GridBagLayout with JScrollPane difficulties

Question

I'm having problems getting the components in a JPanel to layout properly. I'm using GridBagLayout and I'm having problems with adding a JScollPane.
The JScrollPane in the layout (holding a subclass of a JPanel as its viewport) does not work properly in some case. When the viewport won't display fully, and requires scroll bars, the JScrollPane shrinks to a tiny size (i think just enough to display minimized scroll bars). What do I mean to add to fix this problem?
Here is the relavent code:
public ScenePanel()
     SceneImagePanel sceneImagePanel = new SceneImagePanel("Images/library.jpg");
     JScrollPane sceneScroller = new JScrollPane(sceneImagePanel);
     GridBagLayout gridbag = new GridBagLayout();
     GridBagConstraints c = new GridBagConstraints();
     this.setLayout(gridbag);
     c.insets = new Insets(5,5,5,5);
     JButton b1 = new JButton("Left");
     c.anchor = GridBagConstraints.WEST;
     c.fill = GridBagConstraints.VERTICAL;
     c.gridx = 0;
     c.gridy = 0;
     c.gridwidth = 5;
     c.gridheight = 5;
     c.weightx = 0.5;
     c.weighty = 0.5;
     gridbag.setConstraints(b1, c);
     this.add(b1);
     c.anchor = GridBagConstraints.CENTER;
     c.fill = GridBagConstraints.NONE;
     c.gridx = 5;
     c.gridwidth = 10;
     c.weightx = 0.0;
     c.weighty = 0.0;
     gridbag.setConstraints(sceneScroller, c);
     this.add(sceneScroller);
     JButton b2 = new JButton("Right");
     c.anchor = GridBagConstraints.EAST;
     c.fill = GridBagConstraints.VERTICAL;
     c.gridx = 15;
     c.gridwidth = 5;
     c.weightx = 0.5;
     c.weighty = 0.5;
     gridbag.setConstraints(b2, c);
     this.add(b2);
     JButton b3 = new JButton("Bottom");
     c.anchor = GridBagConstraints.SOUTH;
     c.fill = GridBagConstraints.HORIZONTAL;
     c.gridwidth = 20;
     c.gridx = 0;
     c.gridy = 5;
     c.weighty = -0.5;
     gridbag.setConstraints(b3, c);
     this.add(b3);
//          this.add(sceneScroller, BorderLayout.CENTER);
}Note: the commented out line at the end displayed the JScrollPane properly (though I want the scroll pane to be sized to fit its viewport, not its container, so I stopped using BorderLayout)

Answer 1

Alright, I've figured out why the JScrollPane gets shrunk to such a small size...the 'fill' paramenter of the constraint can't be set to NONE. I've set it to 'BOTH' and changed the other constraints of some other components to fit.
The problem now is that the scroll pane is too big...the scroll pane does not need to actually have either scroll bar in all cases. To accomidate these situations, I want the scroll pane to only be as large as it needs to be to display as much of its viewport is possible. Meaning, if the viewport does not need the scroll pane to take up as much room as is avaliable to it in the JPanel, the scroll pane should only be as large as needed, and leave empty space around it.
Here is what I have now:
GridBagLayout gridbag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
this.setLayout(gridbag);
c.insets = new Insets(5,5,5,5);
JButton b1 = new JButton("Left");
c.anchor = GridBagConstraints.WEST;
c.fill = GridBagConstraints.VERTICAL;
c.gridx = 0;
c.gridy = 0;
c.gridwidth = 5;
c.gridheight = 5;
c.weightx = -0.5;
c.weighty = 0.5;
gridbag.setConstraints(b1, c);
this.add(b1);
c.anchor = GridBagConstraints.CENTER;
c.fill = GridBagConstraints.BOTH;
c.gridx = 5;
c.gridwidth = 10;
c.weightx = 0.5;
gridbag.setConstraints(sceneScroller, c);
this.add(sceneScroller);
JButton b2 = new JButton("Right");
c.anchor = GridBagConstraints.EAST;
c.fill = GridBagConstraints.VERTICAL;
c.gridx = 15;
c.gridwidth = 5;
c.weightx = -0.5;
c.weighty = 0.5;
gridbag.setConstraints(b2, c);
this.add(b2);
JButton b3 = new JButton("Bottom");
c.anchor = GridBagConstraints.SOUTH;
c.fill = GridBagConstraints.HORIZONTAL;
c.gridwidth = 20;
c.gridx = 0;
c.gridy = 5;
c.weighty = -0.5;
gridbag.setConstraints(b3, c);
this.add(b3);