没有借助任何第三方库，完全基于JAVA Socket实现一个最小化的HTTP文件下载客户端。完整的演示如何通过Socket实现下载文件的HTTP请求(request header)发送如何从Socket中接受HTTP响应(Response header, Response body)报文并解析与保存文件内容。如何通过SwingWork实现UI刷新，实时显示下载进度。
首先看一下UI部分：
【添加下载】按钮：
点击弹出URL输入框，用户Copy要下载文件URL到输入框以后，点击[OK]按钮即开始
下载
【清除完成】按钮：
清除所有已经下载完成的文件列表
文件下载状态分为以下几种：
package com.gloomyfish.socket.tutorial.http.download; public enum DownLoadStatus { NOT_STARTED, IN_PROCESS, COMPLETED, ERROR } UI部分主要是利用Swing组件完成。点击【添加下载】执行的代码如下：
final JDialog dialog = new JDialog(this,"Add File Link",true); dialog.getContentPane().setLayout(new BorderLayout()); // dialog.setSize(new Dimension(400,200)); final URLFilePanel panel = new URLFilePanel(); panel.setUpListener(new ActionListener(){ @Override public void actionPerformed(ActionEvent e) { if("OK".equals(e.getActionCommand())){ if(panel.validateInput()) { DownloadDetailStatusInfoModel data = new DownloadDetailStatusInfoModel(panel.getValidFileURL()); tableModel.getData().add(data); startDownlaod(); refreshUI(); } dialog.setVisible(false); dialog.dispose(); } else if("Cancel".equals(e.getActionCommand())) { dialog.setVisible(false); dialog.dispose(); } }}); dialog.getContentPane().add(panel, BorderLayout.CENTER); dialog.pack(); centre(dialog); dialog.setVisible(true); 【清除完成】按钮执行的代码如下：
private void clearDownloaded() { List<DownloadDetailStatusInfoModel> downloadedList = new ArrayList<DownloadDetailStatusInfoModel>(); for(DownloadDetailStatusInfoModel fileStatus : tableModel.getData()) { if(fileStatus.getStatus().toString().equals(DownLoadStatus.COMPLETED.toString())) { downloadedList.add(fileStatus); } } tableModel.getData().removeAll(downloadedList); refreshUI(); } 让JFrame组件居中显示的代码如下：
public static void centre(Window w) { Dimension us = w.getSize(); Dimension them = Toolkit.getDefaultToolkit().getScreenSize(); int newX = (them.width - us.width) / 2; int newY = (them.height - us.height) / 2; w.setLocation(newX, newY); } HTTP协议实现部分：
概述：HTTP请求头与相应头报文基本结构与解释
HTTP请求：一个标准的HTTP请求报文如
其中请求头可以有多个，message-body可以没有，不是必须的。请求行的格式如下：
Request-Line = Method SP Request-URI SPHTTP-Version CRLF 举例说明如下：
Request-Line = GET http://www.w3.org/pub/WWW/TheProject.htmlHTTP/1.1/r/n
其中SP表示空格， CRLF表示回车换行符/r/n
当你想要上传文件时候，使用Post方式来填写数据到message-body中即可。发送一个
简单的HTTP请求报文如下：
HTTP响应：一个标准的HTTP响应报文如下
最先得到是状态行，其格式如下：
Status-Line = HTTP-Version SP Status-CodeSP Reason-Phrase CRLF, 一个状态行的简单例子如下：Status-Line = HTTP/1.1 200 OK一般大家最喜欢的就是Status-Code会给你很多提示，最常见的就是404，500等状态码。状态码的意思可以参考RFC2616中的解释。下载文件最要紧是的检查HTTP响应头中的Content-Length与Content-Type两
个中分别声明了文件的长度与文件的类型。其它如Accept-Ranges表示接受多少到多少的字节。可能在多线程下载中使用。搞清楚了HTTP请求与响应的报文格式以后，我们就可以通过Socket按照报文格式解析内容，发送与读取HTTP请求与响应。具体步骤
如下：
一、根据用户输入的文件URL建立Socket连接
URL url = new URL(fileInfo.getFileURL()); String host = url.getHost(); int port = (url.getPort() == -1) ? url.getDefaultPort():url.getPort(); System.out.println("Host Name = " + host); System.out.println("port = " + port); System.out.println("File URI = " + url.getFile()); // create socket and start to construct the request line Socket socket = new Socket(); SocketAddress address = new InetSocketAddress(host, port); socket.connect(address); 用了URL类来把用户输入的url string变成容易解析一点的URL。
二、构造HTTP请求
