Reading the remark of Kleopatra (her 2nd time she suggested to have a look at javax.swing.JXTable, and now I Am sorry I didn't have a look the first time :) )
I suggest you follow the link
I had this solution for the same problem: (but I suggest you follow the link above)
On resize the table, scale the table column widths to the current table total width.
to do this I use a global array of ints for the (relative) column widths):
private int[] columnWidths=null;
I use this function to set the table column widths:
public void setColumnWidths(int[] widths){
    int nrCols=table.getModel().getColumnCount();
    if(nrCols==0||widths==null){
        return;
    }
    this.columnWidths=widths.clone();
    //current width of the table:
    int totalWidth=table.getWidth();
    
    int totalWidthRequested=0;
    int nrRequestedWidths=columnWidths.length;
    int defaultWidth=(int)Math.floor((double)totalWidth/(double)nrCols);
    for(int col=0;col<nrCols;col++){
        int width = 0;
        if(columnWidths.length>col){
            width=columnWidths[col];
        }
        totalWidthRequested+=width;
    }
    //Note: for the not defined columns: use the defaultWidth
    if(nrRequestedWidths<nrCols){
        log.fine("Setting column widths: nr of columns do not match column widths requested");
        totalWidthRequested+=((nrCols-nrRequestedWidths)*defaultWidth);
    }
    //calculate the scale for the column width
    double factor=(double)totalWidth/(double)totalWidthRequested;
    for(int col=0;col<nrCols;col++){
        int width = defaultWidth;
        if(columnWidths.length>col){
            //scale the requested width to the current table width
            width=(int)Math.floor(factor*(double)columnWidths[col]);
        }
        table.getColumnModel().getColumn(col).setPreferredWidth(width);
        table.getColumnModel().getColumn(col).setWidth(width);
    }
    
}
When setting the data I call:
    setColumnWidths(this.columnWidths);
and on changing I call the ComponentListener set to the parent of the table (in my case the JScrollPane that is the container of my table):
public void componentResized(ComponentEvent componentEvent) {
    this.setColumnWidths(this.columnWidths);
}
note that the JTable table is also global:
private JTable table;
And here I set the listener:
    scrollPane=new JScrollPane(table);
    scrollPane.addComponentListener(this);