我几天前开始学习 Spring 安全。在两个教程中发现了相同的代码，我不确定它是如何工作的。我意识到这只是简单的java，但我似乎不理解它。

public Set<SimpleGrantedAuthority> getGrantedAuthority(){
        Set<SimpleGrantedAuthority> permissions = getPermissions().stream()
                .map(permission -> new SimpleGrantedAuthority(permission.getPermission()))
                .collect(Collectors.toSet());
        permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name()));
        return permissions;
    }

根据我对代码的理解，使用stream（）我用simplegrantedauthority对象填充集合，这很好，但是这行是怎么工作的呢 permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name())); ? 整个方法应该只返回给定角色的权限，但我不知道如何在返回的方法中只返回几个正确的权限。
方法调用：

protected UserDetailsService userDetailsService() {
        UserDetails annaS = User.builder()
                .username("annasmith")
                .password(passwordEncoder.encode("password"))
                .authorities(STUDENT.getGrantedAuthority())
                .build();
}

角色枚举：

public enum ApplicationUserRole {
    STUDENT(Sets.newHashSet()),
    ADMIN(Sets.newHashSet(COURSE_READ,COURSE_WRITE, STUDENT_WRITE, STUDENT_READ)),
    ADMINTRAINEE(Sets.newHashSet(COURSE_READ,STUDENT_READ));
    private final Set<ApplicationUserPermission> permissions;
    ApplicationUserRole(Set<ApplicationUserPermission> permissions) {
        this.permissions = permissions;
    }
    public Set<ApplicationUserPermission> getPermissions() {
        return permissions;
    }
    public Set<SimpleGrantedAuthority> getGrantedAuthority(){
        Set<SimpleGrantedAuthority> permissions = getPermissions().stream()
                .map(permission -> new SimpleGrantedAuthority(permission.getPermission()))
                .collect(Collectors.toSet());
        permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name()));
        return permissions;
    } 
}

权限枚举：

public enum ApplicationUserPermission {
    STUDENT_READ("student:read"),
    STUDENT_WRITE("student:write"),
    COURSE_READ("course:read"),
    COURSE_WRITE("course:write");
    private final String permission;
    ApplicationUserPermission(String permission) {
        this.permission = permission;
    }
    public String getPermission() {
        return permission;
    }
}

如果有什么需要分析的话，如果有人能给我详细解释一下，我将不胜感激。