// 通過SPI方式導入實現(xiàn)類：
// META-INF/services/javax.servlet.ServletContainerInitializer 
public interface ServletContainerInitializer {
	/** 
	* Receives notification during startup of a web application of the classes within the web application 
	* that matched the criteria defined via the annotation:
	* javax.servlet.annotation.HandlesTypes 
	* 
	* 處理javax.servlet.annotation.HandlesTypes注解標注類型的實現(xiàn)類
	**/
    void onStartup(Set<Class<?>> c, ServletContext ctx) throws ServletException;
}

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
	@Override
	public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
			throws ServletException {
		List<WebApplicationInitializer> initializers = Collections.emptyList();
		...
		// 添加
		if (webAppInitializerClasses != null) {
			initializers = new ArrayList<>(webAppInitializerClasses.size());
			for (Class<?> waiClass : webAppInitializerClasses) {
						initializers.add((WebApplicationInitializer)
								ReflectionUtils.accessibleConstructor(waiClass).newInstance());
			}
		}
		...
		// 排序
		AnnotationAwareOrderComparator.sort(initializers);
		// 執(zhí)行
		for (WebApplicationInitializer initializer : initializers) {
			initializer.onStartup(servletContext);
		}
	}
}

public abstract class AbstractSecurityWebApplicationInitializer implements WebApplicationInitializer {
	public static final String DEFAULT_FILTER_NAME = "springSecurityFilterChain";
	...
	@Override
	public final void onStartup(ServletContext servletContext) {
		beforeSpringSecurityFilterChain(servletContext);
		...
		insertSpringSecurityFilterChain(servletContext);
		afterSpringSecurityFilterChain(servletContext);
	}
	...
}

/**
 * 不同于WebApplicationInitializer，實現(xiàn)該接口的類（且沒有實現(xiàn)WebApplicationInitializer）
 * 不會被SpringServletContainerInitializer檢測到，所以不會由servlet容器自動啟動。
 * 該類的目的和ServletContainerInitializer一樣，但是 其中的Servlet的生命周期由Spring控制而不是Servlet容器。
 */
@FunctionalInterface
public interface ServletContextInitializer {
	void onStartup(ServletContext servletContext) throws ServletException;
}

@AutoConfiguration(after = SecurityAutoConfiguration.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(SecurityProperties.class)
@ConditionalOnClass({ AbstractSecurityWebApplicationInitializer.class, SessionCreationPolicy.class })
public class SecurityFilterAutoConfiguration {
	// DEFAULT_FILETER_NAME = "springSecurityFilterChain"
	private static final String DEFAULT_FILTER_NAME = AbstractSecurityWebApplicationInitializer.DEFAULT_FILTER_NAME;
	// 必須存在名稱為springSecurityFilterChain的bean
	// 名稱為springSecurityFilterChain的bean實際上類型即是 org.springframework.security.web.FilterChainProxy
	@Bean
	@ConditionalOnBean(name = DEFAULT_FILTER_NAME)
	public DelegatingFilterProxyRegistrationBean securityFilterChainRegistration(
			SecurityProperties securityProperties) {
		DelegatingFilterProxyRegistrationBean registration = new DelegatingFilterProxyRegistrationBean(
				DEFAULT_FILTER_NAME);
		registration.setOrder(securityProperties.getFilter().getOrder());
		registration.setDispatcherTypes(getDispatcherTypes(securityProperties));
		return registration;
	}
	...
}

public class DelegatingFilterProxyRegistrationBean ... {
	...
	@Override
	public DelegatingFilterProxy getFilter() {
		// 創(chuàng)建真正的代理(匿名子類)，并具有延遲加載的能力
		return new DelegatingFilterProxy(this.targetBeanName, getWebApplicationContext()) {
			@Override
			protected void initFilterBean() throws ServletException {
				// Don't initialize filter bean on init()
			}
		};
	}
	...
}

public class DelegatingFilterProxy extends GenericFilterBean {
	// 就是 springSecurityFilterChain，代表FilterChainProxy的beanName
	@Nullable
	private String targetBeanName;
	// 代理的FilterChainProxy
	@Nullable
	private volatile Filter delegate;
	...
	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {
		// Lazily initialize the delegate if necessary.
		Filter delegateToUse = this.delegate;
		if (delegateToUse == null) {
			synchronized (this.delegateMonitor) {
				delegateToUse = this.delegate;
				if (delegateToUse == null) {
					...
					// 初始化代理類
					delegateToUse = initDelegate(wac);
				}
				this.delegate = delegateToUse;
			}
		}
		// Let the delegate perform the actual doFilter operation.
		invokeDelegate(delegateToUse, request, response, filterChain);
	}
	...
	protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
		String targetBeanName = getTargetBeanName();
		// 容器中獲取名稱為springSecurityFilterChain 類型為Filter的bean
		// 即 FilterChainProxy
		// 所以 注冊 DelegatingFilterProxyRegistrationBean 時必須有 @ConditionalOnBean(name="springSecurityFilterChain")
		Filter delegate = wac.getBean(targetBeanName, Filter.class);
		...
		return delegate;
	}
}

