生成固定长度的随机数字

RandomStringUtils.randomNumeric(生成随机数的长度)

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

public class RandomStringUtilsTest {

    @Test
    public void testGenerateString4(){
        String code = RandomStringUtils.randomNumeric(4);
        System.out.println("code = " + code);
    }
}

结果