一、框架原理
概述
前面源码篇文章（篇尾附上链接）提到，整个框架的核心就是一个过滤器
FilterChainProxy，这个过滤器维护了一组过滤器链，真正起作用的其实是这个过滤器里的过滤器链。我们知道过滤器链可是有执行顺序的，关于它是如何排序的，本篇来聊聊。
过滤器链实战示例
先来看看一个请求进来需要走过的过滤器链有哪些，以下为前面实战篇（篇尾附上链接）中过滤器链debug截图，断点打在核心过滤器
FilterChainProxy的doFilter()上，自行走一下代码，会发现请求需要经过如下过滤器：
可以看到很多熟悉的过滤器，包括我们自己定义的两个过滤器
UserAuthenticationFilter、JwtAuthenticationFilter
二、FilterComparator
内部其实是使用这个类来对Filter的实例进行排序，以确保它们的顺序正确。
源码
final class FilterComparator implements Comparator<Filter>, Serializable {
private static final int STEP = 100;
private Map<String, Integer> filterToOrder = new HashMap<String, Integer>();
FilterComparator() {
int order = 100;
put(ChannelProcessingFilter.class, order);
order += STEP;
put(ConcurrentSessionFilter.class, order);
order += STEP;
put(WebAsyncManagerIntegrationFilter.class, order);
order += STEP;
put(SecurityContextPersistenceFilter.class, order);
order += STEP;
put(HeaderWriterFilter.class, order);
order += STEP;
put(CorsFilter.class, order);
order += STEP;
put(CsrfFilter.class, order);
order += STEP;
put(LogoutFilter.class, order);
order += STEP;
put(X509AuthenticationFilter.class, order);
order += STEP;
put(AbstractPreAuthenticatedProcessingFilter.class, order);
order += STEP;
filterToOrder.put("org.springframework.security.cas.web.CasAuthenticationFilter",
order);
order += STEP;
put(UsernamePasswordAuthenticationFilter.class, order);
order += STEP;
put(ConcurrentSessionFilter.class, order);
order += STEP;
filterToOrder.put(
"org.springframework.security.openid.OpenIDAuthenticationFilter", order);
order += STEP;
put(DefaultLoginPageGeneratingFilter.class, order);
order += STEP;
put(ConcurrentSessionFilter.class, order);
order += STEP;
put(DigestAuthenticationFilter.class, order);
order += STEP;
put(BasicAuthenticationFilter.class, order);
order += STEP;
put(RequestCacheAwareFilter.class, order);
order += STEP;
put(SecurityContextHolderAwareRequestFilter.class, order);
order += STEP;
put(JaasApiIntegrationFilter.class, order);
order += STEP;
put(RememberMeAuthenticationFilter.class, order);
order += STEP;
put(AnonymousAuthenticationFilter.class, order);
order += STEP;
put(SessionManagementFilter.class, order);
order += STEP;
put(ExceptionTranslationFilter.class, order);
order += STEP;
put(FilterSecurityInterceptor.class, order);
order += STEP;
put(SwitchUserFilter.class, order);
}
public int compare(Filter lhs, Filter rhs) {
Integer left = getOrder(lhs.getClass());
Integer right = getOrder(rhs.getClass());
return left - right;
}
/**
* Determines if a particular {@link Filter} is registered to be sorted
*
* @param filter
* @return
*/
public boolean isRegistered(Class<? extends Filter> filter) {
return getOrder(filter) != null;
}
/**
* Registers a {@link Filter} to exist after a particular {@link Filter} that is
* already registered.
* @param filter the {@link Filter} to register
* @param afterFilter the {@link Filter} that is already registered and that
* {@code filter} should be placed after.
*/
public void registerAfter(Class<? extends Filter> filter,
Class<? extends Filter> afterFilter) {
Integer position = getOrder(afterFilter);
if (position == null) {
throw new IllegalArgumentException(
"Cannot register after unregistered Filter " + afterFilter);
}
put(filter, position + 1);
}
/**
* Registers a {@link Filter} to exist at a particular {@link Filter} position
* @param filter the {@link Filter} to register
* @param atFilter the {@link Filter} that is already registered and that
* {@code filter} should be placed at.
