无法通过java split()方法从字符串中获取数字

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args) {
        String str = "abc123def456ghi";
        Pattern pattern = Pattern.compile("\\d+"); // 匹配数字的正则表达式
        Matcher matcher = pattern.matcher(str);
        
        while (matcher.find()) {
            System.out.println(matcher.group());
        }
    }
}

123
456

public class Main {
    public static void main(String[] args) {
        String str = "abc123def456ghi";
        StringBuilder sb = new StringBuilder();
        
        for (char c : str.toCharArray()) {
            if (Character.isDigit(c)) {
                sb.append(c);
            }
        }
        
        String number = sb.toString();
        System.out.println(number);
    }
}

123456