Shiro（二）：Spring-boot如何集成Shiro（上）

这篇文章主要介绍了spring-boot是如何集成shiro的authentication流程的。

从shiro-spring-boot-web-starter提及

shiro-spring-boot-web-starter是shiro在web环境下快速集成至spring-boot的配置包。其自己引入了shiro的必要模块。并在Configuration中以@Bean的形式声明了Shiro各组件，交由spring容器统一管理。先看META-INF定义了配置类：

org.springframework.boot.autoconfigure.EnableAutoConfiguration = \
  org.apache.shiro.spring.config.web.autoconfigure.ShiroWebAutoConfiguration,\
  org.apache.shiro.spring.config.web.autoconfigure.ShiroWebFilterConfiguration

能够看到主要有两个配置：ShiroWebAutoConfiguration和ShiroWebFilterConfiguration。

• ShiroWebAutoConfiguration
  ShiroWebAutoConfiguration声明了Shiro须要的各个对象，在须要shiro框架进行处理的地方，能够方便注入，从而到达应用shiro特性的目的。同理，咱们也能够根据须要替换上述部分Bean，让Shiro的流程更负责本身的业务需求。

/**
 * @since 1.4.0
 */
@Configuration
@AutoConfigureBefore(ShiroAutoConfiguration.class)
@ConditionalOnProperty(name = "shiro.web.enabled", matchIfMissing = true)
public class ShiroWebAutoConfiguration extends AbstractShiroWebConfiguration {

    //声明了认证时的策略，默认是AtLeastOneSuccessfulStrategy
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected AuthenticationStrategy authenticationStrategy() {
        return super.authenticationStrategy();
    }

    //声明Authenticator对象，负责认证的过程
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected Authenticator authenticator() {
        return super.authenticator();
    }

    //声明Authorizer的对象，负责受权的过程
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected Authorizer authorizer() {
        return super.authorizer();
    }

    //声明Subject数据访问对象，经过该对象能够对Subject数据进行CRUD操做
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SubjectDAO subjectDAO() {
        return super.subjectDAO();
    }

    //声明SessionStorageEvaluator对象，用来决定Session是否须要持久化
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SessionStorageEvaluator sessionStorageEvaluator() {
        return super.sessionStorageEvaluator();
    }

    //声明SubjectFactory，用来建立Subject对象
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SubjectFactory subjectFactory() {
        return super.subjectFactory();
    }

    //声明SessionFactory对象，用来建立Session
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SessionFactory sessionFactory() {
        return super.sessionFactory();
    }

    //声明Session数据访问对象，提供对Session的CRUD操做
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SessionDAO sessionDAO() {
        return super.sessionDAO();
    }

    //声明SessionManager对象，负责Session管理
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SessionManager sessionManager() {
        return super.sessionManager();
    }

    //声明SecurityMananger，Shiro中最重要的组件，对象内封装了各个其余对象，用来处理不一样的业务
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected SessionsSecurityManager securityManager(List<Realm> realms) {
        return createSecurityManager();
    }

    //建立会话cookie时的模板，后期应用该模板的属性到建立的cookie对象上
    @Bean
    @ConditionalOnMissingBean(name = "sessionCookieTemplate")
    @Override
    protected Cookie sessionCookieTemplate() {
        return super.sessionCookieTemplate();
    }

    //Remember Me Manager，管理RememerMe
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected RememberMeManager rememberMeManager() {
        return super.rememberMeManager();
    }

    //RememberMe模板
    @Bean
    @ConditionalOnMissingBean(name = "rememberMeCookieTemplate")
    @Override
    protected Cookie rememberMeCookieTemplate() {
        return super.rememberMeCookieTemplate();
    }

    //定义了Shiro的Filter和URL的映射关系
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected ShiroFilterChainDefinition shiroFilterChainDefinition() {
        return super.shiroFilterChainDefinition();
    }
}

• ShiroWebFilterConfiguration
  以往spring项目的权限控制大多也是经过过滤器或是拦截器实现的，即请求在到达控制器以前，先通过过滤器或拦截器的处理，若是校验成功，再将数据发送至控制器。Shiro也是利用一样的道理。

package org.apache.shiro.spring.config.web.autoconfigure;

import javax.servlet.DispatcherType;
import org.apache.shiro.spring.web.ShiroFilterFactoryBean;
import org.apache.shiro.spring.web.config.AbstractShiroWebFilterConfiguration;
import org.apache.shiro.web.servlet.AbstractShiroFilter;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @since 1.4.0
 */
@Configuration
@ConditionalOnProperty(name = "shiro.web.enabled", matchIfMissing = true)
public class ShiroWebFilterConfiguration extends AbstractShiroWebFilterConfiguration {

