jdk1.4中加入了java.util.regex包提供對正則表達式的支持。而且Java.lang.String類中的replaceAll和split函數也是調用的正則表達式來實現的。
正則表達式對字符串的操作主要包括：字符串匹配，指定字符串替換，指定字符串查找和字符串分割。下面就用一個例子來說明這些操作是如何實現的：
<%@ page import="java.util.regex.*"%>
<%
Pattern p=null; //正則表達式
Matcher m=null; //操作的字符串
boolean b;
String s=null;
StringBuffer sb=null;
int i=0;
//字符串匹配，這是不符合的
p = Pattern.compile("a*b");
m = p.matcher("baaaaab");
b = m.matches();
out.println(b+"<br>");
//字符串匹配，這是符合的
p = Pattern.compile("a*b");
m = p.matcher("aaaaab");
b = m.matches();
out.println(b+"<br>");
//字符串替換
p = Pattern.compile("ab");
m = p.matcher("aaaaab");
s = m.replaceAll("d");
out.println(s+"<br>");
p = Pattern.compile("a*b");
m = p.matcher("aaaaab");
s = m.replaceAll("d");
out.println(s+"<br>");
p = Pattern.compile("a*b");
m = p.matcher("caaaaab");
s = m.replaceAll("d");
out.println(s+"<br>");
//字符串查找
p = Pattern.compile("cat");
m = p.matcher("one cat two cats in the yard");
sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "dog");
i++;
}
m.appendTail(sb);
out.println(sb.toString()+"<br>");
out.println(i+"<br>");
i=0;
p = Pattern.compile("cat");
m = p.matcher("one cat two ca tsi nthe yard");
sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "dog");
i++;
}
m.appendTail(sb);
out.println(sb.toString()+"<br>");
out.println(i+"<br>");
p = Pattern.compile("cat");
m = p.matcher("one cat two cats in the yard");
p=m.pattern();
m = p.matcher("bacatab");
b = m.matches();
out.println(b+"<br>");
s = m.replaceAll("dog");
out.println(s+"<br>");
i=0;
p = Pattern.compile("(fds){2,}");
m = p.matcher("dsa da fdsfds aaafdsafds aaf");
sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "dog");
i++;
}
m.appendTail(sb);
out.println(sb.toString()+"<br>");
out.println(i+"<br>");
p = Pattern.compile("cat");
m = p.matcher("one cat two cats in the yard");
sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "<font color="red">cat</font>");
}
m.appendTail(sb);
out.println(sb.toString()+"<br>");
String aa=sb.toString();
out.println(aa+"<br>");
//字符串分割
p = Pattern.compile("a+");
String[] a=p.split("caaaaaat");
for(i=0;i<a.length;i++)
{
out.println(a[i]+"<br>");
}
p = Pattern.compile("a+");
a=p.split("c aa aaaa t",0);
for(i=0;i<a.length;i++)
{
out.println(a[i]+"<br>");
}
p = Pattern.compile(" +");
a=p.split("c aa aaaa t",0);
for(i=0;i<a.length;i++)
{
out.println(a[i]+"<br>");
}
p = Pattern.compile("\\+");
a=p.split("dsafasdfdsafsda+dsagfasdfa+sdafds");
out.println(a.length+"<br>");
for(i=0;i<a.length;i++)
{
out.println(a[i]+"<br>");
}
%>
