最近在项目中遇到一个下载文件的老问题。之所以说是老问题,因为在以前的很多项目中都遇到过,但是当时赶进度,所以在找到解决方案后就草草了事,没有深入的研究、总结一下各种方法,实乃憾事。
既然再次遇到,就不能放过。争取在依然很紧张的项目进度中,找出一点时间总结一下Java Web Application开发中涉及到的文件上传、下载解决方案。鉴于博客是写给自己看的,加上时间紧张,所以我会持续更新,不求一气呵成。
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Upload File through Html FORM:
/html/body/form/@enctype: ENCTYPE determines how the form data is encoded. Whenever data is transmitted from one place to another, there needs to be an agreed upon means of representing that data.
FORM ENCTYPE has three different values:
- application/x-www-form-urlencoded : All characters are encoded in URL encoding before sent (this is default). Only value attribute inside form will be processed.
- multipart/form-data : data will be transformed in byte code stream. This value is required when you are using forms that have a file upload control. In
- text/plain : Spaces are converted to "+" symbols, but no special characters are encoded
So if you want to upload file through web, you have to first set form ENCTYPE to be "multipart/form-data".
Using pure Servlet:
In fact, file download and upload in Java Web Application are to manage files through InputStream from HttpServletRequest and OutputStream from HttpServletResponse.
Even we can simply the development and configuration by using some framework, but anyway we should know what is the kernel for file uploading and download.
File Upload web interface:
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fileUpload.html <html> ? <head> ??? <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> ??? <title>Upload a File</title> ? </head> ? <body> ??? <h1>Upload File </h1> ??? <h2>Warning: Please make sure your web browser support file uploading.</h2> ??? <form action="servlet/uploadServlet" method="POST" enctype="multipart/form-data "> ??????? Select a file to upload: <input type="file" size="40" name="upl-file"/> </BR> ??? ???? <input type="submit" value="Upload"/> <input type="reset" value="Reset"/> ??? </form> ? </body> </html> |
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Read file from HttpServletRequest Inputstream:
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??????????? /** ??????????? ? * Servlet.doPost: reads the uploaded data from the request and writes it to ??????????? ? * a file. ??????????? ? */ ??????????? public void doPost(HttpServletRequest request, HttpServletResponse response) { ??????????????????????? DataInputStream in = null; ??????????????????????? try { ??????????????????????????????????? // get content type of client request ??????????????????????????????????? String contentType = request.getContentType(); ? ??????????????????????????????????? // make sure content type is multipart/form-data ??????????????????????????????????? if (contentType != null ??????????????????????????????????????????????????????????? && contentType.indexOf("multipart/form-data ") != -1) { ??????????????????????????????????????????????? // open input stream from client to capture upload file ??????????????????????????????????????????????? in = new DataInputStream(request.getInputStream()) ; ??????????????????????????????????????????????? // get length of content data ??????????????????????????????????????????????? int formDataLength = request.getContentLength(); ??????????????????????????????????????????????? byte dataBytes[] = new byte[1024]; ??????????????????????????????????????????????? int bytesRead; ??????????????????????????????????????????????? while ((bytesRead = in.read(dataBytes)) != -1) { ??????????????????????????????????????????????????????????? // write the data to server file. ??????????????????????????????????????????????? } ? ??????????????????????????????????????????????? // here you can perform some other checks. ??????????????????????????????????? } ??????????????????????? } catch (Exception e) { ??????????????????????? } ??????????? } |
This is just a draft demo on how to upload file through servlet. There is no control on large files and user rights.
