HttpClient文件上传下载

1 HTTP

HTTP 协议可能是如今 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序须要直接通过 HTTP 协议来訪问网络资源。

尽管在 JDK 的 java.net 包中已经提供了訪问 HTTP 协议的基本功能，可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client编程工具包，而且它支持 HTTP 协议最新的版本号和建议。

一般的情况下我们都是使用Chrome或者其它浏览器来訪问一个WEBserver，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。所訪问的这些页面有的不过一些普通的页面，有的须要用户登录后方可使用，或者须要认证以及是一些通过加密方式传输，比如HTTPS。

眼下我们使用的浏览器处理这些情况都不会构成问题。

可是一旦我们有需求不通过浏览器来訪问server的资源呢？那该怎么办呢？

以下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

文件上传能够使用两种方式实现，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。都能够同一时候传递其它的參数。

2.1 client处理

2.1.1 PostMethod方式

将文件封装到FilePart中。放入Part数组。同一时候。其它參数能够放入StringPart中。这里没有写，仅仅是单纯的将參数以setParameter的方式进行设置。

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

 1 public void upload(String localFile){
 2         File file = new File(localFile);
 3         PostMethod filePost = new PostMethod(URL_STR);
 4         HttpClient client = new HttpClient();
 5
 6         try {
 7             // 通过下面方法能够模拟页面參数提交
 8             filePost.setParameter("userName", userName);
 9             filePost.setParameter("passwd", passwd);
10
11             Part[] parts = { new FilePart(file.getName(), file) };
12             filePost.setRequestEntity(new MultipartRequestEntity(parts, filePost.getParams()));
13
14             client.getHttpConnectionManager().getParams().setConnectionTimeout(5000);
15
16             int status = client.executeMethod(filePost);
17             if (status == HttpStatus.SC_OK) {
18                 System.out.println("上传成功");
19             } else {
20                 System.out.println("上传失败");
21             }
22         } catch (Exception ex) {
23             ex.printStackTrace();
24         } finally {
25             filePost.releaseConnection();
26         }
27     }

记得搞完之后。要通过releaseConnection释放连接。

2.1.2 HttpPost方式

这样的方式，与上面类似，仅仅只是变成了FileBody。上面的Part数组在这里相应HttpEntity。此处的HttpClient是org.apache.http.client.methods下的。

 1 public void upload(String localFile){
 2         CloseableHttpClient httpClient = null;
 3         CloseableHttpResponse response = null;
 4         try {
 5             httpClient = HttpClients.createDefault();
 6
 7             // 把一个普通參数和文件上传给以下这个地址 是一个servlet
 8             HttpPost httpPost = new HttpPost(URL_STR);
 9
10             // 把文件转换成流对象FileBody
11             FileBody bin = new FileBody(new File(localFile));
12
13             StringBody userName = new StringBody("Scott", ContentType.create(
14                     "text/plain", Consts.UTF_8));
15             StringBody password = new StringBody("123456", ContentType.create(
16                     "text/plain", Consts.UTF_8));
17
18             HttpEntity reqEntity = MultipartEntityBuilder.create()
19                     // 相当于<input type="file" name="file"/>
20                     .addPart("file", bin)
21
22                     // 相当于<input type="text" name="userName" value=userName>
23                     .addPart("userName", userName)
24                     .addPart("pass", password)
25                     .build();
26
27             httpPost.setEntity(reqEntity);
28
29             // 发起请求 并返回请求的响应
30             response = httpClient.execute(httpPost);
31
32             System.out.println("The response value of token:" + response.getFirstHeader("token"));
33
34             // 获取响应对象
35             HttpEntity resEntity = response.getEntity();
36             if (resEntity != null) {
37                 // 打印响应长度
38                 System.out.println("Response content length: " + resEntity.getContentLength());
39                 // 打印响应内容
40                 System.out.println(EntityUtils.toString(resEntity, Charset.forName("UTF-8")));
41             }
42
43             // 销毁
44             EntityUtils.consume(resEntity);
45         }catch (Exception e){
46             e.printStackTrace();
47         }finally {
48             try {
49                 if(response != null){
50                     response.close();
51                 }
52             } catch (IOException e) {
53                 e.printStackTrace();
54             }
55
56             try {
57                 if(httpClient != null){
58                     httpClient.close();
59                 }
60             } catch (IOException e) {
61                 e.printStackTrace();
62             }
63         }
64     }

