MD5比较多个文件是否一样

linux 生成MD5秘钥 cat 

//注意文件排列顺序

public String md5(Map<String, String> map) {

// 缓冲区大小
int bufferSize = 256 * 1024;
String md5 = null;
String dir = map.get("dir");
File fileDir = new File(dir);
if(!fileDir.isDirectory()) {
System.out.println(fileDir + "is not directory!");
}
File[] files = fileDir.listFiles();
List fileList = Arrays.asList(files);
Collections.sort(fileList, new Comparator<File>() {
@Override
public int compare(File o1, File o2) {
if(o1.isDirectory() && o1.isFile()) {
return -1;
}
if(o2.isDirectory() && o2.isFile()) {
return 1;
}
return o1.getName().compareTo(o2.getName());
}
});
FileInputStream input = null;
try {
MessageDigest messageDigest = MessageDigest.getInstance("MD5");
byte[] dataBytes = new byte[bufferSize];
int nread = 0;
//遍历路径下所有文件
for(int i=0; i<files.length; i++) {
input = new FileInputStream(files[i]);
while ((nread = input.read(dataBytes)) != -1) {
messageDigest.update(dataBytes, 0, nread);
}
}
//返回结果，16个元素字节数组
byte[] md5bytes = messageDigest.digest();
    //转换字节为16进制格式
StringBuffer sb = new StringBuffer("");
        for (int i = 0; i < md5bytes.length; i++) {
            sb.append(Integer.toString((md5bytes[i] & 0xff) + 0x100, 16).substring(1));
        }
        md5 = sb.toString();
} catch (NoSuchAlgorithmException e) {
System.out.println(e.getMessage());
} catch (FileNotFoundException e) {
System.out.println(e.getMessage());
} catch (IOException e) {
System.out.println(e.getMessage());
} finally {
try {
if(null != input) {
input.close();
}
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
return md5;
}