    //ShiroFilter的FactoryBean，用来建立ShiroFilter
    @Bean
    @ConditionalOnMissingBean
    @Override
    protected ShiroFilterFactoryBean shiroFilterFactoryBean() {
        return super.shiroFilterFactoryBean();
    }

    //ShiroFilter的RegistrationBean，spring-boot舍弃了web.xml的配置，FilterRegistrationBean就成了添加filter的入口
    @Bean(name = "filterShiroFilterRegistrationBean")
    @ConditionalOnMissingBean
    protected FilterRegistrationBean filterShiroFilterRegistrationBean() throws Exception {

        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE, DispatcherType.ERROR);
        filterRegistrationBean.setFilter((AbstractShiroFilter) shiroFilterFactoryBean().getObject());
        filterRegistrationBean.setOrder(1);

        return filterRegistrationBean;
    }
}

FilterRegistrationBean主要设置了要添加的Filter
是由ShiroFilterFactoryBean所建立。所以，咱们重点关注ShiroFilterFactoryBean。

ShiroFilterFactoryBean

ShiroFilterFactoryBean同时实现了FactoryBean和BeanPostProcessor。说明他同时有建立Bean和Bean的后置处理两种能力。简单看一下源代码：

package org.apache.shiro.spring.web;




public class ShiroFilterFactoryBean implements FactoryBean, BeanPostProcessor {

    private static transient final Logger log = LoggerFactory.getLogger(ShiroFilterFactoryBean.class);

    private SecurityManager securityManager;

    //定义了拦截器name和Filter的映射关系
    private Map<String, Filter> filters;
    //定义了拦截器URL和name的映射关系
    private Map<String, String> filterChainDefinitionMap; //urlPathExpression_to_comma-delimited-filter-chain-definition

    private String loginUrl;
    private String successUrl;
    private String unauthorizedUrl;

    private AbstractShiroFilter instance;

    public ShiroFilterFactoryBean() {
        this.filters = new LinkedHashMap<String, Filter>();
        this.filterChainDefinitionMap = new LinkedHashMap<String, String>(); //order matters!
    }

    
    public SecurityManager getSecurityManager() {
        return securityManager;
    }

    
    public void setSecurityManager(SecurityManager securityManager) {
        this.securityManager = securityManager;
    }

    
    public String getLoginUrl() {
        return loginUrl;
    }

    
    public void setLoginUrl(String loginUrl) {
        this.loginUrl = loginUrl;
    }

    
    public String getSuccessUrl() {
        return successUrl;
    }

    
    public void setSuccessUrl(String successUrl) {
        this.successUrl = successUrl;
    }

    
    public String getUnauthorizedUrl() {
        return unauthorizedUrl;
    }

    
    public void setUnauthorizedUrl(String unauthorizedUrl) {
        this.unauthorizedUrl = unauthorizedUrl;
    }

    
    public Map<String, Filter> getFilters() {
        return filters;
    }

    
    public void setFilters(Map<String, Filter> filters) {
        this.filters = filters;
    }

    
    public Map<String, String> getFilterChainDefinitionMap() {
        return filterChainDefinitionMap;
    }

    
    public void setFilterChainDefinitionMap(Map<String, String> filterChainDefinitionMap) {
        this.filterChainDefinitionMap = filterChainDefinitionMap;
    }

    //提供了经过ini配置文件初始化Filter的能力
    public void setFilterChainDefinitions(String definitions) {
        Ini ini = new Ini();
        ini.load(definitions);
        //did they explicitly state a 'urls' section?  Not necessary, but just in case:
        Ini.Section section = ini.getSection(IniFilterChainResolverFactory.URLS);
        if (CollectionUtils.isEmpty(section)) {
            //no urls section.  Since this _is_ a urls chain definition property, just assume the
            //default section contains only the definitions:
            section = ini.getSection(Ini.DEFAULT_SECTION_NAME);
        }
        setFilterChainDefinitionMap(section);
    }

    //FactoryBean获取Bean的方法，这里就是获取对应Filter Bean
    public Object getObject() throws Exception {
        if (instance == null) {
            instance = createInstance();
        }
        return instance;
    }

    //FactoryBean获取生成的Bean的类型
    public Class getObjectType() {
        return SpringShiroFilter.class;
    }

    //要生成的Bean是否须要是单例
    public boolean isSingleton() {
        return true;
    }

    //建立FilterChainManager对象，该对象能够将对应的url和filter组成过滤器链
    protected FilterChainManager createFilterChainManager() {

        DefaultFilterChainManager manager = new DefaultFilterChainManager();
        //Shiro自带的Filter，不须要额外配置，能够开箱即用，详见DefualtFilter
        Map<String, Filter> defaultFilters = manager.getFilters();
        
        for (Filter filter : defaultFilters.values()) {
            applyGlobalPropertiesIfNecessary(filter);
        }

