正则表达式学习-蒲公英云

正则表达式学习

水深无声 2023-07-04 04:58 92阅读 0赞

文章目录

- 零宽度断言
- - (?= X )
  - (?! X )
  - (?<= X )
  - (?!= X )
- 模式修正符
- - i
  - x
  - m
  - s
- 捕获组与非捕获组
- - 捕获组
  - 非捕获组

零宽度断言

主要包括四种：(?= X )，(?! X )，(?<= X )，(?<! X )。前两种是位于表达式右侧，后两种是位于表达式左侧。带“=”的是匹配模式，带“!”是非匹配模式。

(?= X )

String testStr = "#5 abc 0#";
        // 含义：数字，且该数字后面紧跟#
        Pattern pattern = Pattern.compile("\\d(?=#)");
        Matcher matcher = pattern.matcher(testStr);
        // 0
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

(?! X )

String testStr = "#5 abc 0#";
        // 含义：数字，且该数字后面不紧跟#
        Pattern pattern = Pattern.compile("\\d(?!#)");
        Matcher matcher = pattern.matcher(testStr);
        // 5
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

(?<= X )

String testStr = "#5 abc 0#";
        // 含义：数字，且该数字前面紧跟#
        Pattern pattern = Pattern.compile("(?<=#)\\d");
        Matcher matcher = pattern.matcher(testStr);
        // 5
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

(?!= X )

String testStr = "#5 abc 0#";
        // 含义：数字，且该数字前面不紧跟#
        Pattern pattern = Pattern.compile("(?<!#)\\d");
        Matcher matcher = pattern.matcher(testStr);
        // 0
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

模式修正符

以(?)开头加上特殊字母(i/x/m/s)表示特定模式

i

忽略大小写

String testStr = "#5 Abc 0#";
        // 含义：忽略abc 字母大小写
        Pattern pattern = Pattern.compile("(?i)abc");
        Matcher matcher = pattern.matcher(testStr);
        // Abc
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }
        // 含义：不忽略abc 字母大小写
        pattern = Pattern.compile("(?-i)abc");
        matcher = pattern.matcher(testStr);
        // 无
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }
        // 含义：只对a忽略字母大小写
        pattern = Pattern.compile("(?i:a)bc");
        matcher = pattern.matcher(testStr);
        // Abc
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

x

忽略空白

String testStr = "#5 abc  a b c 0#";
        // 含义：忽略a b c 中空格
        Pattern pattern = Pattern.compile("(?x)a b c");
        Matcher matcher = pattern.matcher(testStr);
        // abc
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

m

视作多行

String testStr = "#5 abc\nabc\n0#";
        // 含义：.不包括换行符\n
        Pattern pattern = Pattern.compile("(?m)abc.");
        Matcher matcher = pattern.matcher(testStr);
        //无
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

s

视作单行

String testStr = "#5 abc\nabc\n0#";
        // 含义：将换行符\n视作普通字符
        Pattern pattern = Pattern.compile("(?s)abc.");
        Matcher matcher = pattern.matcher(testStr);
        /* abc
           abc
        */
        while (matcher.find()) {
            System.out.println(matcher.group(0));
        }

捕获组与非捕获组

捕获组

以（）作为捕获组的分割符，以（?:）作为非捕获组的分割符。
捕获组中：group(0)代表全部；从左至右的”(“决定捕获组的序号。

String testStr = "ppsd 12#Amm 3#sa";
        // 含义：12#Amm
        Pattern pattern = Pattern.compile("((12)(#A))mm");
        Matcher matcher = pattern.matcher(testStr);
        /*
            12#Amm
            12#A
            12
            #A
         */
        while (matcher.find()) {
            System.out.println(matcher.group(0));
            System.out.println(matcher.group(1));
            System.out.println(matcher.group(2));
            System.out.println(matcher.group(3));
        }

非捕获组

以（?:）开头，不具有捕获组序号。

String testStr = "ppsd 12#Amm 3#sa";
        // 含义：12#Amm
        Pattern pattern = Pattern.compile("((?:12)(#A))mm");
        Matcher matcher = pattern.matcher(testStr);
        /*
            12#Amm
            12#A
            #A
         */
        while (matcher.find()) {
            System.out.println(matcher.group(0));
            System.out.println(matcher.group(1));
            System.out.println(matcher.group(2));
        }