过在java中使用正则表达式，可以很方便进行字符串校验。
附（例子）：邮件格式校验
System.out.println(
"aa.a-aaa@163.com".matches("[\\w[.-]]+@[\\w[.-]]+\\.[\\w]+"));
等价于以下代码：
Pattern pp = Pattern.compile("[\\w[.-]]+@[\\w[.-]]+\\.[\\w]+");
Matcher m =pp.matcher("aa.a-aaa@163.com");
System.out.println(m.matches());
如果符合matches里面的校验规则，则打印出true，否则是false。
matches方法是String里面一个方法，看源码实现
1public boolean matches(String regex) {
2 return Pattern.matches(regex, this);
3 }
1public static boolean matches(String regex, CharSequence input) {
2 Pattern p = Pattern.compile(regex);
3 Matcher m = p.matcher(input);
4 return m.matches();
5 }
总结：深入一些框架的底层，其中很多校验功能都是用到正则表达式，你会发觉使用正则表达式功能很强大。
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posted on 2008-12-06 23:42
apple0668 阅读(2529)
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