        //获取ShiroFactoryBean中自定义的Filters，添加至manager中
        Map<String, Filter> filters = getFilters();
        if (!CollectionUtils.isEmpty(filters)) {
            for (Map.Entry<String, Filter> entry : filters.entrySet()) {
                String name = entry.getKey();
                Filter filter = entry.getValue();
                applyGlobalPropertiesIfNecessary(filter);
                if (filter instanceof Nameable) {
                    ((Nameable) filter).setName(name);
                }
                //'init' argument is false, since Spring-configured filters should be initialized
                //in Spring (i.e. 'init-method=blah') or implement InitializingBean:
                manager.addFilter(name, filter, false);
            }
        }

        //根据定义的url和filter映射关系，建立过滤器链
        Map<String, String> chains = getFilterChainDefinitionMap();
        if (!CollectionUtils.isEmpty(chains)) {
            for (Map.Entry<String, String> entry : chains.entrySet()) {
                String url = entry.getKey();
                String chainDefinition = entry.getValue();
                manager.createChain(url, chainDefinition);
            }
        }

        return manager;
    }

   //建立ShiroFilter的实例
    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:
        //建立FilterChainResolver对象，FilterChainResolver包装了Manager，ShiroFilter不须要知道Manager对象
        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:
        //建立ShiroFilter对象
        return new SpringShiroFilter((WebSecurityManager) securityManager, chainResolver);
    }

    private void applyLoginUrlIfNecessary(Filter filter) {
        String loginUrl = getLoginUrl();
        if (StringUtils.hasText(loginUrl) && (filter instanceof AccessControlFilter)) {
            AccessControlFilter acFilter = (AccessControlFilter) filter;
            //only apply the login url if they haven't explicitly configured one already:
            String existingLoginUrl = acFilter.getLoginUrl();
            if (AccessControlFilter.DEFAULT_LOGIN_URL.equals(existingLoginUrl)) {
                acFilter.setLoginUrl(loginUrl);
            }
        }
    }

    private void applySuccessUrlIfNecessary(Filter filter) {
        String successUrl = getSuccessUrl();
        if (StringUtils.hasText(successUrl) && (filter instanceof AuthenticationFilter)) {
            AuthenticationFilter authcFilter = (AuthenticationFilter) filter;
            //only apply the successUrl if they haven't explicitly configured one already:
            String existingSuccessUrl = authcFilter.getSuccessUrl();
            if (AuthenticationFilter.DEFAULT_SUCCESS_URL.equals(existingSuccessUrl)) {
                authcFilter.setSuccessUrl(successUrl);
            }
        }
    }

    private void applyUnauthorizedUrlIfNecessary(Filter filter) {
        String unauthorizedUrl = getUnauthorizedUrl();
        if (StringUtils.hasText(unauthorizedUrl) && (filter instanceof AuthorizationFilter)) {
            AuthorizationFilter authzFilter = (AuthorizationFilter) filter;
            //only apply the unauthorizedUrl if they haven't explicitly configured one already:
            String existingUnauthorizedUrl = authzFilter.getUnauthorizedUrl();
            if (existingUnauthorizedUrl == null) {
                authzFilter.setUnauthorizedUrl(unauthorizedUrl);
            }
        }
    }

    //配置全局属性，只要是针对特定类型的Filter配置其所须要的URL属性
    private void applyGlobalPropertiesIfNecessary(Filter filter) {
        applyLoginUrlIfNecessary(filter);
        applySuccessUrlIfNecessary(filter);
        applyUnauthorizedUrlIfNecessary(filter);
    }

    //经过后置处理器的机制，直接Filter类型的bean，无需配置
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof Filter) {
            log.debug("Found filter chain candidate filter '{}'", beanName);
            Filter filter = (Filter) bean;
            applyGlobalPropertiesIfNecessary(filter);
            getFilters().put(beanName, filter);
        } else {
            log.trace("Ignoring non-Filter bean '{}'", beanName);
        }
        return bean;
    }

    /**
     * Does nothing - only exists to satisfy the BeanPostProcessor interface and immediately returns the
     * {@code bean} argument.
     */
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    //SpringShiroFilter只是简单的集成了AbstractShirlFilter，在构造函数中封装了设置SecurityManager和Resolver的操做
    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);
            }
        }
    }
}

最重要的步骤是在createInstance()中，该方法主要用来建立ShiroFilter的实例，大体过程分红三步：

1. 经过createFilterChainManager()建立FilterChainManager对象：
   • 建立FilterChainManager
   • 加载Shiro默认的Filter
   • 加载用户添加的Filter
   • 根据URL和Filter的映射关系，建立过滤器链
2. 建立FilterChainResolver对象，封装FilterChainManager
   
