沒有借助任何第三方庫，完全基於JAVA Socket實現一個最小化的HTTP文件下載客戶端。完整的演示如何通過Socket實現下載文件的HTTP請求(request header)發送如何從Socket中接受HTTP響應(Response header, Response body)報文並解析與保存文件內容。如何通過SwingWork實現UI刷新，實時顯示下載進度。
首先看一下UI部分：
【添加下載】按鈕：
點擊彈出URL輸入框，用戶Copy要下載文件URL到輸入框以後，點擊[OK]按鈕即開始
下載
【清除完成】按鈕：
清除所有已經下載完成的文件列表
文件下載狀態分為以下幾種：
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組件完成。點擊【添加下載】執行的代碼如下：
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】按鈕執行的代碼如下：
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(); }讓JFrame組件居中顯示的代碼如下：
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協議實現部分：
概述：HTTP請求頭與相應頭報文基本結構與解釋
HTTP請求：一個標準的HTTP請求報文如
其中請求頭可以有多個，message-body可以沒有，不是必須的。請求行的格式如下：
Request-Line = Method SP Request-URI SPHTTP-Version CRLF 舉例說明如下：
Request-Line = GET http://www.w3.org/pub/WWW/TheProject.htmlHTTP/1.1/r/n
其中SP表示空格， CRLF表示回車換行符/r/n
當你想要上傳文件時候，使用Post方式來填寫數據到message-body中即可。發送一個
簡單的HTTP請求報文如下：
HTTP響應：一個標準的HTTP響應報文如下
最先得到是狀態行，其格式如下：
Status-Line = HTTP-Version SP Status-CodeSP Reason-Phrase CRLF, 一個狀態行的簡單例子如下：Status-Line = HTTP/1.1 200 OK一般大家最喜歡的就是Status-Code會給你很多提示，最常見的就是404，500等狀態碼。狀態碼的意思可以參考RFC2616中的解釋。下載文件最要緊是的檢查HTTP響應頭中的Content-Length與Content-Type兩
個中分別聲明了文件的長度與文件的類型。其它如Accept-Ranges表示接受多少到多少的字節。可能在多線程下載中使用。搞清楚了HTTP請求與響應的報文格式以後，我們就可以通過Socket按照報文格式解析內容，發送與讀取HTTP請求與響應。具體步驟
如下：
一、根據用戶輸入的文件URL建立Socket連接
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類來把用戶輸入的url string變成容易解析一點的URL。
二、構造HTTP請求
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 - 構造HTTP請求頭(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、發送HTTP請求
// 發送HTTP請求bufferedWriter.write(requestStr); bufferedWriter.write(hostHeader); bufferedWriter.write(acceptHeader); bufferedWriter.write(charsetHeader); bufferedWriter.write(languageHeader); bufferedWriter.write(keepHeader); bufferedWriter.write("/r/n"); // 請求頭信息發送結束標誌bufferedWriter.flush();四、接受HTTP響應並解析內容，寫入創建好的文件
// 準備接受HTTP響應頭並解析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; } }簡單的HTTP響應頭解析類HttpResponseHeaderParser代碼如下：
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，關於HTTP響應頭，請看RFC文檔，描寫的很詳細啊！ ！ */ 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內容，希望對大家的學習java程序設計有所幫助。