Spring Security常用过滤器介绍

Spring Security常见的15个拦截器
1 . org.springframework.security.web.context.SecurityContextPersistenceFilter
     首当其冲的一个过滤器，作用之重要，自不必多言。
     SecurityContextPersistenceFilter主要是使用SecurityContextRepository在session中保存或更新一个
     SecurityContext，并将SecurityContext给以后的过滤器使用，来为后续filter建立所需的上下文。
     SecurityContext中存储了当前用户的认证以及权限信息。
2 . org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter
     此过滤器用于集成SecurityContext到Spring异步执行机制中的WebAsyncManager
3 . org.springframework.security.web.header.HeaderWriterFilter
    向请求的Header中添加相应的信息,可在http标签内部使用security:headers来控制
4 . org.springframework.security.web.csrf.CsrfFilter
    csrf又称跨域请求伪造，SpringSecurity会对所有post请求验证是否包含系统生成的csrf的token信息，
     如果不包含，则报错。起到防止csrf攻击的效果。
5. org.springframework.security.web.authentication.logout.LogoutFilter
    匹配 URL为/logout的请求，实现用户退出,清除认证信息。
6 . org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter
    认证操作全靠这个过滤器，默认匹配URL为/login且必须为POST请求。
7 . org.springframework.security.web.authentication.ui.DefaultLoginPageGeneratingFilter
    如果没有在配置文件中指定认证页面，则由该过滤器生成一个默认认证页面。
8 . org.springframework.security.web.authentication.ui.DefaultLogoutPageGeneratingFilter
     由此过滤器可以生产一个默认的退出登录页面
9 . org.springframework.security.web.authentication.www.BasicAuthenticationFilter
    此过滤器会自动解析HTTP请求中头部名字为Authentication，且以Basic开头的头信息。
10 . org.springframework.security.web.savedrequest.RequestCacheAwareFilter
    通过HttpSessionRequestCache内部维护了一个RequestCache，用于缓存HttpServletRequest
11 . org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter
   针对ServletRequest进行了一次包装，使得request具有更加丰富的API
12 . org.springframework.security.web.authentication.AnonymousAuthenticationFilter
   当SecurityContextHolder中认证信息为空,则会创建一个匿名用户存入到SecurityContextHolder中。
   spring security为了兼容未登录的访问，也走了一套认证流程，只不过是一个匿名的身份。
13 . org.springframework.security.web.session.SessionManagementFilter
   SecurityContextRepository限制同一用户开启多个会话的数量
14 . org.springframework.security.web.access.ExceptionTranslationFilter
   异常转换过滤器位于整个springSecurityFilterChain的后方，用来转换整个链路中出现的异常
15 . org.springframework.security.web.access.intercept.FilterSecurityInterceptor
   获取所配置资源访问的授权信息，根据SecurityContextHolder中存储的用户信息来决定其是否有权限。

那么，是不是spring security一共就这么多过滤器呢？答案是否定的！随着spring-security.xml配置的添加，还
会出现新的过滤器。
那么，是不是spring security每次都会加载这些过滤器呢？答案也是否定的！随着spring-security.xml配置的修
改，有些过滤器可能会被去掉。
spring security 过滤器链加载原理

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);
}
}

第二步debug结果如下：

由此可知， DelegatingFilterProxy通过springSecurityFilterChain这个名称，得到了一个FilterChainProxy过滤器，
最终在第三步执行了这个过滤器。
 FilterChainProxy

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<SecurityFilterChain> 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<SecurityFilterChain> 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<Filter> 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<Filter> 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();
}
}

SecurityFilterChain
最后看SecurityFilterChain，这是个接口，实现类也只有一个，这才是web.xml中配置的过滤器链对象！

public interface SecurityFilterChain {

    boolean matches(HttpServletRequest request);

    List<Filter> getFilters();
}

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

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

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

    public RequestMatcher getRequestMatcher() {
        return requestMatcher;
    }

    public List<Filter> getFilters() {
        return filters;
    }

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

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