3. 建立ShiroFilter对象，传入SecurityManager和FilterChainReslover

SpringShiroFilter

SpringShiroFilter就是咱们经过容器添加的Filter对象。Shiro经过添加该过滤器实现了往集成Spring框架集成的目的。
其实SpringShiroFilter只是单纯的集成了AbstractShiroFilter，在构造函数中增长了设置SecurityManager和FilterChainResolver的过程。全部的逻辑在AbstractShiroFilter中已经定义好了。先从UML图中了解下整个类的继承关系：

其中从上到下看：

• Filter
  Filter是Serlvet包提供的。由Servlet规范定义Filter基本的行为。
  
• ServletContextSupport
  提供了操做ServletContext的能力
  
• AbstractFilter
  初步实现了Filter，定义了init的过程（分红setFilterConfig和onFilterConfigSet两部分），提供了设置和获取配置的方法。
  
• Nameable
  增长了命名的能力
  
• NameableFilter
  为Filter增长命名能力
  
• OncePerRequestFilter
  主要定义了doFilter的过程，并在该过程当中限制了一次请求该Filter只处理一次。

public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
            //先判断是否已经被处理过
        String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
        if ( //已经处理过，则再也不处理 request.getAttribute(alreadyFilteredAttributeName) != null ) {
            log.trace("Filter '{}' already executed.  Proceeding without invoking this filter.", getName());
            filterChain.doFilter(request, response);
        } else //noinspection deprecation
        //未处理过，可是不可用，也不处理
            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 {
        //调用Filter处理，并添加已处理属性
            // Do invoke this filter...
            log.trace("Filter '{}' not yet executed.  Executing now.", getName());
            request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);

            try {
            //抽象方法，交给子类实现
                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);
            }
        }
    }

• AbstractShiroFilter
  AbstractShiroFilter已经在Filter的处理过程当中添加了Shiro的验证。
  

package org.apache.shiro.web.servlet;

import org.apache.shiro.SecurityUtils;
import org.apache.shiro.session.Session;
import org.apache.shiro.subject.ExecutionException;
import org.apache.shiro.subject.Subject;
import org.apache.shiro.web.filter.mgt.FilterChainResolver;
import org.apache.shiro.web.mgt.DefaultWebSecurityManager;
import org.apache.shiro.web.mgt.WebSecurityManager;
import org.apache.shiro.web.subject.WebSubject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.concurrent.Callable;


public abstract class AbstractShiroFilter extends OncePerRequestFilter {

    private static final Logger log = LoggerFactory.getLogger(AbstractShiroFilter.class);

    private static final String STATIC_INIT_PARAM_NAME = "staticSecurityManagerEnabled";

    // Reference to the security manager used by this filter
    private WebSecurityManager securityManager;

    // Used to determine which chain should handle an incoming request/response
    private FilterChainResolver filterChainResolver;

    /**
     * Whether or not to bind the constructed SecurityManager instance to static memory (via
     * SecurityUtils.setSecurityManager).  This was added to support https://issues.apache.org/jira/browse/SHIRO-287
     * @since 1.2
     */
    private boolean staticSecurityManagerEnabled;

    protected AbstractShiroFilter() {
        this.staticSecurityManagerEnabled = false;
    }

    public WebSecurityManager getSecurityManager() {
        return securityManager;
    }

    public void setSecurityManager(WebSecurityManager sm) {
        this.securityManager = sm;
    }

    public FilterChainResolver getFilterChainResolver() {
        return filterChainResolver;
    }

    public void setFilterChainResolver(FilterChainResolver filterChainResolver) {
        this.filterChainResolver = filterChainResolver;
    }


    public boolean isStaticSecurityManagerEnabled() {
        return staticSecurityManagerEnabled;
    }


    public void setStaticSecurityManagerEnabled(boolean staticSecurityManagerEnabled) {
        this.staticSecurityManagerEnabled = staticSecurityManagerEnabled;
    }

    //重写了AbstractFilter中的空实现，主要设置额外的配置
    protected final void onFilterConfigSet() throws Exception {
        //added in 1.2 for SHIRO-287:
        applyStaticSecurityManagerEnabledConfig();
        init();
        ensureSecurityManager();
        //added in 1.2 for SHIRO-287:
        if (isStaticSecurityManagerEnabled()) {
            SecurityUtils.setSecurityManager(getSecurityManager());
        }
    }

    
    private void applyStaticSecurityManagerEnabledConfig() {
        String value = getInitParam(STATIC_INIT_PARAM_NAME);
        if (value != null) {
            Boolean b = Boolean.valueOf(value);
            if (b != null) {
                setStaticSecurityManagerEnabled(b);
            }
        }
    }

    public void init() throws Exception {
    }

    
    private void ensureSecurityManager() {
        WebSecurityManager securityManager = getSecurityManager();
        if (securityManager == null) {
            log.info("No SecurityManager configured.  Creating default.");
            securityManager = createDefaultSecurityManager();
            setSecurityManager(securityManager);
        }
    }

    protected WebSecurityManager createDefaultSecurityManager() {
        return new DefaultWebSecurityManager();
    }

    protected boolean isHttpSessions() {
        return getSecurityManager().isHttpSessionMode();
    }

    
    protected ServletRequest wrapServletRequest(HttpServletRequest orig) {
        return new ShiroHttpServletRequest(orig, getServletContext(), isHttpSessions());
    }

