1 HTTP
HTTP 協(xié)議可能是現(xiàn)在 Internet 上使用得最多、最重要的協(xié)議了，越來(lái)越多的 Java 應(yīng)用程序需要直接通過(guò) HTTP 協(xié)議來(lái)訪問(wèn)網(wǎng)絡(luò)資源。
雖然在 JDK 的 java.net 包中已經(jīng)提供了訪問(wèn) HTTP 協(xié)議的基本功能，但是對(duì)于大部分應(yīng)用程序來(lái)說(shuō)，JDK 庫(kù)本身提供的功能還不夠豐富和靈活。HttpClient 用來(lái)提供高效的、最新的、功能豐富的支持 HTTP 協(xié)議的客戶(hù)端編程工具包，并且它支持 HTTP 協(xié)議最新的版本和建議。
一般的情況下我們都是使用Chrome或者其他瀏覽器來(lái)訪問(wèn)一個(gè)WEB服務(wù)器，用來(lái)瀏覽頁(yè)面查看信息或者提交一些數(shù)據(jù)、文件上傳下載等等。所訪問(wèn)的這些頁(yè)面有的僅僅是一些普通的頁(yè)面，有的需要用戶(hù)登錄后方可使用，或者需要認(rèn)證以及是一些通過(guò)加密方式傳輸，例如HTTPS。目前我們使用的瀏覽器處理這些情況都不會(huì)構(gòu)成問(wèn)題。但是一旦我們有需求不通過(guò)瀏覽器來(lái)訪問(wèn)服務(wù)器的資源呢？那該怎么辦呢？
下面以本地客戶(hù)端發(fā)起文件的上傳、下載為例做個(gè)小Demo。HttpClient有兩種形式，一種是org.apache.http下的，一種是org.apache.commons.httpclient.HttpClient。
2 文件上傳
文件上傳可以使用兩種方式實(shí)現(xiàn)，一種是PostMethod方式，一種是HttpPost方式。兩者的處理大同小異。PostMethod是使用FileBody將文件包裝流包裝起來(lái)，HttpPost是使用FilePart將文件流包裝起來(lái)。在傳遞文件流給服務(wù)端的時(shí)候，都可以同時(shí)傳遞其他的參數(shù)。
2.1 客戶(hù)端處理
2.1.1 PostMethod方式
將文件封裝到FilePart中，放入Part數(shù)組，同時(shí)，其他參數(shù)可以放入StringPart中，這里沒(méi)有寫(xiě)，只是單純的將參數(shù)以setParameter的方式進(jìn)行設(shè)置。此處的HttpClient是org.apache.commons.httpclient.HttpClient。
public void upload(String localFile){ File file = new File(localFile); PostMethod filePost = new PostMethod(URL_STR); HttpClient client = new HttpClient(); try { // 通過(guò)以下方法可以模擬頁(yè)面參數(shù)提交 filePost.setParameter("userName", userName); filePost.setParameter("passwd", passwd); Part[] parts = { new FilePart(file.getName(), file) }; filePost.setRequestEntity(new MultipartRequestEntity(parts, filePost.getParams())); client.getHttpConnectionManager().getParams().setConnectionTimeout(5000); int status = client.executeMethod(filePost); if (status == HttpStatus.SC_OK) { System.out.println("上傳成功"); } else { System.out.println("上傳失敗"); } } catch (Exception ex) { ex.printStackTrace(); } finally { filePost.releaseConnection(); } }記得搞完之后，要通過(guò)releaseConnection釋放連接。
2.1.2 HttpPost方式
這種方式，與上面類(lèi)似，只不過(guò)變成了FileBody。上面的Part數(shù)組在這里對(duì)應(yīng)HttpEntity。此處的HttpClient是org.apache.http.client.methods下的。
public void upload(String localFile){ CloseableHttpClient httpClient = null; CloseableHttpResponse response = null; try { httpClient = HttpClients.createDefault(); // 把一個(gè)普通參數(shù)和文件上傳給下面這個(gè)地址 是一個(gè)servlet HttpPost httpPost = new HttpPost(URL_STR); // 把文件轉(zhuǎn)換成流對(duì)象FileBody FileBody bin = new FileBody(new File(localFile)); StringBody userName = new StringBody("Scott", ContentType.create( "text/plain", Consts.UTF_8)); StringBody password = new StringBody("123456", ContentType.create( "text/plain", Consts.UTF_8)); HttpEntity reqEntity = MultipartEntityBuilder.create() // 相當(dāng)于<input type="file" name="file"/> .addPart("file", bin) // 相當(dāng)于<input type="text" name="userName" value=userName> .addPart("userName", userName) .addPart("pass", password) .build(); httpPost.setEntity(reqEntity); // 發(fā)起請(qǐng)求 并返回請(qǐng)求的響應(yīng) response = httpClient.execute(httpPost); System.out.println("The response value of token:" + response.getFirstHeader("token")); // 獲取響應(yīng)對(duì)象 