java - OutputStream 的 Flush 方法不执行任何操作

Question

尝试涉及部分加密文件的操作。除了这个小问题，一切都很好。因为某些原因。刷新方法一直有效，直到 n > 52，其中 n 是循环计数。可以在解密方法中看到。如果我将 n fomr < 10 更改为 < 53 它会刷新。我通过查看文件进行了测试。直到53才添加新内容。但是应该有。

public class DesEncrypter {
Cipher ecipher;
Cipher dcipher;

DesEncrypter(SecretKey key) {
    // Create an 8-byte initialization vector
    byte[] iv = new byte[]{
        (byte)0x8E, 0x12, 0x39, (byte)0x9C,
        0x07, 0x72, 0x6F, 0x5A
    };
    AlgorithmParameterSpec paramSpec = new IvParameterSpec(iv);
    try {
        ecipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
        dcipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

        // CBC requires an initialization vector
        ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
        dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
    } catch (java.security.InvalidAlgorithmParameterException e) {
    } catch (javax.crypto.NoSuchPaddingException e) {
    } catch (java.security.NoSuchAlgorithmException e) {
    } catch (java.security.InvalidKeyException e) {
    }
}

// Buffer used to transport the bytes from one stream to another
byte[] buf = new byte[1024];

public void encrypt(InputStream in, OutputStream out) {
    try {
        // Bytes written to out will be encrypted
       AppendableOutputStream out_append = new AppendableOutputStream(out);

       OutputStream out_c = new CipherOutputStream(out_append, ecipher);

        // Read in the cleartext bytes and write to out to encrypt
        int numRead = 0;
        int count = 0;
        int max = 1024;
        boolean first = true;

        while ((numRead = in.read(buf, 0, max)) > 0) {                 
            System.out.println("running Total: " + count);
            count += numRead;
            // if this read puts as at less than a meg, encrypt
            if(count <= 1024*1024){
                System.out.println("encrypted " + numRead + " of " + max +" bytes : total " + count);
                out_c.write(buf, 0, numRead);
                // last encryption pass, close buffer and fix max
                if(count == 1024*1024){
                    // fix reading 1k in case max was decreased
                    max = 1024;
                    out_c.close();
                }
                // if next read will go over a meg, read less than 1k
                else if(count + max > 1024*1024)
                    max = 1024*1024 - count;
            }
            // past the first meg, don't encrypt
            else{
                System.out.println("processed " + numRead + " of " + max +" bytes : total " + count);
                out.write(buf, 0, numRead);
            }

        }
        out.close();

    } catch (java.io.IOException e) {}

}

// Movies encrypt only 1 MB 128 passes.

public void decrypt(InputStream in, OutputStream out) {
    try {
        // Bytes read from in will be decrypted
        InputStream in_c = new CipherInputStream(in, dcipher);

        // Read in the decrypted bytes and write the cleartext to out
        int numRead = 0;
        int count = 0;
        int max = 1024;

        while ((numRead = in_c.read(buf, 0, max)) > 0) {
            count += numRead;
            System.out.println("decrypted " + numRead + " of " + max +" bytes : total " + count);
            out.write(buf, 0, numRead);
            if(count + max > 1024*1024){
                max = 1024*1024 - count;
            }
            if(count == 1024*1024)
                max = 0;
        }

        //in.skip(count);
        int n = 0;
        while((numRead = in.read(buf)) > 0 && n < 10){
        count += numRead;
        System.out.println("processed " + numRead + " of 1024 bytes : total " + count);
            out.write(buf,0,numRead);
            //System.out.println("buf"+buf.length  +" numered" + numRead+ " n"+n);
            // If i look at the file after anything under n < 51 the file  doesn't change.
            n++;

        }
        out.flush();
        out.close();
    } catch (java.io.IOException e) {
        System.out.println("AHHHHHHHH!!!!!!");
    }
}

Answer 1

根据给定的信息，我只能推测。至少如果您指定 OutputStream 的类型会非常有帮助。 out当您调用 decrypt 时方法。 flush() 的行为不同的具体实现方法不同。

例如，如果您的输出流恰好是 CipherOutputStream ，或连接到该类型流的其他一些流，则其 flush() 的文档方法说明以下内容(我强调的重要部分):

Flushes this output stream by forcing any buffered output bytes that have already been processed by the encapsulated cipher object to be written out. Any bytes buffered by the encapsulated cipher and waiting to be processed by it will not be written out. For example, if the encapsulated cipher is a block cipher, and the total number of bytes written using one of the write methods is less than the cipher's block size, no bytes will be written out.

这听起来确实可能是您问题的原因。但是，正如我所说，了解有关您的特定流类型的更多详细信息将非常有帮助。