谷歌guava提供了一个新的API。找到下面的一个:

public static HashCode hash(File file,
            HashFunction hashFunction)
                     throws IOException

Computes the hash code of the file using hashFunction.

Parameters:
    file - the file to read
    hashFunction - the hash function to use to hash the data
Returns:
    the HashCode of all of the bytes in the file
Throws:
    IOException - if an I/O error occurs
Since:
    12.0

使用Java 7的简单方法，没有第三方库

String path = "your complete file path";
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(Files.readAllBytes(Paths.get(path)));
byte[] digest = md.digest();

如果你需要打印这个字节数组。使用方法如下

System.out.println(Arrays.toString(digest));

如果你需要十六进制字符串出这个摘要。使用方法如下

String digestInHex = DatatypeConverter.printHexBinary(digest).toUpperCase();
System.out.println(digestInHex);

其中DatatypeConverter是javax.xml.bind.DatatypeConverter

使用Apache Commons Codec库中的DigestUtils:

try (InputStream is = Files.newInputStream(Paths.get("file.zip"))) {
    String md5 = org.apache.commons.codec.digest.DigestUtils.md5Hex(is);
}

Guava现在提供了一个新的、一致的哈希API，它比JDK中提供的各种哈希API更友好。参见哈希的解释。对于一个文件，你可以很容易地得到MD5和，CRC32(14.0+版本)或许多其他哈希值:

HashCode md5 = Files.hash(file, Hashing.md5());
byte[] md5Bytes = md5.asBytes();
String md5Hex = md5.toString();

HashCode crc32 = Files.hash(file, Hashing.crc32());
int crc32Int = crc32.asInt();

// the Checksum API returns a long, but it's padded with 0s for 32-bit CRC
// this is the value you would get if using that API directly
long checksumResult = crc32.padToLong();

在Real的Java-How-to中有一个使用MessageDigest类的例子。

请查看该页面中使用CRC32和SHA-1的示例。

import java.io.*;
import java.security.MessageDigest;

public class MD5Checksum {

   public static byte[] createChecksum(String filename) throws Exception {
       InputStream fis =  new FileInputStream(filename);

       byte[] buffer = new byte[1024];
       MessageDigest complete = MessageDigest.getInstance("MD5");
       int numRead;

       do {
           numRead = fis.read(buffer);
           if (numRead > 0) {
               complete.update(buffer, 0, numRead);
           }
       } while (numRead != -1);

       fis.close();
       return complete.digest();
   }

   // see this How-to for a faster way to convert
   // a byte array to a HEX string
   public static String getMD5Checksum(String filename) throws Exception {
       byte[] b = createChecksum(filename);
       String result = "";

       for (int i=0; i < b.length; i++) {
           result += Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring( 1 );
       }
       return result;
   }

   public static void main(String args[]) {
       try {
           System.out.println(getMD5Checksum("apache-tomcat-5.5.17.exe"));
           // output :
           //  0bb2827c5eacf570b6064e24e0e6653b
           // ref :
           //  http://www.apache.org/dist/
           //          tomcat/tomcat-5/v5.5.17/bin
           //              /apache-tomcat-5.5.17.exe.MD5
           //  0bb2827c5eacf570b6064e24e0e6653b *apache-tomcat-5.5.17.exe
       }
       catch (Exception e) {
           e.printStackTrace();
       }
   }
}

谷歌guava提供了一个新的API。找到下面的一个:

public static HashCode hash(File file,
            HashFunction hashFunction)
                     throws IOException

Computes the hash code of the file using hashFunction.

Parameters:
    file - the file to read
    hashFunction - the hash function to use to hash the data
Returns:
    the HashCode of all of the bytes in the file
Throws:
    IOException - if an I/O error occurs
Since:
    12.0