CS-Notes/notes/Java IO.md

<!-- GFM-TOC -->
* [????](#????)
* [???????](#???????)
* [??????](#??????)
* [???????](#???????)
* [???????](#???????)
* [???????](#???????)
    * [1. InetAddress](#1-inetaddress)
    * [2. URL](#2-url)
    * [3. Sockets](#3-sockets)
    * [4. Datagram](#4-datagram)
* [NIO](#nio)
    * [1. ?????](#1-?????)
    * [2. ?????????](#2-?????????)
        * [2.1 ???](#21-???)
        * [2.2 ??????](#22-??????)
    * [3. ????????????](#3-????????????)
    * [4. ??<3F><>??????](#4-??<3F><>??????)
    * [5. ???????????](#5-???????????)
        * [5.1 ????? I/O](#51-?????-io)
        * [5.2 ??????? I/O](#52-???????-io)
    * [6. ????????](#6-????????)
        * [6.1 ServerSocketChannel](#61-serversocketchannel)
        * [6.2 Selectors](#62-selectors)
        * [6.3 ?????](#63-?????)
        * [6.4 ??????????](#64-??????????)
        * [6.5 ???????????](#65-???????????)
        * [6.6 ?????????? SelectionKey](#66-??????????-selectionkey)
        * [6.7 ????? I/O](#67-?????-io)
* [?<3F><>?????](#?<3F><>?????)
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# ????

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

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

# ???????

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

# ??????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/8143787f-12eb-46ea-9bc3-c66d22d35285.jpg)

Java I/O ???????????????????? InputStream ?????InputStream ??????????FileInputStream ?? InputStream ??????????????????????????????????????FilterInputStream ????????????????????????????????????????????????? BufferedInputStream ? FileInputStream ??????????????????????<3F><>??<3F><>????????????????????? FileInputStream ????????????? BufferedInputStream ????<3F><>?

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

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

????????????<3F><>???????????????

```java
byte[] buf = new byte[20*1024];
int bytes = 0;
// ????? buf.length ????????????????????????????? -1 ??????????? eof???????<3F><>
while((bytes = in.read(buf, 0 , buf.length)) != -1) {
    // ...
}
```

# ???????

???????????????<3F><>????<3F><>??<3F><>?????????????????????????? I/O ????????????????????????????????<3F><>??????????????????????????????????????<3F><>??????????

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

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

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

GBK ?????<3F><>?????? 2 ?????????? 1 ??????UTF-8 ?????<3F><>?????? 3 ?????????? 1 ??????Java ?????????? UTF-16be???????????? 2 ??????

????????????????<3F><>??????????????????????

# ???????

???<3F><>????????????????????????<3F><>?????<3F><>?????

???<3F><>???ObjectOutputStream.writeObject()

?????<3F><>???ObjectInputStream.readObject()

???<3F><>??????????? Serializable ?????????????????????<3F>ʦ<EFBFBD>??????????

transient ??????????<3F><>??????????<3F><>???

**ArrayList ???<3F><>???????<3F><>??????**??ArrayList ?<3F>՛<EFBFBD>????????????? transient ???<3F><>???????????????????????????????<3F><>????????????????????<3F><>???????????<3F><>????????<3F><>???<3F><>???????<3F><>?????????????????<3F><>????????????????????????

```
private transient Object[] elementData;
```

# ???????

Java ?<3F><>?????????

1. InetAddress????????????????????????? IP ?????
2. URL?????????<3F><>??????? URL ?????????????<3F><>??????????????
3. Sockets????? TCP <20><>?????????????
4. Datagram????? UDP <20><>?????????????

## 1. InetAddress

??<3F><>??<3F><>??????????????????????????????????? InetAddress.getByName(String host)??InetAddress.getByAddress(byte[] addr)??

