如何讀取和計算互聯網上的文件的哈希值

Question

我有一個互聯網上的文件的網址。我需要計算SHA1散列，並按每行讀取此文件。我知道如何做到這一點，但我讀了兩次這個文件，這可能不是一個很好的解決方案。

我該如何更有效地做到這一點？

這裏是我的代碼：

URL url = new URL(url); 
URLConnection urlConnection = url.openConnection(); 
urlConnection.setConnectTimeout(1000); 
urlConnection.setReadTimeout(1000); 
logger.error(urlConnection.getContent() + " "); 
InputStream is = urlConnection.getInputStream(); 


// first reading of file is: 

int i; 
File file = new File("nameOfFile"); 
BufferedInputStream bis = new BufferedInputStream(is); 
BufferedOutputStream bos = 
      new BufferedOutputStream(new FileOutputStream(file.getName())); 
while ((i = bis.read()) != -1) { 
    bos.write(i); 
} 
bos.flush(); 
bis.close(); 
sha1(file); 

// second reading of file is: 

BufferedReader reader = new BufferedReader(new InputStreamReader(is)); 
String line; 

while ((line = reader.readLine()) != null) { 
    // do something 
} 

protected byte[] sha1(final File file) throws Exception { 
    if (file == null || !file.exists()) { 
     return null; 
    } 
    final MessageDigest messageDigest = MessageDigest.getInstance(SHA1); 

    InputStream is = new BufferedInputStream(new FileInputStream(file)); 
    try { 
     final byte[] buffer = new byte[1024]; 
     for (int read = 0; (read = is.read(buffer)) != -1;) { 
      messageDigest.update(buffer, 0, read); 
     } 
    } finally { 
     IOUtils.closeQuietly(is); 
    } 
    return messageDigest.digest(); 
} 

Answer 1

如果你之通過DigestInputStream，它會做的MessageDigest，仍然是可用作InputStream。

DigestInputStream dis = new DigestInputStream(is, 
    MessageDigest.getInstance(SHA1)); 
BufferedInputStream bis = new BufferedInputStream(dis); 
BufferedOutputStream bos = new BufferedOutputStream(
    new FileOutputStream(file.getName())); 
while ((i = bis.read()) != -1) { 
    bos.write(i); 
} 
bos.close(); 
return dis.getMessageDigest().digest();