微信支付 --- MD5 工具类

public class MD5Util {

private static final String hexDigits[] = { "0", "1", "2", "3", "4", "5",  
    "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };  

private static String byteArrayToHexString(byte b[]) {  
    StringBuffer resultSb = new StringBuffer();  
    for (int i = 0; i < b.length; i++)  
        resultSb.append(byteToHexString(b[i]));  

    return resultSb.toString();  
}  

private static String byteToHexString(byte b) {  
    int n = b;  
    if (n < 0)  
        n += 256;  
    int d1 = n / 16;  
    int d2 = n % 16;  
    return hexDigits[d1] + hexDigits[d2];  
}  

public static String MD5Encode(String origin, String charsetname) {  
    String resultString = null;  
    try {  
        resultString = new String(origin);  
        MessageDigest md = MessageDigest.getInstance("MD5");  
        if (charsetname == null || "".equals(charsetname))  
            resultString = byteArrayToHexString(md.digest(resultString  
                    .getBytes()));  
        else  
            resultString = byteArrayToHexString(md.digest(resultString  
                    .getBytes(charsetname)));  
    } catch (Exception exception) {  
    }  
    return resultString;  
}  

  
  
/** 
 * 创建md5摘要,规则是:按参数名称a-z排序,遇到空值的参数不参加签名。 
 */  
public static String createMD5Sign(SortedMap<String, String> signParams,  
        String paykey) {  
    StringBuffer sb = new StringBuffer();  
    Set es = signParams.entrySet();  
    Iterator it = es.iterator();  
    while (it.hasNext()) {  
        Map.Entry entry = (Map.Entry) it.next();  
        String k = (String) entry.getKey();  
        String v = (String) entry.getValue();  
        if (null != v && !"".equals(v) && !"sign".equals(k)  
                && !"key".equals(k)) {  
            sb.append(k + "=" + v + "&");  
        }  
    }  
    sb.append("key=" + paykey);  
    String sign = MD5Encode(sb.toString(), "UTF-8").toUpperCase();  
    return sign;  
}  

}