Java Tip 77: Enable copy and paste functionality between Swing's JTables and Excel

This adapter makes it easy to transfer data from one type of spreadsheet to the other

Many business applications have been developed using Java and more are in development. Many of these applications display data in a spreadsheet-like format using Swing's JTable component. It would be convenient if these business applications could import and export data to and from Microsoft Excel so that users could have access to the power of that omnipresent spreadsheet program. This Java Tip will help you understand the system clipboard and enable your JTable to interact and interoperate with Excel. As you'll see, adding this valuable functionality can be accomplished by adding just one extra line of code to your existing applications.

All you need to do to achieve this goal is copy the file ExcelAdapter.java represented here, compile it, and make sure your applications can find the ExcelAdapter.class file; once you've done that, your JTable is ready to talk with Excel! We'll show you how, with this single line of code, to enable copy (control-C) and paste (control-V) to and from Excel. A sample application using the ExcelAdapter is also provided.

The code

Here is the adapter code, called ExcelAdapter.java, that actually accomplishes this task:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.datatransfer.*;
import java.util.*;
/**
 * ExcelAdapter enables Copy-Paste Clipboard functionality on JTables.
 * The clipboard data format used by the adapter is compatible with
 * the clipboard format used by Excel. This provides for clipboard
 * interoperability between enabled JTables and Excel.
 */
public class ExcelAdapter implements ActionListener
   {
   private String rowstring,value;
   private Clipboard system;
   private StringSelection stsel;
   private JTable jTable1 ;
   /**
    * The Excel Adapter is constructed with a
    * JTable on which it enables Copy-Paste and acts
    * as a Clipboard listener.
    */
public ExcelAdapter(JTable myJTable)
   {
      jTable1 = myJTable;
      KeyStroke copy = KeyStroke.getKeyStroke(KeyEvent.VK_C,ActionEvent.CTRL_MASK,false);
      // Identifying the copy KeyStroke user can modify this
      // to copy on some other Key combination.
      KeyStroke paste = KeyStroke.getKeyStroke(KeyEvent.VK_V,ActionEvent.CTRL_MASK,false);
      // Identifying the Paste KeyStroke user can modify this
      //to copy on some other Key combination.
jTable1.registerKeyboardAction(this,"Copy",copy,JComponent.WHEN_FOCUSED);
jTable1.registerKeyboardAction(this,"Paste",paste,JComponent.WHEN_FOCUSED);
      system = Toolkit.getDefaultToolkit().getSystemClipboard();
   }
   /**
    * Public Accessor methods for the Table on which this adapter acts.
    */
public JTable getJTable() {return jTable1;}
public void setJTable(JTable jTable1) {this.jTable1=jTable1;}
   /**
    * This method is activated on the Keystrokes we are listening to
    * in this implementation. Here it listens for Copy and Paste ActionCommands.
    * Selections comprising non-adjacent cells result in invalid selection and
    * then copy action cannot be performed.
    * Paste is done by aligning the upper left corner of the selection with the
    * 1st element in the current selection of the JTable.
    */
public void actionPerformed(ActionEvent e)
   {
      if (e.getActionCommand().compareTo("Copy")==0)
      {
         StringBuffer sbf=new StringBuffer();
         // Check to ensure we have selected only a contiguous block of
         // cells
         int numcols=jTable1.getSelectedColumnCount();
         int numrows=jTable1.getSelectedRowCount();
         int[] rowsselected=jTable1.getSelectedRows();
         int[] colsselected=jTable1.getSelectedColumns();
         if (!((numrows-1==rowsselected[rowsselected.length-1]-rowsselected[0] &&
                numrows==rowsselected.length) &&
(numcols-1==colsselected[colsselected.length-1]-colsselected[0] &&
                numcols==colsselected.length)))
         {
            JOptionPane.showMessageDialog(null, "Invalid Copy Selection",
                                          "Invalid Copy Selection",
                                          JOptionPane.ERROR_MESSAGE);
            return;
         }
         for (int i=0;i<numrows;i++)
         {
            for (int j=0;j<numcols;j++)
            {
sbf.append(jTable1.getValueAt(rowsselected[i],colsselected[j]));
               if (j<numcols-1) sbf.append("\t");
            }
            sbf.append("\n");
         }
         stsel  = new StringSelection(sbf.toString());
         system = Toolkit.getDefaultToolkit().getSystemClipboard();
         system.setContents(stsel,stsel);
      }
      if (e.getActionCommand().compareTo("Paste")==0)
      {
          System.out.println("Trying to Paste");
          int startRow=(jTable1.getSelectedRows())[0];
          int startCol=(jTable1.getSelectedColumns())[0];
          try
          {
             String trstring= (String)(system.getContents(this).getTransferData(DataFlavor.stringFlavor));
             System.out.println("String is:"+trstring);
             StringTokenizer st1=new StringTokenizer(trstring,"\n");
             for(int i=0;st1.hasMoreTokens();i++)
             {
                rowstring=st1.nextToken();
                StringTokenizer st2=new StringTokenizer(rowstring,"\t");
                for(int j=0;st2.hasMoreTokens();j++)
                {
                   value=(String)st2.nextToken();
                   if (startRow+i< jTable1.getRowCount()  &&
                       startCol+j< jTable1.getColumnCount())
                      jTable1.setValueAt(value,startRow+i,startCol+j);
                   System.out.println("Putting "+ value+"at
row="+startRow+i+"column="+startCol+j);
               }
            }
         }
         catch(Exception ex){ex.printStackTrace();}
      }
   }
}

