干货!java文件上传判重姿势浅谈

@Testpublicvoidtest1()
Stringpath="your file path";
try {
longbegin=System.currentTimeMillis();
Stringmd5=DigestUtils.md5Hex(newFileInputStream(path));
longend=System.currentTimeMillis();
System.out.println(md5);
System.out.println("time:"+ ((end-begin) /1000) +"s");
    } catch (FileNotFoundExceptione) {
e.printStackTrace();
    } catch (IOExceptione) {
e.printStackTrace();
    }
  }

@Testpublicvoidtest2() {
Stringpath="file path";
longbegin=System.currentTimeMillis();
BigIntegerbi=null;
try {
byte[] buffer=newbyte[8192*10];
intlen=0;
MessageDigestmd=MessageDigest.getInstance("MD5");
Filef=newFile(path);
FileInputStreamfis=newFileInputStream(f);
while ((len=fis.read(buffer)) !=-1) {
md.update(buffer, 0, len);
      }
fis.close();
byte[] b=md.digest();
bi=newBigInteger(1, b);
    } catch (NoSuchAlgorithmExceptione) {
e.printStackTrace();
    } catch (IOExceptione) {
e.printStackTrace();
    }
Stringmd5=bi.toString(16);
longend=System.currentTimeMillis();
System.out.println(md5);
System.out.println("time:"+ ((end-begin) /1000) +"s");
  }

@Testpublicvoidtest3() {
Stringpath="file path";
longbegin=System.currentTimeMillis();
try {
Stringmd5=MD5.asHex(MD5.getHash(newFile(path)));
longend=System.currentTimeMillis();
System.out.println(md5);
System.out.println("time:"+ ((end-begin) /1000) +"s");
    } catch (IOExceptione) {
e.printStackTrace();
    }
  }

publicclassMD5FileUtil {
/*** 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校 验下载的文件的正确性用的就是默认的这个组合*/protectedstaticcharhexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
'f' };
protectedstaticMessageDigestmessagedigest=null;
static {
try {
messagedigest=MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmExceptione) {
e.printStackTrace();
    }
  }
/*** 生成文件的md5校验值* @param file 文件路径* @return MD5码返回* @throws IOException*/publicstaticStringgetFileMD5(Filefile) throwsIOException {
StringencrStr="";
// 读取文件FileInputStreamfis=newFileInputStream(file);
// 当文件<2G可以直接读取if (file.length() <=Integer.MAX_VALUE) {
encrStr=getMD5Lt2G(file, fis);
    } else { // 当文件>2G需要切割读取encrStr=getMD5Gt2G(fis);
    }
fis.close();
returnencrStr;
  }
/*** 小于2G文件* * @param fis 文件输入流* @return* @throws IOException*/publicstaticStringgetMD5Lt2G(Filefile, FileInputStreamfis) throwsIOException {
// 加密码StringencrStr="";
FileChannelch=fis.getChannel();
MappedByteBufferbyteBuffer=ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());
messagedigest.update(byteBuffer);
encrStr=bufferToHex(messagedigest.digest());
returnencrStr;
  }
/*** 超过2G文件的md5算法* * @param fileName* @param InputStream* @return* @throws Exception*/publicstaticStringgetMD5Gt2G(InputStreamfis) throwsIOException {
// 自定义文件块读写大小，一般为4M，对于小文件多的情况可以降低byte[] buffer=newbyte[1024*1024*4];
intnumRead=0;
while ((numRead=fis.read(buffer)) >0) {
messagedigest.update(buffer, 0, numRead);
    }
returnbufferToHex(messagedigest.digest());
  }
/*** * @param bt           文件字节流* @param stringbuffer 文件缓存*/privatestaticvoidappendHexPair(bytebt, StringBufferstringbuffer) {
// 取字节中高 4 位的数字转换, >>> 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同charc0=hexDigits[(bt&0xf0) >>4];
// 取字节中低 4 位的数字转换charc1=hexDigits[bt&0xf];
stringbuffer.append(c0);
stringbuffer.append(c1);
  }
privatestaticStringbufferToHex(bytebytes[], intm, intn) {
StringBufferstringbuffer=newStringBuffer(2*n);
intk=m+n;
for (intl=m; l<k; l++) {
appendHexPair(bytes[l], stringbuffer);
    }
returnstringbuffer.toString();
  }
privatestaticStringbufferToHex(bytebytes[]) {
returnbufferToHex(bytes, 0, bytes.length);
  }
/*** 判断字符串的md5校验码是否与一个已知的md5码相匹配* @param password  要校验的字符串* @param md5PwdStr 已知的md5校验码* @return*/publicstaticbooleancheckPassword(Stringpassword, Stringmd5PwdStr) {
Strings=getMD5String(password);
returns.equals(md5PwdStr);
  }
/*** 生成字符串的md5校验值* @param s* @return*/publicstaticStringgetMD5String(Strings) {
returngetMD5String(s.getBytes());
  }
/*** 生成字节流的md5校验值* @param s* @return*/publicstaticStringgetMD5String(byte[] bytes) {
messagedigest.update(bytes);
returnbufferToHex(messagedigest.digest());
  }
publicstaticvoidmain(String[] args) throwsIOException {
Stringpath="path";
Filebig=newFile(path);
longbegin=System.currentTimeMillis();
Stringmd5=getFileMD5(big);
longend=System.currentTimeMillis();
System.out.println("md5:"+md5);
System.out.println("time "+ (end-begin));
System.out.println("time:"+ ((end-begin) /1000) +"s");
  }
}