When downloading a file over internet, the uploader usually provides an MD5 checksum for the file to ensure the integrity of the file. MD5 checksum (message digest) is something like a fingerprint or digital signature for a file. The checksum is unique for a file and there is very small possibility of getting two identical checksums for two different files. In Android, using java security package we can compute the md5 message digest for a file. Here is a sample class to get MD5 checksum from an input stream:
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| package net.londatiga.android.util;import java.security.MessageDigest;import java.io.File;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;public class Util { private static char[] hexDigits = "0123456789abcdef".toCharArray(); public static String md5(InputStream is) throws IOException { String md5 = ""; try { byte[] bytes = new byte[4096]; int read = 0; MessageDigest digest = MessageDigest.getInstance("MD5"); while ((read = is.read(bytes)) != -1) { digest.update(bytes, 0, read); } byte[] messageDigest = digest.digest(); StringBuilder sb = new StringBuilder(32); for (byte b : messageDigest) { sb.append(hexDigits[(b >> 4) & 0x0f]); sb.append(hexDigits[b & 0x0f]); } md5 = sb.toString(); } catch (Exception e) { e.printStackTrace(); } return md5; }} |
To get md5 checksum from a file and compare it with original md5:
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| try { String md5Origin = "";//original file's md5 checksum String filePath = ""; //fill with the real file path name FileInputStream fis = new FileInputStream(filePath); String md5Checksum = Util.md5(fis); if (md5Checksum.equals(md5Origin)) { //file is valid }} catch (Exception e) {} |
