java 读取文件的前 4 个字节
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Read First 4 Bytes of File
提问by Z61
I'm used to C#, but I'm trying to make an app which reads the first 4 bytes into an array, but I have been unsuccessful.
I also need to reverse the Endian on the file which I don't know how in Java, in C# it is Array.Reverse(bytes);. I've tried reading the file into an Int32, but from there I cannot get it into an array for some reason.
我习惯了 C#，但我正在尝试制作一个应用程序，将前 4 个字节读入一个数组，但我没有成功。我还需要反转文件上的字节序，我不知道在 Java 中如何，在 C# 中它是Array.Reverse(bytes);. 我试过将文件读入 Int32，但由于某种原因，我无法将其放入数组。
回答by poussma
Like that :
像那样 ：
byte[] buffer = new byte[4];
InputStream is = new FileInputStream("somwhere.in.the.dark");
if (is.read(buffer) != buffer.length) {
// do something
}
is.close();
// at this point, the buffer contains the 4 bytes...
回答by Peter Lawrey
You can change the Endianness with ByteBuffer
您可以使用 ByteBuffer 更改字节顺序
FileChannel fc = new FileInputStream(filename).getChannel();
ByteBuffer bb = ByteBuffer.allocate(4);
bb.order(ByteBuffer.nativeOrder()); // or whatever you want.
fc.read(bb);
bb.flip();
int n = bb.getInt();
The simple way to reverse the byte of an Integer
反转整数字节的简单方法
int n = ...
int r = Integer.reverseByte(n);
similarly
相似地
long l = Long.reverseBytes(n);
