public SocialAuthenticationToken getAuthToken(HttpServletRequest request, HttpServletResponse response) throws SocialAuthenticationRedirectException {
		String code = request.getParameter("code");
		if (!StringUtils.hasText(code)) {//参数中没有code
			OAuth2Parameters params =  new OAuth2Parameters();
			params.setRedirectUri(buildReturnToUrl(request));
			setScope(request, params);
			params.add("state", generateState(connectionFactory, request));
			addCustomParameters(params);
			//没有传入code,抛出重定向异常重定向到QQ的授权网址上去
			throw new SocialAuthenticationRedirectException(getConnectionFactory().getOAuthOperations().buildAuthenticateUrl(params));
		} else if (StringUtils.hasText(code)) {//请求参数中有code
			try {
				String returnToUrl = buildReturnToUrl(request);
				//拿到ConnectionFactory(QQConnectionFactory)和OAuthOperations(QQOAthTemplate)去换取令牌(accessToken)
				AccessGrant accessGrant = getConnectionFactory().getOAuthOperations().exchangeForAccess(code, returnToUrl, null);
				// TODO avoid API call if possible (auth using token would be fine)
				Connection<S> connection = getConnectionFactory().createConnection(accessGrant);
				return new SocialAuthenticationToken(connection, null);
			} catch (RestClientException e) {
				logger.debug("failed to exchange for access", e);
				return null;
			}
		} else {
			return null;
		}
	}

public class QQAutoConfiguration extends SocialAutoConfigurerAdapter {
    
    ...
    
    /**
    	 * 创建QQConnectionFactory
    	 * 父类的addConnectionFactories方法会将QQConnectionFactory加入到ConnectionFactoryConfigurer中
    	 * @return
    	 */
    	@Override
    	protected ConnectionFactory<?> createConnectionFactory() {
    		QQProperties qqConfig = securityProperties.getSocial().getQq();
    		return new QQConnectionFactory(qqConfig.getProviderId(), qqConfig.getAppId(), qqConfig.getAppSecret());
    	}
}

    @Override
	public void addConnectionFactories(ConnectionFactoryConfigurer configurer,
			Environment environment) {
        //这里的configurer其实就是SecurityEnabledConnectionFactoryConfigurer
		configurer.addConnectionFactory(createConnectionFactory());
	}

	protected abstract ConnectionFactory<?> createConnectionFactory();

    private SocialAuthenticationServiceRegistry registry;
	...
	public void addConnectionFactory(ConnectionFactory<?> connectionFactory) {
	    //将SocialAuthenticationService加入到SocialAuthenticationServiceRegistry中的authenticationServices集合中
		registry.addAuthenticationService(wrapAsSocialAuthenticationService(connectionFactory));
	}
	...
	private <A> SocialAuthenticationService<A> wrapAsSocialAuthenticationService(ConnectionFactory<A> cf) {
		if (cf instanceof OAuth1ConnectionFactory) {
			return new OAuth1AuthenticationService<A>((OAuth1ConnectionFactory<A>) cf);
		} else if (cf instanceof OAuth2ConnectionFactory) {
		    
		    //这里就是真正的把QQConnectionFactory注入到OAuth2AuthenticationService中
			final OAuth2AuthenticationService<A> authService = new OAuth2AuthenticationService<A>((OAuth2ConnectionFactory<A>) cf);
			authService.setDefaultScope(((OAuth2ConnectionFactory<A>) cf).getScope());
			return authService;
		}
		throw new IllegalArgumentException("The connection factory must be one of OAuth1ConnectionFactory or OAuth2ConnectionFactory");
	}

public class SpringSocialConfigurer extends SecurityConfigurerAdapter<DefaultSecurityFilterChain, HttpSecurity> {
    
    ...
    