    
    @SuppressWarnings({"UnusedDeclaration"})
    protected ServletRequest prepareServletRequest(ServletRequest request, ServletResponse response, FilterChain chain) {
        ServletRequest toUse = request;
        if (request instanceof HttpServletRequest) {
            HttpServletRequest http = (HttpServletRequest) request;
            toUse = wrapServletRequest(http);
        }
        return toUse;
    }

    
    protected ServletResponse wrapServletResponse(HttpServletResponse orig, ShiroHttpServletRequest request) {
        return new ShiroHttpServletResponse(orig, getServletContext(), request);
    }

    
    @SuppressWarnings({"UnusedDeclaration"})
    protected ServletResponse prepareServletResponse(ServletRequest request, ServletResponse response, FilterChain chain) {
        ServletResponse toUse = response;
        if (!isHttpSessions() && (request instanceof ShiroHttpServletRequest) &&
                (response instanceof HttpServletResponse)) {
            //the ShiroHttpServletResponse exists to support URL rewriting for session ids.  This is only needed if
            //using Shiro sessions (i.e. not simple HttpSession based sessions):
            toUse = wrapServletResponse((HttpServletResponse) response, (ShiroHttpServletRequest) request);
        }
        return toUse;
    }

    
    protected WebSubject createSubject(ServletRequest request, ServletResponse response) {
        return new WebSubject.Builder(getSecurityManager(), request, response).buildWebSubject();
    }

    //对Session生命周期未交给Web容器管理的状况，由Shiro本身维护
    @SuppressWarnings({"UnusedDeclaration"})
    protected void updateSessionLastAccessTime(ServletRequest request, ServletResponse response) {
        if (!isHttpSessions()) { //'native' sessions
            Subject subject = SecurityUtils.getSubject();
            //Subject should never _ever_ be null, but just in case:
            if (subject != null) {
                Session session = subject.getSession(false);
                if (session != null) {
                    try {
                        session.touch();
                    } catch (Throwable t) {
                        log.error("session.touch() method invocation has failed.  Unable to update" +
                                "the corresponding session's last access time based on the incoming request.", t);
                    }
                }
            }
        }
    }

    //重写OncePerRequestFilter的空实现，定义了Filter处理逻辑
    protected void doFilterInternal(ServletRequest servletRequest, ServletResponse servletResponse, final FilterChain chain)
            throws ServletException, IOException {

        Throwable t = null;

        try {
            //封装ServletRequest和ServletResponse
            final ServletRequest request = prepareServletRequest(servletRequest, servletResponse, chain);
            final ServletResponse response = prepareServletResponse(request, servletResponse, chain);

            //建立Subject对象    
            final Subject subject = createSubject(request, response);

            //noinspection unchecked
            subject.execute(new Callable() {
                public Object call() throws Exception {
                    //更新Session访问时间
                    updateSessionLastAccessTime(request, response);
                    //执行任务链
                    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);
        }
    }

    //获取待执行的过滤器链
    protected FilterChain getExecutionChain(ServletRequest request, ServletResponse response, FilterChain origChain) {
        FilterChain chain = origChain;

        //获取过滤器链解析器
        FilterChainResolver resolver = getFilterChainResolver();
        if (resolver == null) {
            log.debug("No FilterChainResolver configured.  Returning original FilterChain.");
            return origChain;
        }

        //使用解析器对请求进行解析，
        FilterChain resolved = resolver.getChain(request, response, origChain);
        if (resolved != null) {
            //若是该请求URI是须要Shiro拦截的，则由shiro建立代理的过滤器链，
            //在执行原始的过滤器前，插入Shiro过滤器的执行过程
            log.trace("Resolved a configured FilterChain for the current request.");
            chain = resolved;
        } else {//不然使用原始过滤器
            log.trace("No FilterChain configured for the current request.  Using the default.");
        }

        return chain;
    }

    //执行拦截器链
    protected void executeChain(ServletRequest request, ServletResponse response, FilterChain origChain)
            throws IOException, ServletException {
        //获取拦截器链        
        FilterChain chain = getExecutionChain(request, response, origChain);
        //拦截器链处理拦截工做
        chain.doFilter(request, response);
    }
}

其中比较重要的有两个：onFilterConfigSet()和doFilterInternal()。
onFilterConfigset()在AbstractFilter中是空实现，这里重写了该方法，主要是添加一些额外配置。
doFilterInternal()主要流程：

