Java 网络编程基础

网络可以使不同物理位置上的计算机达到资源共享和数据传输的目的，网络编程主要就是面向底层数据的传输。Java 中提供了专门的网络编程程序包 java.net。

@Test
  public void testInetAddress() throws UnknownHostException {
    // 使用getLocalHost()方法创建InetAddress对象
    InetAddress netAddress = InetAddress.getLocalHost();
    // 获取本机ip
    System.out.println(netAddress.getHostAddress());
    // 获取本机计算机名
    System.out.println(netAddress.getHostName());

    // 根据域名使用getByName方法创建InetAddress对象
    netAddress = InetAddress.getByName("www.baidu.com");
    // 返回 163服务器的ip:61.135.169.121
    System.out.println(netAddress.getHostAddress());
    // 输出：www.baidu.com
    System.out.println(netAddress.getHostName());

    // 根据ip使用getByName方法创建InetAddress对象
    netAddress = InetAddress.getByName("61.135.169.121");
    // 返回 baidu服务器的ip:61.135.169.121
    System.out.println(netAddress.getHostAddress());
    // 如果这个IP地址不存在或DNS服务器不允许进行IP地址和域名的映射，getHostName方法就直接返回这个IP地址
    System.out.println(netAddress.getHostName());
  }

192.168.1.1
JPM
61.135.169.125
www.baidu.com
61.135.169.121

@Test
  public void testInetSocketAddress() throws UnknownHostException {
    //InetSocketAddress类可以指定端口
    InetSocketAddress netSocketAddress = new InetSocketAddress("www.baidu.com", 8080);
    System.out.println(netSocketAddress.getHostName());
    System.out.println(netSocketAddress.getPort());

    InetAddress addr = netSocketAddress.getAddress();
    System.out.println(addr.getHostAddress());
    System.out.println(addr.getHostName());
  }

www.baidu.com
8080
61.135.169.125
www.baidu.com

@Test
  public void testURL() throws IOException {
    // 绝对路径构建URL
    URL url = new URL("https://www.baidu.com:80/index.html?para=Java");
    System.out.println("URL的协议:" + url.getProtocol());
    System.out.println("URL的域名:" + url.getHost());
    System.out.println("URL的端口:" + url.getPort());
    System.out.println("URL的资源:" + url.getFile());
    System.out.println("URL的参数:" + url.getQuery());

    // 相对路径URL
    url = new URL("https://www.baidu.com:80/aaa/");
    url = new URL(url, "aaa.html");
    System.out.println("URL的路径" + url.toString());

    // URLConnection是封装访问远程网络资源的类，可以通过它建立与远程服务器的连接，检查远程资源的一些属性
    URL url1 = new URL("https://www.baidu.com");
    URLConnection urlConn = url1.openConnection();
    // 取得内容大小
    System.out.println(urlConn.getContentLength());
    // 取得内容类型
    System.out.println(urlConn.getContentType());

    // URLEncoder编码，URLDecoder解码
    String msg = "你好，中国";
    String msgEncod = URLEncoder.encode(msg, "utf-8");
    System.out.println(msg + " 编码之后：" + msgEncod);
    String msgDecod = URLDecoder.decode(msg, "utf-8");
    System.out.println(msgEncod + " 解码之后：" + msgDecod);
  }

URL的协议:https
URL的域名:www.baidu.com
URL的端口:80
URL的资源:/index.html?para=Java
URL的参数:para=Java
URL的路径https://www.baidu.com:80/aaa/aaa.html
2443
text/html
你好，中国 编码之后：%E4%BD%A0%E5%A5%BD%EF%BC%8C%E4%B8%AD%E5%9B%BD
%E4%BD%A0%E5%A5%BD%EF%BC%8C%E4%B8%AD%E5%9B%BD 解码之后：你好，中国

@Test
  public void test() throws IOException {
    URL url = new URL("https://www.baidu.com"); // 获取百度主页的资源
    // 通过流获取网络资源
    InputStream is = url.openStream();
    byte[] bytes = new byte[1024];
    int len = 0;
    while ((len = is.read(bytes)) != -1) {
      System.out.println(new String(bytes, 0, len));
    }
    is.close();

    // 以上代码获取到的内容会有乱码，可以使用转换流InputStreamReader来指定utf-8编码
    BufferedReader br = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
    String msg = null;
    while ((msg = br.readLine()) != null) {
      System.out.println(msg);
    }
    br.close();

    // 以上代码解决了乱码的问题，我们也可以通过io流把获取到的内容输出到一个文件中
    BufferedReader br1 = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
    BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("baidu.html"), "utf-8"));
    String msg1 = null;
    while ((msg1 = br1.readLine()) != null) {
      bw.append(msg1);
      bw.newLine();
    }
    bw.flush();
    bw.close();
    br1.close();
  }