class OpenAction extends AbstractAction{
    public OpenAction(){
        super("打开",new ImageIcon("open.jpg"));
    }

    public void actionPerformed(ActionEvent e){
        ...
    }
}

JToolBar toolbar = new JToolBar();
toolbar.add(new OpenAction());

------解决方案--------------------
public void setVerticalAlignment(int alignment)设置图标和文本的垂直对齐方式。