最近要弄一下Java读取文件MD5，注意这里是小文件，网上找了一下，有两种解决方案，一种是用MessageDigest来实现，另种是用org.apache.commons.codec.digest来实现，代码如下：

package cdm;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;

import org.apache.commons.codec.digest.*; 
import org.apache.commons.io.IOUtils;

public class testMD5 {
	
	 public static String getMd5ByFile(File file) throws FileNotFoundException {
	        String value = null;
	        FileInputStream in = new FileInputStream(file);
		try {
		    MappedByteBuffer byteBuffer = in.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length());
		    MessageDigest md5 = MessageDigest.getInstance("MD5");
		    md5.update(byteBuffer);
		    BigInteger bi = new BigInteger(1, md5.digest());
		    value = bi.toString(16);
		} catch (Exception e) {
		    e.printStackTrace();
		} finally {
	            if(null != in) {
		            try {
			        in.close();
			    } catch (IOException e) {
			        e.printStackTrace();
			    }
		    }
		}
		return value;
	    }
	 
	public static void main(String[] args) throws IOException {
		
		String path="E:\\commons-codec-1.9-bin.zip";
		
		String v = getMd5ByFile(new File(path));
		System.out.println("MD5:"+v.toUpperCase());
		
		FileInputStream fis= new FileInputStream(path);  
		String md5 = DigestUtils.md5Hex(IOUtils.toByteArray(fis));  
		IOUtils.closeQuietly(fis);  
		System.out.println("MD5:"+md5); 
		
		//System.out.println("MD5:"+DigestUtils.md5Hex("WANGQIUYUN"));
	}

}

运行：

结果在官网提供的MD5一致。

附commons-codec-1.9.jar下载地址：http://commons.apache.org/proper/commons-codec/download_codec.cgi

如果要处理过G的文件，请参照：http://www.cnblogs.com/yaowukonga/p/3523668.html