编码，解码（Base64,md5,sha）

1.Base64作用
编码和解码,
兼容一些老系统比如邮件发送

   //按钮事件
   public void base64EncodeDemo(View view) {
       String content = mEt.getText().toString();
       //使用base64进行编码
       String encode_content = Base64.encodeToString(content.getBytes(),Base64.DEFAULT);
       mEt.setText(encode_content);
   }
   public void base64DecodeDemo(View view) {
       String content = mEt.getText().toString();
       //使用base64进行解码
       byte[] decodeContent = Base64.decode(content.getBytes(),Base64.DEFAULT);
       mEt.setText(new String(decodeContent));
   }
2.md5
单项加密
16进制字符串的个数32
校验传输内容
public void md5MessageDigest(View view) {
       try {
           //获取对应算法的加密实体
           MessageDigest md = MessageDigest.getInstance("MD5");
           //设置要加密的文本
           md.update(mEt.getText().toString().getBytes());
           //生成摘要
           byte[] digest = md.digest();
           bytes2Hex(digest);
           //10010101
           //00000000 11111111
           //00000000 10010101
           //255
           // byte & byte[2] 00000000 11111111
           //00000000 10010101
       } catch (NoSuchAlgorithmException e) {
           e.printStackTrace();
       }
   }
private String bytes2Hex(byte[] data){
       StringBuffer buffer = new StringBuffer();
       int v = 0xa;
       for (int i = 0; i < data.length; i++) {
           //                           10101010
           //00000000 00000000 00000000 11111111
           //00000000 00000000 00000000 10101010
           int value = data[i] & 255;
           //
           //value =17 11
           //value =10 a;
           //10
           //16进制的表现形式 0a
           System.out.println("value="+value);
           String temp = "";
           if (value<16){
               temp = "0"+Integer.toHexString(value);
           }else {
               temp = Integer.toHexString(value);
           }
           buffer.append(temp);
       }
       System.out.println("hexString="+buffer.toString());
       System.out.println("hexStringLen="+buffer.toString().length());
       return buffer.toString();
   }

3.sha 高级的单项加密算法

sha-1 40位
sha-224 56位
sha-256 64位
sha-384 96位
sha-512 128位
try {
           MessageDigest messageDigest =MessageDigest.getInstance("SHA-1");
           messageDigest =MessageDigest.getInstance("SHA-224");
           messageDigest =MessageDigest.getInstance("SHA-256");
           messageDigest =MessageDigest.getInstance("SHA-384");
           messageDigest =MessageDigest.getInstance("SHA-512");
           messageDigest.update(mEt.getText().toString().getBytes());
           byte[] result = messageDigest.digest();
           String hexString = bytes2Hex(result);
           ((TextView)findViewById(R.id.tv_digest)).setText(hexString);