正则表达式

申明：正则表达式可以大大的简化代码，不过对于看不懂的人来说，那也只能骂娘。切身体会，所以感觉有必要撸下来正则表达式！（后期会不断添加各种正则判断）

基本概念不多说我，直接上例子，通过例子说明吧。

一、正则基础

Demo1:

在java中对反斜线的处理与其它语言不同，在其它语言中,\表示“我想要在正则表达式中插入一个普通的（字面上的）反斜线”，请不要给它任何特殊的意义。而在java中，\的意思是“我要插入一个正则表达式的反斜线，所以其后的写符具有特殊的意义。"例如，如果我想要表示一位数字，那么正则表达式应该是\d。如果你想插入一个普通的反斜线，则应该这样\\，不过换行和制表之类的东西只需要使用单反斜线：

package com.rah;
/***
 * 
 * @author team
 *
 */
public class Demo1 {

    public static void main(String[] args) {
        /***
         * 反斜线在程序中必须以\表示如下：
         */
        System.out.println("\".matches("\\"));
        /***
         * ("-?\d+")匹配：可能有一个负号，或者后面跟着一位或多位数字
         */
        System.out.println("-1234".matches("-?\d+"));
        System.out.println("5678".matches("-?\d+"));
        System.out.println("+911".matches("-?\d+"));
        /***
         * ("(-|\+)?\d+")匹配:表示字符串的起始字符可能是一个-或者+（+有特殊意义，需要用\转义）,后面跟着一位或多位数字
         */
        System.out.println("+911".matches("(-|\+)?\d+"));
    }

}

运行结果：

true
true
true
false
true

Demo2
String.spilt是一个非常有用的正则表达式工具，其功能是”将字符串从正则表达式匹配的地方切开“。

package com.rah;

import java.util.Arrays;

/***
 * 
 * @author team
 * 
 */
public class Demo2 {
    public static String knights = "Then, when you have found the shrubbery, you must "
            + "cut down the mightiest tree in the forest..."
            + "with... a herring!";

    public static void split(String regex) {
        System.out.println(Arrays.toString(knights.split(regex)));
    }

    public static void main(String[] args) {
        /***
         * 按空格划分字符串
         */
        split(" ");
        /***
         * W(\W转义)意思是非单词字符如果是小写W，w则表示一个单词字符
         * 该正则可以标点字符给删了
         */
        split("\W+");
        /***
         * 字母n后面跟着一个单词字符
         */
        split("n\W+");
    }
}

运行结果：

[Then,, when, you, have, found, the, shrubbery,, you, must, cut, down, the, mightiest, tree, in, the, forest...with..., a, herring!]
[Then, when, you, have, found, the, shrubbery, you, must, cut, down, the, mightiest, tree, in, the, forest, with, a, herring]
[The, whe, you have found the shrubbery, you must cut dow, the mightiest tree i, the forest...with... a herring!]

Demo3

String.replaceFirst()/replaceAll(),也是可以匹配正则的

package com.rah;
/***
 * 
 * @author team
 * 
 */
public class Demo3 {
    public static String  sqlOne = "select * from students";
    public static String  sqlTwo = "seelct count(*) from students";
    public static void main(String[] args) {
        /***
         * 从前四个输出可以看出[]里面是只匹配他就会在第一时间匹配到就不会往下找，就是因为这个小知识点，在开发中浪费了我好多时间Q_Q
         */
        System.out.println(sqlOne.replaceFirst("s", "count(*)"));
        System.out.println(sqlOne.replaceFirst("[s]", "count(*)"));
        /***
         * 找到se匹配
         */
        System.out.println(sqlOne.replaceFirst("se", "count(*)"));
        /***
         * 找到s匹配，就不会往下找
         */
        System.out.println(sqlOne.replaceFirst("[se]", "count(*)"));
        
        System.out.println(sqlOne.replaceFirst("[*]", "count(*)"));
        System.out.println(sqlTwo.replaceFirst("count\(\*\)", "*"));
    }
}

运行结果：

count(*)elect * from students
count(*)elect * from students
count(*)lect * from students
count(*)elect * from students
select count(*) from students
seelct * from students

Demo4:

检查句子以大写字母开头、以句号结尾

package com.rah;
/***
 * 
 * @author team
 *
 */
public class Demo4 {
    public static boolean matches(String text) {
        /***
         * \p{javaUpperCase} 大写字母，不明白的可以看jdk文档
         */
        return text.matches("\p{javaUpperCase}.*\.");
    }
    public static void main(String[] args) {
        System.out.println(matches("This is correct."));
        System.out.println(matches("bad sentence 1."));
        System.out.println(matches("Bad sentence 2"));
        System.out.println(matches("This is also correct..."));
    }
}

运行结果:

true
false
false
true

Demo5:

package com.rah;

import java.util.Arrays;

/***
 * 
 * @author team
 * 
 */
public class Demo5 {
    public static String knights = "Then, when you have found the shrubbery, you must "
            + "cut down the mightiest tree in the forest..."
            + "with... a herring!";

    public static void split(String regex) {
        System.out.println(Arrays.toString(knights.split(regex)));
    }

    public static void main(String[] args) {
        /***
         * 在the和you处分割
         */
        split("the|you");
    }
}

运行结果：

[Then, when ,  have found ,  shrubbery, ,  must cut down ,  mightiest tree in ,  forest...with... a herring!]

