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：\n\t

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:\njava 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\n" +
"Did gyre and gimble in the wabe.\n" +
"All mimsy were raths outgrabe.\n" +
"And the mome raths outgrabe.\n\n" +
"Beware the Jabberwock, my son,\n" +
"The jaws that bite, the claws that catch.\n" +
"Beware the Jubjub bird, and shun\n" +
"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。。。