*/
public void registerAt(Class<? extends Filter> filter,
Class<? extends Filter> atFilter) {
Integer position = getOrder(atFilter);
if (position == null) {
throw new IllegalArgumentException(
"Cannot register after unregistered Filter " + atFilter);
}
put(filter, position);
}
/**
* Registers a {@link Filter} to exist before a particular {@link Filter} that is
* already registered.
* @param filter the {@link Filter} to register
* @param beforeFilter the {@link Filter} that is already registered and that
* {@code filter} should be placed before.
*/
public void registerBefore(Class<? extends Filter> filter,
Class<? extends Filter> beforeFilter) {
Integer position = getOrder(beforeFilter);
if (position == null) {
throw new IllegalArgumentException(
"Cannot register after unregistered Filter " + beforeFilter);
}
put(filter, position - 1);
}
private void put(Class<? extends Filter> filter, int position) {
String className = filter.getName();
filterToOrder.put(className, position);
}
/**
* Gets the order of a particular {@link Filter} class taking into consideration
* superclasses.
*
* @param clazz the {@link Filter} class to determine the sort order
* @return the sort order or null if not defined
*/
private Integer getOrder(Class<?> clazz) {
while (clazz != null) {
Integer result = filterToOrder.get(clazz.getName());
if (result != null) {
return result;
}
clazz = clazz.getSuperclass();
}
return null;
}
}
说明
-
可以看到该类被实例化的时候，就将框架中存在的过滤器都设置了一个顺序值，保存在 filterToOrder。
-
该类还实现了Comparator接口，实现了它的 compare() 方法，里面是根据过滤器的顺序值进行排序的。
-
类中提供了一些给外部添加过滤器的接口，比如：
-
registerBefore(Filter filter, Filter beforeFilter)：在beforeFilter过滤器之前添加过滤器。 -
registerAfter(Filter filter, Filter afterFilter)：在afterFilter过滤器之后添加过滤器。 -
registerAt(Filter filter, Filter atFilter)：加入和atFilter过滤器相同顺序的过滤器。
自定义过滤器顺序设置
- 在登录过滤器配置UserLoginConfigurer 中配置 UserAuthenticationFilter 过滤器顺序：
@Override
public void configure(B http) throws Exception {
UserAuthenticationFilter authFilter = new UserAuthenticationFilter();
authFilter.setAuthenticationManager(http.getSharedObject(AuthenticationManager.class));
authFilter.setSessionAuthenticationStrategy(new NullAuthenticatedSessionStrategy());
// 登录成功处理器
authFilter.setAuthenticationSuccessHandler(new UserLoginSuccessHandler(securityConfig));
// 登录失败处理器
authFilter.setAuthenticationFailureHandler(new HttpStatusLoginFailureHandler());
// 拦截器位置
UserAuthenticationFilter filter = postProcess(authFilter);
http.addFilterAfter(filter, LogoutFilter.class);
}
- 点进 addFilterAfter() 方法查看，其实调用的就是 FilterComparator 中的方法：
public HttpSecurity addFilterAfter(Filter filter, Class<? extends Filter> afterFilter) {
comparator.registerAfter(filter.getClass(), afterFilter);
return addFilter(filter);
}
三、如何排序
上面小节只是给过滤器加上一个顺序，而对于我们的过滤器链并没有排序，实际上过滤器链还没生成呢，在启动项目的时候才开始创建过滤器，来看看创建过程中是如何对过滤器进行排序的。
实际排序
- 还记得实际上过滤器是在哪创建的吗，在《Spring Security源码（五）：FilterChainProxy是如何创建的？》一章中提到过，过滤器是在 HttpSecurity 中的 performBuild()方法中创建的，可以看到在这里会把已经创建好保存到 filters 中的过滤器进行排序，其实就是每创建一个过滤器都对过滤器链进行一个排序。
@Override
protected DefaultSecurityFilterChain performBuild() throws Exception {
Collections.sort(filters, comparator);
return new DefaultSecurityFilterChain(requestMatcher, filters);
}
FilterSecurityInterceptor
这是一个特殊的过滤器，特殊在每条过滤器链都是以这个过滤器结尾，这个过滤器是
Spring Security框架做权限访问控制的核心过滤器，请求最后能否通过是否有权限访问后台资源都是由它决定，关于这个过滤器咱们下一篇详细讲解，链接在篇尾。