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)(yw)(z)” 中，存在三个这样的组：
1. x
2. yw
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}-(dd))
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)(yw*)(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

返回顶部

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!