Servlets - File Uploading-alljchome-开发者的教程家园

Servlets Tutorial

Servlets Useful Resources

Selected Reading

Servlets - File Uploading

A Servlet can be used with an HTML form tag to allow users to upload files to the server. An uploaded file could be a text file or image file or any document.

Creating a File Upload Form

The following HTM code below creates an uploader form. Following are the important points to be noted down −

The form method attribute should be set to POST method and GET method can not be used

The form enctype attribute should be set to multipart/form-data.

The form action attribute should be set to a servlet file which would handle file uploading at backend server. Following example is using UploadServlet servlet to upload file.

To upload a single file you should use a single <input .../> tag with attribute type="file". To allow multiple files uploading, include more than one input tags with different values for the name attribute. The browser associates a Browse button with each of them.

 
<html>
   <head>
      <title>File Uploading Form</title>
   </head>
   
   <body>
      <h3>File Upload:</h3>
      Select a file to upload: <br />
      <form action = "UploadServlet" method = "post" enctype = "multipart/form-data">
         <input type = "file" name = "file" size = "50" />
         <br />
         <input type = "submit" value = "Upload File" />
      </form>
   </body>
</html>

This will display following result which would allow to select a file from local PC and when user would cpck at "Upload File", form would be submitted along with the selected fil −

 
File Upload: 
Select a file to upload: 
 
 

 
 

 
NOTE: This is just dummy form and would not work.

Writing Backend Servlet

Following is the servlet UploadServlet which would take care of accepting uploaded file and to store it in directory <Tomcat-installation-directory>/webapps/data. This directory name could also be added using an external configuration such as a context-param element in web.xml as follows −

 
<web-app>
   ....
   <context-param> 
      <description>Location to store uploaded file</description> 
      <param-name>file-upload</param-name> 
      <param-value>
         c:apache-tomcat-5.5.29webappsdata
      </param-value> 
   </context-param>
   ....
</web-app>

Following is the source code for UploadServlet which can handle multiple file uploading at a time. Before proceeding you have make sure the followings −

Following example depends on FileUpload, so make sure you have the latest version of commons-fileupload.x.x.jar file in your classpath. You can download it from https://commons.apache.org/fileupload/.

FileUpload depends on Commons IO, so make sure you have the latest version of commons-io-x.x.jar file in your classpath. You can download it from https://commons.apache.org/io/.

While testing following example, you should upload a file which has less size than maxFileSize otherwise file would not be uploaded.

Make sure you have created directories c: emp and c:apache-tomcat8.0.28webappsdata well in advance.

// Import required java pbraries
import java.io.*;
import java.util.*;
 
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.output.*;

pubpc class UploadServlet extends HttpServlet {
   
   private boolean isMultipart;
   private String filePath;
   private int maxFileSize = 50 * 1024;
   private int maxMemSize = 4 * 1024;
   private File file ;

   pubpc void init( ){
      // Get the file location where it would be stored.
      filePath = getServletContext().getInitParameter("file-upload"); 
   }
   
   pubpc void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, java.io.IOException {
   
      // Check that we have a file upload request
      isMultipart = ServletFileUpload.isMultipartContent(request);
      response.setContentType("text/html");
      java.io.PrintWriter out = response.getWriter( );
   
      if( !isMultipart ) {
         out.println("<html>");
         out.println("<head>");
         out.println("<title>Servlet upload</title>");  
         out.println("</head>");
         out.println("<body>");
         out.println("<p>No file uploaded</p>"); 
         out.println("</body>");
         out.println("</html>");
         return;
      }
  
      DiskFileItemFactory factory = new DiskFileItemFactory();
   
      // maximum size that will be stored in memory
      factory.setSizeThreshold(maxMemSize);
   
      // Location to save data that is larger than maxMemSize.
      factory.setRepository(new File("c:\temp"));

      // Create a new file upload handler
      ServletFileUpload upload = new ServletFileUpload(factory);
   
      // maximum file size to be uploaded.
      upload.setSizeMax( maxFileSize );

      try { 
         // Parse the request to get file items.
         List fileItems = upload.parseRequest(request);
	
         // Process the uploaded file items
         Iterator i = fileItems.iterator();

         out.println("<html>");
         out.println("<head>");
         out.println("<title>Servlet upload</title>");  
         out.println("</head>");
         out.println("<body>");
   
         while ( i.hasNext () ) {
            FileItem fi = (FileItem)i.next();
            if ( !fi.isFormField () ) {
               // Get the uploaded file parameters
               String fieldName = fi.getFieldName();
               String fileName = fi.getName();
               String contentType = fi.getContentType();
               boolean isInMemory = fi.isInMemory();
               long sizeInBytes = fi.getSize();
            
               // Write the file
               if( fileName.lastIndexOf("\") >= 0 ) {
                  file = new File( filePath + fileName.substring( fileName.lastIndexOf("\"))) ;
               } else {
                  file = new File( filePath + fileName.substring(fileName.lastIndexOf("\")+1)) ;
               }
               fi.write( file ) ;
               out.println("Uploaded Filename: " + fileName + "<br>");
            }
         }
         out.println("</body>");
         out.println("</html>");
         } catch(Exception ex) {
            System.out.println(ex);
         }
      }
      
      pubpc void doGet(HttpServletRequest request, HttpServletResponse response)
         throws ServletException, java.io.IOException {

         throw new ServletException("GET method used with " +
            getClass( ).getName( )+": POST method required.");
      }
   }
}

Compile and Running Servlet

Compile above servlet UploadServlet and create required entry in web.xml file as follows.

 
<servlet>
   <servlet-name>UploadServlet</servlet-name>
   <servlet-class>UploadServlet</servlet-class>
</servlet>

<servlet-mapping>
   <servlet-name>UploadServlet</servlet-name>
   <url-pattern>/UploadServlet</url-pattern>
</servlet-mapping>

Now try to upload files using the HTML form which you created above. When you would try http://localhost:8080/UploadFile.htm, it would display following result which would help you uploading any file from your local machine.

File Upload:

Select a file to upload:

If your servlet script works fine, your file should be uploaded in c:apache-tomcat8.0.28webappsdata directory.

Servlets - File Uploading

Creating a File Upload Form

Writing Backend Servlet

Compile and Running Servlet

友情链接