Java网络编程初探

IP地址案例

package ch17;

import javax.swing.text.Style;
import java.net.InetAddress;

/**
 * Created by Jiqing on 2017/1/5.
 */
public class InetAddressTest {
    public static void main(String[] args) throws Exception{
        InetAddress ip = InetAddress.getByName("www.baidu.com");
        // 判断是否可达
        System.out.println("百度是否可达:"+ip.isReachable(2000));
        // 获取该实例的IP
        System.out.println(ip.getHostAddress());
        // 根据原始IP地址获取对应的InetAddress实例
        InetAddress local = InetAddress.getByAddress(new byte[]{127,0,0,1});
        System.out.println("本机是否可达："+local.isReachable(5000));
        System.out.println(local.getCanonicalHostName());
    }
}

结果：
百度是否可达:true
111.13.100.92
本机是否可达：true
127.0.0.1

下载图片案例

package ch17;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownUtil
{
    // 定义下载资源的路径
    private String path;
    // 指定所下载的文件的保存位置
    private String targetFile;
    // 定义需要使用多少线程下载资源
    private int threadNum;
    // 定义下载的线程对象
    private DownThread[] threads;
    // 定义下载的文件的总大小
    private int fileSize;

    public DownUtil(String path, String targetFile, int threadNum)
    {
        this.path = path;
        this.threadNum = threadNum;
        // 初始化threads数组
        threads = new DownThread[threadNum];
        this.targetFile = targetFile;
    }

    public void download() throws Exception
    {
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(5 * 1000);
        conn.setRequestMethod("GET");
        conn.setRequestProperty(
                "Accept",
                "image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
                        + "application/x-shockwave-flash, application/xaml+xml, "
                        + "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
                        + "application/x-ms-application, application/vnd.ms-excel, "
                        + "application/vnd.ms-powerpoint, application/msword, */*");
        conn.setRequestProperty("Accept-Language", "zh-CN");
        conn.setRequestProperty("Charset", "UTF-8");
        conn.setRequestProperty("Connection", "Keep-Alive");
        // 得到文件大小
        fileSize = conn.getContentLength();
        conn.disconnect();
        int currentPartSize = fileSize / threadNum + 1;//这里不必一定要加1,不加1也可以
        RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
        // 设置本地文件的大小
        file.setLength(fileSize);
        file.close();
        for (int i = 0; i < threadNum; i++)
        {
            // 计算每条线程的下载的开始位置
            int startPos = i * currentPartSize;
            // 每个线程使用一个RandomAccessFile进行下载
            RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");
            // 定位该线程的下载位置
            currentPart.seek(startPos);
            // 创建下载线程
            threads[i] = new DownThread(startPos, currentPartSize, currentPart);
            // 启动下载线程
            threads[i].start();
        }
    }

    // 获取下载的完成百分比
    public double getCompleteRate()
    {
        // 统计多条线程已经下载的总大小
        int sumSize = 0;
        for (int i = 0; i < threadNum; i++)
        {
            sumSize += threads[i].length;
        }
        // 返回已经完成的百分比
        return sumSize * 1.0 / fileSize;
    }

    private class DownThread extends Thread
    {
        // 当前线程的下载位置
        private int startPos;
        // 定义当前线程负责下载的文件大小
        private int currentPartSize;
        // 当前线程需要下载的文件块
        private RandomAccessFile currentPart;
        // 定义已经该线程已下载的字节数
        public int length;

        public DownThread(int startPos, int currentPartSize,RandomAccessFile currentPart)
        {
            this.startPos = startPos;
            this.currentPartSize = currentPartSize;
            this.currentPart = currentPart;
        }

        @Override
        public void run()
        {
            try
            {
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                conn.setConnectTimeout(5 * 1000);
                conn.setRequestMethod("GET");
                conn.setRequestProperty(
                        "Accept",
                        "image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
                                + "application/x-shockwave-flash, application/xaml+xml, "
                                + "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
                                + "application/x-ms-application, application/vnd.ms-excel, "
                                + "application/vnd.ms-powerpoint, application/msword, */*");
                conn.setRequestProperty("Accept-Language", "zh-CN");
                conn.setRequestProperty("Charset", "UTF-8");
                InputStream inStream = conn.getInputStream();
                // 跳过startPos个字节，表明该线程只下载自己负责哪部分文件。
                inStream.skip(this.startPos);
                byte[] buffer = new byte[1024];
                int hasRead = 0;
                // 读取网络数据，并写入本地文件
                while (length < currentPartSize
                        && (hasRead = inStream.read(buffer)) != -1)
                {
                    currentPart.write(buffer, 0, hasRead);
                    // 累计该线程下载的总大小
                    length += hasRead;
                }
                currentPart.close();
                inStream.close();
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }
}

package ch17;
import java.net.*;

/**
 * Created by Jiqing on 2017/1/5.
 */
public class MultiThreadDown {
    public static void main(String[] args) throws Exception{
        // 初始化DownUtil对象
        final DownUtil downUtil = new DownUtil("http://imgs.aixifan.com/live/1482830873793/1482830873793.jpg","demo.jpg",4);
        // 开始下载
        downUtil.download();
        new Thread(() -> {
           while(downUtil.getCompleteRate() < 1) {
               // 每隔0.01秒查询一次任务完成进度
               System.out.println("已完成："+ downUtil.getCompleteRate());
               try {
                   Thread.sleep(10);
               }catch (Exception ex) {}
           }
        }).start();
    }
}

结果：

已完成：0.0
已完成：0.04389803969303463
已完成：0.09210067667384099
已完成：0.16440463214505055
已完成：0.39150257003269945
已完成：0.7543834411326956
已完成：0.9892219080763762

socket案例

服务端

package ch17;

import com.sun.xml.internal.ws.policy.privateutil.PolicyUtils;

import java.io.IOException;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * Created by Jiqing on 2017/1/6.
 */
public class Server {
    public static void main(String[] args) throws IOException{
        // 创建一个ServerSocket
        ServerSocket ss = new ServerSocket(10000);
        // 采用循环不断地接收来自客户端的请求
        while(true) {
            // 每当客户端Socket请求时，服务器端也产生一个socket
            Socket s = ss.accept();
            PrintStream ps = new PrintStream(s.getOutputStream());
            ps.println("服务器的新年祝福！");
            ps.close();
            s.close();
        }
    }
}

客户端

package ch17;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;

/**
 * Created by Jiqing on 2017/1/6.
 */
public class Client {
    public static void main(String[] args) throws IOException{
        Socket socket = new Socket("127.0.0.1",10000);
        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String line = br.readLine();
        System.out.println("来自服务器的数据："+line);
        br.close();
        socket.close();
    }
}

通过ip+端口号进行数据传输。先运行服务器端，再运行客户端。

结果：
来自服务器的数据：服务器的新年祝福！