Java IO和网络编程
作者:陆金龙
发表时间:2024-02-24 05:44
关键词:
17.2.1 使用InetAddress
// 根据主机名来获取对应的InetAddress实例 InetAddress ip = InetAddress.getByName("www.crazyit.org"); // 判断是否可达 System.out.println("crazyit是否可达:" + ip.isReachable(2000)); // 获取该InetAddress实例的IP字符串 System.out.println(ip.getHostAddress()); // 根据原始IP地址来获取对应的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)); // 获取该InetAddress实例对应的全限定域名 System.out.println(local.getCanonicalHostName()); 17.2.2 使用URLEncoder和URLDecoder // 将application/x-www-form-urlencoded字符串转换成普通字符串 String keyWord = URLDecoder.decode("%E7%96%AF%E7%8B%82java", "utf-8"); System.out.println(keyWord); // 将普通字符串转换成 application/x-www-form-urlencoded字符串 String urlStr = URLEncoder.encode("疯狂Android讲义" , "GBK"); System.out.println(urlStr); 17.2.3 URL、URLConnection、URLPermission 多线程下载 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; 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(); } } } } public static void main(String[] args) throws Exception { // 初始化DownUtil对象 final DownUtil downUtil = new DownUtil("http://www.crazyit.org/" + "attachments/month_1403/1403202355ff6cc9a4fbf6f14a.png" , "ios.png", 4); // 开始下载 downUtil.download(); new Thread(() -> { while(downUtil.getCompleteRate() < 1) { // 每隔0.1秒查询一次任务的完成进度, // GUI程序中可根据该进度来绘制进度条 System.out.println("已完成:"+ downUtil.getCompleteRate()); try { Thread.sleep(1000); } catch (Exception ex){} } }).start(); }
17.2.4 Http Get和Post请求
public class GetPostTest { /** * 向指定URL发送GET方法的请求 * @param url 发送请求的URL * @param param 请求参数,格式满足name1=value1&name2=value2的形式。 * @return URL所代表远程资源的响应 */ public static String sendGet(String url , String param) { String result = ""; String urlName = url + "?" + param; try { URL realUrl = new URL(urlName); // 打开和URL之间的连接 URLConnection conn = realUrl.openConnection(); // 设置通用的请求属性 conn.setRequestProperty("accept", "*/*"); conn.setRequestProperty("connection", "Keep-Alive"); conn.setRequestProperty("user-agent" , "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)"); // 建立实际的连接 conn.connect(); // 获取所有响应头字段 Map<String, List<String>> map = conn.getHeaderFields(); // 遍历所有的响应头字段 for (String key : map.keySet()) { System.out.println(key + "--->" + map.get(key)); } try( // 定义BufferedReader输入流来读取URL的响应 BufferedReader in = new BufferedReader( new InputStreamReader(conn.getInputStream() , "utf-8"))) { String line; while ((line = in.readLine())!= null) { result += "\n" + line; } } } catch(Exception e) { System.out.println("发送GET请求出现异常!" + e); e.printStackTrace(); } return result; } /** * 向指定URL发送POST方法的请求 * @param url 发送请求的URL * @param param 请求参数,格式应该满足name1=value1&name2=value2的形式。 * @return URL所代表远程资源的响应 */ public static String sendPost(String url , String param) { String result = ""; try { URL realUrl = new URL(url); // 打开和URL之间的连接 URLConnection conn = realUrl.openConnection(); // 设置通用的请求属性 conn.setRequestProperty("accept", "*/*"); conn.setRequestProperty("connection", "Keep-Alive"); conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)"); // 发送POST请求必须设置如下两行 conn.setDoOutput(true); conn.setDoInput(true); try( // 获取URLConnection对象对应的输出流 PrintWriter out = new PrintWriter(conn.getOutputStream())) { // 发送请求参数 out.print(param); // flush输出流的缓冲 out.flush(); } try( // 定义BufferedReader输入流来读取URL的响应 BufferedReader in = new BufferedReader(new InputStreamReader (conn.getInputStream() , "utf-8"))) { String line; while ((line = in.readLine())!= null) { result += "\n" + line; } } } catch(Exception e) { System.out.println("发送POST请求出现异常!" + e); e.printStackTrace(); } return result; } // 提供主方法,测试发送GET请求和POST请求 public static void main(String args[]) { // 发送GET请求 String s = GetPostTest.sendGet("http://localhost:8888/abc/a.jsp" , null); System.out.println(s); // 发送POST请求 String s1 = GetPostTest.sendPost("http://localhost:8888/abc/login.jsp" , "name=crazyit.org&pass=leegang"); System.out.println(s1); } }