使用HttpClient上传文件

怼烎@ 2022-09-26 15:55 256阅读 0赞

## 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。

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。

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。

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;
            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。

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~