另一种实现:Java中的快速MD5实现

String hash = MD5.asHex(MD5.getHash(new File(filename)));

public static void main(String[] args) throws Exception {
    MessageDigest md = MessageDigest.getInstance("MD5");
    FileInputStream fis = new FileInputStream("c:\\apache\\cxf.jar");

    byte[] dataBytes = new byte[1024];

    int nread = 0;
    while ((nread = fis.read(dataBytes)) != -1) {
        md.update(dataBytes, 0, nread);
    };
    byte[] mdbytes = md.digest();
    StringBuffer sb = new StringBuffer();
    for (int i = 0; i < mdbytes.length; i++) {
        sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
    }
    System.out.println("Digest(in hex format):: " + sb.toString());
}

或者你可以得到更多的信息 http://www.asjava.com/core-java/java-md5-example/

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

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();
       }
   }
}

有一个输入流装饰器，java。security。DigestInputStream，这样您就可以像往常一样在使用输入流时计算摘要，而不必对数据进行额外的传递。

MessageDigest md = MessageDigest.getInstance("MD5");
try (InputStream is = Files.newInputStream(Paths.get("file.txt"));
     DigestInputStream dis = new DigestInputStream(is, md)) 
{
  /* Read decorated stream (dis) to EOF as normal... */
}
byte[] digest = md.digest();

从其他答案中提取想法，这里有一个简单的代码，没有第三方依赖关系(或DatatypeConverter，在最新的jdk中更长)，将其生成为与md5sum工具输出兼容的十六进制字符串:

import java.io.IOException;
import java.math.BigInteger;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
...

static String calculateMD5(String path) throws IOException
{
    try {
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(Files.readAllBytes(Paths.get(path)));
        return String.format("%032x", new BigInteger(1, md.digest())); // hex, padded to 32 chars
    } catch (NoSuchAlgorithmException ex)
    {
        throw new RuntimeException(ex); // MD5 is always available so this should be impossible
    }
}