public class DelegatingFilterProxy extends GenericFilterBean {
@Nullable
private String contextAttribute;
@Nullable
private WebApplicationContext webApplicationContext;
@Nullable
private String targetBeanName;
private boolean targetFilterLifecycle;
@Nullable
private volatile Filter delegate;//注：这个过滤器才是真正加载的过滤器
private final Object delegateMonitor;
//注：doFilter才是过滤器的入口，直接从这看！
public void doFilter(ServletRequest request, ServletResponse response, FilterChain
filterChain) throws ServletException, IOException {
Filter delegateToUse = this.delegate;
if (delegateToUse == null) {
synchronized(this.delegateMonitor) {
delegateToUse = this.delegate;
if (delegateToUse == null) {
WebApplicationContext wac = this.findWebApplicationContext();
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: no
ContextLoaderListener or DispatcherServlet registered?");
}
//第一步：doFilter中最重要的一步，初始化上面私有过滤器属性delegate
delegateToUse = this.initDelegate(wac);
}
this.delegate = delegateToUse;
}
}
//第三步：执行FilterChainProxy过滤器
this.invokeDelegate(delegateToUse, request, response, filterChain);
}
//第二步：直接看最终加载的过滤器到底是谁
protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
//debug得知targetBeanName为：springSecurityFilterChain
String targetBeanName = this.getTargetBeanName();
Assert.state(targetBeanName != null, "No target bean name set");
//debug得知delegate对象为：FilterChainProxy
Filter delegate = (Filter)wac.getBean(targetBeanName, Filter.class);
if (this.isTargetFilterLifecycle()) {
delegate.init(this.getFilterConfig());
}
return delegate;
}
protected void invokeDelegate(Filter delegate, ServletRequest request, ServletResponse
response, FilterChain filterChain) throws ServletException, IOException {
delegate.doFilter(request, response, filterChain);
}
}

public class FilterChainProxy extends GenericFilterBean {
private static final Log logger = LogFactory.getLog(FilterChainProxy.class);
private static final String FILTER_APPLIED =
FilterChainProxy.class.getName().concat(".APPLIED");
private List filterChains;
private FilterChainProxy.FilterChainValidator filterChainValidator;
private HttpFirewall firewall;
//咿！？可以通过一个叫SecurityFilterChain的对象实例化出一个FilterChainProxy对象
//这FilterChainProxy又是何方神圣？会不会是真正的过滤器链对象呢？先留着这个疑问！
public FilterChainProxy(SecurityFilterChain chain) {
this(Arrays.asList(chain));
}
//又是SecurityFilterChain这家伙！嫌疑更大了！
public FilterChainProxy(List filterChains) {
this.filterChainValidator = new FilterChainProxy.NullFilterChainValidator();
this.firewall = new StrictHttpFirewall();
this.filterChains = filterChains;
}
//注：直接从doFilter看
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
boolean clearContext = request.getAttribute(FILTER_APPLIED) == null;
if (clearContext) {
try {
request.setAttribute(FILTER_APPLIED, Boolean.TRUE);
this.doFilterInternal(request, response, chain);
} finally {
SecurityContextHolder.clearContext();
request.removeAttribute(FILTER_APPLIED);
}
} else {
//第一步：具体操作调用下面的doFilterInternal方法了
this.doFilterInternal(request, response, chain);
}
}
private void doFilterInternal(ServletRequest request, ServletResponse response, FilterChain
chain) throws IOException, ServletException {
FirewalledRequest fwRequest =
this.firewall.getFirewalledRequest((HttpServletRequest)request);
HttpServletResponse fwResponse =
this.firewall.getFirewalledResponse((HttpServletResponse)response);
//第二步：封装要执行的过滤器链，那么多过滤器就在这里被封装进去了！
List filters = this.getFilters((HttpServletRequest)fwRequest);
if (filters != null && filters.size() != 0) {
FilterChainProxy.VirtualFilterChain vfc = new
FilterChainProxy.VirtualFilterChain(fwRequest, chain, filters);
//第四步：加载过滤器链
vfc.doFilter(fwRequest, fwResponse);
} else {
if (logger.isDebugEnabled()) {
logger.debug(UrlUtils.buildRequestUrl(fwRequest) + (filters == null ? " has no
matching filters" : " has an empty filter list"));
}
fwRequest.reset();
chain.doFilter(fwRequest, fwResponse);
}
}
private List getFilters(HttpServletRequest request) {
Iterator var2 = this.filterChains.iterator();
//第三步：封装过滤器链到SecurityFilterChain中！
SecurityFilterChain chain;
do {
if (!var2.hasNext()) {
return null;
}
chain = (SecurityFilterChain)var2.next();
} while(!chain.matches(request));
return chain.getFilters();
}
}

public interface SecurityFilterChain {
  boolean matches(HttpServletRequest request);
  List getFilters();
}

public final class DefaultSecurityFilterChain implements SecurityFilterChain {
  private static final Log logger = LogFactory.getLog(DefaultSecurityFilterChain.class);
  private final RequestMatcher requestMatcher;
  private final List filters;

  public DefaultSecurityFilterChain(RequestMatcher requestMatcher, Filter... filters) {
    this(requestMatcher, Arrays.asList(filters));
  }

  public DefaultSecurityFilterChain(RequestMatcher requestMatcher, List filters) {
    logger.info("Creating filter chain: " + requestMatcher + ", " + filters);
    this.requestMatcher = requestMatcher;
    this.filters = new ArrayList<>(filters);
  }

  public RequestMatcher getRequestMatcher() {
    return requestMatcher;
  }

  public List getFilters() {
    return filters;
  }

  public boolean matches(HttpServletRequest request) {
    return requestMatcher.matches(request);
  }

  @Override
  public String toString() {
    return "[ " + requestMatcher + ", " + filters + "]";
  }
}