Using File Attachments on Forms

How to use the file attachment control on a form.

About this technique	Details
Category	Java Client Techniques> General techniques for controls
Description	You'll learn about: Uploading a new file into the database Downloading content from the database as a file Saving modified content to the database
	You can run this technique code from: Database: Examples3_Java Form: frmFileAttachments NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	See the chapter on the Form Designer in the Tools Guide

The example lets users upload documents and images into a database. It adds a file to the database as a new record, downloads content from the database as a file, and updates the database with file contents the user has changed.

Uploading a new file into the database   

The following code shows how to display a dialog to obtain the file to upload and the file's path. The code creates a new record in the database for this file, uploads it, and (if requested by the user) deletes the local file.

  private void handle_btnAttach_actionPerformed(ActionEvent evt) 
  { 
  File fileSelected; 
  try 
  { 
     fileSelected = attachFile.chooseFile( 
        "Please select a file to upload", null, false); 
     if (fileSelected != null) 
     { 
        if (!filename.isEnabled()) 
        { 
           filename.setEnabled(true); 
           fldFileDescription.setEnabled(true); 
        } 
   
        agData.gotoLast(); 
        agData.insertAfter(); 
        filename.setText(fileSelected.getName()); 
        // Save the entire path name 
        lblFilePath.setText(fileSelected.getPath()); 
        agData.updateRows(); 
   
        if (chkDelete.getState() ) 
           attachFile.upload(fileSelected, true); 
        else 
           attachFile.upload(fileSelected, false); 
     } 
  } 
  catch (Exception e) 
  { 
     agDialog.displayError(e); 
  } 
  } 

Notes about the code

• attachFile is the name of an AgcFileAttachment control on the form.

• chooseFile() displays a dialog to get the name and path of the file to upload into the database.

• gotoLast() moves to the last record in the buffer.

• insertAfter() inserts a new row after the current row, which is the last row.

• filename.setText() sets the File Name text field to the user-specified name obtained from the dialog. (filename has previously been bound to a field in the database.)

• lblFilePath.setText() sets the invisible label to the file path that is also obtained from the dialog. This path is used for uploading the file contents into the database.

• updateRows() updates the database rows. This sets the file name and file description. When creating a new record in the database, always call updateRows() before calling upload().

• Verify if the Delete local copy when saving file check box is selected. If it is, upload the file contents to the database, then delete the local file. Set the second argument in upload() to true to delete the local file after upload; set it to false otherwise.

Downloading content from the database as a file   

The following code downloads field contents from the database. It creates a user-specified file from the content and runs it using the appropriate executable.

  private void handle_btnEdit_actionPerformed(ActionEvent evt) 
  { 
   
   
  File fileDownload = new File(filename.getText()); 
   
  try 
  { 
     attachFile.download(fileDownload, true); 
     lblFilePath.setText(fileDownload.getPath()); 
     m_bFileChanged = true; 
  } 
  catch (Exception e) 
  { 
     e.printStackTrace(); 
     agDialog.displayError("Error downloading file", e); 
  } 
  } 

Notes about the code

• Get the user-supplied file name from the File Name text box and create a file with that name. The downloaded content will take on this file name.

• Download the content from the database to the local file system and run the created file. The second argument, if set to true, specifies to run the file after downloading it. download() automatically finds the appropriate executable (such as MSWord or MSExcel) to run the file.

• Set the file path as a text in the invisible label. If the user did not specify a path in the File Name text box, the file path is, by default, the location where SilverStream is running.

• Set m_bFileChanged to true to specify that the file in the local file system has been changed, that is, a download has occurred. This is necessary for future save attempts. The code for saving a modified file relies on the bgFileChanged value to indicate whether the file was previously downloaded from the database. If the file was previously downloaded, its content can be saved to the database.

Saving modified content to the database   

The following code saves the content of a file to the database. The user must have previously downloaded the content of this file from the database.

  public boolean saveFileAttachment() 
  { 
  if (m_bFileChanged) 
  { 
     File fileSelected = new File(lblFilePath.getText()); 
     try 
     { 
        if (chkDelete.getState() ) 
           attachFile.upload(fileSelected, true); 
        else 
           attachFile.upload(fileSelected, false); 
        m_bFileChanged = false; 
        return true; 
     } 
     catch (Exception e) 
     { 
        agDialog.displayError(e); 
        return false; 
     } 
  } 
  else 
  { 
     agDialog.showMessage("File Upload Error",  
        "No file has been changed. There is nothing to update."); 
     return false; 
  } 
  } 

Notes about the code

• Verify if the user has previously downloaded the content. The m_bFileChanged variable is set to true when the user clicks the Edit File button.

• Create a File object using the text from the invisible label. This text indicates the file name and file path, and was set during the download. (The path might be the default path, that is, where SilverStream is running. This is the case if the user did not specify a path during the download.)

• Upload the file contents by calling upload(). If the user sets the Delete local copy when saving file check box, the second parameter of upload() is set to true, and the method deletes the local file after the upload; otherwise, the method does not delete the local file after the upload.

  By using the file name and path from the invisible label, upload() saves the file that is in the location where the previous download occurred. Even if the user types in a different file and path, this method will upload the correct one.

• After uploading the file contents into the database, set the m_bFileChanged parameter to false. This prevents all save attempts of files that have not been preceded by a download. That is, the user can save a file only after it has downloaded it from the database.