一 正常下载
服务使用断点下载时，响应的信息是206。
UrlConnection － HttpurlConnection。-通过URL来获取urlconnection实例。
正常下载示例
package cn.demo;import java.io.FileOutputStream;import java.io.InputStream;import java.io.OutputStream;import java.math.BigDecimal;import java.net.HttpURLConnection;import java.net.URL;public class CommonDown { public static void main(String[] args) throws Exception { String path = "http://localhost:6666/day22_cos/up/video.avi"; URL url = new URL(path); HttpURLConnection con = (HttpURLConnection) url.openConnection(); con.setRequestMethod("GET"); con.setDoInput(true); con.connect(); int code = con.getResponseCode(); System.err.println(code); if (code == 200) { //获取文件大小 long size = con.getContentLength(); System.err.println("总大小是:"+size); //声明下载到的字节 long sum=0; BigDecimal bd = new BigDecimal(0D); double already = 0D; InputStream in = con.getInputStream(); byte[] b = new byte[1024]; int len = -1; OutputStream out = new FileOutputStream("d:/a/video.avi"); while ((len = in.read(b)) != -1) { out.write(b, 0, len); sum=sum+len; double percent = ((double)sum)/((double)size); percent*=100; bd = new BigDecimal(percent); bd = bd.divide(new BigDecimal(1),0,BigDecimal.ROUND_HALF_UP); if(bd.doubleValue()!=already){ System.err.println(bd.intValue()+"%"); already=bd.doubleValue(); } } out.close(); } }}
二 URLConnection
此类用于在java代码中模拟浏览器组成http协议向服务发请求（get/post）。
代码：package cn.hx;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class OneServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse resp) throws ServletException, IOException { String name = request.getParameter("name"); System.err.println("这是get、、、、"+name); resp.setContentType("text/html;charset=UTF-8"); resp.getWriter().print("你好:"+name); } public void doPost(HttpServletRequest request, HttpServletResponse resp) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String name = request.getParameter("name"); System.err.println("这是post请求......."+name); resp.setContentType("text/html;charset=UTF-8"); resp.getWriter().print("你好:"+name); }}
用urlconnection访问oneSerlvet
package cn.demo;import java.io.File;import java.io.InputStream;import java.io.OutputStream;import java.net.HttpURLConnection;import java.net.URL;import org.junit.Test;public class Demo { /** * 发送get请求 * @throws Exception */ @Test public void testConn() throws Exception{ //第一步：声明url String urlPath = "http://localhost:6666/day22_cos/OneServlet?name=Jack"; //第二步：声明URL对象 URL url = new URL(urlPath); //第三步：从url上获取连接 HttpURLConnection con= (HttpURLConnection) url.openConnection(); //第四步：设置访问的类型 con.setRequestMethod("GET"); //第五步：设置可以向服务器发信息。也可以从服务器接收信息 con.setDoInput(true); //也可以从服务器接收信息 con.setDoOutput(true); //设置可以向服务器发信息 //第六步：连接 con.connect(); //7:检查连接状态 int code = con.getResponseCode(); if(code==200){ //8：从服务器读取数据 InputStream in = con.getInputStream(); byte[] b = new byte[1024]; int len = 0; while((len=in.read(b))!=-1){ String s = new String(b,0,len,"UTF-8"); System.err.print(s); } } //9：断开 con.disconnect(); } /** * 以下发送post请求 */ @Test public void post() throws Exception{ //第一步：声明url String urlPath = "http://localhost:6666/day22_cos/OneServlet"; //第二步：声明URL对象 URL url = new URL(urlPath); //第三步：从url上获取连接 HttpURLConnection con= (HttpURLConnection) url.openConnection(); //第四步：设置访问的类型 con.setRequestMethod("POST"); con.setRequestProperty("Content-Type","application/x-www-form-urlencoded"); //第五步：设置可以向服务器发信息。也可以从服务器接收信息 con.setDoInput(true);//设置可以向服务器发信息 con.setDoOutput(true);//也可以从服务器接收信息 //第六步：发信息 //获取输出流 OutputStream out = con.getOutputStream(); out.write("name=张三".getBytes("UTF-8")); //7:检查连接状态 int code = con.getResponseCode(); if(code==200){ //8：从服务器读取数据 InputStream in = con.getInputStream(); byte[] b = new byte[1024]; int len = 0; while((len=in.read(b))!=-1){ String s = new String(b,0,len,"UTF-8"); System.err.print(s); } } //9：断开 con.disconnect(); }}