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# 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 click at "Upload File", form would be submitted along with the selected file:

    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-5.5.29\webapps\data\
         </param-value>
    </context-param>
    ....
    </web-app>

Following is the source code for UploadServlet which can handle multiple file uploading at a time. Before procedding 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 http://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 http://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:\temp and c:\apache-tomcat-5.5.29\webapps\data well in advance.

    // Import required java libraries
    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.*;

    public class UploadServlet extends HttpServlet {

       private boolean isMultipart;
       private String filePath;
       private int maxFileSize = 50 * 1024;
       private int maxMemSize = 4 * 1024;
       private File file ;

       public void init( ){
          // Get the file location where it would be stored.
          filePath =
                 getServletContext().getInitParameter("file-upload");
       }
       public 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);
       }
       }
       public 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 servelt script works fine, your file should be uploaded in c:\apache-tomcat-5.5.29\webapps\data\ directory.

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