HttpEntity resEntity = response.getEntity(); if (resEntity != null) { // 打印響應(yīng)長(zhǎng)度 System.out.println("Response content length: " + resEntity.getContentLength()); // 打印響應(yīng)內(nèi)容 System.out.println(EntityUtils.toString(resEntity, Charset.forName("UTF-8"))); } // 銷(xiāo)毀 EntityUtils.consume(resEntity); }catch (Exception e){ e.printStackTrace(); }finally { try { if(response != null){ response.close(); } } catch (IOException e) { e.printStackTrace(); } try { if(httpClient != null){ httpClient.close(); } } catch (IOException e) { e.printStackTrace(); } } }2.2 服務(wù)端處理
無(wú)論客戶(hù)端是哪種上傳方式，服務(wù)端的處理都是一樣的。在通過(guò)HttpServletRequest獲得參數(shù)之后，把得到的Item進(jìn)行分類(lèi)，分為普通的表單和File表單。
通過(guò)ServletFileUpload 可以設(shè)置上傳文件的大小及編碼格式等。
總之，服務(wù)端的處理是把得到的參數(shù)當(dāng)做HTML表單進(jìn)行處理的。
public void processUpload(HttpServletRequest request, HttpServletResponse response){ File uploadFile = new File(uploadPath); if (!uploadFile.exists()) { uploadFile.mkdirs(); } System.out.println("Come on, baby ......."); request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); //檢測(cè)是不是存在上傳文件 boolean isMultipart = ServletFileUpload.isMultipartContent(request); if(isMultipart){ DiskFileItemFactory factory = new DiskFileItemFactory(); //指定在內(nèi)存中緩存數(shù)據(jù)大小,單位為byte,這里設(shè)為1Mb factory.setSizeThreshold(1024*1024); //設(shè)置一旦文件大小超過(guò)getSizeThreshold()的值時(shí)數(shù)據(jù)存放在硬盤(pán)的目錄 factory.setRepository(new File("D://temp")); // Create a new file upload handler ServletFileUpload upload = new ServletFileUpload(factory); // 指定單個(gè)上傳文件的最大尺寸,單位:字節(jié)，這里設(shè)為50Mb upload.setFileSizeMax(50 * 1024 * 1024); //指定一次上傳多個(gè)文件的總尺寸,單位:字節(jié)，這里設(shè)為50Mb upload.setSizeMax(50 * 1024 * 1024); upload.setHeaderEncoding("UTF-8"); List<FileItem> items = null; try { // 解析request請(qǐng)求 items = upload.parseRequest(request); } catch (FileUploadException e) { e.printStackTrace(); } if(items!=null){ //解析表單項(xiàng)目 Iterator<FileItem> iter = items.iterator(); while (iter.hasNext()) { FileItem item = iter.next(); //如果是普通表單屬性 if (item.isFormField()) { //相當(dāng)于input的name屬性 <input type="text" name="content"> String name = item.getFieldName(); //input的value屬性 String value = item.getString(); System.out.println("屬性:" + name + " 屬性值:" + value); } //如果是上傳文件 else { //屬性名 String fieldName = item.getFieldName(); //上傳文件路徑 String fileName = item.getName(); fileName = fileName.substring(fileName.lastIndexOf("/") + 1);// 獲得上傳文件的文件名 try { item.write(new File(uploadPath, fileName)); } catch (Exception e) { e.printStackTrace(); } } } } } response.addHeader("token", "hello"); }服務(wù)端在處理之后，可以在Header中設(shè)置返回給客戶(hù)端的簡(jiǎn)單信息。如果返回客戶(hù)端是一個(gè)流的話，流的大小必須提前設(shè)置！
response.setContentLength((int) file.length());
3 文件下載
文件的下載可以使用HttpClient的GetMethod實(shí)現(xiàn)，還可以使用HttpGet方式、原始的HttpURLConnection方式。
3.1 客戶(hù)端處理
3.1.1 GetMethod方式
此處的HttpClient是org.apache.commons.httpclient.HttpClient。
