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Httpclient实现文件上传、文件下载看这篇文章就够了

前言:

使用 HttpClient 实现文件的上传下载,废话补不多说,直接上概念上代码。


1、相关概念:

1 HTTP

HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了,越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。

虽然在 JDK 的 java.net 包中已经提供了访问 HTTP 协议的基本功能,但是对于大部分应用程序来说,JDK 库本身提供的功能还不够丰富和灵活。HttpClient 用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包,并且它支持 HTTP 协议最新的版本和建议。

一般的情况下我们都是使用Chrome或者其他浏览器来访问一个WEB服务器,用来浏览页面查看信息或者提交一些数据、文件上传下载等等。所访问的这些页面有的仅仅是一些普通的页面,有的需要用户登录后方可使用,或者需要认证以及是一些通过加密方式传输,例如HTTPS。目前我们使用的浏览器处理这些情况都不会构成问题。但是一旦我们有需求不通过浏览器来访问服务器的资源呢?那该怎么办呢?

下面以本地客户端发起文件的上传、下载为例做个小Demo。HttpClient有两种形式,一种是org.apache.http下的,一种是org.apache.commons.httpclient.HttpClient。


2、文件上传:

文件上传可以使用两种方式实现,一种是PostMethod方式,一种是HttpPost方式。两者的处理大同小异。PostMethod是使用FileBody将文件包装流包装起来,HttpPost是使用FilePart将文件流包装起来。在传递文件流给服务端的时候,都可以同时传递其他的参数。

2.1 客户端处理

2.1.1 PostMethod方式

将文件封装到 file Part中,放入Part数组,同时,其他参数可以放入StringPart中,这里没有写,只是单纯的将参数以setParameter的方式进行设置。此处的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 {
 // 通过以下方法可以模拟页面参数提交
 filePost.setParameter("userName", userName);
 filePost.setParameter("passwd", passwd);
 Part[] parts = { new FilePart(file.getName(), file) };
 filePost.set request Entity(new MultipartRequestEntity(parts, filePost.getParams()));
 
 client.getHttpConnectionManager().getParams().setConnectionTimeout(5000);
 
 int status = client.executeMethod(filePost);
 if (status == HttpStatus.SC_OK) {
 System.out.println("上传成功");
 } else {
 System.out.println("上传失败");
 }
 } catch (Exception ex) {
 ex.printStackTrace();
 } finally {
 filePost.releaseConnection();
 }
 }
 

记得搞完之后,要通过releaseConnection释放连接。

2.1.2 HttpPost方式

这种方式,与上面类似,只不过变成了FileBody。上面的Part数组在这里对应HttpEntity。此处的HttpClient是org.apache.http.client.methods下的。

public void upload(String localFile){
  close ableHttpClient httpClient = null;
 CloseableHttpResponse response = null;
 try {
 httpClient = HttpClients.createDefault();
 
 // 把一个普通参数和文件上传给下面这个地址 是一个servlet
 HttpPost httpPost = new HttpPost(URL_STR);
 
 // 把文件转换成流对象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()
 // 相当于<input type="file" name="file"/>
 .addPart("file", bin)
 
 // 相当于<input type="text" name="userName" value=userName>
 .addPart("userName", userName)
 .addPart("pass", password)
 .build();
 httpPost.setEntity(reqEntity);
 // 发起请求 并返回请求的响应
 response = httpClient.execute(httpPost);
 
 System.out.println("The response value of token:" + response.getFirstHeader("token"));
 
 // 获取响应对象
 HttpEntity resEntity = response.getEntity();
 if (resEntity != null) {
 // 打印响应长度
 System.out.println("Response content length: " + resEntity.getContentLength());
 // 打印响应内容
 System.out.println(EntityUtils.toString(resEntity, Charset.forName("UTF-8")));
 }
 
 // 销毁
 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 服务端处理

无论客户端是哪种上传方式,服务端的处理都是一样的。在通过HttpServletRequest获得参数之后,把得到的Item进行分类,分为普通的表单和File表单。

通过ServletFileUpload 可以设置上传文件的大小及编码格式等。

总之,服务端的处理是把得到的参数当做HTML表单进行处理的。

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"); 
 
