JAVA如何按字节截取字符串

public class SubStringTest {

  @Test
  public void test() {

    String s = "北京市丰台区东铁营街道政馨园社区1区1号楼1层";
    System.out.println(subString(s, 58));
  }

  public static String subString(String source, int length) {

    StringBuffer buffer = new StringBuffer();
    char[] chars = source.toCharArray();
    char c;
    for (int i = 0;; i++) {
      if (length <= 0) {
        break;
      }
      c = source.charAt(i);
      buffer.append(c);
      length -= String.valueOf(c).getBytes().length;
      if (i + 1 < chars.length) {
        if (String.valueOf(chars[i + 1]).getBytes().length > length) {
          break;
        };
      }
    }
    return buffer.toString();
  }
}