使用HttpClient实现文件的上传下载方法

网友投稿 918 2023-06-24


使用HttpClient实现文件的上传下载方法

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

.addPart("file", bin)

// 相当于

.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 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 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

String name = item.getFieldName();

//input的value属性

String value = item.getString();

http:// 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(Exceptihttp://on 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~


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