CS-Notes/notes/Java IO.md

• ????
• ???????
• ??????
• ???????
• ???????
• ???????
  • 1. InetAddress
  • 2. URL
  • 3. Sockets
  • 4. Datagram
• NIO
  • 1. ?????
  • 2. ?????????
    • 2.1 ???
    • 2.2 ??????
  • 3. ????????????
  • 4. ??§Õ??????
  • 5. ???????????
    • 5.1 ????? I/O
    • 5.2 ??????? I/O
  • 6. ????????
    • 6.1 ServerSocketChannel
    • 6.2 Selectors
    • 6.3 ?????
    • 6.4 ??????????
    • 6.5 ???????????
    • 6.6 ?????????? SelectionKey
    • 6.7 ????? I/O
• ?¦Ï?????

????

Java ?? I/O ???????????????

1. ?????????File
2. ????????InputStream ?? OutputStream
3. ?????????Reader ?? Writer
4. ?????????Serializable
5. ?????????Socket
6. ??????? IO??NIO

???????

File ????????????????????????????????????????????????????????????

??????

Java I/O ???????????????????? InputStream ?????InputStream ??????????FileInputStream ?? InputStream ??????????????????????????????????????FilterInputStream ????????????????????????????????????????????????? BufferedInputStream ? FileInputStream ??????????????????????§Ý??œ¤????????????????????? FileInputStream ????????????? BufferedInputStream ????¨À?

BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));

DataInputStream ?????????????????????????????????????? int??double ??????????

????????????§Ö???????????????

byte[] buf = new byte[20*1024];
int bytes = 0;
// ????? buf.length ????????????????????????????? -1 ??????????? eof???????¦Â
while((bytes = in.read(buf, 0 , buf.length)) != -1) {
    // ...
}

???????

???????????????×Ï????§³??›¥?????????????????????????? I/O ????????????????????????????????§Ó??????????????????????????????????????§Ó??????????

InputStreamReader ?????????????????????????????OutputStreamWriter ??????????????????????????????????????? Reader ?? Writer??

????????????????????????????????????????????

byte[] bytes = str.getBytes(encoding);     // ????
String str = new String(bytes, encoding)?? // ????

GBK ?????§µ?????? 2 ?????????? 1 ??????UTF-8 ?????§µ?????? 3 ?????????? 1 ??????Java ?????????? UTF-16be???????????? 2 ??????

????????????????¨°??????????????????????

???????

???§Ý????????????????????????§µ?????›¥?????

???§Ý???ObjectOutputStream.writeObject()

?????§Ý???ObjectInputStream.readObject()

???§Ý??????????? Serializable ?????????????????????¦Ê¦Ç??????????

transient ??????????§»??????????§Ý???

ArrayList ???§Ý???????§Ý????????ArrayList ?§Õ›¥????????????? transient ???¦Å???????????????????????????????§Ö????????????????????§Ö???????????§Ý????????§Õ???§Ý???????§Ý?????????????????§Ý????????????????????????

private transient Object[] elementData;

???????

Java ?§Ö?????????

1. InetAddress????????????????????????? IP ?????
2. URL?????????¦Ë??????? URL ?????????????§Õ??????????????
3. Sockets????? TCP §¿?????????????
4. Datagram????? UDP §¿?????????????

1. InetAddress

??§Û??§Û??????????????????????????????????? InetAddress.getByName(String host)??InetAddress.getByAddress(byte[] addr)??

2. URL

???????? URL ?§Ø???????????

URL url = new URL("http://www.baidu.com");
InputStream is = url.openStream(); // ?????
InputStreamReader isr = new InputStreamReader(is, "utf-8");                              // ?????
BufferedReader br = new BufferedReader(isr);
String line = br.readLine();
while (line != null) {
    System.out.println(line);
    line = br.readLine();
}
br.close();
isr.close();
is.close();

3. Sockets

Socket ??????

• ServerSocket????????????
• Socket?????????

??????????????? InputStream ?? OutputStream ?????????????

4. Datagram

• DatagramPacket?????????
• DatagramSocket???????

NIO

NIO ???????? I/O ???? ( ??????????????? ) ?????????????? ??????????????????????????????????

1. ?????

I/O ?? NIO ?????????????????????????????????????????I/O ??????????????????? NIO ???????????????

???????? I/O ???????????§Õ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? I/O ?????????

????????? I/O ??????????????????????????????????§Ó??????????????????î•???ø„????????????????????????????????? I/O ????§»???????? I/O ?????§Ö????????????

I/O ???? NIO ?????????????java.io.* ????? NIO ????????????????????????????????? NIO ???§»????????íà java.io.* ???§Ö??§»??????????????§Õ??????????????¨¹????????????????§µ??????????????

2. ?????????

2.1 ???

??? Channel ???? I/O ???§Ö??????????????????????§Õ???????

????????????????????????????????????????(??????????? InputStream ???? OutputStream ??????)?? ???????????????????????§Õ???????????§Õ??

????????????????

• FileChannel????????§Ø?§Õ?????
• DatagramChannel????? UDP ??§Õ???????????
• SocketChannel????? TCP ??§Õ???????????
• ServerSocketChannel???????????????? TCP ?????????????????????????????? SocketChannel??

2.2 ??????

????????????????§Ø???????????????????§µ?????????????§Ø?????¦Ê??????????????????§³???????????????????????§Ø?§Õ??????????????????????

???????????????????ï…??????????????????î•?????????????????????????????????????????/§Õ?????

???????????????????