public void downLoad(String remoteFileName, String localFileName) { HttpClient client = new HttpClient(); GetMethod get = null; FileOutputStream output = null; try { get = new GetMethod(URL_STR); get.setRequestHeader("userName", userName); get.setRequestHeader("passwd", passwd); get.setRequestHeader("fileName", remoteFileName); int i = client.executeMethod(get); if (SUCCESS == i) { System.out.println("The response value of token:" + get.getResponseHeader("token")); File storeFile = new File(localFileName); output = new FileOutputStream(storeFile); // 得到網(wǎng)絡(luò)資源的字節(jié)數(shù)組,并寫(xiě)入文件 output.write(get.getResponseBody()); } else { System.out.println("DownLoad file occurs exception, the error code is :" + i); } } catch (Exception e) { e.printStackTrace(); } finally { try { if(output != null){ output.close(); } } catch (IOException e) { e.printStackTrace(); } get.releaseConnection(); client.getHttpConnectionManager().closeIdleConnections(0); } }3.1.2 HttpGet方式
此處的HttpClient是org.apache.http.client.methods下的。
public void downLoad(String remoteFileName, String localFileName) { DefaultHttpClient httpClient = new DefaultHttpClient(); OutputStream out = null; InputStream in = null; try { HttpGet httpGet = new HttpGet(URL_STR); httpGet.addHeader("userName", userName); httpGet.addHeader("passwd", passwd); httpGet.addHeader("fileName", remoteFileName); HttpResponse httpResponse = httpClient.execute(httpGet); HttpEntity entity = httpResponse.getEntity(); in = entity.getContent(); long length = entity.getContentLength(); if (length <= 0) { System.out.println("下載文件不存在！"); return; } System.out.println("The response value of token:" + httpResponse.getFirstHeader("token")); File file = new File(localFileName); if(!file.exists()){ file.createNewFile(); } out = new FileOutputStream(file); byte[] buffer = new byte[4096]; int readLength = 0; while ((readLength=in.read(buffer)) > 0) { byte[] bytes = new byte[readLength]; System.arraycopy(buffer, 0, bytes, 0, readLength); out.write(bytes); } out.flush(); } catch (IOException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); }finally{ try { if(in != null){ in.close(); } } catch (IOException e) { e.printStackTrace(); } try { if(out != null){ out.close(); } } catch (IOException e) { e.printStackTrace(); } } }3.1.3 HttpURLConnection方式
public void download3(String remoteFileName, String localFileName) { FileOutputStream out = null; InputStream in = null; try{ URL url = new URL(URL_STR); URLConnection urlConnection = url.openConnection(); HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection; // true -- will setting parameters httpURLConnection.setDoOutput(true); // true--will allow read in from httpURLConnection.setDoInput(true); // will not use caches httpURLConnection.setUseCaches(false); // setting serialized httpURLConnection.setRequestProperty("Content-type", "application/x-java-serialized-object"); // default is GET httpURLConnection.setRequestMethod("POST"); httpURLConnection.setRequestProperty("connection", "Keep-Alive"); httpURLConnection.setRequestProperty("Charsert", "UTF-8"); // 1 min httpURLConnection.setConnectTimeout(60000); // 1 min