正则表达式

正则表达式

一、正则表达式概述

1.1一句话概括

查找、处理某些规则的字符串

1.2例子

模式串的书写是关键，也就是通过占位符的方式来表达一个串。

举个简单的例子，要查找某个字符串是否包含某个子串？应该怎么写

需要用到的模板串应该是(.*AK47.*),而不是(AK47)。

 

二、正则表达式的符号

2.1常用符号

.	^	$	[]	[^]	AK	X|Z	/b
匹配一个 字符	匹配开头	匹配结尾	可选字符	非可选	严格匹配AK	匹配X或者Z	单词分界

 

三、正则表达式能干什么事情？

3.1判断一个字符串是否满足Pattern

 //1、判断一个字符串是不是一个模板的字符串
        String str = "img.jpg";
        //需要满足的规则
        String pattern = ".*jpg.*";
        System.out.println("str中是否包含pattern模式的字串" + Pattern.matches(pattern, str));

3.2满足Pattern的子串分组

//2、分组已匹配子串
        String line = "This order was placed for QT3000! OK?";
        String pattern2 = "(\\D*)(\\d+)(.*)";
        //创建Pattern对象
        Pattern p = Pattern.compile(pattern2);
        //创建Matcher对象
        Matcher m = p.matcher(line);
        while (m.find()) {
            int n = m.groupCount();
            while (n >= 0) {
                System.out.println("Found value: " + m.group(n));
                n--;
            }
        }
        //System.out.println("一共有" + n + "个捕获组");

3.3统计单词个数

//统计给定单词中个数
        String regex = "\\bcat\\b";
        String input = "cat cat ,cat cat cat sdasdasda sda";

        Pattern pattern1 = Pattern.compile(regex);
        Matcher matcher = pattern1.matcher(input);

        int count = 0;
        while (matcher.find()) {
            count++;
            System.out.println("Match Number is " + count);
            System.out.println("Match Number start at " + matcher.start());
            System.out.println("Match Number end with " + matcher.end());
            System.out.println();
        }

3.4替换子串

 //替换子串
        String regex1 = "a*b";
        String input1 = "aabfooaabfooabfoobkkk";
        Pattern pattern3 = Pattern.compile(regex1);
        Matcher matcher1 = pattern3.matcher(input1);
        StringBuffer stringBuffer = new StringBuffer();
        while (matcher1.find()) {
            //替换
            matcher1.appendReplacement(stringBuffer, "zous");
        }
//        System.out.println("没有拼接到尾部之前的matcher: "+matcher1);
//        matcher1.appendTail(stringBuffer);
//        System.out.println("拼接到尾部之后的matcher: "+matcher1);
        System.out.println("替换后结果放到stringBuffer为 " + stringBuffer.toString());

        //使用replace和replaceALL来替换子串
        String regex2 = "dog";
        String input2 = " dog says meow. All dogs say meow.";
        Pattern pattern4 = Pattern.compile(regex2);
        Matcher matcher2 = pattern4.matcher(input2);

        String result = matcher2.replaceAll("cat");
        System.out.println("dog替换为cat: " + result);
        String result1 = matcher2.replaceFirst("mouse");
        System.out.println("cat替换成mouse: " + result1);

 

最后、测试的工具

JS：https://jex.im/regulex/#!flags=&re=%5E(a%7Cb)*%3F%24

Java:http://www.regexplanet.com/advanced/java/index.html

 

参考

http://deerchao.net/tutorials/regex/regex.htm

https://blog.youkuaiyun.com/zpz2411232428/article/details/83549502