在修改数据时需要回显数据。
UserBean代码:

java">public class User {

    private Long id;
    private String username;
    private String email;
    private String password;
    private String phoneNum;
    private List<Role> roles; //复选框
	......

后台Java代码：

java">@RequestMapping("/alterUI/{userId}")
    public ModelAndView alterUI(@PathVariable Long userId, ModelAndView modelAndView){
        User user = userService.findUserByUserId(userId);
        List<Role> roleList = roleService.list();
        List<String> roleNames=new ArrayList<String>();
        for (Role role : user.getRoles()) {
            String roleName = role.getRoleName();
            roleNames.add(roleName);
        }

        modelAndView.addObject("roleList",roleList);
        modelAndView.addObject("roleNames",roleNames);
        modelAndView.addObject("user",user);

        modelAndView.setViewName("user-alter");
        return modelAndView;
    }

导入JSP标签库：

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

JSP实现:
先从数据库中查出所有复选框，再对每个复选框进行判断是否被选中，即roleNames数组中包含即被选中。

<div class="col-md-10 data">
	<c:forEach items="${roleList}" var="role">
		<input class="" id="${role.id}" type="checkbox" name="roleIds" value="${role.id}" ${fn:contains(roleNames,role.roleName)?'checked':''} >${role.roleName}
	</c:forEach>
</div>