Thinking in java之正则表达式小例子

public static final String POEM= 
            "Twas brilling, and the slithy toves\n" +
            "Did gyre and gimble in the wabe.\n"+ 
            "All mimsy were the borogoves,\n" +
            "And the mome rathsoutgrable.\n\n"+ 
            "Beware the Jabberwork, my son,\n"+
            "The jaws that bite, the claws that catch.\n"+ 
            "Beware hte Jubjub bird, and shun\n"+
            "The frumious Bandersnatch.";
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Matcher m= Pattern.compile("(?m)(\\S+)\\s+((\\S+)\\s+(\\S+))$")
                .matcher(POEM);
        while (m.find()) {
            for (int j = 0; j <= m.groupCount(); j++) {
                System.out.print("["+ m.group(j)+ "]");
            }
            System.out.println();
        }
    }

output:
[the slithy toves][the][slithy toves][slithy][toves]
[in the wabe.][in][the wabe.][the][wabe.]
[were the borogoves,][were][the borogoves,][the][borogoves,]
[the mome rathsoutgrable.][the][mome rathsoutgrable.][mome][rathsoutgrable.]
[Jabberwork, my son,][Jabberwork,][my son,][my][son,]
[claws that catch.][claws][that catch.][that][catch.]
[bird, and shun][bird,][and shun][and][shun]
[The frumious Bandersnatch.][The][frumious Bandersnatch.][frumious][Bandersnatch.]

解析：

m.groupCout():匹配器匹配的组的总数，不包括0组。

m.group(j):匹配的第j组的值。group(0)是整个表达式

(?m):多行模式

\S:非空白字符

\s:空白字符 ==[ \t\n\x0B\f\r]

2.Matcher.find() vs .lookingAt() vs .matchers()

package com.westward;

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

public class Demo31 {
    public static String input= 
      "As long as there is injustice, whenever a\n"+
      "Targathian baby cries out.wherever a distress\n" +
      "signal sounds among the stars ... We'll be there.\n"+ 
      "This fine ship, and this fine crew ...\n" +
      "Never give up! Never surrender!";
    
    private static class Display{
        private boolean regexPrinted= false;
        private String regex;
        Display(String regex) {
            this.regex= regex;
        }
        void display(String message){
            if (!regexPrinted) {
                System.out.println(regex);
                regexPrinted = true;
            }
            System.out.println(message);
        }
    }
    static void examine(String s,String regex){
        Display d= new Display(regex);
        Pattern p= Pattern.compile(regex);
        Matcher m= p.matcher(s);
        while (m.find()) {
            d.display("find() '"+ m.group() +
            "' start= "+m.start()+ " end= "+ m.end());
        }
        if (m.lookingAt()) {
            d.display("lookingAt() '"+ m.group() +
                    "' start= "+m.start()+ " end= "+ m.end());
        }
        if (m.matches()) {
            d.display("matches() '"+ m.group() +
                    "' start= "+m.start()+ " end= "+ m.end());
        }
    }
    public static void main(String[] args) {
        for (String in : input.split("\n")) {
            System.out.println("input :"+ in);
            for (String regex : new String[]{"\\w*ere\\w*",
                    "\\w*ever","T\\w+","Never.*?!"}) {
                examine(in, regex);
            }
        }
    }
}

output:
input :As long as there is injustice, whenever a
\w*ere\w*
find() 'there' start= 11 end= 16
\w*ever
find() 'whenever' start= 31 end= 39
input :Targathian baby cries out.wherever a distress
\w*ere\w*
find() 'wherever' start= 26 end= 34
\w*ever
find() 'wherever' start= 26 end= 34
T\w+
find() 'Targathian' start= 0 end= 10
lookingAt() 'Targathian' start= 0 end= 10
input :signal sounds among the stars ... We'll be there.
\w*ere\w*
find() 'there' start= 43 end= 48
input :This fine ship, and this fine crew ...
T\w+
find() 'This' start= 0 end= 4
lookingAt() 'This' start= 0 end= 4
input :Never give up! Never surrender!
\w*ever
find() 'Never' start= 0 end= 5
find() 'Never' start= 15 end= 20
lookingAt() 'Never' start= 0 end= 5
Never.*?!
find() 'Never give up!' start= 0 end= 14
find() 'Never surrender!' start= 15 end= 31
lookingAt() 'Never give up!' start= 0 end= 14
matches() 'Never give up! Never surrender!' start= 0 end= 31

总结：

Matcher.find():匹配字符串的任意位置

Matcher.lookingAt():匹配字符串的开始位置

Matcher.matchers():匹配整个字符串，String.matchers()底层就是调用的它。

3.Pattern标记 (Pattern的几个成员变量)

public static void main(String[] args) {
        // TODO Auto-generated method stub
        Pattern p= Pattern.compile("^java", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE);
        Matcher m= p.matcher(
                "java has regex\nJava has regex\n"+
                "JAVA has pretty good regular expressions\n"+
                "Regular expressions are in Java");
        while (m.find()) {
            System.out.println(m.group(0));
//            System.out.println(m.group());//the same
        }
    }

output:
java
Java
JAVA

总结：不同的Pattern标记可以用 或| 来连接。 

Pattern.CASE_INSENSITIVE(?i):字母大小写不敏感

Pattern.MULTILINE(?m):多行模式