浅入深出Re:正则表达式的养成方法

以下出自图灵丛书精通正则表达式一书,实验遇到的问题及解决方法，记载在此

Java正则的使用姿势

Regular Expressions API

• Pattern 描述了一种字符串模式。
• Matcher 测试一个字符串，查看它是否与该模式匹配。

正则表达式结构	符合匹配条件的内容
.	任何字符
?	前面的0或1个字符或数字
*	前面的零 (0) 或更多个字符或数字
+	前面的一 (1) 或更多个字符或数字
[ ]	一个字符或数字范围
^	后面的条件的否定条件（即 “非后面的条件”）
/d	任何数字（也可表示为 [0-9]）
/D	任何非数字（也可表示为 [^0-9]）
/s	任何空格字符（也可表示为 [\n\t\f\r]）
/S	任何非空格字符（也可表示为 [^\n\t\f\r]）
\w	任何单词字符（也可表示为 [a-zA-Z_0-9]）
\W	任何非单词字符（也可表示为 [^\w]）
\b	查找位于单词的开头或结尾的匹配
$	检查行尾是否如下
(?:pattern)	匹配 pattern 但不捕获该匹配的子表达式

Test1 : 找到一个具有以下形式的字符串：A 或 a 后跟零或多个字符，后跟 string。

 //4nd way
        Pattern pattern = Pattern.compile("[Aa].*string");//匹配string字符串之前的0或者更多字符和数字
        Matcher matcher = pattern.matcher("A string");
        boolean didMatch = matcher.matches();
        System.out.println(didMatch);
        int patternStartIndex = matcher.start();
        System.out.println(patternStartIndex);
        int patternEndIndex = matcher.end();
        System.out.println(patternEndIndex);

• 匹配方法

每个 Java 语言字符串都是一个带索引的字符集合，索引从 0 开始，到字符串长度减 1 结束。Matcher 从 0 开始解析该字符串，寻找与它匹配的结果。完成处理后，Matcher 包含有关在输入字符串中找到（或未找到）匹配结果的信息。如果字符串中包含的元素比您搜索的模式中字符数要多，可以使用 lookingAt() 代替 matches()。

Test2 : 搜索匹配的较长的字符串信息

matches()

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by 26645 on 2017/8/31.
 */
public class RegexTest {
    public static void main(String[] args) {
        Pattern p = Pattern.compile(".s");//表示单个字符
        Matcher m= p.matcher("as");
        boolean b =m.matches();

        //2nd way
        boolean b2 = Pattern.compile(".s").matcher("as").matches();

        //3nd way
        boolean b3 = Pattern.matches(".s","as");

        //4nd way
        Pattern pattern = Pattern.compile("[Aa].*string");//匹配string字符串之前的0或者更多字符和数字
        Scanner scan = new Scanner(System.in);
        if (scan.hasNextLine()){
            Matcher matcher = pattern.matcher(scan.nextLine());
            boolean didMatch = matcher.matches();
            System.out.println(didMatch);
            int patternStartIndex = matcher.start();
            System.out.println(patternStartIndex);
            int patternEndIndex = matcher.end();
            System.out.println(patternEndIndex);
        }
        
    }
}

console output : 字符串中包含比模式中更多的内容,查找失败

false
Exception in thread "main" java.lang.IllegalStateException: No match available
    at java.util.regex.Matcher.start(Matcher.java:343)
    at RegexTest.main(RegexTest.java:28)

lookingAt()

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by 26645 on 2017/8/31.
 */
public class RegexTest {
    public static void main(String[] args) {
        Pattern p = Pattern.compile(".s");//表示单个字符
        Matcher m= p.matcher("as");
        boolean b =m.matches();

        //2nd way
        boolean b2 = Pattern.compile(".s").matcher("as").matches();

        //3nd way
        boolean b3 = Pattern.matches(".s","as");

        //4nd way
        Pattern pattern = Pattern.compile("[Aa].*string");//匹配string字符串之前的0或者更多字符和数字
        Scanner scan = new Scanner(System.in);
        if (scan.hasNextLine()){
            Matcher matcher = pattern.matcher(scan.nextLine());
            boolean didLookingAt = matcher.lookingAt();
            //boolean didMatch = matcher.matches();
            System.out.println(didLookingAt);
            int patternStartIndex = matcher.start();
            System.out.println(patternStartIndex);
            int patternEndIndex = matcher.end();
            System.out.println(patternEndIndex);
        }

