java上传相同的文件,java快速比较两个文件是否相同

像百度网盘有秒传的功能，其实他的原理主要是比较需要上传的文件和网盘中的文件是否一样，如果不一样则上传，如果一样就没必要上传文件，只是将网盘中的文件指向你的用户名即可，从而实现了秒传。

通过计算文件的MD5或SHA-1是否一致，代码如下

MD5算法

public static String getFileMD5(File file) {

if (!file.isFile()) {

return null;

}

MessageDigest digest = null;

FileInputStream in = null;

byte buffer[] = new byte[8192];

int len;

try {

digest =MessageDigest.getInstance("MD5");

in = new FileInputStream(file);

while ((len = in.read(buffer)) != -1) {

digest.update(buffer, 0, len);

}

BigInteger bigInt = new BigInteger(1, digest.digest());

return bigInt.toString(16);

} catch (Exception e) {

e.printStackTrace();

return null;

} finally {

try {

in.close();

} catch (Exception e) {

e.printStackTrace();

}

}

}

SHA1算法

public static String getFileSha1(File file) {

if (!file.isFile()) {

return null;

}

MessageDigest digest = null;

FileInputStream in = null;

byte buffer[] = new byte[8192];

int len;

try {

digest =MessageDigest.getInstance("SHA-1");

in = new FileInputStream(file);

while ((len = in.read(buffer)) != -1) {

digest.update(buffer, 0, len);

}

BigInteger bigInt = new BigInteger(1, digest.digest());

return bigInt.toString(16);

} catch (Exception e) {

e.printStackTrace();

return null;

} finally {

try {

in.close();

} catch (Exception e) {

e.printStackTrace();

}

}

}

获取网络文件的MD5

public static String getNetFileMD5(String path) throws Exception{

URL url = new URL(path);

HttpURLConnection con = (HttpURLConnection) url.openConnection();

InputStream inStream = con.getInputStream();

MessageDigest digest = null;

byte buffer[] = new byte[8192];

int len;

try {

digest =MessageDigest.getInstance("MD5");

while ((len = inStream.read(buffer)) != -1) {

digest.update(buffer, 0, len);

}

BigInteger bigInt = new BigInteger(1, digest.digest());

return bigInt.toString(16);

} catch (Exception e) {

e.printStackTrace();

return null;

} finally {

try {

inStream.close();

} catch (Exception e) {

e.printStackTrace();

}

}

}