@Configuration(proxyBeanMethods = false)
public class WebSecurityConfiguration implements ImportAware, BeanClassLoaderAware {
	...
	private WebSecurity webSecurity;
	// 多個SecurityFilterChain
	private List<SecurityFilterChain> securityFilterChains = Collections.emptyList();
	// 多個WebSecurityCustomizer
	private List<WebSecurityCustomizer> webSecurityCustomizers = Collections.emptyList();
	...
	// 注入一個Filter,指定名稱為springSecurityFilterChain
	@Bean(name = AbstractSecurityWebApplicationInitializer.DEFAULT_FILTER_NAME)
	public Filter springSecurityFilterChain() throws Exception {
		...
		for (SecurityFilterChain securityFilterChain : this.securityFilterChains) {
			this.webSecurity.addSecurityFilterChainBuilder(() -> securityFilterChain);
			// 為每個SecurityFilterChain中的每個Filter添加攔截方法
			for (Filter filter : securityFilterChain.getFilters()) {
				if (filter instanceof FilterSecurityInterceptor) {
					this.webSecurity.securityInterceptor((FilterSecurityInterceptor) filter);
					break;
				}
			}
		}
		// 自定義器對每個SecurityFilterChain均生效
		for (WebSecurityCustomizer customizer : this.webSecurityCustomizers) {
			customizer.customize(this.webSecurity);
		}
		// 這里build()方法返回  org.springframework.security.web.FilterChainProxy
		return this.webSecurity.build();
	}
	...
	// 自動注入, 通常我們需要自定義的就是這個SecurityFilterChain類型
	// 只需要在業(yè)務(wù)配置類中注冊一個SecurityFilterChain類型的bean就能被注入到這里
	@Autowired(required = false)
	void setFilterChains(List<SecurityFilterChain> securityFilterChains) {
		this.securityFilterChains = securityFilterChains;
	}
	// 自動注入
	@Autowired(required = false)
	void setWebSecurityCustomizers(List<WebSecurityCustomizer> webSecurityCustomizers) {
		this.webSecurityCustomizers = webSecurityCustomizers;
	}
}

@Configuration
public class SecurityConfig {
	@Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http.csrf().disable();
        // 必須顯式注明，配合CorsConfigurationSource的Bean，不然即使在web里面配置了跨域，security這里依然會cors error
        http.cors();
        http.authorizeRequests()
                .antMatchers(AUTH_WHITELIST).permitAll()
                .anyRequest().authenticated();
        http.formLogin().successHandler(loginSuccessHandler);
        http.oauth2Login().successHandler(giteeSuccessHandler);
        http.exceptionHandling().accessDeniedHandler(restAccessDeniedHandler);
        http.addFilterBefore(bearAuthenticationFilter, UsernamePasswordAuthenticationFilter.class);
        return http.build();
    }
	@Bean
    public WebSecurityCustomizer webSecurityCustomizer() {
        return (web) -> web.ignoring().antMatchers("/ignore1", "/ignore2");
    }
}

public class FilterChainProxy extends GenericFilterBean {
	private List<SecurityFilterChain> filterChains;
	private HttpFirewall firewall = new StrictHttpFirewall();
	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		...
		doFilterInternal(request, response, chain);
		...
	}
	private void doFilterInternal(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		// 轉(zhuǎn)化為org.springframework.security.web.firewall.FirewalledRequest
		// reject potentially dangerous requests and/or wrap them to control their behaviour.
		FirewalledRequest firewallRequest = this.firewall.getFirewalledRequest((HttpServletRequest) request);
		HttpServletResponse firewallResponse = this.firewall.getFirewalledResponse((HttpServletResponse) response);
		// #getFilters會在所有SecurityFilterChain中進行匹配
		List<Filter> filters = getFilters(firewallRequest);
		...
		// 轉(zhuǎn)化為 VirtualFilterChain
		// VirtualFilterChain是FilterChainProxy內(nèi)部靜態(tài)類
		VirtualFilterChain virtualFilterChain = new VirtualFilterChain(firewallRequest, chain, filters);
		// 開啟 SecurityFilterChain中所有filter過程
		virtualFilterChain.doFilter(firewallRequest, firewallResponse);
	}
	private List<Filter> getFilters(HttpServletRequest request) {
		for (SecurityFilterChain chain : this.filterChains) {
			// 返回第一個符合規(guī)則的SecurityFilterChain
			if (chain.matches(request)) {
				return chain.getFilters();
			}
		}
		return null;
	}
	/**
	 * 執(zhí)行額外的 filters，控制filters執(zhí)行過程
	 * Internal {@code FilterChain} implementation that is used to pass a request through
	 * the additional internal list of filters which match the request.
	 */
	private static final class VirtualFilterChain implements FilterChain {
		...
		private final FilterChain originalChain;
		private final List<Filter> additionalFilters;
		private final FirewalledRequest firewalledRequest;
		// 該SecurityFilterChain中所有filter的數(shù)量
		private final int size;
		// 當前filter的位置
		private int currentPosition = 0;
		...
		@Override
		public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
			if (this.currentPosition == this.size) {
				// 執(zhí)行完畢
				// Deactivate path stripping as we exit the security filter chain
				this.firewalledRequest.reset();
				this.originalChain.doFilter(request, response);
				return;
			}
			// 繼續(xù)執(zhí)行filterChain中下一個filter
			this.currentPosition++;
			Filter nextFilter = this.additionalFilters.get(this.currentPosition - 1);
			nextFilter.doFilter(request, response, this);
		}
		...
	}
	...
}