    }
}

console output:匹配失败,lookingAt()方法只匹配正则表达式与文本的开头。

false
Exception in thread "main" java.lang.IllegalStateException: No match available
    at java.util.regex.Matcher.start(Matcher.java:343)
    at RegexTest.main(RegexTest.java:28)

那么如果我们想要在模式匹配中找到非0索引开头的字符串，我们应该怎么做呢?
Bingo! find() 方法,stackoverflow提议传送门

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by 26645 on 2017/8/31.
 */
public class RegexTest {
    public static void main(String[] args) {
        Pattern p = Pattern.compile(".s");//表示单个字符
        Matcher m= p.matcher("as");
        boolean b =m.matches();

        //2nd way
        boolean b2 = Pattern.compile(".s").matcher("as").matches();

        //3nd way
        boolean b3 = Pattern.matches(".s","as");

        //4nd way
        Pattern pattern = Pattern.compile("[Aa].*string");//匹配string字符串之前的0或者更多字符和数字
        Scanner scan = new Scanner(System.in);
        String str1="7-11";
        String regex = "-";
        Pattern ptest = Pattern.compile(regex);
        Matcher m1 = ptest.matcher(str1);
        System.out.println(m1.lookingAt());

        if (scan.hasNextLine()){
            Matcher matcher = pattern.matcher(scan.nextLine());
            //boolean didLookingAt = matcher.lookingAt();
            //boolean didMatch = matcher.matches();
            boolean didfind = matcher.find();
            System.out.println(didfind);
            int patternStartIndex = matcher.start();
            System.out.println(patternStartIndex);
            int patternEndIndex = matcher.end();
            System.out.println(patternEndIndex);
        }

    }
}

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=61963:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
false
Here is a vbery string
true
8
22

Process finished with exit code 0

• 正则表达式中的复杂模式

Tips:Wiki 几乎完全基于正则表达式。Wiki 内容基于来自用户的字符串输入，该输入被使用正则表达式解析和格式化。任何用户都可以通过输入一个 wiki 词组在 wiki 中创建另一个主题的链接，这个词组通常是一系列串联的单词，每个单词以一个大写字母开头
匹配目标: HereAllowed is a WikiWord followed by AnotherWikiWord,then SomeWikiWord.

  String input = "HereAllowed is a WikiWord followed by AnotherWikiWord,then SomeWikiWord.";
        Pattern pattern1 = Pattern.compile("[A-Z][a-z]*([A-Z][a-z]*)*");
        Matcher matcher = pattern1.matcher(input);
        while(matcher.find()){
            System.out.println(matcher.group());
        }

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=62138:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
HereAllowed
WikiWord
AnotherWikiWord
SomeWikiWord

• 匹配和操作分组

那么回归上一节,正则表达式复杂模式下匹配大写字母开头的字符串类型,并用小括号进行分隔匹配，但我们只能用这种方法么? 在对字符串操作分组更多时,matcher.group(0),matcher.group(1)的效率显然不理想，所以我们引入"分组"的概念，将匹配得到的字符串作为模板，通过在替换字符串中包含 $0 来引用完整匹配结果,即matcher.group(0).当我们需要制定分组时，只需要指定模板变量$之后的数字下标即可

 //6th way
        String input = "Here is a WikiWord followed by AnotherWikiWord,then SomeWikiWord";
        Pattern pattern = Pattern.compile("[A-Z][a-z]*([A-z][a-z]*)*");
        Matcher mathcer = pattern.matcher(input);
        System.out.println("Before: "+input);
        String result = mathcer.replaceAll("blah$0blah");
        System.out.println("After:"+result);
        String result_update = mathcer.replaceAll("blah$1blah");
        System.out.println("After_update: "+result_update);

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=52384:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
Before: Here is a WikiWord followed by AnotherWikiWord,then SomeWikiWord
After:blahHereblah is a blahWikiWordblah followed by blahAnotherWikiWordblah,then blahSomeWikiWordblah
After_update: blahblah is a blahWordblah followed by blahWordblah,then blahWordblah

Process finished with exit code 0

• 替换字符串

 //6th way
        String input = "Here is a WikiWord followed by AnotherWikiWord,then SomeWikiWord";
        Pattern pattern = Pattern.compile("[A-Z][a-z]*([A-z][a-z]*)*");
        Matcher mathcer = pattern.matcher(input);
        System.out.println("Before: "+input);
        String result = mathcer.replaceAll("blah$0blah");
        System.out.println("After:"+result);
        String result_update = mathcer.replaceAll("blah$1blah");
        System.out.println("After_update: "+result_update);

