• 正则表达式之group
  • 1 基本概念
  • 2 实例
    • 2.1 实例1
    • 2.2 实例2
    • 2.3 实例3
  • 3 思考
    • 3.1 需求
    • 3.2 实现1
    • 3.3 实现2
    • 3.4 实现3
  • 4 推荐阅读

正则表达式之group

1 基本概念

捕获组就是把正则表达式中子表达式匹配的内容，保存到内存中以数字编号或手动命名的组里，方便后面引用

在Java中使用正则表达式返回符合正则表达式的字符串就要用到group()，group中记录了所有符合指定表达式的字符串

捕获组也就是Pattern中以括号对“()”分割出的子Pattern。至于为什么要用捕获组呢，主要是为了能找出在一次匹配中你更关心的部分。 捕获组可以通过从左到右计算其开括号来编号。例如，在表达式 “(x)(y\w)(z)” 中，存在三个这样的组：
1. x
2. y\w
3. z
捕获组的编号是按照“(”出现的顺序，从左到右编号的,组零group(0)始终代表整个表达式。
(\d{4})-(\d{2}-(\d\d))
1 1 2 3 3 2

2 实例

2.1 实例1

java code

    @Test    public void test2(){        Pattern p = Pattern.compile("(\\d+,)(\\d+)");        String s = "123,456-34,345";        Matcher m = p.matcher(s);        while (m.find()) {            System.out.println(m.group());            System.out.println(m.group(1));            System.out.println(m.group(2));        }        System.out.println(m.groupCount());    }

console

123,456
123,
456
34,345
34,
345
2

2.2 实例2

java code

    @Test    public void test3(){        String regex = "(x)(y\\w*)(z)";        String input = "exY123z,xy456z";        Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);        Matcher m = p.matcher(input);        while (m.find()) {            System.out.println(m.group());            System.out.println(m.group(2));        }        System.out.println(m.groupCount());    }

console

xY123z
Y123
xy456z
y456
3

2.3 实例3

java code

    @Test    public void test4() {        String str = "Hello,World! in Java.";        Pattern pattern = Pattern.compile("W(or)(ld!)");        Matcher matcher = pattern.matcher(str);        while (matcher.find()) {            System.out.println("Group 0:" + matcher.group(0));            System.out.println("Group 1:" + matcher.group(1));            System.out.println("Group 2:" + matcher.group(2));            System.out.println("Start 0:" + matcher.start(0) + " End 0:"                    * matcher.end(0));            System.out.println("Start 1:" + matcher.start(1) + " End 1:"                    * matcher.end(1));            System.out.println("Start 2:" + matcher.start(2) + " End 2:"                    * matcher.end(2));            System.out.println(str.substring(matcher.start(0), matcher.end(1)));        }    }

console

Group 0:World!
Group 1:or
Group 2:ld!
Start 0:6 End 0:12
Start 1:7 End 1:9
Start 2:9 End 2:12
Wor

3 思考

3.1 需求

我们用正则表达式的时候, 有时候会需要取到匹配到的字符串的某一部分, 比如:

http://xxx.xx.com/index.jsp?user=linzhicong&aaa=1

http://xxx.xx.com/index.jsp?user=yangfangwei&aaa=1

http://xxx.xx.com/index.jsp?login=hahaha&aaa=1

假设有这样一个需求: 取到这些url中参数user对应的值(linzhicong和yangfangwei)

3.2 实现1

java code

    @Test    public void test5() {        String str = "http://xxx.xx.com/index.jsp?user=linzhicong&aaa=1";        Pattern pattern = Pattern.compile("user=(.*)&");        Matcher matcher = pattern.matcher(str);        while (matcher.find()) {            System.out.println(matcher.group(1));        }    }

console

linzhicong

3.3 实现2

java code

    @Test    public void test5() {        String str = "http://xxx.xx.com/index.jsp?user=linzhicong&aaa=1"                + "http://xxx.xx.com/index.jsp?user=yangfangwei&aaa=1"                + "http://xxx.xx.com/index.jsp?login=hahaha&aaa=1";        Pattern pattern = Pattern.compile("user=(.*)&");        Matcher matcher = pattern.matcher(str);        while (matcher.find()) {            System.out.println(matcher.group(1));        }    }

console

linzhicong&aaa=1http://xxx.xx.com/index.jsp?user=yangfangwei&aaa=1http://xxx.xx.com/index.jsp?login=hahaha

请思考为什么出现这个结果？怎么修改才能实现需求？

3.4 实现3

“user=([^\.])&” “user=([\w])&” “user=([a-z]*)&” ......

java code

    @Test    public void test5() {        String str = "http://xxx.xx.com/index.jsp?user=linzhicong&aaa=1"                + "http://xxx.xx.com/index.jsp?user=yangfangwei&aaa=1"                + "http://xxx.xx.com/index.jsp?login=hahaha&aaa=1";        Pattern pattern = Pattern.compile("user=([a-z]*)&");        Matcher matcher = pattern.matcher(str);        while (matcher.find()) {            System.out.println(matcher.group(1));        }    }

console

linzhicong
yangfangwei

4 推荐阅读

java正则表达式语法详解及其使用代码实例

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