## 2. URL

???????? URL ?<3F><>???????????

```java
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 ??????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/fa4101d7-19ce-4a69-a84f-20bbe64320e5.jpg)

- ServerSocket????????????
- Socket?????????

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

## 4. Datagram

- DatagramPacket?????????
- DatagramSocket???????

# NIO

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

## 1. ?????

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

???????? I/O ???????????<3F><>????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? I/O ?????????

????????? I/O ??????????????????????????????????<3F><>??????????????????<3F><>???<3F><>????????????????????????????????? I/O ????<3F><>???????? I/O ?????<3F><>????????????

I/O ???? NIO ?????????????java.io.\* ????? NIO ????????????????????????????????? NIO ???<3F><>????????<3F><> java.io.\* ???<3F><>??<3F><>??????????????<3F><>??????????????<3F><>????????????????<3F><>??????????????

## 2. ?????????

### 2.1 ???

??? Channel ???? I/O ???<3F><>??????????????????????<3F><>???????

????????????????????????????????????????(??????????? InputStream ???? OutputStream ??????)?? ???????????????????????<3F><>???????????<3F><>??

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

- FileChannel????????<3F><>?<3F><>?????
- DatagramChannel????? UDP ??<3F><>???????????
- SocketChannel????? TCP ??<3F><>???????????
- ServerSocketChannel???????????????? TCP ?????????????????????????????? SocketChannel??

### 2.2 ??????

????????????????<3F><>???????????????????<3F><>?????????????<3F><>?????<3F><>??????????????????<3F><>???????????????????????<3F><>?<3F><>??????????????????????

???????????????????<3F><>??????????????????<3F><>?????????????????????????????????????????/<2F><>?????

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

- ByteBuffer
- CharBuffer
- ShortBuffer
- IntBuffer
- LongBuffer
- FloatBuffer
- DoubleBuffer


## 3. ????????????

- capacity???????????
- position??????????<3F><>?????????
- limit?????????<3F><>?????????

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

1\. ????????<3F><>? 8 ???????????????? position ? 0???? limit == capacity == 9??capacity ???????????????????????????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/1bea398f-17a7-4f67-a90b-9e2d243eaa9a.png)

2\. ??????????<3F><>?? 3 ?????????<3F><>???????<3F><>???? position ?????? 3??limit ???????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/4628274c-25b6-4053-97cf-d1239b44c43d.png)

3\. ???????????????<3F><>???????????????????? flip() ??????????????? limit ???????? position?????? position ????? 0??

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/952e06bd-5a65-4cab-82e4-dd1536462f38.png)

4\. ?????????? 4 ??????????????<3F><>???? position ??? 4??

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/b5bdcbe2-b958-4aef-9151-6ad963cb28b4.png)

5\. ?????????? clear() ??????????????????? position ?? limit ????????????<3F><>?<3F><>?

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/67bf5487-c45d-49b6-b9c0-a058d8c68902.png)

## 4. ??<3F><>??????

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

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

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

```java
ByteBuffer buffer = ByteBuffer.allocate(1024);
```

3\. ??????????? FileChannel <20><>?? Buffer ?<3F><>??????????????? read() ???????? -1

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

4\. ??<3F><>?????????? FileOutputStream???????? FileOutputStream ?????? FileChannel

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

5\. ???? flip() ?<3F><>???<3F><>

```java
buffer.flip();
```

6\. ?? Buffer ?<3F><>???????????? FileChannel ??

```java
foc.write(buffer);
```

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

```java
buffer.clear();
```

## 5. ???????????

??????FileChannel ?????<3F><>?????????????????? Channel ?????

### 5.1 ????? I/O

????? I/O ????? InputStream.read() ?????????????????????????????????????? ServerSocket.accept() ???????????????????<3F><>??????????????????????????????????????????????????????????????

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/edc23f99-c46c-4200-b64e-07516828720d.jpg)

### 5.2 ??????? I/O

?????????????????????<3F><>? I/O ???????????????

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

???????????????? wait()??notify() ?????????????????????<3F><>???????????????????<3F><>??????<3F><>???

![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/7fcb2fb0-2cd9-4396-bc2d-282becf963c3.jpg)

## 6. ????????

### 6.1 ServerSocketChannel

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

```java
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 ?????<3F><>??SelectionKey ?????????????????????

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

### 6.3 ?????

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

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

??????????? SelectionKeys ?????<3F><>?????? SelectionKey ??????????????????? SelectionKey????????????????????? I/O ???????????????????<3F><> I/O ????

```java
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 ??????????

??????<3F><>??????????????? ServerSocketChannel??????????????????????????????????????? SelectionKey ???? readyOps() ??????????<3F><>????????????????

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

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

### 6.5 ???????????

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

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

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

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

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

### 6.6 ?????????? SelectionKey

????? SelectionKey ???????????????????????????????????????????????? SelectionKey ????????????????????????????????????????????????????????????????????????????????????????????<3F><>????????????????????? remove() ???????????????? SelectionKey??

```java
it.remove();
```

???????????????????????????????????<3F><>????????(???????????? I/O ???)???

### 6.7 ????? I/O

?????????????????????????????????? I/O ??????????????????<3F><>??? Selector.select()????????????????? I/O ?????????<3F><>? SelectionKey ???????? OP_READ ??????????????

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


# ?<3F><>?????

- Eckel B, ????? , ??? , ?? . Java ?????? [M]. ??<3F><>????????? , 2002.
- [IBM: NIO ????](https://www.ibm.com/developerworks/cn/education/java/j-nio/j-nio.html)
- [ ??????? Java I/O ????????? ](https://www.ibm.com/developerworks/cn/java/j-lo-javaio/index.html)
- [NIO ??? IO ?????? ](http://blog.csdn.net/shimiso/article/details/24990499)