java基础之 正则表达式

在web开发中，字符串的处理往往最为麻烦,处理的过程中，正则表达式用得非常频繁，最常见的如登陆校验，注册校验，以及邮箱等信息验证

Pattern 类的对象是正则表达式编译后在中的表示形式，因此正则表达式的对象必须先编译为Pattern对象，然后再用Pattern对象创建Matcher对象，执行所匹配的状态封装在Matcher对象里面；多个Matcher对象可以共享一个Pattern对象，如：
Pattern p=Pattern.compile("a*b");//把一个字符串编译成Pattern对象；
Matcher m=p.matcher("aaaaaab");//使用Pattern对象创建Matcher对象；
boolean b=m.matches();//返回true;
上面定义的Pattern对象可以多次被使用，Pattern是不可变类，可供多个线程安全使用。

Matcher 类提供了如下常用的方法：<wbr><br> find:返回目标字符串是否包含与Pattern匹配的子串（每次调用都是在上一次find方法找到的匹配字符串后开始查找）。<br> group:返回上一次与Pattern匹配的子串。:<br> start：返回上一次与Pattern匹配的子串在目标字符串中开始位置。<br> end:返回上一次与Pattern匹配的子串在目标字符串中结束位置加1。<br> lookingAt:返回目标字符串前面部分与Pattern是否匹配。<br> matches:返回整个目标字符串是否与Pattern匹配。<br> reset:可一将现有的Matcher对象应用到一个新的字符序列。<br> 下面程序演示了各个方法的用途：<br> import java.util.regex.*;<br> public class FindGroup<br> {<span style="color:#6fe072">//演示findf方法该方法可以传入一个参数</span><br><wbr><wbr><wbr> public static void main(String[] args)<br><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr> Matcher m = Pattern.compile("\\w+")<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> .matcher("Java is very easy!");<br><wbr><wbr><wbr><wbr><wbr><wbr> while(m.find())<br><wbr><wbr><wbr><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println(m.group());<br><wbr><wbr><wbr><wbr><wbr><wbr> }<br><wbr><wbr><wbr><wbr><wbr><wbr> int i = 0;<br><wbr><wbr><wbr><wbr><wbr><wbr> while(m.find(i))<br><wbr><wbr><wbr><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> System.out.print(m.group() + "\t");<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> i++;<br><wbr><wbr><wbr><wbr><wbr><wbr> }<br><wbr><wbr><wbr> }<br> }<br> 运行结果<br> Java<br> is<br> very<br> easy<br> Java<wbr><wbr><wbr> ava<wbr><wbr><wbr> va<wbr><wbr><wbr> a<wbr><wbr><wbr> is<wbr><wbr><wbr> is<wbr><wbr><wbr> s<wbr><wbr><wbr> very<wbr><wbr><wbr> very<wbr><wbr><wbr> ery<wbr><wbr><wbr> ry<wbr><wbr><wbr> y<wbr><wbr><wbr> easy<wbr><wbr><wbr> easy<wbr><wbr><wbr> asy<wbr><wbr><wbr> sy<wbr><wbr><wbr> y<br> 从上面的结果可以看出，find方法依次查找字符串中与Pattern匹配的子串，一旦找到对应的子串，下次调用find方法会接着向下查找。除此之外find方法还可以传入一个带Int类型的参数，find从该int索引处向下找。<br> start和end主要确定子串在目标字符串中的位置如下：<br> import java.util.regex.*;<br> public class StartEnd<br> {<br><wbr><wbr><wbr> public static void main(String[] args)<br><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr> String regStr = "Java is very easy!";<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("目标字符串是：" + regStr);<br><wbr><wbr><wbr><wbr><wbr><wbr> Matcher m = Pattern.compile("\\w+")<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> .matcher(regStr);<br><wbr><wbr><wbr><wbr><wbr><wbr> while(m.find())<br><wbr><wbr><wbr><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println(m.group() + "子串的起始位置：" + m.start()<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> + "，其结束位置：" + m.end());<br><wbr><wbr><wbr><wbr><wbr><wbr> }<br><wbr><wbr><wbr> }<br> }<br> 输出结果：<br> is子串的起始位置：5，其结束位置：7<br> very子串的起始位置：8，其结束位置：12<br> easy子串的起始位置：13，其结束位置：17<br> matches 和lookingAt相似，但前者要求匹配整个字符串，后者只要字符串因Pattern开头就会返回true.<br> 看下面例子：<br> import java.util.regex.*;<br><br> public class TestMatches<br> {<br><wbr><wbr><wbr> public static void main(String[] args)<br><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr> String[] mails =<br><wbr><wbr><wbr><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> "kongyeeku@163.com" ,<br><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>