Java中正则表达式的一些特殊用法

最近在研究数据库迁移工具，阅读源码的过程中学习了一些正则表达式的特殊用法，于是记录一下。

1@Test
2    public void test() {
3        String sql = "CREATE TABLE `test_table` (\n" +
4                "  `id` int(11) NOT NULL AUTO_INCREMENT,\n" +
5                "  `test_column` int(11) DEFAULT NULL COMMENT '测试字段备注',\n" +
6                "  PRIMARY KEY (`id`)\n" +
7                ") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci COMMENT='测试表备注'";
8        String regex = "^\\s*create\\s+table\\s+(?<tableName>\\S+)?[^()]*\\(" +
9                "(?<columnSql>[\\s\\S]+)" +
10                "\\)[\\s]+" +
11                "(engine=(?<tableEngine>\\S+))?" +
12                "[\\s]*" +
13                "(default charset=(?<tableCharset>\\S+))?" +
14                "[\\s]*" +
15                "(collate=(?<tableCollate>\\S+))?" +
16                "[\\s]*" +
17                "(comment=(?<tableComment>\\S+))?" +
18                "$";
19        Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
20        Matcher matcher = pattern.matcher(sql);
21        if (matcher.find()) {
22            System.out.println("tableName:" + matcher.group("tableName"));
23            System.out.println("columnSql:" + matcher.group("columnSql"));
24            System.out.println("tableEngine:" + matcher.group("tableEngine"));
25            System.out.println("tableCharset:" + matcher.group("tableCharset"));
26            System.out.println("tableCollate:" + matcher.group("tableCollate"));
27            System.out.println("tableComment:" + matcher.group("tableComment"));
28        }
29
30    }

输出结果为

1tableName:`test_table`
2columnSql:
3  `id` int(11) NOT NULL AUTO_INCREMENT,
4  `test_column` int(11) DEFAULT NULL COMMENT '测试字段备注',
5  PRIMARY KEY (`id`)
6
7tableEngine:InnoDB
8tableCharset:utf8mb4
9tableCollate:utf8mb4_unicode_ci
10tableComment:'测试表备注'

搜索发现jdk7之后正则表达式就已经支持了这种写法，而安卓端也有第三方的类库Github地址在几年前提供了支持。

语法:

(?<foo>bar)

英文解释:

Define a named group named "foo" consisting of pattern bar. Matches within the group can be referenced in a replacement using the backreference $foo.

大概意思就是定义一个命名组foo，命名组的匹配规则是bar，这样做还可以使用$foo的形式引用，当然这里也适用其它的正则语法，比如适用: (?:<foo>bar) 取消引用降低性能损耗