2.2 服务端处理

不管client是哪种上传方式，服务端的处理都是一样的。

在通过HttpServletRequest获得參数之后，把得到的Item进行分类，分为普通的表单和File表单。

通过ServletFileUpload 能够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參数当做HTML表单进行处理的。

 1 public void processUpload(HttpServletRequest request, HttpServletResponse response){
 2         File uploadFile = new File(uploadPath);
 3         if (!uploadFile.exists()) {
 4             uploadFile.mkdirs();
 5         }
 6
 7         System.out.println("Come on, baby .......");
 8
 9         request.setCharacterEncoding("utf-8");
10         response.setCharacterEncoding("utf-8");
11
12         //检測是不是存在上传文件
13         boolean isMultipart = ServletFileUpload.isMultipartContent(request);
14
15         if(isMultipart){
16             DiskFileItemFactory factory = new DiskFileItemFactory();
17
18             //指定在内存中缓存数据大小,单位为byte,这里设为1Mb
19             factory.setSizeThreshold(1024*1024);
20
21             //设置一旦文件大小超过getSizeThreshold()的值时数据存放在硬盘的文件夹
22             factory.setRepository(new File("D:\\temp"));
23
24             // Create a new file upload handler
25             ServletFileUpload upload = new ServletFileUpload(factory);
26
27             // 指定单个上传文件的最大尺寸,单位:字节，这里设为50Mb
28             upload.setFileSizeMax(50 * 1024 * 1024);
29
30             //指定一次上传多个文件的总尺寸,单位:字节。这里设为50Mb
31             upload.setSizeMax(50 * 1024 * 1024);
32             upload.setHeaderEncoding("UTF-8");
33
34             List<FileItem> items = null;
35
36             try {
37                 // 解析request请求
38                 items = upload.parseRequest(request);
39             } catch (FileUploadException e) {
40                 e.printStackTrace();
41             }
42
43             if(items!=null){
44                 //解析表单项目
45                 Iterator<FileItem> iter = items.iterator();
46                 while (iter.hasNext()) {
47                     FileItem item = iter.next();
48
49                     //假设是普通表单属性
50                     if (item.isFormField()) {
51                         //相当于input的name属性   <input type="text" name="content">
52                         String name = item.getFieldName();
53
54                         //input的value属性
55                         String value = item.getString();
56
57                         System.out.println("属性:" + name + " 属性值:" + value);
58                     }
59                     //假设是上传文件
60                     else {
61                         //属性名
62                         String fieldName = item.getFieldName();
63
64                         //上传文件路径
65                         String fileName = item.getName();
66                         fileName = fileName.substring(fileName.lastIndexOf("/") + 1);// 获得上传文件的文件名称
67
68                         try {
69                             item.write(new File(uploadPath, fileName));
70                         } catch (Exception e) {
71                             e.printStackTrace();
72                         }
73                     }
74                 }
75             }
76         }
77
78         response.addHeader("token", "hello");
79     }

服务端在处理之后。能够在Header中设置返回给client的简单信息。假设返回client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

