What is purpouse of GWT browser plug-in? Please help me to understand. And why browser can receive Java object from server? Gwt technologyy must work without plugins.
GWT browser plugin is only for development mode to allow JAVA/GWT Developers to debug code.
Once GWT code is compiled in javascript and deployed into production webserver the browser plugin is not required. So users of your gwt website need not install any gwt plugin in their browser.
Dev Mode -http://www.gwtproject.org/doc/latest/DevGuideCompilingAndDebugging.html#DevGuideDevMode
Production Mode - http://www.gwtproject.org/doc/latest/DevGuideDeploying.html