好的。对于那些已经有Spring和Apache Commons依赖关系或计划添加它的人，我必须添加。

DigestUtils.md5DigestAsHex(FileUtils.readFileToByteArray(file))

对于和Apache共享的唯一选项(credit @duleshi):

DigestUtils.md5Hex(FileUtils.readFileToByteArray(file))

希望这能帮助到一些人。

标准Java运行时环境方式:

public String checksum(File file) {
  try {
    InputStream fin = new FileInputStream(file);
    java.security.MessageDigest md5er =
        MessageDigest.getInstance("MD5");
    byte[] buffer = new byte[1024];
    int read;
    do {
      read = fin.read(buffer);
      if (read > 0)
        md5er.update(buffer, 0, read);
    } while (read != -1);
    fin.close();
    byte[] digest = md5er.digest();
    if (digest == null)
      return null;
    String strDigest = "0x";
    for (int i = 0; i < digest.length; i++) {
      strDigest += Integer.toString((digest[i] & 0xff) 
                + 0x100, 16).substring(1).toUpperCase();
    }
    return strDigest;
  } catch (Exception e) {
    return null;
  }
}

结果等于linux md5sum实用程序。

public static String getMd5OfFile(String filePath)
{
    String returnVal = "";
    try 
    {
        InputStream   input   = new FileInputStream(filePath); 
        byte[]        buffer  = new byte[1024];
        MessageDigest md5Hash = MessageDigest.getInstance("MD5");
        int           numRead = 0;
        while (numRead != -1)
        {
            numRead = input.read(buffer);
            if (numRead > 0)
            {
                md5Hash.update(buffer, 0, numRead);
            }
        }
        input.close();

        byte [] md5Bytes = md5Hash.digest();
        for (int i=0; i < md5Bytes.length; i++)
        {
            returnVal += Integer.toString( ( md5Bytes[i] & 0xff ) + 0x100, 16).substring( 1 );
        }
    } 
    catch(Throwable t) {t.printStackTrace();}
    return returnVal.toUpperCase();
}

public static String MD5Hash(String toHash) throws RuntimeException {
   try{
       return String.format("%032x", // produces lower case 32 char wide hexa left-padded with 0
      new BigInteger(1, // handles large POSITIVE numbers 
           MessageDigest.getInstance("MD5").digest(toHash.getBytes())));
   }
   catch (NoSuchAlgorithmException e) {
      // do whatever seems relevant
   }
}

下面是一个简单的函数，它包装了Sunil的代码，以File作为参数。该函数不需要任何外部库，但需要Java 7。

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.xml.bind.DatatypeConverter;

public class Checksum {

    /**
     * Generates an MD5 checksum as a String.
     * @param file The file that is being checksummed.
     * @return Hex string of the checksum value.
     * @throws NoSuchAlgorithmException
     * @throws IOException
     */
    public static String generate(File file) throws NoSuchAlgorithmException,IOException {

        MessageDigest messageDigest = MessageDigest.getInstance("MD5");
        messageDigest.update(Files.readAllBytes(file.toPath()));
        byte[] hash = messageDigest.digest();

        return DatatypeConverter.printHexBinary(hash).toUpperCase();
    }

    public static void main(String argv[]) throws NoSuchAlgorithmException, IOException {
        File file = new File("/Users/foo.bar/Documents/file.jar");          
        String hex = Checksum.generate(file);
        System.out.printf("hex=%s\n", hex);            
    }


}

示例输出:

hex=B117DD0C3CBBD009AC4EF65B6D75C97B

使用nio2 (Java 7+)，不使用外部库:

byte[] b = Files.readAllBytes(Paths.get("/path/to/file"));
byte[] hash = MessageDigest.getInstance("MD5").digest(b);

将结果与期望的校验和进行比较:

String expected = "2252290BC44BEAD16AA1BF89948472E8";
String actual = DatatypeConverter.printHexBinary(hash);
System.out.println(expected.equalsIgnoreCase(actual) ? "MATCH" : "NO MATCH");