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Download file through HttpServletResponse OutputStream
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??????????? /** ??????????? ? * Servlet.doPost: get data to be sent to client and output it through Response.outputStream. Web browser will pop-up a save file window to let User download file. ??????????? ? */ ??????????? public void doPost(HttpServletRequest request, HttpServletResponse response) { ??????????????????????? response.setContentType("text/csv"); ??????????????????????? response.setHeader("Content-Disposition", ??????????????????????????????????????????????? "attachment; filename=unknownModels.csv"); ?? ? ? ? ? ? ? ? ? ? ??? OutputStream out; ?? ? ? ? ? ? ? ? ? ? ???// PrintWriter printWriter; ?? ? ? ? ? ? ? ? ? ? ? ? try { ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ???out? = response.getOutputStream(); ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?// printWriter = response.getWriter(); ?? ?... ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? // output your content with printWriter. It will output content to client. ?? ?... ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? out.flush(); ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?// printWriter.flush(); ?? ? ? ? ? ? ? ? ? ? ? ? } catch (IOException e) { ??????????????????????????????????? System.err.println("Met a error when download file."); ??????????????????????????????????? System.exit(1); ??????????????????????? } ??????????? } |
Content-Disposition used to define download file or open a file in web browsers:
attachment; filename=myfile.txt: download a file with default name myfile.txt inline; filename=myfile.txt: open the file in web browser. default file name myfile.txt
Using commons-fileupload.jar to Upload file
TBD
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Using Struts1
File upload through Struts1:
In struts-config_1_3.dtd, we can find controller definition to control file uploading through struts1.*
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struts-config/controller: |
By default struts 1 provide org.apache.struts.upload.CommonsMultipartRequestHandler to process file uploading transform.?CommonsMultipartRequestHandler encapsulate apache-commons-fileupload for file uploading processing. If you want to know how?CommonsMultipartRequestHandler ?manage file uploading or you want to implement your own MultipartRequestHandler, please refer to struts source code for that.
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Your form should extends ActionForm and contains a FileForm named with same value as html:file/@name.
Then config your upload Action in struts-config.xml to map to this form-bean.
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After that, we can use FormFile.getInputStream() to get file data and no need to care about file uploading processing.
File download through Struts1:
Struts 1 provide DownloadAction:
org.apache.struts.actions.DownloadAction.
Here is a snapshot of org.apache.struts.actions.DownloadAction.java:
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public abstract class DownloadAction extends BaseAction { ? |
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So we should define an Action that extends DownloadAction and implement method:
StreamInfo getStreamInfo(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response);
Using Struts2
Struts2 vs Struts1:
Since Struts2 realize webwork2 and provides different configuration as struts1. So it is more like a new MVC framework rather than upgrade of struts1. Here are some new features in struts2:
- ?? ?Action should implement ActionSupport
- ?? ?Each action's parameter fields will represent dedicated HTML/form data, so there is no need to define ActionForm (form-beans/form-bean in struts1) again.
- ?? ?Struts2 introduce AOP interceptor and IOC (like /package/action/param)
- ?? ?Configuration file changed a lot.
- ?? ?...
File uploading through struts2:
For file uploading, struts2 introduce three new parameters in Action to represent File information:
- File XXX: ?? ??? ??? ??? ? represent the File to be uploaded. XXX is the value of attribute: HTML/form/file/@name.?
- String XXXFileName: ?? ? represent the original file name of file XXX.
- String XXXContentType:? represent the content type of file XXX.?
If you want to upload a set of files, those three parameters should be defined as:
- File[] XXX: ?? ??? ??? ??? ? represent the File to be uploaded. XXX is the value of attribute: HTML/form/file/@name. ??All the file upload form should use same file/@name definition.
- String[] XXXFileName: ?? ??? ? represent the original file names of file XXX.
- String[] XXXContentType:?? ? represent the content types of files XXX.?
So you should define your own upload Action as following:
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- First extend ActionSupport and contain those three necessary parameters
- Then you can use File XXX to read data from InputStream.
Because in my current project, we do not use struts2, so I do not study the source code of struts2. But anyway, we can image there is a MultipartRequestHandler which?will process file uploading and convert it into Action.XXX for us.
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File Download through Struts2
About download, we can talk about it later.
But anyway, I am always thinking that even framework provide encapsulation of complex operation for us, but the kernel should always the same: send file data through Response OutputStream.
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Attach file management in SOAP
TBD
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