    @Override
    	public void configure(HttpSecurity http) throws Exception {		
    		ApplicationContext applicationContext = http.getSharedObject(ApplicationContext.class);
    		UsersConnectionRepository usersConnectionRepository = getDependency(applicationContext, UsersConnectionRepository.class);
    		//从容器中获取SocialAuthenticationServiceLocator(SocialAuthenticationServiceRegistry)
    		**SocialAuthenticationServiceLocator authServiceLocator = getDependency(applicationContext, SocialAuthenticationServiceLocator.class);**
    		SocialUserDetailsService socialUsersDetailsService = getDependency(applicationContext, SocialUserDetailsService.class);
    		
    		//将从容器中获取的SocialAuthenticationServiceLocator传入SocialAuthenticationFilter构造函数
    		SocialAuthenticationFilter filter = new SocialAuthenticationFilter(
    				http.getSharedObject(AuthenticationManager.class), 
    				userIdSource != null ? userIdSource : new AuthenticationNameUserIdSource(), 
    				usersConnectionRepository, 
    				authServiceLocator);
    		
    		...
    		
    		//注册SocialAuthenticationFilter
    		http.authenticationProvider(
            				new SocialAuthenticationProvider(usersConnectionRepository, socialUsersDetailsService))
            			.addFilterBefore(postProcess(filter), AbstractPreAuthenticatedProcessingFilter.class);
}

@Configuration
public class SocialConfiguration {
    ...
    @Bean
    	public ConnectionFactoryLocator connectionFactoryLocator() {
    		if (securityEnabled) {
    			SecurityEnabledConnectionFactoryConfigurer cfConfig = new SecurityEnabledConnectionFactoryConfigurer();
    			for (SocialConfigurer socialConfigurer : socialConfigurers) {
    				socialConfigurer.addConnectionFactories(cfConfig, environment);
    			}
    			return cfConfig.getConnectionFactoryLocator();
    		} else {
    			DefaultConnectionFactoryConfigurer cfConfig = new DefaultConnectionFactoryConfigurer();
    			for (SocialConfigurer socialConfigurer : socialConfigurers) {
    				socialConfigurer.addConnectionFactories(cfConfig, environment);
    			}
    			return cfConfig.getConnectionFactoryLocator();
    		}
    	}
}

@Controller
@RequestMapping("/connect")
public class ConnectController implements InitializingBean {
    //...
    
    @RequestMapping(method=RequestMethod.GET)
    	public String connectionStatus(NativeWebRequest request, Model model) {
    		setNoCache(request);
    		processFlash(request, model);
    		Map<String, List<Connection<?>>> connections = connectionRepository.findAllConnections();
    		model.addAttribute("providerIds", connectionFactoryLocator.registeredProviderIds());		
    		model.addAttribute("connectionMap", connections);
    		//返回connect/status的视图
    		return connectView();
    	}
}

/**
 * 接收绑定信息的视图
 */
@Component("connect/status")
public class ImoocConnectionStatusView extends AbstractView {
	
	@Autowired
	private ObjectMapper objectMapper;

	@SuppressWarnings("unchecked")
	@Override
	protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		
		Map<String, List<Connection<?>>> connections = (Map<String, List<Connection<?>>>) model.get("connectionMap");
		
		Map<String, Boolean> result = new HashMap<>();
		for (String key : connections.keySet()) {
			result.put(key, CollectionUtils.isNotEmpty(connections.get(key)));
		}
		
		response.setContentType("application/json;charset=UTF-8");
		response.getWriter().write(objectMapper.writeValueAsString(result));
	}
}

@Controller
@RequestMapping("/connect")
public class ConnectController implements InitializingBean {
   
    //...
   
    @RequestMapping(value="/{providerId}", method=RequestMethod.GET)
    	public String connectionStatus(@PathVariable String providerId, NativeWebRequest request, Model model) {
    		setNoCache(request);
    		processFlash(request, model);
    		List<Connection<?>> connections = connectionRepository.findConnections(providerId);
    		setNoCache(request);
    		if (connections.isEmpty()) {
    			return connectView(providerId); 
    		} else {
    			model.addAttribute("connections", connections);
    			return connectedView(providerId);			
    		}
    	}
    	
    	//...
}