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF8")); String requestStr = "GET " + url.getFile() + " HTTP/1.1/r/n"; // request line // construct the request header - 构造HTTP请求头(request header) String hostHeader = "Host: " + host + "/r/n"; String acceptHeader = "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8/r/n"; String charsetHeader = "Accept-Charset: GBK,utf-8;q=0.7,*;q=0.3/r/n"; String languageHeader = "Accept-Language: zh-CN,zh;q=0.8/r/n"; String keepHeader = "Connection: close/r/n";
三、发送HTTP请求
// 发送HTTP请求 bufferedWriter.write(requestStr); bufferedWriter.write(hostHeader); bufferedWriter.write(acceptHeader); bufferedWriter.write(charsetHeader); bufferedWriter.write(languageHeader); bufferedWriter.write(keepHeader); bufferedWriter.write("/r/n"); // 请求头信息发送结束标志 bufferedWriter.flush(); 四、接受HTTP响应并解析内容，写入创建好的文件
// 准备接受HTTP响应头并解析 CustomDataInputStream input = new CustomDataInputStream(socket.getInputStream()); File myFile = new File(fileInfo.getStoreLocation() + File.separator + fileInfo.getFileName()); String content = null; HttpResponseHeaderParser responseHeader = new HttpResponseHeaderParser(); BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream(myFile)); boolean hasData = false; while((content = input.readHttpResponseHeaderLine()) != null) { System.out.println("response header contect -->> " + content); responseHeader.addResponseHeaderLine(content); if(content.length() == 0) { hasData = true; } if(hasData) { int totalBytes = responseHeader.getFileLength(); if(totalBytes == 0) break; // no response body and data int offset = 0; byte[] myData = null; if(totalBytes >= 2048) { myData = new byte[2048]; } else { myData = new byte[totalBytes]; } int numOfBytes = 0; while((numOfBytes = input.read(myData, 0, myData.length)) > 0 && offset < totalBytes) { offset += numOfBytes; float p = ((float)offset) / ((float)totalBytes) * 100.0f; if(offset > totalBytes) { numOfBytes = numOfBytes + totalBytes - offset; p = 100.0f; } output.write(myData, 0, numOfBytes); updateStatus(p); } hasData = false; break; } } 简单的HTTP响应头解析类HttpResponseHeaderParser代码如下：
package com.gloomyfish.socket.tutorial.http.download; import java.util.HashMap; import java.util.Map; /** * it can parse entity header, response head * and response line <status code, CharSet, ect...> * refer to RFC2616，关于HTTP响应头，请看RFC文档，描写的很详细啊！！ */ public class HttpResponseHeaderParser { public final static String CONTENT_LENGTH = "Content-Length"; public final static String CONTENT_TYPE = "Content-Type"; public final static String ACCEPT_RANGES = "Accetp-Ranges"; private Map<String, String> headerMap; public HttpResponseHeaderParser() { headerMap = new HashMap<String, String>(); } /** * <p> get the response header key value pair </p> * @param responseHeaderLine */ public void addResponseHeaderLine(String responseHeaderLine) { if(responseHeaderLine.contains(":")) { String[] keyValue = responseHeaderLine.split(": "); if(keyValue[0].equalsIgnoreCase(CONTENT_LENGTH)) { headerMap.put(CONTENT_LENGTH, keyValue[1]); } else if(keyValue[0].equalsIgnoreCase(CONTENT_TYPE)) { headerMap.put(CONTENT_TYPE, keyValue[1]); } else { headerMap.put(keyValue[0], keyValue[1]); } } } public int getFileLength() { if(headerMap.get(CONTENT_LENGTH) == null){ return 0; } return Integer.parseInt(headerMap.get(CONTENT_LENGTH)); } public String getFileType() { return headerMap.get(CONTENT_TYPE); } public Map<String, String> getAllHeaders() { return headerMap; } } 以上就是本文的全部内容，希望对大家的学习java程序设计有所帮助。