文件的下载能够使用HttpClient的GetMethod实现。还能够使用HttpGet方式、原始的HttpURLConnection方式。

3.1 client处理

3.1.1 GetMethod方式

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

 1 public void downLoad(String remoteFileName, String localFileName) {
 2         HttpClient client = new HttpClient();
 3         GetMethod get = null;
 4         FileOutputStream output = null;
 5
 6         try {
 7             get = new GetMethod(URL_STR);
 8             get.setRequestHeader("userName", userName);
 9             get.setRequestHeader("passwd", passwd);
10             get.setRequestHeader("fileName", remoteFileName);
11
12             int i = client.executeMethod(get);
13
14             if (SUCCESS == i) {
15                 System.out.println("The response value of token:" + get.getResponseHeader("token"));
16
17                 File storeFile = new File(localFileName);
18                 output = new FileOutputStream(storeFile);
19
20                 // 得到网络资源的字节数组,并写入文件
21                 output.write(get.getResponseBody());
22             } else {
23                 System.out.println("DownLoad file occurs exception, the error code is :" + i);
24             }
25         } catch (Exception e) {
26             e.printStackTrace();
27         } finally {
28             try {
29                 if(output != null){
30                     output.close();
31                 }
32             } catch (IOException e) {
33                 e.printStackTrace();
34             }
35
36             get.releaseConnection();
37             client.getHttpConnectionManager().closeIdleConnections(0);
38         }
39     }

3.1.2 HttpGet方式

此处的HttpClient是org.apache.http.client.methods下的。

 1 public void downLoad(String remoteFileName, String localFileName) {
 2         DefaultHttpClient httpClient = new DefaultHttpClient();
 3         OutputStream out = null;
 4         InputStream in = null;
 5
 6         try {
 7             HttpGet httpGet = new HttpGet(URL_STR);
 8
 9             httpGet.addHeader("userName", userName);
10             httpGet.addHeader("passwd", passwd);
11             httpGet.addHeader("fileName", remoteFileName);
12
13             HttpResponse httpResponse = httpClient.execute(httpGet);
14             HttpEntity entity = httpResponse.getEntity();
15             in = entity.getContent();
16
17             long length = entity.getContentLength();
18             if (length <= 0) {
19                 System.out.println("下载文件不存在。");
20                 return;
21             }
22
23             System.out.println("The response value of token:" + httpResponse.getFirstHeader("token"));
24
25             File file = new File(localFileName);
26             if(!file.exists()){
27                 file.createNewFile();
28             }
29
30             out = new FileOutputStream(file);
31             byte[] buffer = new byte[4096];
32             int readLength = 0;
33             while ((readLength=in.read(buffer)) > 0) {
34                 byte[] bytes = new byte[readLength];
35                 System.arraycopy(buffer, 0, bytes, 0, readLength);
36                 out.write(bytes);
37             }
38
39             out.flush();
40
41         } catch (IOException e) {
42             e.printStackTrace();
43         } catch (Exception e) {
44             e.printStackTrace();
45         }finally{
46             try {
47                 if(in != null){
48                     in.close();
49                 }
50             } catch (IOException e) {
51                 e.printStackTrace();
52             }
53
54             try {
55                 if(out != null){
56                     out.close();
57                 }
58             } catch (IOException e) {
59                 e.printStackTrace();
60             }
61         }
62     }

