4.熟悉Java基本类库系列——Java 正则表达式类库

正则表达式语法结构图：

Java正则表达式类库结构图：

Java典型例子

1、String类 matches()方法

判断字符串是否符合特定正则表达式

@Test public void testRegex(){
	String regex = ".*\\d{3}.*";
	String str1 = "11tec34";
	String str2 = "285dffd";
	String str3 = "bac7736db";
	//输出：false, true, true
	System.out.println(str1.matches(regex) + "," + str2.matches(regex) + "," + str3.matches(regex));
}

2、String类 split()方法

用正则表达式分割字符串

@Test public void testRegex2(){
	String input = "hello3world8my9name1is5jacket";
	String regex = "\\d";  //以数字作为分隔符
	String strs[] = input.split(regex);
	//输出：hello world my name is jacket
	for(String str : strs){
		System.out.print(str + " ");
	}
	System.out.println();

	input = "hellodogworlddogmydognamedogisdogjacket";
	regex = "dog";  //以"dog"字符作为分隔符
	strs = input.split(regex);
	//输出：hello world my name is jacket
	for(String str : strs){
		System.out.print(str + " ");
	}
}

3、String类 replace()方法

用正则表达式替换字符

@Test public void testRegex3(){
	String input = "hello3world8my9name1is5jacket";
	String regex = "\\d";  //以数字作为分隔符
	String firstStr = input.replaceFirst(regex, ":"); //只替换第一个匹配的字符
	String allStr = input.replaceAll(regex, ":");  //替换所有匹配的字符
	//输出：
	//hello:world8my9name1is5jacket
	//hello:world:my:name:is:jacket
	System.out.println(firstStr);
	System.out.println(allStr);
}

4、Pattern.matches() 静态方法

判断字符串是否符合正则表达式，等同于String类的matches()方法

@Test public void testRegex4(){
	String regex1 = "\\bdog\\b";
	String regex2 = ".*\\bdog\\b.*";
	String input = "dog dog dog doggie dogg";
	//输出：false,true
	System.out.println(Pattern.matches(regex1, input) + "," + Pattern.matches(regex2, input));
}

5、Pattern类 split()方法

根据正则表达式分割字符串，等同于String类的split()方法

//6.split() 分割字符串  -> 等同于String的split()方法
@Test public void testRegex6(){
	String regex = "\\d";
	String input = "hello3world5hello8java";
	Pattern p = Pattern.compile(regex);
	String strs[] = p.split(input);
	//输出：hello world hello java
	for(String str : strs){
		System.out.print(str + " ");
	}
}

6、Pattern.quote() 静态方法

获取匹配此字符串的正则表达式

@Test public void testRegex6(){
	//例子1
	String input = ".";
	String regex = Pattern.quote(input);
	boolean flag = Pattern.matches(regex, input);
	//输出：\Q353434\E	true
	System.out.println(regex);
	System.out.println(flag);

	//例子2
	input = "test.test";
	String errorOutput = input.replaceAll(".", "/");
	//输出：/////////
	System.out.println(errorOutput);

	//例子3
	String correctOutput = input.replaceAll(Pattern.quote("."), "/");
	//输出：test/test
	System.out.println(correctOutput);
}

7、Matcher类 find()方法，start()方法，end()方法

@Test public void testRegex7(){
	//m.start()   m.end()
	String regex = "\\bdog\\b";
	String input = "dog dog dog doggie dogg";
	Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(input);        // 获得匹配器对象
    int count = 0;
    while (m.find()) {
           count++;
           //Match number 1,start(): 0,end(): 3
           //Match number 2,start(): 4,end(): 7
           //Match number 3,start(): 8,end(): 11
           System.out.print("Match number " + count);
           System.out.print(",start(): " + m.start());
           System.out.println(",end(): " + m.end());
    }
}

8、Matcher类 find(int index)方法，start(int index)，end(int index)

@Test public void testRegex8(){
	//m.start()   m.end()
	String regex = "\\bdog\\b";
	String input = "dog dog dog doggie dogg";
	Pattern p = Pattern.compile(regex);
　　    Matcher m = p.matcher(input);        // 获得匹配器对象

    //m.find(int start)
    //输出：start(): 0,end(): 3
    //start(): 4,end(): 7
    m.find(0);  //从要匹配的字符串的第几个字符开始寻找
    System.out.print("start(): " + m.start());
    System.out.println("end(): " + m.end());
    m.find();
    System.out.print("start(): " + m.start());
    System.out.println("end(): " + m.end()); 

    //m.find(int start)
    //输出：start(): 4,end(): 7
    //start(): 8,end(): 11
    m.find(4);
    System.out.print("start(): " + m.start());
    System.out.println("end(): " + m.end());
    m.find();
    System.out.print("start(): " + m.start());
    System.out.println("end(): " + m.end()); 

    //m.start(int group)	m.end(int group)
    m.find(0);	//
    int firstStartGroupIndex = m.start(0);
    System.out.println(firstStartGroupIndex);
}

9、Matcher类 lookingAt()方法，matches()方法

判断字符串是否匹配特定的正则表达式，lookingAt()方法不要求全部匹配，而matches()方法要求全部匹配

@Test public void testRegex9(){
	String regex = "foo";
	String str = "fooooooooooooooooo";
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(str); 

        System.out.println("Current regex is: " + regex);
        System.out.println("Current str is: " + str); 

        System.out.println("lookingAt(): " + matcher.lookingAt());  //true
        System.out.println("matches(): " + matcher.matches()); 	//false，因为matches要求全部匹配
}

此外还有其他的Matcher类的方法未整理，

//还有Matcher类的其他方法未整理：

//1.group(int group)方法

//2.appendReplacement() / appendTail() / replaceAll() / replaceFirst() / quoteReplacement()

//99.Matcher类的find()方法,start()方法，end()方法

更多详细的正则表达式博文可以参考：

微软官方文档：https://msdn.microsoft.com/zh-cn/library/ae5bf541(v=vs.80).aspx

一个很好的正则表达式教程：http://www.java3z.com/cwbwebhome/article/article8/Regex/Java.Regex.Tutorial.html#reg7