How to populate multiple beans in a request using Spring @MVC

Question 1

If you give Person a reference of Department then it will be easy. In your app, if the person works in a department it will be logical to create a Has-A relationship in your Person class like this:

@Component
@Scope("prototype")
public class Person {
    private String firstName;

    private Department department;

    public Department getDepartment() {
        return department;
    }
    public void setDepartment(Department department) {
        this.department = department;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
}

You can create a Controller that gets a Person bean from the Context and renders a view.

@Controller
public class TestController implements ApplicationContextAware{

    private ApplicationContext appContext;

    @RequestMapping(value="/handleGet",method=RequestMethod.GET)
    public String handleGet(ModelMap map){
        map.addAttribute("person", appContext.getBean("person"));
        return "test";
    }
    @RequestMapping(value="/handlePost",method=RequestMethod.POST)
    public @ResponseBody String handlePost(@ModelAttribute("person") Person person){
        return person.getDepartment().getDepartmentName();
    }

    @Override
    public void setApplicationContext(ApplicationContext appContext)
            throws BeansException {
        this.appContext=appContext;
    }
}

Then inside your JSP view you can write something like this:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="sf" uri="http://www.springframework.org/tags/form" %>    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Test</title>
</head>
<body>
    <sf:form commandName="person" action="/appname/handlePost.html" method="post">
        <sf:input path="firstName"/>
        <sf:input path="department.departmentName"/>
        <sf:button name="Submit">Submit</sf:button>
    </sf:form>
</body>
</html>

Question 2

Form backing objects are not mandatory, you can use @RequestParam annotation to obtain the form values directly. See Binding request parameters to method parameters with @RequestParam on Spring Manual.

I don't think Map is a supported by the default Spring MVC type converters, but you can register a custom converter. See Customizing WebDataBinder initialization.