• ByteBuffer
• CharBuffer
• ShortBuffer
• IntBuffer
• LongBuffer
• FloatBuffer
• DoubleBuffer

3. ????????????

• capacity???????????
• position??????????§Õ?????????
• limit?????????§Õ?????????

??????????????

1. ????????§³? 8 ???????????????? position ? 0???? limit == capacity == 9??capacity ???????????????????????????

2. ??????????§Ø?? 3 ?????????§Õ???????§µ???? position ?????? 3??limit ???????

3. ???????????????§Õ???????????????????? flip() ??????????????? limit ???????? position?????? position ????? 0??

4. ?????????? 4 ??????????????§µ???? position ??? 4??

5. ?????????? clear() ??????????????????? position ?? limit ????????????¦Ë?¨¢?

4. ??§Õ??????

1. ?????????????? FileInputStream???????? FileInputStream ??????? FileChannel??

FileInputStream fin = new FileInputStream("readandshow.txt");
FileChannel fic = fin.getChannel();

2. ???????????? 1024 ?? Buffer

ByteBuffer buffer = ByteBuffer.allocate(1024);

3. ??????????? FileChannel §Õ?? Buffer ?§µ??????????????? read() ???????? -1

int r = fcin.read(buffer);
if (r == -1) {
     break;
}

4. ??§Õ?????????? FileOutputStream???????? FileOutputStream ?????? FileChannel

FileOutputStream fout = new FileOutputStream("writesomebytes.txt");
FileChannel foc = fout.getChannel();

5. ???? flip() ?§Ý???§Õ

buffer.flip();

6. ?? Buffer ?§Ö???????????? FileChannel ??

foc.write(buffer);

7. ?????? clear() ?????????

buffer.clear();

5. ???????????

??????FileChannel ?????§Ý?????????????????? Channel ?????

5.1 ????? I/O

????? I/O ????? InputStream.read() ?????????????????????????????????????? ServerSocket.accept() ???????????????????§á??????????????????????????????????????????????????????????????

5.2 ??????? I/O

?????????????????????§Ö? I/O ???????????????

??????????????????????????????????????????????

???????????????? wait()??notify() ?????????????????????§Ý???????????????????¦Í??????§Ý???

6. ????????

6.1 ServerSocketChannel

???????????????? ServerSocketChannel ?????????????

ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking(false); // ???????????

ServerSocket ss = ssc.socket();
InetSocketAddress address = new InetSocketAddress(ports[i]);
ss.bind(address); // ?????

6.2 Selectors

?? I/O ??? Selector ??????? I/O ???????? ?D ?????????????????????????????????????????????????????????

???? Selectors ?????????????????????? register() ??????register() ????????????????? Selector????????????? OP_ACCEPT?????????????????????? accept ????????????????????????????????????

SelectionKey ????????????? Selector ?????????????? Selector ????????????????????????????????????? SelectionKey ?????§Ö??SelectionKey ?????????????????????

Selector selector = Selector.open();
SelectionKey key = ssc.register(selector, SelectionKey.OP_ACCEPT);

6.3 ?????

???????????? Selector ?? select() ??????????????????????????????????????????????????????????????????????? select() ?????????????????????????????

??????????????? Selector ?? selectedKeys() ?????????????????????? SelectionKey ???????? ???? ??

??????????? SelectionKeys ?????¦Ä?????? SelectionKey ??????????????????? SelectionKey????????????????????? I/O ???????????????????§» I/O ????

int num = selector.select();
 
Set selectedKeys = selector.selectedKeys();
Iterator it = selectedKeys.iterator();
 
while (it.hasNext()) {
     SelectionKey key = (SelectionKey)it.next();
     // ... deal with I/O event ...
}

6.4 ??????????

??????§Ö??????????????? ServerSocketChannel??????????????????????????????????????? SelectionKey ???? readyOps() ??????????ú€????????????????

if ((key.readyOps() & SelectionKey.OP_ACCEPT)
     == SelectionKey.OP_ACCEPT) {
     // Accept the new connection
     // ...
}

??????????? readOps() ??????????????????????????

6.5 ???????????

?????????????????????????????????????????????????????????????????????????????? accept() ????????????

ServerSocketChannel ssc = (ServerSocketChannel)key.channel();
SocketChannel sc = ssc.accept();

??????????????? SocketChannel ??????????????????????????????????????????????????????????????????????? SocketChannel ??? Selector????????????

sc.configureBlocking( false );
SelectionKey newKey = sc.register( selector, SelectionKey.OP_READ );

?????????? register() ?? OP_READ ???????? SocketChannel ??????? ??? ?????? ???? ???????

6.6 ?????????? SelectionKey

????? SelectionKey ???????????????????????????????????????????????? SelectionKey ????????????????????????????????????????????????????????????????????????????????????????????¦Ä????????????????????? remove() ???????????????? SelectionKey??

it.remove();

???????????????????????????????????§Õ????????(???????????? I/O ???)???

6.7 ????? I/O

?????????????????????????????????? I/O ??????????????????§Ö??? Selector.select()????????????????? I/O ?????????¦²? SelectionKey ???????? OP_READ ??????????????

} else if ((key.readyOps() & SelectionKey.OP_READ)
     == SelectionKey.OP_READ) {
     // Read the data
     SocketChannel sc = (SocketChannel)key.channel();
     // ...
}

?¦Ï?????

• Eckel B, ????? , ??? , ?? . Java ?????? [M]. ??§Ö????????? , 2002.
• IBM: NIO ????
• ??????? Java I/O ?????????
• NIO ??? IO ??????