import org.apache.commons.codec.binary.Base64

import java.security.MessageDigest

class ExpressApiSign {

    static String sfGenerateOpenSign(String postData, Long appId, String appKey) {
        StringBuilder sb =  new StringBuilder()
        sb.append(postData)
        sb.append("&" + appId + "&" + appKey)
        MessageDigest md = MessageDigest.getInstance("MD5")
        byte[] md5 = md.digest(sb.toString().getBytes("utf-8"))
        int i
        StringBuffer buf = new StringBuffer("")
        for (int offset = 0; offset < md5.length; offset++) {
            i = md5[offset]
            if (i < 0) {
                i += 256
            }
            if (i < 16) {
                buf.append("0")
            }
            buf.append(Integer.toHexString(i))
        }
        String ret = Base64.encodeBase64String(buf.toString().getBytes("utf-8"))
        return  ret
    }
}