Example of file upload and download of Struts2 in java

File upload

1. Form preparation
   • To upload one or more files using HTML forms
   • The enctype property of the HTML form must be set to multipart/form-data
   • The method attribute of the HTML form must be set to post
   • The <input type=“file”> field needs to be added.
2. Struts support for file uploads
   • In the Struts application, the FileUpload interceptor and the Jakarta Commons FileUpload components can complete the upload of files.
   • step:
     1. Use file tags in the file upload form of the Jsp page. If you need to upload multiple files at once, you must use multiple file tags, but their names must be the same
     2. Add 3 new attributes related to file upload in Action. The names of these 3 attributes must be in the following format
        • Upload basic files: define the following 3 properties directly in Action, and provide corresponding getters and setters
        • [File Name] : Type-File - The file uploaded . For example: data ( the fileName requirement is consistent with the name of the file form item )
        • [File Name]ContentType : Type-String - File type of uploaded file . For example: dataContentType ( used to receive file type (MIME value) )
        • [File Name]FileName : String - The file name of the uploaded file . For example: dataFileName ( name used to receive the file )
     3. If you upload multiple files, you can use List
        • If multiple files are passed, the above three attributes can be changed to List type! The name attribute values ​​of multiple file fields need to be consistent.
3. Sample code

 <s:form action="testUpload" enctype="multipart/form-data"> <s:textfield name="userName[0]" label="user-1"></s:textfield> <s:file name="photos" label="photos"></s:file> <s:textfield name="userName[1]" label="user-2"></s:textfield> <s:file name="photos" label="photos"></s:file> <s:textfield name="userName[2]" label="user-3"></s:textfield> <s:file name="photos" label="photo"></s:file> <s:submit value="submit"></s:submit></s:form>

 public class UploadAction extends ActionSupport{ @Setter@Getter private List<File> photos; @Setter@Getter private List<String> photosContentType; @Setter@Getter private List<String> photosFileName; @Setter@Getter private List<String> userName; public String testUpload() throws IOException { System.out.println("userName: "+userName); System.out.println("photos: "+photos); System.out.println("photosFileName: "+photosFileName); System.out.println("photosContentType: "+photosContentType); // Pass the file to the upload file in the server root directory// Get ServletContext ServletContext servletContext = ServletActionContext.getServletContext(); // Get the real path String realPath = servletContext.getRealPath("/upload"); System.out.println(realPath); File uploadFile = new File(realPath); //Judge whether the path exists if (!uploadFile.exists()){ //Create uploadFile.mkdir(); } for (int i = 0; i < photos.size(); i++) { UUID uuid = UUID.randomUUID(); FileUtils.copyFile(photos.get(i), new File(realPath + "/" + uuid + photosFileName.get(i))); } return SUCCESS; }}

1. How many small problems should be dealt with?

1. File name has a duplicate name. Generally, a UUID can be generated before the file name as a prefix.

2. Limit the size of a single file

3. Restrict file types

4. Limit the total file size

2. The FileUpload interceptor is provided in Struts2 to set these attribute values.

The FileUpload interceptor has 3 properties that can be set.

• maximumSize: The maximum length (in bytes) of a single file upload, the default value is 2 MB
  
• allowedTypes: The types that allow uploading files, separated by commas.
• allowedExtensions: Allows uploading file extensions, separated by commas
• These 3 properties can be overwritten in the struts.xml file

Note: There is a limit on the total size of uploaded files in default.properties under org.apache.struts2. You can use constants to modify this limit struts.multipart.maxSize=2097152

 <constant name="struts.devMode" value="true"/> <!-- Change the size of the total file here --> <constant name="struts.multipart.maxSize" value="2097152"/> <package name="default" namespace="/" extends="struts-default"> <interceptors> <interceptor-stack name="myInterceptor"> <interceptor-ref name="defaultStack"> <!-- Change the size of a single file, the Commons FileUpload component accepts uploaded files by default is 2M --> <param name="fileUpload.maximumSize">57,408</param> <!-- File type allowed to upload --> <param name="fileUpload.allowedTypes">image/pjpeg,image/gif</param> <!-- Extensions for uploading files --> <param name="fileUpload.allowedExtensions">jpg,gif</param> </interceptor-ref> </interceptor-stack> </interceptors> <default-interceptor-ref name="myInterceptor"></default-interceptor-ref> <action name="testUpload" method="testUpload"> <result name="success">/WEB-INF/views/success.jsp</result> <result name="input">/upload.jsp</result> </action></package>

1. Error messages related to uploading files?

1. Error messages related to file upload are predefined in the struts-messages.properties file.

2. You can upload the resource file corresponding to the Action in the file or redefine the error message in the i18n_zh_CN.properties international resource file

 struts.messages.error.file.too.large=The file you passes is too large struts.messages.error.content.type.not.allowed=File type error struts.messages.error.file.extension.not.allowed=Extension error struts.messages.upload.error.SizeLimitExceededException=Total file size exceeds the upper limit

File download

1. In some applications, it may be necessary to send a file to the user's browser dynamically, and the name and storage location of the file are unpredictable when programming

2. Stream Result Type
   • Struts provides a Stream result type specifically for file downloads. When using a Stream result, you do not have to prepare a JSP page.
   • The Stream result type can be set as follows:
     • contentType : The MIME type of the downloaded file. The default value is text/plain
     • contentLength : The size of the downloaded file, in bytes
     • contentDisposition : You can set the ContentDispositon response header for downloading file names. The default value is inline , which is usually set to the following format:
       • attachment;filename="document.pdf".
     • inputName : The input stream of the file provided in Action. The default value is inputStream
     • bufferSize : The size of the buffer when the file is downloaded. The default value is 1024
     • allowCaching : Whether to allow cache when downloading files. The default value is true
     • contentCharSet : character encoding when downloading the file.
       • The above parameters can be provided in Action in the form of a getter method!
         
   • Parameters of Stream result type can be overridden in Action as attributes
   • For details, please refer to struts-2.3.15.3-all/struts-2.3.15.3/docs/WW/docs/stream-result.html

3. Sample code

 <a href="testDownLoad">Download</a>

 public class DownloadLoadAction extends ActionSupport{ //Usually the following parameters will be provided in the Action @Setter@Getter private String contentType; @Setter@Getter private long contentLength; @Setter@Getter private String contentDisposition; @Setter@Getter private InputStream inputStream; public String testDownLoad() throws FileNotFoundException, UnsupportedEncodingException { //Get ServletContext ServletContext servletContext = ServletActionContext.getServletContext(); //Get the path of the file String realPath = servletContext.getRealPath("/WEB-INF/file/at least you.mp3"); //Get the stream of the file inputStream = new FileInputStream(realPath); //Set the file type contentType = servletContext.getMimeType(realPath); //Get the length of the file contentLength = new File(realPath).length(); //Set the file name String fileName = "At least you.mp3"; fileName = new String(fileName.getBytes("gbk"),"iso8859-1"); contentDisposition = "attachment;filename="+fileName; return SUCCESS; }}

 <!-- File Download--><action name="testDownLoad" method="testDownLoad"> <result type="stream"> <!-- File Buffer Size--> <param name="bufferSize">2048</param> </result></action>

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