A sample application

Here is a sample application, Frame1.java, that uses the ExcelAdapter to make a JTable Excel-compatible.

import java.awt.*;
import javax.swing.*;
public class Frame1 extends Frame
   {
   BorderLayout borderLayout1 = new BorderLayout();
   JTable jTable1 ;
   Object[][] data=new Object[4][4];
   Object header[]= {"Jan","Feb","Mar","Apr"};
public static void main(String args[])
   {
   Frame1 myframe=new Frame1();
   myframe.setSize(new Dimension(250,250));
   myframe.setVisible(true);
   }
public Frame1()
   {
      super();
      try
      {
         jbInit();
      }
      catch (Exception e)
      {
         e.printStackTrace();
      }
   }
private void jbInit() throws Exception
   {
   for (int i=0;i<4;i++)
      for (int j=0;j<4;j++)
         data[i][j]=new Integer(i*10+j);
   System.out.println("Header length="+header[1]);
   jTable1=new JTable(data,header);
   jTable1.setCellSelectionEnabled(true);
   this.setTitle("Excel Lent JTABLE");
   jTable1.setBackground(Color.pink);
   this.setLayout(borderLayout1);
   this.setSize(new Dimension(400, 300));
   this.setBackground(Color.white);
   this.add(jTable1, BorderLayout.CENTER);
   // This is the line that does all the magic!
   ExcelAdapter myAd = new ExcelAdapter(jTable1);
   }
}

Excel's clipboard format

Excel has a very simple clipboard format. It separates elements on the same row with tabs and separates rows with newline characters. So, when you copy a set of contiguous and/or adjacent cells, Excel simply tokenizes the spreadsheet data into one long string, with the individual cell values separated by tabs and newlines within that string. What if the cells selected are not adjacent? Simple: Excel will not let you copy your selection to the clipboard. This behavior is mimicked by the adapter described here, which will also not let you copy data if the cells selected are not adjacent. In Excel, a dialog box pops up to tell us that you have not been permitted to copy; again, this behavior is mimicked by the adapter.

A brief explanation of the code

To use this feature, you need to download the ExcelAdapter.java file, compile it, and add the last line from the sample application to your code somewhere in order to activate the adapter on the JTable.

Within the adapter, the activating keystrokes for both copy and paste functions are registered. Thereafter, any time the activating key is typed, the actionPerformed method is called. If it is the copy action, then the selected cells' data are tokenized appropriately for Excel and written to the system clipboard. If the action is paste, then the data within the system clipboard are converted to its string flavor and parsed to populate the JTable cells, depending on which cell is selected.

Conclusion

Users of tables written in Java often want to be able to do something familiar in Excel with the data from JTables. Instead of writing code to enable copy-paste functionality on each JTable, it is much simpler to write a generic adapter that brings the desired functionality to every JTable with just one line of additional code. The adapter presented in this Java Tip does just that.

Ashok Banerjee and Jignesh Mehta are both currently working with Oracle Corporation on manufacturing applications. They have been using Java for around two years.

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