签名操作：实现参数ASCII码从小到大排序，然后拼接为url参数形式

做签名操作时经常要对参数进行排序后再进行加密，下面是自己项目中用到的一小段代码

public String createSign(Map<String, String> params, String privateKey){
        StringBuilder sb = new StringBuilder();
        // 将参数以参数名的字典升序排序
        Map<String, String> sortParams = new TreeMap<String, String>(params);
        // 遍历排序的字典,并拼接"key=value"格式
        for (Map.Entry<String, String> entry : sortParams.entrySet()) {
            String key = entry.getKey();
            String value =  entry.getValue().trim();
            if (StringUtils.isNotEmpty(value))
                sb.append("&").append(key).append("=").append(value);
        }
        String stringA = sb.toString().replaceFirst("&","");
        String stringSignTemp = stringA + privateKey;
        String signValue = Md5Encrypt.md5(stringSignTemp);
        return signValue;
    }

用到的md5工具类：

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5Encrypt {
	/**
	 * Used building output as Hex
	 */
	private static final char[] DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a',
			'b', 'c', 'd', 'e', 'f' };

	/**
	 * 对字符串进行MD5加密
	 * 
	 * @param text
	 *            明文
	 * 
	 * @return 密文
	 */
	public static String md5(String text) {
		MessageDigest msgDigest = null;

		try {
			msgDigest = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalStateException("System doesn't support MD5 algorithm.");
		}

		try {
			msgDigest.update(text.getBytes("UTF-8")); // 注意改接口是按照指定编码形式签名

		} catch (UnsupportedEncodingException e) {

			throw new IllegalStateException("System doesn't support your  EncodingException.");

		}

		byte[] bytes = msgDigest.digest();

		String md5Str = new String(encodeHex(bytes));

		return md5Str;
	}

	private static char[] encodeHex(byte[] data) {

		int l = data.length;

		char[] out = new char[l << 1];

		// two characters form the hex value.
		for (int i = 0, j = 0; i < l; i++) {
			out[j++] = DIGITS[(0xF0 & data[i]) >>> 4];
			out[j++] = DIGITS[0x0F & data[i]];
		}

		return out;
	}
	
	public static void main(String[] args) {
		System.out.println(Md5Encrypt.md5(Md5Encrypt.md5("123456" + "longon_login")));
	}

}