• 先封装了请求和响应
• 获取请求表明的Subject对象
• 更新session最后访问的时间（托管给WEB容器的session不须要shiro管理访问时间）
• 执行拦截器链executeChain:
  • 获取拦截器链： 若是FilterChainResolver解析到请求的URL是shiro拦截器拦截的URL，则产生代理的FilterChain，让shiro的拦截器集成进拦截器；不然使用原始的拦截器链
    
  • 拦截器链开始工做

FilterChainResolver和FilterChainManager的工做

以前简单介绍过FilterChainResolver封装了FilterChainManger对象，如今再来看下FilterChainResovler的代码：

public class PathMatchingFilterChainResolver implements FilterChainResolver {

    private static transient final Logger log = LoggerFactory.getLogger(PathMatchingFilterChainResolver.class);

    //封装了FilterChainManager
    private FilterChainManager filterChainManager;

    //负责比较URL
    private PatternMatcher pathMatcher;

    public PathMatchingFilterChainResolver() {
        this.pathMatcher = new AntPathMatcher();
        this.filterChainManager = new DefaultFilterChainManager();
    }

    public PathMatchingFilterChainResolver(FilterConfig filterConfig) {
        this.pathMatcher = new AntPathMatcher();
        this.filterChainManager = new DefaultFilterChainManager(filterConfig);
    }

    
    public PatternMatcher getPathMatcher() {
        return pathMatcher;
    }

    
    public void setPathMatcher(PatternMatcher pathMatcher) {
        this.pathMatcher = pathMatcher;
    }

    public FilterChainManager getFilterChainManager() {
        return filterChainManager;
    }

    @SuppressWarnings({"UnusedDeclaration"})
    public void setFilterChainManager(FilterChainManager filterChainManager) {
        this.filterChainManager = filterChainManager;
    }

    //获取拦截器链
    public FilterChain getChain(ServletRequest request, ServletResponse response, FilterChain originalChain) {
        FilterChainManager filterChainManager = getFilterChainManager();
        if (!filterChainManager.hasChains()) {
            return null;
        }

        //获取URL
        String requestURI = getPathWithinApplication(request);

        //匹配URL
        for (String pathPattern : filterChainManager.getChainNames()) {

            //若是匹配，则由filterChainManager建立代理过的Filter Chain
            if (pathMatches(pathPattern, requestURI)) {
                if (log.isTraceEnabled()) {
                    log.trace("Matched path pattern [" + pathPattern + "] for requestURI [" + requestURI + "].  " +
                            "Utilizing corresponding filter chain...");
                }
                return filterChainManager.proxy(originalChain, pathPattern);
            }
        }

        return null;
    }

    
    protected boolean pathMatches(String pattern, String path) {
        PatternMatcher pathMatcher = getPathMatcher();
        return pathMatcher.matches(pattern, path);
    }

    
    protected String getPathWithinApplication(ServletRequest request) {
        return WebUtils.getPathWithinApplication(WebUtils.toHttp(request));
    }
}

这个类的代码相对简单，大概过程是根据FilterChainManager配置的URI和Filter的映射关系，比较请求是否须要通过Shiro的Filter，若是须要则交给了FilterChainManager对象建立代理过的FilterChain，从而加入了Shiro的处理流程。能够看到主要的内容都是由FilterChainManager完成。所以咱们再来看FilterChainManager类的proxy方法：

public FilterChain proxy(FilterChain original, String chainName) {
        //NamedFilterList对象能够简单理解为一个命名了Filter的list，是以前解析filter时，建立的
        NamedFilterList configured = getChain(chainName);
        if (configured == null) {
            String msg = "There is no configured chain under the name/key [" + chainName + "].";
            throw new IllegalArgumentException(msg);
        }
        //建立代理
        return configured.proxy(original);
    }

NamedFilterList建立代理的过程其实就是建立ProxiedFilterChain对象。

public class ProxiedFilterChain implements FilterChain {

    //TODO - complete JavaDoc

    private static final Logger log = LoggerFactory.getLogger(ProxiedFilterChain.class);

    private FilterChain orig;
    private List<Filter> filters;
    private int index = 0;

    public ProxiedFilterChain(FilterChain orig, List<Filter> filters) {
        if (orig == null) {
            throw new NullPointerException("original FilterChain cannot be null.");
        }
        //封装了原始filterChain对象和shiro的filter对象
        this.orig = orig;
        this.filters = filters;
        this.index = 0;
    }

    //实现了filterChain的doFilter方法
    public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
        //若是不含有shiro的filter，或是已经遍历完了shiro的filter，则调用原始的fiter chain的方法
        if (this.filters == null || this.filters.size() == this.index) {
            //we've reached the end of the wrapped chain, so invoke the original one:
            if (log.isTraceEnabled()) {
                log.trace("Invoking original filter chain.");
            }
            this.orig.doFilter(request, response);
        } else {
            if (log.isTraceEnabled()) {
                log.trace("Invoking wrapped filter at index [" + this.index + "]");
            }
            //调用shiro的filter
            this.filters.get(this.index++).doFilter(request, response, this);
        }
    }
}

