java按字节截取中英文混合字符串

public String subStringByByte(String str, int len){

String result = null;

if(str != null){

byte[] a = str.getBytes();

if(a.length <= len){

result = str;

}else if(len > 0){

result = new String(a, 0, len);

System.out.println(result);

int length = result.length();

if(str.charAt(length - 1) != result.charAt(length-1)){

if(length < 2){

result = null;

}else{

result = result.substring(0, length - 1);

}

}

}

}

return result;

}