捕获组分为:
- 普通捕获组(Expression)
- 命名捕获组(? Expression)
普通捕获组
从正则表达式左侧开始,每出现一个左括号”(“记做一个分组,分组编号从 1 开始。0 代表整个表达式。
对于时间字符串:2017-04-25,表达式如下
(\\d{4})-((\\d{2})-(\\d{2}))
有 4 个左括号,所以有 4 个分组:
编号 | 捕获组 | 匹配 |
---|---|---|
0 | (\d{4})-((\d{2})-(\d{2})) | 2017-04-25 |
1 | (\d{4}) | 2017 |
2 | ((\d{2})-(\d{2})) | 04-25 |
3 | (\d{2}) | 04 |
4 | (\d{2}) | 25 |
public
static
final
String
DATE_STRING
=
“
2017-04-25
“
;
public
static
final
String
P_COMM
=
“
(
\\
d{4})-((
\\
d{2})-(
\\
d{2}))
“
;
Pattern
pattern
=
Pattern
.
compile
(
P_COMM
)
;
Matcher
matcher
=
pattern
.
matcher
(
DATE_STRING
)
;
matcher
.
find
(
)
;
//
必须要有这句
System
.
out
.
printf
(
“
\n
matcher.group(0) value:%s
“
,
matcher
.
group
(
0
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(1) value:%s
“
,
matcher
.
group
(
1
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(2) value:%s
“
,
matcher
.
group
(
2
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(3) value:%s
“
,
matcher
.
group
(
3
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(4) value:%s
“
,
matcher
.
group
(
4
)
)
;
命名捕获组
每个以左括号开始的捕获组,都紧跟着 ?,而后才是正则表达式。
对于时间字符串:2017-04-25,表达式如下:
(?<year>\\d{4})-(?<md>(?<month>\\d{2})-(?<date>\\d{2}))
有 4 个命名的捕获组,分别是:
编号 | 名称 | 捕获组 | 匹配 |
---|---|---|---|
0 | 0 | (?\d{4})-(?(?\d{2})-(?\d{2})) | 2017-04-25 |
1 | year | (?\d{4})- | 2017 |
2 | md | (?(?\d{2})-(?\d{2})) | 04-25 |
3 | month | (?\d{2}) | 04 |
4 | date | (?\d{2}) | 25 |
命名的捕获组同样也可以使用编号获取相应值。
public
static
final
String
P_NAMED
=
“
(?<year>
\\
d{4})-(?<md>(?<month>
\\
d{2})-(?<date>
\\
d{2}))
“
;
public
static
final
String
DATE_STRING
=
“
2017-04-25
“
;
Pattern
pattern
=
Pattern
.
compile
(
P_NAMED
)
;
Matcher
matcher
=
pattern
.
matcher
(
DATE_STRING
)
;
matcher
.
find
(
)
;
System
.
out
.
printf
(
“
\n
===========使用名称获取=============
“
)
;
System
.
out
.
printf
(
“
\n
matcher.group(0) value:%s
“
,
matcher
.
group
(
0
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(‘year’) value:%s
“
,
matcher
.
group
(
“
year
“
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(‘md’) value:%s
“
,
matcher
.
group
(
“
md
“
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(‘month’) value:%s
“
,
matcher
.
group
(
“
month
“
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(‘date’) value:%s
“
,
matcher
.
group
(
“
date
“
)
)
;
matcher
.
reset
(
)
;
System
.
out
.
printf
(
“
\n
===========使用编号获取=============
“
)
;
matcher
.
find
(
)
;
System
.
out
.
printf
(
“
\n
matcher.group(0) value:%s
“
,
matcher
.
group
(
0
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(1) value:%s
“
,
matcher
.
group
(
1
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(2) value:%s
“
,
matcher
.
group
(
2
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(3) value:%s
“
,
matcher
.
group
(
3
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(4) value:%s
“
,
matcher
.
group
(
4
)
)
;
PS:非捕获组
在左括号后紧跟 ?:,而后再加上正则表达式,构成非捕获组 (?:Expression)。
对于时间字符串:2017-04-25,表达式如下:
(?:\\d{4})-((\\d{2})-(\\d{2}))
这个正则表达式虽然有四个左括号,理论上有 4 个捕获组。但是第一组 (?:\d{4}),其实是被忽略的。当使用 matcher.group(4) 时,系统会报错。
编号 | 捕获组 | 匹配 |
---|---|---|
0 | (\d{4})-((\d{2})-(\d{2})) | 2017-04-25 |
1 | ((\d{2})-(\d{2})) | 04-25 |
2 | (\d{2}) | 04 |
3 | (\d{2}) | 25 |
public
static
final
String
P_UNCAP
=
“
(?:
\\
d{4})-((
\\
d{2})-(
\\
d{2}))
“
;
public
static
final
String
DATE_STRING
=
“
2017-04-25
“
;
Pattern
pattern
=
Pattern
.
compile
(
P_UNCAP
)
;
Matcher
matcher
=
pattern
.
matcher
(
DATE_STRING
)
;
matcher
.
find
(
)
;
System
.
out
.
printf
(
“
\n
matcher.group(0) value:%s
“
,
matcher
.
group
(
0
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(1) value:%s
“
,
matcher
.
group
(
1
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(2) value:%s
“
,
matcher
.
group
(
2
)
)
;
System
.
out
.
printf
(
“
\n
matcher.group(3) value:%s
“
,
matcher
.
group
(
3
)
)
;
//
Exception in thread “main” java.lang.IndexOutOfBoundsException: No group 4
System
.
out
.
printf
(
“
\n
matcher.group(4) value:%s
“
,
matcher
.
group
(
4
)
)
;
总结
- 普通捕获组使用方便;
- 命名捕获组使用清晰;
- 非捕获组目前在项目中还没有用武之地。
原文地址:https://blog.csdn.net/just4you/article/details/70767928
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