## Java專題十二：網絡 [TOC] ### 12.1.套接字 - `Socket`: 客戶端套接字 - `ServerSocket`: 服務器端套接字 > Linux中Socket編程：[http://www.man7.org/linux/man-pages/man2/socket.2.html](http://www.man7.org/linux/man-pages/man2/socket.2.html) <table > <tr> <th style="width:70%">SOCKET_API</th> <th style="width:30%">DESCRIPTION</th> </tr> <tr> <td>int socket(int domain, int type, int protocol);</td> <td>create an endpoint for communication</td> </tr> <tr> <td>int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); </td> <td>accept a connection on a socket</td> </tr> <tr> <td> int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);</td> <td>initiate a connection on a socket</td> </tr> <tr> <td> int bind(int sockfd, const struct sockaddr *add, socklen_t addrlen);</td> <td>bind a name to a socket </td> </tr> <tr> <td>int listen(int sockfd, int backlog);</td> <td> listen for connections on a socket </td> </tr> <tr> <td>ssize_t send(int sockfd, const void *buf, size_t len, int flags); </td> <td>send a message on a socket </td> </tr> <tr> <td>ssize_t sendto(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen); </td> <td>send a message on a socket </td> </tr> <tr> <td>ssize_t recv(int sockfd, const void *buf, size_t len, int flags);</td> <td>receive a message on a socket</td> </tr> <tr> <td>ssize_t recvfrom(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen);</td> <td>receive a message on a socket</td> </tr> <tr> <td>ssize_t read(int fd, void *buf, size_t count); </td> <td>read from a file descriptor</td> </tr> <tr> <td>ssize_t write(int fd, const void *buf, size_t count); </td> <td>write to a file descriptor</td> </tr> <tr> <td>int close(int fd); </td> <td>close a file descriptor</td> </tr> </table> #### 12.1.1 服務器端（`java.net.ServerSocket`） * 創建Socket（`new ServerSocket()`） * 綁定端口（`bind(SocketAddress endpoint)`） * 監聽端口（`accept()`） * 等待客戶端連接 * 接收和發送數據（`getInputStream()、getOutputStream()`） * 關閉Socket（`close()`） #### 12.1.2客戶端（`java.net.Socket`） * 創建Socket（`Socket()`） * 發起連接（`connect(SocketAddress endpoint)`） * 發送和接收數據（`getOutputStream()、getInputStream()`） * 關閉Socket（`close()`）  ### 12.2.高級API java.net 包中的許多類可以提供更加高級的抽象，允許方便地訪問網絡上的資源。 - `URI`: 表示統一資源標識符（URI）引用 - `URL`: 表示統一資源定位器，即指向萬維網上“資源”的指針 - `URLConnection`: 表示應用程序和URL之間的通信鏈接 - `HttpURLConnection`: 支持HTTP特定功能的URLConnection，規范見[http://www.w3.org/pub/www/Protocols/](http://www.w3.org/pub/www/Protocols) 例：從網絡上下載文件并保存到本地，詳細參考[NetTools](https://github.com/15045120/git-docs/blob/master/tools/NetTools.java) ``` NetTools.download("https://dl.google.com/android/repository/platform-tools-latest-windows.zip",""); ``` ``` public static boolean download(String url, String saveDir) throws URISyntaxException, IOException { // get download file name String fileName = url.substring(url.indexOf('/')); if (saveDir == null || saveDir.trim().equals("")){ saveDir = ""; }else{ File out = new File(saveDir); if (!out.exists() || !out.isDirectory()){ throw new FileNotFoundException(); } } // open connection URI uri = new URI(url); URL url0 = uri.toURL(); HttpURLConnection conn = (HttpURLConnection)url0.openConnection(); conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36"); conn.connect(); // response is ok if (conn.getResponseCode() == HttpURLConnection.HTTP_OK){ InputStream is = conn.getInputStream(); File file = new File(saveDir, fileName); FileOutputStream fos = new FileOutputStream(new File("platform-tools-latest-windows.zip")); byte[] buf = new byte[1024]; int readCount; while((readCount = is.read(buf)) > 0){ fos.write(buf, 0, readCount); } is.close(); fos.close(); return true; } return false; } ```