源码读到这里已经大体了解到shiro是如何集成至spring-boot的。接下来再以一个Shiro的Filter为例，具体了解下authentication的流程。

从FormAuthenticatingFilter了解Shiro的authentication过程

同样先看Filter的继承结构：

OncePerRequestFilter父级的结构已经在前文介绍过。如今关注点放在它的子类上。

• AdviceFilter：
  主要实现了doFilterInternal方法，将filter的过程再切成preHandle，executeChain，postHandle和cleanup四个阶段。有点相似spring中的拦截器。在方法前，方法后作了拦截。并根据返回的结果决定是否继续再filterChain中往下走：
  

public void doFilterInternal(ServletRequest request, ServletResponse response, FilterChain chain)
            throws ServletException, IOException {

        Exception exception = null;

        try {
            //前置处理，根据返回结构决定是否继续走以后的filter
            boolean continueChain = preHandle(request, response);
            if (log.isTraceEnabled()) {
                log.trace("Invoked preHandle method.  Continuing chain?: [" + continueChain + "]");
            }
            
            //继续调用以后的filter
            if (continueChain) {
                executeChain(request, response, chain);
            }
            
            //后置处理
            postHandle(request, response);
            if (log.isTraceEnabled()) {
                log.trace("Successfully invoked postHandle method");
            }

        } catch (Exception e) {
            exception = e;
        } finally {
        //清理
            cleanup(request, response, exception);
        }
    }

• PathMatchingFilter：根据url是否匹配的逻辑实现preHandle方法。并提供onPreHandle方法让子类能够修改preHandle方法返回的值。
  

protected boolean preHandle(ServletRequest request, ServletResponse response) throws Exception {

        if (this.appliedPaths == null || this.appliedPaths.isEmpty()) {
            if (log.isTraceEnabled()) {
                log.trace("appliedPaths property is null or empty.  This Filter will passthrough immediately.");
            }
            return true;
        }

        //匹配请求URL，决定是否须要通过shiro的filter
        for (String path : this.appliedPaths.keySet()) {
            
            if (pathsMatch(path, request)) {
                log.trace("Current requestURI matches pattern '{}'.  Determining filter chain execution...", path);
                Object config = this.appliedPaths.get(path);

                return isFilterChainContinued(request, response, path, config);
            }
        }

        //no path matched, allow the request to go through:
        return true;
    }

    
    @SuppressWarnings({"JavaDoc"})
    private boolean isFilterChainContinued(ServletRequest request, ServletResponse response,
                                           String path, Object pathConfig) throws Exception {

        if (isEnabled(request, response, path, pathConfig)) { //isEnabled check added in 1.2
            if (log.isTraceEnabled()) {
                log.trace("Filter '{}' is enabled for the current request under path '{}' with config [{}].  " +
                        "Delegating to subclass implementation for 'onPreHandle' check.",
                        new Object[]{getName(), path, pathConfig});
            }
            //添加onPreHandle方法
            return onPreHandle(request, response, pathConfig);
        }

        if (log.isTraceEnabled()) {
            log.trace("Filter '{}' is disabled for the current request under path '{}' with config [{}].  " +
                    "The next element in the FilterChain will be called immediately.",
                    new Object[]{getName(), path, pathConfig});
        }
        //This filter is disabled for this specific request,
        //return 'true' immediately to indicate that the filter will not process the request
        //and let the request/response to continue through the filter chain:
        return true;
    }

    //默认返回true，子类能够重写该方法实现本身的控制逻辑
    protected boolean onPreHandle(ServletRequest request, ServletResponse response, Object mappedValue) throws Exception {
        return true;
    }

• AccessControlFilter:主要重写了onPreHandle方法，增长了isAccessAllowed和onAccessDenied方法。能够在该方法中实现访问控制的逻辑。
  

public boolean onPreHandle(ServletRequest request, ServletResponse response, Object mappedValue) throws Exception {
        return isAccessAllowed(request, response, mappedValue) || onAccessDenied(request, response, mappedValue);
    }

• AuthenticationFilter:实现了isAccessAllowed方法，经过subject.isAuthenticated()决定是否容许访问。
  

protected boolean isAccessAllowed(ServletRequest request, ServletResponse response, Object mappedValue) {
        Subject subject = getSubject(request, response);
        return subject.isAuthenticated();
    }

