Net
目录
URL
URL url=new URL("http://www.swu.edu.cn/");
InputStream in= url.openStream();
URLConnection
```
URL url=new URL("http://www.swu.edu.cn/");
URLConnection con=URL.openConnection;
InputStream in= con.getInputStream();
```
TCP/UDP
TCP是面向连接的传输协议，UDP是没有建立连接的。UDP客户端只管往指定IP和端口发送数据包，UDP服务器只管接受从指定端口接受数据包，不管是不是想要的客户端发的数据包都接收，因为双方不知道对方的状态。不管对方是否在线，都只管发和收。
客户端用DatagramPacket对象来对数据包进行写入数据，再用DatagramSocket数据报套接字发送该数据包；服务器用DatagramSocket接受网络发来的数据包，再DatagramPacket对象打开数据包，读取数据。
由于UDP不保证数据传输的可靠性，数据量大的情况下会有丢包产生
TCP: Socket/ServerSocket
客户端
Socket client = new Socket("localhost",8888) ; // 客户端连服务器
BufferedReader buf = new BufferedReader(new InputStreamReader(client.getInputStream())) ; // 输入流，之后用于读取
PrintStream out = new PrintStream(client.getOutputStream()) ; // 输出流，发送数据
服务器
ServerSocket ss=new ServerSocket(8888);
Socket byclient = ss.accept() ; // 这个client是服务器到客户端的socket； 注意后面IO流！！！得到连接，程序进入到阻塞状态
out = new PrintStream(byclient.getOutputStream()) ; //输出流
BufferedReader buf = new BufferedReader(new InputStreamReader(byclient.getInputStream())) ;// 输入流 ！！！注意对比！准备接收客户端的输入信息
scanner | bufferedreader
BufferedReader input = new BufferedReader(new InputStreamReader(System.in)) ; // 接收键盘数据
Scanner input=new Scanner(System.in)
UDP DatagramPacket DatagramSocket
//只有点对点，不分sv，clt！
DatagramSocket skt=new DatagramSocket(8000);//接收端
DatagramPacket box=new DatagramPacket(c,1024);//接收容器
DatagramPacket pkt=new DatagramPacket(b,b.length,InetAddress.getLocalHost(),8000);//发送容器
skt.send(pkt)
skt.receive(box)
UDP传输文件代码
使用方法：先运行接收端，再运行发送端
但是存在一个问题：接收端需要手动关闭，改了半天还是只能用超时来限制
skt.setSoTimeout(5000);
发送端
import java.io.*;
import java.io.InputStream;
import java.net.*;
class sender {//sender
public static void main(String[] args) throws Exception {
DatagramSocket skt=new DatagramSocket(6666);//???????reply?
File f=new File("bank.txt");
byte[] d=new byte[1024];
InputStream in = new FileInputStream(f);
ByteArrayOutputStream bos = new ByteArrayOutputStream();
while (in.read(d)!=-1) {
DatagramPacket pkt=new DatagramPacket(d,d.length,InetAddress.getLocalHost(),8000);
skt.send(pkt);
}
System.out.println("sent");
skt.close();
}
}
接收端
改之前
import java.io.*;
import java.net.*;
class receive {//receiver
public static void main(String[] args) throws Exception {
DatagramSocket skt=new DatagramSocket(8000);
byte c[]=new byte[1024];
DatagramPacket box=new DatagramPacket(c,1024);//receive 到c[]
File f=new File("a.txt");
FileOutputStream fos= new FileOutputStream(f);
int l=0;
int x=0;
while (l==0){
skt.receive(box);
l=box.getLength();
if(box instanceof DatagramPacket){
fos.write(c,0,l);
fos.flush();
System.out.println(l+"bytes");
x=l;
l=0;
}
else if(x>0){ //没用
break;
}
}
System.out.println("ok");
}
}
改后
import java.io.*;
import java.util.Scanner;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.*;
class receive {//receiver
public static void main(String[] args) throws SocketException, FileNotFoundException {
DatagramSocket skt=new DatagramSocket(8000);
byte c[]=new byte[1024];
DatagramPacket box=new DatagramPacket(c,1024);//receive 到c[]
skt.setSoTimeout(5000);//!!!!!!!!!!!!!
int l=0;
try{
File f=new File("a.txt");
FileOutputStream fos= new FileOutputStream(f);
while (true) {
skt.receive(box);
// System.out.println(box);
fos.write(c);
fos.flush();
l++;
}
} catch (IOException e) {
skt.close();
e.printStackTrace();
System.out.println(l + "kb");
}
}
}