button - Render A Button Input Field
Renders an HTML <input> element of type button, populated from the specified value or the content of this tag body. This tag is only valid when nested inside a form tag body.
If a graphical button is needed (a button with an image), then the image tag is more appropriate
上面是struts 1.2.7的User and Developer Guides,看样子就是用image实现了,自己在onclick里submit吧