Demo6

package com.rah;

/***
 * 
 * @author team
 * 
 */
public class Demo5 {
    public static String knights = "Then, when you have found the shrubbery, you must "
            + "cut down the mightiest tree in the forest..."
            + "with... a herring!";

    /*
     * 对应的内嵌标志表达式是 (?i)，它有四种形式：
     *  1，(?i) 
     *  2，(?-i) 
     *  3，(?i:X) 
     *  4，(?-i:X) 
     *  不带有 - 的是开标志，带有 - 的是关标志。
     */
    public static void main(String[] args) {
        /***
         * 对book都忽略大写
         */
        System.out.println("Book".matches("(?i)Book"));
        /***
         * 对b都忽略大写，ook还是得比较大小写，下面的方法作用一样，写的更简洁
         */
        System.out.println("Book".matches("(?i)b(?-i)ook"));
        /***
         * 对b都忽略大写，ook还是得比较大小写
         */
        System.out.println("Book".matches("(?i:b)ook"));

        /***
         * (?-i) 的作用域是前面，如a(?-i) (?-i)的作用域是后面，如(?i)B
         */
        System.out.println("bOOk".matches("b(?-i)(?i)ook"));
        System.out.println("aBook".matches("a(?-i:B)ook"));
        
        /***
         * [] 只要匹配到一个再往下匹配，匹配不到了就把当前的替换
         * 没有[] 他要满足字符串到匹配到才换
         */
        System.out.println("ouahoahuah".replaceAll("[ou]", ""));
        System.out.println("ouahoahuah".replaceAll("ou", ""));
        /***
         * 忽略大小写匹配aeiou
         */
        System.out.println(knights.replaceAll("(?i)[aeiou]", ""));
    }
}

运行结果：

true
true
true
true
true
ahahah
ahoahuah
Thn, whn y hv fnd th shrbbry, y mst ct dwn th mghtst tr n th frst...wth...  hrrng!

二、创建正则表达式

写法参考java.util.regex包下的Pattern类

Demo7:

package com.rah;

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

public class Demo7 {
    public static void main(String[] args) {
        if(args.length<2){
            System.out.println("Usage:
java TestRegularExpression " + 
                             "characterSequence regularExpression");
            System.exit(0);
        }
        System.out.println("Input: "" + args[0] + """);
        for(String arg : args){
            System.out.println("Regulqr expression: "" +arg +""");
            Pattern p = Pattern.compile(arg);
            Matcher m = p.matcher(args[0]);
            while(m.find()){
                System.out.println("Match "" + m.group() + "" at position " + m.start() + "-" + (m.end()-1));
            }
        }
    }
}

传入的参数：

abcabcabcdefabc abc+ (abc)+ (abc){2,}

运行结果：

Input: "abcabcabcdefabc"
Regulqr expression: "abcabcabcdefabc"
Match "abcabcabcdefabc" at position 0-14
Regulqr expression: "abc+"
Match "abc" at position 0-2
Match "abc" at position 3-5
Match "abc" at position 6-8
Match "abc" at position 12-14
Regulqr expression: "(abc)+"
Match "abcabcabc" at position 0-8
Match "abc" at position 12-14
Regulqr expression: "(abc){2,}"
Match "abcabcabc" at position 0-8

 Demo8:

package com.rah;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
/***
 * 
 * @author team
 *
 */
public class Demo8 {
    public static void main(String[] args) {
        Matcher m = Pattern.compile("\w+").matcher("Evening is full of the linnet's wings");
        while(m.find())
            System.out.print(m.group() + " ");
        System.out.println();
        int i = 0;
        /***
         * find(args) 是字符的起始位置，注意输出结果
         */
        while(m.find(i)) {
            System.out.print(m.group() + " ");
            i++;
        }    
    }
}

运行结果：

Evening is full of the linnet s wings 
Evening vening ening ning ing ng g is is s full full ull ll l of of f the the he e linnet linnet innet nnet net et t s s wings wings ings ngs gs s 

Demo9 （Group组）

组是用括号提供划分的正则表达式，可以根据组的编号来引用某个组。组号为0表示整个表达式组号为1表示被第一对括号括起来的组。

a(b(c))d    abcd是组0 bc是组1 c是组2

package com.rah;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/***
 * 
 * @author team
 *
 */
public class Demo9 {
    static public final String POEM = 
            "Twas brillig, and the slithy toves
" +
            "Did gyre and gimble in the wabe.
" +
            "All mimsy were raths outgrabe.
" +
            "And the mome raths outgrabe.

" +
            "Beware the Jabberwock, my son,
" +
            "The jaws that bite, the claws that catch.
" +
            "Beware the Jubjub bird, and shun
" +
            "The frumious Bandersnatch.";
    public static void main(String[] args) {
        /***
         * 检索每行的3个单词，每行最后以$结尾。通常$是与整个输入序列的末端进行匹配的，为了达到每行最后以$结尾，我们需要显示的通知正则表达式注意输入
         * 序列中的换行符，这个工作就由模式标记(?m)来完成。
         */
        Matcher m = Pattern.compile("(?m)(\S+)\s+((\S+)\s+(\S+))$").matcher(POEM);
        while(m.find()) {
            for (int i = 0; i <= m.groupCount(); i++) {
                System.out.print("[" + m.group(i) + "]" + " ");
            }
            System.out.println();
        }
    }

}

运行结果：

[the slithy toves] [the] [slithy toves] [slithy] [toves] 
[in the wabe.] [in] [the wabe.] [the] [wabe.] 
[were raths outgrabe.] [were] [raths outgrabe.] [raths] [outgrabe.] 
[mome raths outgrabe.] [mome] [raths outgrabe.] [raths] [outgrabe.] 
[Jabberwock, my son,] [Jabberwock,] [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.] 

Demo10

 ?:、?!、?s、?i、?x、?m、?u、?d等的使用  

未完待续。。。