• AuthenticatingFilter：除了主要的isAccessAllowed和cleanup方法以外，还实现了executeLogin方法，主要是从请求中获取登陆的用户名密码，经过shiro进行登陆验证
• FormAuthenticationFilter:最后具体看一下FormAuthenticationFilter。
  

public class FormAuthenticationFilter extends AuthenticatingFilter {

    //TODO - complete JavaDoc

    public static final String DEFAULT_ERROR_KEY_ATTRIBUTE_NAME = "shiroLoginFailure";

    public static final String DEFAULT_USERNAME_PARAM = "username";
    public static final String DEFAULT_PASSWORD_PARAM = "password";
    public static final String DEFAULT_REMEMBER_ME_PARAM = "rememberMe";

    private static final Logger log = LoggerFactory.getLogger(FormAuthenticationFilter.class);

    private String usernameParam = DEFAULT_USERNAME_PARAM;
    private String passwordParam = DEFAULT_PASSWORD_PARAM;
    private String rememberMeParam = DEFAULT_REMEMBER_ME_PARAM;

    private String failureKeyAttribute = DEFAULT_ERROR_KEY_ATTRIBUTE_NAME;

    public FormAuthenticationFilter() {
        setLoginUrl(DEFAULT_LOGIN_URL);
    }

    @Override
    public void setLoginUrl(String loginUrl) {
        String previous = getLoginUrl();
        if (previous != null) {
            this.appliedPaths.remove(previous);
        }
        super.setLoginUrl(loginUrl);
        if (log.isTraceEnabled()) {
            log.trace("Adding login url to applied paths.");
        }
        this.appliedPaths.put(getLoginUrl(), null);
    }

    public String getUsernameParam() {
        return usernameParam;
    }


    public void setUsernameParam(String usernameParam) {
        this.usernameParam = usernameParam;
    }

    public String getPasswordParam() {
        return passwordParam;
    }


    public void setPasswordParam(String passwordParam) {
        this.passwordParam = passwordParam;
    }

    public String getRememberMeParam() {
        return rememberMeParam;
    }


    public void setRememberMeParam(String rememberMeParam) {
        this.rememberMeParam = rememberMeParam;
    }

    public String getFailureKeyAttribute() {
        return failureKeyAttribute;
    }

    public void setFailureKeyAttribute(String failureKeyAttribute) {
        this.failureKeyAttribute = failureKeyAttribute;
    }

    //
    protected boolean onAccessDenied(ServletRequest request, ServletResponse response) throws Exception {
        //若是isAccessAllowed校验失败，则判断是不是登陆请求
        if (isLoginRequest(request, response)) {
            //若是是表单提交的登陆请求，则执行登陆，
            if (isLoginSubmission(request, response)) {
                if (log.isTraceEnabled()) {
                    log.trace("Login submission detected.  Attempting to execute login.");
                }
                //登陆
                return executeLogin(request, response);
            } else {
                if (log.isTraceEnabled()) {
                    log.trace("Login page view.");
                }
                //allow them to see the login page ;)
                return true;
            }
        } else {
            if (log.isTraceEnabled()) {
                log.trace("Attempting to access a path which requires authentication.  Forwarding to the " +
                        "Authentication url [" + getLoginUrl() + "]");
            }

            saveRequestAndRedirectToLogin(request, response);
            return false;
        }
    }

    @SuppressWarnings({"UnusedDeclaration"})
    protected boolean isLoginSubmission(ServletRequest request, ServletResponse response) {
        return (request instanceof HttpServletRequest) && WebUtils.toHttp(request).getMethod().equalsIgnoreCase(POST_METHOD);
    }

    protected AuthenticationToken createToken(ServletRequest request, ServletResponse response) {
        String username = getUsername(request);
        String password = getPassword(request);
        return createToken(username, password, request, response);
    }

    protected boolean isRememberMe(ServletRequest request) {
        return WebUtils.isTrue(request, getRememberMeParam());
    }

    //定义了一些重定向动做
    protected boolean onLoginSuccess(AuthenticationToken token, Subject subject,
                                     ServletRequest request, ServletResponse response) throws Exception {
        issueSuccessRedirect(request, response);
        //we handled the success redirect directly, prevent the chain from continuing:
        return false;
    }

    protected boolean onLoginFailure(AuthenticationToken token, AuthenticationException e,
                                     ServletRequest request, ServletResponse response) {
        if (log.isDebugEnabled()) {
            log.debug( "Authentication exception", e );
        }
        setFailureAttribute(request, e);
        //login failed, let request continue back to the login page:
        return true;
    }

    protected void setFailureAttribute(ServletRequest request, AuthenticationException ae) {
        String className = ae.getClass().getName();
        request.setAttribute(getFailureKeyAttribute(), className);
    }

    protected String getUsername(ServletRequest request) {
        return WebUtils.getCleanParam(request, getUsernameParam());
    }

    protected String getPassword(ServletRequest request) {
        return WebUtils.getCleanParam(request, getPasswordParam());
    }


}

总结

shiro经过FilterRegistrationBean添加了ShiroFilter。ShiroFilter在针对须要登陆验证的请求，将原始的fiterChain进行代理，从而集成了shiro权限验证的filter。