你也可以使用NIO api来实现。只要总文件大小(以字节为单位)适合int类型，我就可以用这段代码做到这一点。

File f = new File("c:\\wscp.script");
FileInputStream fin = null;
FileChannel ch = null;
try {
    fin = new FileInputStream(f);
    ch = fin.getChannel();
    int size = (int) ch.size();
    MappedByteBuffer buf = ch.map(MapMode.READ_ONLY, 0, size);
    byte[] bytes = new byte[size];
    buf.get(bytes);

} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} finally {
    try {
        if (fin != null) {
            fin.close();
        }
        if (ch != null) {
            ch.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

我认为它非常快，因为它使用MappedByteBuffer。

你也可以使用NIO api来实现。只要总文件大小(以字节为单位)适合int类型，我就可以用这段代码做到这一点。

File f = new File("c:\\wscp.script");
FileInputStream fin = null;
FileChannel ch = null;
try {
    fin = new FileInputStream(f);
    ch = fin.getChannel();
    int size = (int) ch.size();
    MappedByteBuffer buf = ch.map(MapMode.READ_ONLY, 0, size);
    byte[] bytes = new byte[size];
    buf.get(bytes);

} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} finally {
    try {
        if (fin != null) {
            fin.close();
        }
        if (ch != null) {
            ch.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

我认为它非常快，因为它使用MappedByteBuffer。

让我添加另一个不使用第三方库的解决方案。它重用了Scott提出的异常处理模式(链接)。我把丑陋的部分移动到一个单独的消息(我会隐藏在一些FileUtils类;))

public void someMethod() {
    final byte[] buffer = read(new File("test.txt"));
}

private byte[] read(final File file) {
    if (file.isDirectory())
        throw new RuntimeException("Unsupported operation, file "
                + file.getAbsolutePath() + " is a directory");
    if (file.length() > Integer.MAX_VALUE)
        throw new RuntimeException("Unsupported operation, file "
                + file.getAbsolutePath() + " is too big");

    Throwable pending = null;
    FileInputStream in = null;
    final byte buffer[] = new byte[(int) file.length()];
    try {
        in = new FileInputStream(file);
        in.read(buffer);
    } catch (Exception e) {
        pending = new RuntimeException("Exception occured on reading file "
                + file.getAbsolutePath(), e);
    } finally {
        if (in != null) {
            try {
                in.close();
            } catch (Exception e) {
                if (pending == null) {
                    pending = new RuntimeException(
                        "Exception occured on closing file" 
                             + file.getAbsolutePath(), e);
                }
            }
        }
        if (pending != null) {
            throw new RuntimeException(pending);
        }
    }
    return buffer;
}

从文件中读取字节的另一种方法

Reader reader = null;
    try {
        reader = new FileReader(file);
        char buf[] = new char[8192];
        int len;
        StringBuilder s = new StringBuilder();
        while ((len = reader.read(buf)) >= 0) {
            s.append(buf, 0, len);
            byte[] byteArray = s.toString().getBytes();
        }
    } catch(FileNotFoundException ex) {
    } catch(IOException e) {
    }
    finally {
        if (reader != null) {
            reader.close();
        }
    }

// Returns the contents of the file in a byte array.
    public static byte[] getBytesFromFile(File file) throws IOException {        
        // Get the size of the file
        long length = file.length();

        // You cannot create an array using a long type.
        // It needs to be an int type.
        // Before converting to an int type, check
        // to ensure that file is not larger than Integer.MAX_VALUE.
        if (length > Integer.MAX_VALUE) {
            // File is too large
            throw new IOException("File is too large!");
        }

        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];

        // Read in the bytes
        int offset = 0;
        int numRead = 0;

        InputStream is = new FileInputStream(file);
        try {
            while (offset < bytes.length
                   && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
                offset += numRead;
            }
        } finally {
            is.close();
        }

        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "+file.getName());
        }
        return bytes;
    }

如果您想将字节读入预分配的字节缓冲区，这个答案可能会有所帮助。

您的第一个猜测可能是使用InputStream read(byte[])。然而，这种方法有一个缺陷，使得它难以使用:即使没有遇到EOF，也不能保证数组实际上会被完全填充。

相反，看一下DataInputStream readFully(byte[])。这是一个输入流的包装器，没有上面提到的问题。此外，该方法在遇到EOF时抛出。好得多。