applet显示tree的问题

用applet动态创建tree结构（代码如下），在applet viewer中能正确显示，但在浏览器中却不能显示树结构内容。把创建tree的代码放在try{ }外，显示一个静态的tree又没有问题，不知道什么原因？String url="jdbc:mysql:///schema";
String sql="SELECT * FROM table1";
try {
            
        Class.forName("org.gjt.mm.mysql.Driver");
        System.out.println("Successfully loading MySQL Driver!");
        Connection con1=DriverManager.getConnection(url,"user","pwd");
        Statement stmt1=con1.createStatement();
        ResultSet rs1=stmt1.executeQuery(sql);              
        while(rs1.next())
            {            
                String id=rs1.getString("id");
                String name=rs1.getString("name");
                String tag=rs1.getString("tag");
               
      DefaultMutableTreeNode root = new DefaultMutableTreeNode(id);
               component = new DefaultMutableTreeNode(tag);
               root.add(component);
               JTree tree = new JTree(root);      
               contentPane.add(new JScrollPane(tree));
            }
            rs1.close();
            stmt1.close();
            con1.close();
        catch(Exception e)
        {
            e.printStackTrace();
        }