创建核心Filter
同其他框架一样，都有个切入点，这个核心Filter就是拦截所有请求的。
通过web.xml中配置的Filer进入，执行init方法获取这个instance，调用下面的createInstance方法创建核心Filter:
protected AbstractShiroFilter createInstance() throws Exception {
log.debug("Creating Shiro Filter instance.");
SecurityManager securityManager = getSecurityManager();
if (securityManager == null) {
String msg = "SecurityManager property must be set.";
throw new BeanInitializationException(msg);
}
if (!(securityManager instanceof WebSecurityManager)) {
String msg = "The security manager does not implement the WebSecurityManager interface.";
throw new BeanInitializationException(msg);
}
FilterChainManager manager = createFilterChainManager();
//Expose the constructed FilterChainManager by first wrapping it in a
// FilterChainResolver implementation. The AbstractShiroFilter implementations
// do not know about FilterChainManagers - only resolvers:
PathMatchingFilterChainResolver chainResolver = new PathMatchingFilterChainResolver();
chainResolver.setFilterChainManager(manager);
//Now create a concrete ShiroFilter instance and apply the acquired SecurityManager and built
//FilterChainResolver. It doesn't matter that the instance is an anonymous inner class
//here - we're just using it because it is a concrete AbstractShiroFilter instance that accepts
//injection of the SecurityManager and FilterChainResolver:
return new SpringShiroFilter((WebSecurityManager) securityManager, chainResolver);
}createFilterChainManager方法比较重要，包含以下必要操作：
-
DefaultFilterChainManager对象的创建
-
defaultFilters的获取和相关url的填充
-
自定义filters的获取和相关url的填充
-
获取FilterChainDefinitionMap (这个就是配置文件中的filterChainDefinitions的映射关系)
- 对url和权限的映射关系作处理
默认的DefaultFilter枚举中包含以下filter类：
anon(AnonymousFilter.class),
authc(FormAuthenticationFilter.class),
authcBasic(BasicHttpAuthenticationFilter.class),
logout(LogoutFilter.class),
noSessionCreation(NoSessionCreationFilter.class),
perms(PermissionsAuthorizationFilter.class),
port(PortFilter.class),
rest(HttpMethodPermissionFilter.class),
roles(RolesAuthorizationFilter.class),
ssl(SslFilter.class),
user(UserFilter.class);执行doFilter方法
看下内部类 SpringShiroFilter：
private static final class SpringShiroFilter extends AbstractShiroFilter {
protected SpringShiroFilter(WebSecurityManager webSecurityManager, FilterChainResolver resolver) {
super();
if (webSecurityManager == null) {
throw new IllegalArgumentException("WebSecurityManager property cannot be null.");
}
setSecurityManager(webSecurityManager);
if (resolver != null) {
setFilterChainResolver(resolver);
}
}
}
在org.apache.shiro.web.servlet.OncePerRequestFilter中实现了doFilter方法：
public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
if ( request.getAttribute(alreadyFilteredAttributeName) != null ) {
log.trace("Filter '{}' already executed. Proceeding without invoking this filter.", getName());
filterChain.doFilter(request, response);
} else //noinspection deprecation
if (/* added in 1.2: */ !isEnabled(request, response) ||
/* retain backwards compatibility: */ shouldNotFilter(request) ) {
log.debug("Filter '{}' is not enabled for the current request. Proceeding without invoking this filter.",
getName());
filterChain.doFilter(request, response);
} else {
// Do invoke this filter...
log.trace("Filter '{}' not yet executed. Executing now.", getName());
request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
try {
doFilterInternal(request, response, filterChain);
} finally {
// Once the request has finished, we're done and we don't
// need to mark as 'already filtered' any more.
request.removeAttribute(alreadyFilteredAttributeName);
}
}
}三种情况，分为两条路线：
1. filterChain.doFilter(request, response); 直接放行
2. doFilterInternal(request, response, filterChain); 走子类实现
在org.apache.shiro.web.servlet.AbstractShiroFilter实现doFilterInternal：
protected void doFilterInternal(ServletRequest servletRequest, ServletResponse servletResponse, final FilterChain chain)
throws ServletException, IOException {
Throwable t = null;
try {
final ServletRequest request = prepareServletRequest(servletRequest, servletResponse, chain);
final ServletResponse response = prepareServletResponse(request, servletResponse, chain);
final Subject subject = createSubject(request, response);
//noinspection unchecked
subject.execute(new Callable() {
public Object call() throws Exception {
updateSessionLastAccessTime(request, response);
executeChain(request, response, chain);
return null;
}
});
} catch (ExecutionException ex) {
t = ex.getCause();
} catch (Throwable throwable) {
t = throwable;
}
if (t != null) {
if (t instanceof ServletException) {
throw (ServletException) t;
}
if (t instanceof IOException) {
throw (IOException) t;
}
//otherwise it's not one of the two exceptions expected by the filter method signature - wrap it in one:
String msg = "Filtered request failed.";
throw new ServletException(msg, t);
}
}将HttpServletRequest和HttpServletResponse包装成shiro自己的ShiroHttpServletRequest和ShiroHttpServletResponse。
利用包装后的对象创建Subject。
然后是执行subject的execute的方法。
protected void executeChain(ServletRequest request, ServletResponse response, FilterChain origChain)
throws IOException, ServletException {
FilterChain chain = getExecutionChain(request, response, origChain);
chain.doFilter(request, response);
}获取的FilterChain是一个代理的ProxiedFilterChain，持有自己的Filter集合，重写doFilter方法：取自己持有的Filter集合，一个个执行其doFilter方法，当所有的Filter都执行完后，再执行servlet的FilterChain。
后面的过程就是一个原始的FilterChain的执行过程。
可以想象，原生的Filter链似乎也是这样一个执行过程，遍历web.xml中配置的所有Filter。
整个过程就是代理模式的运用。