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=52384:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
Before: Here is a WikiWord followed by AnotherWikiWord,then SomeWikiWord
After:blahHereblah is a blahWikiWordblah followed by blahAnotherWikiWordblah,then blahSomeWikiWordblah
After_update: blahblah is a blahWordblah followed by blahWordblah,then blahWordblah

• Re构造:标识符
  \b为零宽度的字符,一侧是构成单词的字符，另一侧为非单词字符、字符串的开始或结束位置。
  在Java中\w等同于[a-zA-Z0-9_]
  我们以几个合法标识符举例abc,_test,$test
  当匹配到一个字符串时，必定不能以数字型前缀开头,例 ： 123abc。

构造思路:字符组建立
1.用\b用来分割字符串左侧为构成单词的字符，排除数字型前缀字符串。右侧为非单词字符，排除空格
2.使用[a-zA-Z_]字符组限制右侧出现的字符类型
3.使用\w*字符组匹配自此之前的字符串

 //7th way
        String line = "imooc";
        String Regex_second ="\\b[a-zA-Z_]\\w*";
        Pattern pattern2 = Pattern.compile(Regex_second);
        Matcher matcher2 = pattern2.matcher(line);
        if(matcher2.find()){
            System.out.println(matcher2.group());
        }
    }

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=49789:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
imooc

• Re构造:提取引号内的字符串

构造思路:
1、以引号开始，任意字符，以引号结束。
2、末尾引号左边不能是 \
3、末尾引号左边可以是 \\
4、末尾引号左边不能是 a\

 //8th way
        String line_second ="the\"laozi\"first";
        String Regex = "\"(.*?)(?

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=64178:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
"laozi"

• Re构造:匹配美元金额(可能包含小数)

构造思路1:将$与.转义分别用+截断分别匹配数字型字符

构造思路2:专用d+代替[0-9]匹配组

//9th way
        String dollar="$1000 fdgdfgdfgfdg";
        String Regex = "\\$[0-9]+(\\.[0-9][0-9])?";
        String Regex_first = "\\$\\d+(?:\\.\\d+)?";
        Pattern pattern = Pattern.compile(Regex_first);
        Matcher matcher = pattern.matcher(dollar);
        if(matcher.find()){
            System.out.println(matcher.group());
        }

console output

D:\java\jdk1.8.0_51\bin\java "-javaagent:D:\idea\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar=55131:D:\idea\IntelliJ IDEA 2017.1.4\bin" -Dfile.encoding=UTF-8 -classpath D:\java\jdk1.8.0_51\jre\lib\charsets.jar;D:\java\jdk1.8.0_51\jre\lib\deploy.jar;D:\java\jdk1.8.0_51\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_51\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_51\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_51\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_51\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_51\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_51\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_51\jre\lib\javaws.jar;D:\java\jdk1.8.0_51\jre\lib\jce.jar;D:\java\jdk1.8.0_51\jre\lib\jfr.jar;D:\java\jdk1.8.0_51\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_51\jre\lib\jsse.jar;D:\java\jdk1.8.0_51\jre\lib\management-agent.jar;D:\java\jdk1.8.0_51\jre\lib\plugin.jar;D:\java\jdk1.8.0_51\jre\lib\resources.jar;D:\java\jdk1.8.0_51\jre\lib\rt.jar;E:\kotlin_learn\out\production\kotlin_learn;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-runtime.jar;C:\Users\26645\.IntelliJIdea2017.1\config\plugins\Kotlin\kotlinc\lib\kotlin-reflect.jar;E:\kotlin_learn\junit-4.12.jar RegexTest
$1000

• Re构造:HTML标签

div标签（不含属性）正则式 : (?<=

).*(?=

)
div标签(含属性)正则式 : ]*>[^<>]*

Tips : 零宽断言
用于查找在某些内容(但并不包括这些内容)之前或之后的东西，也就是说它们像 \b ^ $ \< \>这样的锚定作用，仅仅用于指定一个位置，不参与内容匹配，这个位置应该满足一定的条件(即断言)，因此它们也被称为零宽断言。 断言用来声明一个应该为真的事实。正则表达式中只有当断言为真时才会继续进行匹配

(?<=

).*(?=

)正则解析

• (?<=
  ) 先从要匹配的字符串中的最左端找到第一个

  ,然后再匹配其后面的表达式，若无法匹配则继续查找第二个

  再匹配第二个

  后面的字符串，若能匹配则匹配。
• (?=

) 从要匹配的字符串中的最右端找到第一个

(然后 再匹配其前面的表达式，若无法匹配则继续查找第二个