X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(pubKey.getBytes());
            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
            RSAPublicKey publicKey = (RSAPublicKey)keyFactory.generatePublic(pubKeySpec);

import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.spec.KeySpec;
import java.security.spec.X509EncodedKeySpec;

public class Cert {

    public static void main(String[] args) throws Exception {
        String str = "30818902818100B6FA647C106B69AD474145F0A5EE8FC7B760" +
                 "E77B049CCB059C0D8E7B15DBE63DD4B260A84E6D1474855328" +
                 "7A022A39C0F69740978088660CC7E26069FE11BFE0BD2F2967" +
                 "71887AF632FB2F5DB0452ADD4D8E00DBC679A9AB95C61CDB2B" +
                 "4B072E37737140DD0131745FCACDF8638309E552F03F0CD00A" +
                 "6313EF72E8E19051BE290203010001";
        
        System.out.println(str.length());
        byte[] keyBytes = toBytes(str);
        
        KeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory factory = KeyFactory.getInstance("RSA");
        PublicKey publicKey = factory.generatePublic(keySpec);
    }
    
    private static byte[] toBytes(String str) {
        if(str == null) {
            throw new IllegalArgumentException("binary string is null");
        }
        char[] chs = str.toCharArray();
        byte[] bys = new byte[chs.length / 2];
        int offset = 0;
        int k = 0;
        while(k < chs.length) {
            bys[offset++] = (byte)((toInt(chs[k++]) << 4) | toInt(chs[k++]));
        }
        return bys;
    }
    
    private static int toInt(char a) {
        if(a >= '0' && a <= '9') {
            return a - '0';
        }
        if(a >= 'a' && a <= 'f') {
            return a - 'a' + 10;
        }
        if(a >= 'A' && a <= 'F') {
            return a - 'A' + 10;
        }
        throw new IllegalArgumentException("parameter \"" + a + "\"is not hex number!");
    }
}