Use the digest stream to obtain the MD5 of an object

Abstract stream is a type of stream filtering. It can be used to read and write the digest information (MD5/Sha) of the stream ).

When packaging a stream using a digest stream, an additional messagedigest object needs to be passed,

 
Messagedigest MD = messagedigest. getinstance ("MD5"); Digestinputstream dis=NewDigestinputstream (in, MD );
 

The Digest stream rewrites the Read and Write methods of the stream. The method internally calls the Upate () of the messagedigest object to update the digest information.

Public IntRead ()ThrowsIoexception {IntCh =In. Read ();If(On & Ch! =-1) {Digest. Update ((Byte) CH );}ReturnCh ;}
 

CallGetdigest ()Bytes [] that can obtain the digest information. Generally, we need to obtain the MD5 value in string form, so we need to convert it.

 /**  * Convert the byte array into a hexadecimal string **  @ Param Bytes *  @ Return  Returns a hexadecimal string.  */      Public   Static String bytearraytohex ( Byte  [] Bytes ){  //  Character array, used to store hexadecimal characters          Char [] Hexreferchars = {'0', '1', '2', '3', '4', '5', '6', '7', '8' , '9', 'A', 'B', 'C', 'D', 'E', 'F' }; //  One byte occupies 8 digits and one hexadecimal character occupies 4 digits. The length of the hexadecimal character array is twice the length of the byte array.          Char [] Hexchars = New   Char [Bytes. length * 2 ];  Int Index = 0 ;  For ( Byte  B: bytes ){  //  4-byte height Hexchars [index ++] = hexreferchars [B >>> 4 & 0xf];  //  4-bit lower in bytes Hexchars [index ++] = hexreferchars [B & 0xf ];}  Return   New  String (hexchars );}