httpURLConnection.setReadTimeout(60000); httpURLConnection.addRequestProperty("userName", userName); httpURLConnection.addRequestProperty("passwd", passwd); httpURLConnection.addRequestProperty("fileName", remoteFileName); // connect to server (tcp) httpURLConnection.connect(); in = httpURLConnection.getInputStream();// send request to // server File file = new File(localFileName); if(!file.exists()){ file.createNewFile(); } out = new FileOutputStream(file); byte[] buffer = new byte[4096]; int readLength = 0; while ((readLength=in.read(buffer)) > 0) { byte[] bytes = new byte[readLength]; System.arraycopy(buffer, 0, bytes, 0, readLength); out.write(bytes); } out.flush(); }catch(Exception e){ e.printStackTrace(); }finally{ try { if(in != null){ in.close(); } } catch (IOException e) { e.printStackTrace(); } try { if(out != null){ out.close(); } } catch (IOException e) { e.printStackTrace(); } } }3.2 服務(wù)端處理
盡管客戶(hù)端的處理方式不同，但是服務(wù)端是一樣的。
public void processDownload(HttpServletRequest request, HttpServletResponse response){ int BUFFER_SIZE = 4096; InputStream in = null; OutputStream out = null; System.out.println("Come on, baby ......."); try{ request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); response.setContentType("application/octet-stream"); String userName = request.getHeader("userName"); String passwd = request.getHeader("passwd"); String fileName = request.getHeader("fileName"); System.out.println("userName:" + userName); System.out.println("passwd:" + passwd); System.out.println("fileName:" + fileName); //可以根據(jù)傳遞來(lái)的userName和passwd做進(jìn)一步處理，比如驗(yàn)證請(qǐng)求是否合法等 File file = new File(downloadPath + "http://" + fileName); response.setContentLength((int) file.length()); response.setHeader("Accept-Ranges", "bytes"); int readLength = 0; in = new BufferedInputStream(new FileInputStream(file), BUFFER_SIZE); out = new BufferedOutputStream(response.getOutputStream()); byte[] buffer = new byte[BUFFER_SIZE]; while ((readLength=in.read(buffer)) > 0) { byte[] bytes = new byte[readLength]; System.arraycopy(buffer, 0, bytes, 0, readLength); out.write(bytes); } out.flush(); response.addHeader("token", "hello 1"); }catch(Exception e){ e.printStackTrace(); response.addHeader("token", "hello 2"); }finally { if (in != null) { try { in.close(); } catch (IOException e) { } } if (out != null) { try { out.close(); } catch (IOException e) { } } } }4 小結(jié)
HttpClient最基本的功能就是執(zhí)行Http方法。一個(gè)Http方法的執(zhí)行涉及到一個(gè)或者多個(gè)Http請(qǐng)求/Http響應(yīng)的交互，通常這個(gè)過(guò)程都會(huì)自動(dòng)被HttpClient處理，對(duì)用戶(hù)透明。用戶(hù)只需要提供Http請(qǐng)求對(duì)象，HttpClient就會(huì)將http請(qǐng)求發(fā)送給目標(biāo)服務(wù)器，并且接收服務(wù)器的響應(yīng)，如果http請(qǐng)求執(zhí)行不成功，httpclient就會(huì)拋出異常。所以在寫(xiě)代碼的時(shí)候注意finally的處理。
所有的Http請(qǐng)求都有一個(gè)請(qǐng)求列（request line），包括方法名、請(qǐng)求的URI和Http版本號(hào)。HttpClient支持HTTP/1.1這個(gè)版本定義的所有Http方法：GET,HEAD,POST,PUT,DELETE,TRACE和OPTIONS。上面的上傳用到了Post，下載是Get。
目前來(lái)說(shuō)，使用org.apache.commons.httpclient.HttpClient多一些。看自己了~
以上就是小編為大家?guī)?lái)的使用HttpClient實(shí)現(xiàn)文件的上傳下載方法全部?jī)?nèi)容了，希望大家多多支持武林網(wǎng)~
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