3.1.3 HttpURLConnection方式

 1 public void download3(String remoteFileName, String localFileName) {
 2         FileOutputStream out = null;
 3         InputStream in = null;
 4
 5         try{
 6             URL url = new URL(URL_STR);
 7             URLConnection urlConnection = url.openConnection();
 8             HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
 9
10             // true -- will setting parameters
11             httpURLConnection.setDoOutput(true);
12             // true--will allow read in from
13             httpURLConnection.setDoInput(true);
14             // will not use caches
15             httpURLConnection.setUseCaches(false);
16             // setting serialized
17             httpURLConnection.setRequestProperty("Content-type", "application/x-java-serialized-object");
18             // default is GET
19             httpURLConnection.setRequestMethod("POST");
20             httpURLConnection.setRequestProperty("connection", "Keep-Alive");
21             httpURLConnection.setRequestProperty("Charsert", "UTF-8");
22             // 1 min
23             httpURLConnection.setConnectTimeout(60000);
24             // 1 min
25             httpURLConnection.setReadTimeout(60000);
26
27             httpURLConnection.addRequestProperty("userName", userName);
28             httpURLConnection.addRequestProperty("passwd", passwd);
29             httpURLConnection.addRequestProperty("fileName", remoteFileName);
30
31             // connect to server (tcp)
32             httpURLConnection.connect();
33
34             in = httpURLConnection.getInputStream();// send request to
35                                                                 // server
36             File file = new File(localFileName);
37             if(!file.exists()){
38                 file.createNewFile();
39             }
40
41             out = new FileOutputStream(file);
42             byte[] buffer = new byte[4096];
43             int readLength = 0;
44             while ((readLength=in.read(buffer)) > 0) {
45                 byte[] bytes = new byte[readLength];
46                 System.arraycopy(buffer, 0, bytes, 0, readLength);
47                 out.write(bytes);
48             }
49
50             out.flush();
51         }catch(Exception e){
52             e.printStackTrace();
53         }finally{
54             try {
55                 if(in != null){
56                     in.close();
57                 }
58             } catch (IOException e) {
59                 e.printStackTrace();
60             }
61
62             try {
63                 if(out != null){
64                     out.close();
65                 }
66             } catch (IOException e) {
67                 e.printStackTrace();
68             }
69         }
70     }

3.2 服务端处理

虽然client的处理方式不同，可是服务端是一样的。

 1 public void processDownload(HttpServletRequest request, HttpServletResponse response){
 2         int BUFFER_SIZE = 4096;
 3         InputStream in = null;
 4         OutputStream out = null;
 5
 6         System.out.println("Come on, baby .......");
 7
 8         try{
 9             request.setCharacterEncoding("utf-8");
10             response.setCharacterEncoding("utf-8");
11             response.setContentType("application/octet-stream");
12
13             String userName = request.getHeader("userName");
14             String passwd = request.getHeader("passwd");
15             String fileName = request.getHeader("fileName");
16
17             System.out.println("userName:" + userName);
18             System.out.println("passwd:" + passwd);
19             System.out.println("fileName:" + fileName);
20
21             //能够依据传递来的userName和passwd做进一步处理，比方验证请求是否合法等
23             File file = new File(downloadPath + "\\" + fileName);
24             response.setContentLength((int) file.length());
25             response.setHeader("Accept-Ranges", "bytes");
26
27             int readLength = 0;
28
29             in = new BufferedInputStream(new FileInputStream(file), BUFFER_SIZE);
30             out = new BufferedOutputStream(response.getOutputStream());
31
32             byte[] buffer = new byte[BUFFER_SIZE];
33             while ((readLength=in.read(buffer)) > 0) {
34                 byte[] bytes = new byte[readLength];
35                 System.arraycopy(buffer, 0, bytes, 0, readLength);
36                 out.write(bytes);
37             }
38
39             out.flush();
40
41             response.addHeader("token", "hello 1");
42
43         }catch(Exception e){
44             e.printStackTrace();
45              response.addHeader("token", "hello 2");
46         }finally {
47             if (in != null) {
48                 try {
49                     in.close();
50                 } catch (IOException e) {
51                 }
52             }
53             if (out != null) {
54                 try {
55                     out.close();
56                 } catch (IOException e) {
57                 }
58             }
59         }
60     }

4 小结

HttpClient最主要的功能就是运行Http方法。一个Http方法的运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己主动被HttpClient处理。对用户透明。

用户仅仅须要提供Http请求对象。HttpClient就会将http请求发送给目标server。而且接收server的响应，假设http请求运行不成功，httpclient就会抛出异常。

所以在写代码的时候注意finally的处理。

全部的Http请求都有一个请求列（request line），包含方法名、请求的URI和Http版本号号。HttpClient支持HTTP/1.1这个版本号定义的全部Http方法：GET,HEAD,POST,PUT,DELETE,TRACE和OPTIONS。

上面的上传用到了Post，下载是Get。

现在的问题是。使用org.apache.commons.httpclient.HttpClient更多。看看你自己~