 //检测是不是存在上传文件 
 boolean isMultipart = ServletFileUpload.isMultipartContent(request); 
 
 if(isMultipart){ 
 DiskFileItemFactory factory = new DiskFileItemFactory(); 
 
 //指定在内存中缓存数据大小,单位为 byte ,这里设为1Mb 
 factory.setSizeThreshold(1024*1024); 
 
 //设置一旦文件大小超过getSizeThreshold()的值时数据存放在硬盘的目录 
 factory.setRepository(new File("D:\\temp")); 
 
 // Create a new file upload handler 
 ServletFileUpload upload = new ServletFileUpload(factory); 
 
 // 指定单个上传文件的最大尺寸,单位:字节,这里设为50Mb 
 upload.setFileSizeMax(50 * 1024 * 1024); 
 
 //指定一次上传多个文件的总尺寸,单位:字节,这里设为50Mb 
 upload.setSizeMax(50 * 1024 * 1024); 
 upload.setHeaderEncoding("UTF-8");
 
 List<FileItem> items = null; 
 
 try { 
 // 解析request请求 
 items = upload.parseRequest(request); 
 } catch (FileUploadException e) { 
 e.printStackTrace(); 
 } 
 
 if(items!=null){ 
 //解析表单项目 
 Iterator<FileItem> iter = items.iterator(); 
 while (iter.hasNext()) { 
 FileItem item = iter.next(); 
 
 //如果是普通表单属性 
 if (item.isFormField()) { 
 //相当于input的name属性 <input type="text" name="content"> 
 String name = item.getFieldName();
 
 //input的value属性 
 String value = item.getString();
 
 System.out.println("属性:" + name + " 属性值:" + value); 
 } 
 //如果是上传文件 
 else { 
 //属性名 
 String fieldName = item.getFieldName(); 
 
 //上传文件路径 
 String fileName = item.getName(); 
 fileName = fileName.substring(fileName.lastIndexOf("/") + 1);// 获得上传文件的文件名 
 
 try { 
 item.write(new File(uploadPath, fileName)); 
 } catch (Exception e) { 
 e.printStackTrace(); 
 } 
 } 
 } 
 } 
 } 
 
 response.addHeader("token", "hello");
 }
 

服务端在处理之后,可以在Header中设置返回给客户端的简单信息。如果返回客户端是一个流的话,流的大小必须提前设置!

response.setContentLength((int) file.length());


3、文件下载:

文件的下载可以使用HttpClient的GetMethod实现,还可以使用HttpGet方式、原始的HttpURLConnection方式。

3.1 客户端处理

3.1.1 GetMethod方式

此处的HttpClient是org.apache.commons.httpclient.HttpClient。

public void downLoad(String remoteFileName, String localFileName) {
 HttpClient client = new HttpClient();
 GetMethod get = null;
 File output Stream 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);
 
 // 得到网络资源的字节数组,并写入文件
 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

此处的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("下载文件不存在!");
 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 服务端处理

尽管客户端的处理方式不同,但是服务端是一样的。

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);
 
 //可以根据传递来的userName和passwd做进一步处理,比如验证请求是否合法等 
 File file = new File(downloadPath + "\\" + 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 、小结

HttpClient最基本的功能就是执行Http方法。一个Http方法的执行涉及到一个或者多个Http请求/Http响应的交互,通常这个过程都会自动被HttpClient处理,对用户透明。用户只需要提供Http请求对象,HttpClient就会将http请求发送给目标服务器,并且接收服务器的响应,如果http请求执行不成功,httpclient就会抛出异常。所以在写代码的时候注意finally的处理。

所有的Http请求都有一个请求列(request line),包括方法名、请求的URI和Http版本号。HttpClient支持HTTP/1.1这个版本定义的所有Http方法:GET,HEAD,POST,PUT,DELETE,TRACE和OPTIONS。上面的上传用到了Post,下载是Get。

目前来说,使用org.apache.commons.httpclient.HttpClient多一些。看自己了~

文章来源:智云一二三科技

文章标题:Httpclient实现文件上传、文件下载看这篇文章就够了

文章地址:https://www.zhihuclub.com/188867.shtml

关于作者: 智云科技

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