String padLeft(String s, int length)
    {
        byte[] bs = new byte[length];
        byte[] ss = s.getBytes();
        Arrays.fill(bs, (byte) (48 & 0xff));
        System.arraycopy(ss, 0, bs,length - ss.length, ss.length);
        return new String(bs);
    }

------解决方案--------------------
自己写一个方法吧：

Java code
import java.util.*;
public class test{
    public static void main(String[] args) {
        String s = "FF"; 
        System.out.println(padLeft(s,8));
    }
    public static String padLeft(String str,int len){
        String pad="0000000000000000";

        return len>str.length()&&len<=16&&len>=0?pad.substring(0,len-str.length())+str:str;
    }
}

------解决方案--------------------
	private static String fill(String input, int size, char symbol) {

		while (input.length() < size) {
			input = symbol + input;
		}
		return input;
	}

------解决方案--------------------
Java code

public static String pad (String str ,int size ,boolean isprefixed) {
        if (str == null)
            str = "";
        int str_size = str.length();
        int pad_len = size - str_size;
        StringBuffer retvalue = new StringBuffer();
        for (int i = 0; i < pad_len; i++) {
            retvalue.append("0");
        }
        if (isprefixed) 
            return retvalue.append(str).toString();
        return retvalue.insert(0, str).toString();
    }