Java Socket编程 - 基于Socket实现HTTP下载客户端

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：

GET /pub/WWW/TheProject.html HTTP/1.1\r\n

Host: www.w3.org\r\n

\r\n

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！！  *   * @author fish  *  */ 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; 	}  } 

可执行的Jar文件下载地址(这次我要点分)：

http://download.csdn.net/detail/jia20003/4862076

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