使用HttpClient实现文件的上传下载方法

时间：2022-07-05 09:01:46

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FilePart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。

 

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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.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。

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public void upload(String localFile){
    CloseableHttpClient 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。  

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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。

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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。

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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

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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。

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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~

以上就是小编为大家带来的使用HttpClient实现文件的上传下载方法全部内容了，希望大家多多支持服务器之家~

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