Spring Security实现原理剖析（一）：filter的构造和初始化

前言

我们知道Spring Security的核心实现原理都是从filter开始的，Spring Security通过构造层层filter来实现登录跳转、权限验证，角色管理等功能。本章通过剖析Spring Security的核心源码来说明Spring Security的filter是如何开始构造并运行的。

从最初开始

往往我们定义一个Spring Security程序都是通过配置一个WebSecurityConfig类开始的，简单代码如下：

@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(final HttpSecurity http) throws Exception {
        http.authorizeRequests()
                .antMatchers("/login").permitAll()
                .anyRequest().authenticated()
                .and().formLogin();
    }
    
}

通过以上代码一个简单的Spring Security应用程序就能成功执行了，该程序能拦截除了/login路径以外的所有请求到登录页面。

我们可以看到以上代码并没有任何显示声明filter的语句，那么Spring Security是如何通过上述代码生成filter的呢？下面就由我来一层层解剖Spring Security的源码来说明。

@EnableWebSecurity注解

我们注意到如上代码有个@EnableWebSecurity注解,进入该注解查看

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
#注意这里！
@Import({WebSecurityConfiguration.class, SpringWebMvcImportSelector.class, OAuth2ImportSelector.class})
@EnableGlobalAuthentication
@Configuration
public @interface EnableWebSecurity {
    boolean debug() default false;
}

WebSecurityConfiguration类

我们可以看到如上该注解导入了WebSecurityConfiguration类，进入该类查看：

@Configuration
public class WebSecurityConfiguration implements ImportAware, BeanClassLoaderAware {
    private WebSecurity webSecurity;
    private Boolean debugEnabled;
    private List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers;
    private ClassLoader beanClassLoader;
    @Autowired(
        required = false
    )
    private ObjectPostProcessor<Object> objectObjectPostProcessor;

    public WebSecurityConfiguration() {
    }

    @Bean
    public static DelegatingApplicationListener delegatingApplicationListener() {
        return new DelegatingApplicationListener();
    }
    ........
}

WebSecurityConfiguration类是作为一个Spring配置源，同时定义了许多bean，这里重点看如下这个方法：

@Autowired(
        required = false
    )
    public void setFilterChainProxySecurityConfigurer(ObjectPostProcessor<Object> objectPostProcessor, 
    @Value("#{@autowiredWebSecurityConfigurersIgnoreParents.getWebSecurityConfigurers()}") 
    List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers) throws Exception {
    
        #这段代码初始化webSecurity
        this.webSecurity = (WebSecurity)objectPostProcessor.postProcess(new WebSecurity(objectPostProcessor));
        if (this.debugEnabled != null) {
            this.webSecurity.debug(this.debugEnabled);
        }
        
        #webSecurityConfigurers该属性是通过@Value注解注入的
        Collections.sort(webSecurityConfigurers, WebSecurityConfiguration.AnnotationAwareOrderComparator.INSTANCE);
        Integer previousOrder = null;
        Object previousConfig = null;

        Iterator var5;
        SecurityConfigurer config;
        for(var5 = webSecurityConfigurers.iterator(); var5.hasNext(); previousConfig = config) {
            config = (SecurityConfigurer)var5.next();
            Integer order = WebSecurityConfiguration.AnnotationAwareOrderComparator.lookupOrder(config);
            if (previousOrder != null && previousOrder.equals(order)) {
                throw new IllegalStateException("@Order on WebSecurityConfigurers must be unique. Order of " + order + " was already used on " + previousConfig + ", so it cannot be used on " + config + " too.");
            }

            previousOrder = order;
        }
        
        #将webSecurityConfigurers依次放入webSecurity
        var5 = webSecurityConfigurers.iterator();
        while(var5.hasNext()) {
            config = (SecurityConfigurer)var5.next();
            this.webSecurity.apply(config);
        }

        this.webSecurityConfigurers = webSecurityConfigurers;
    }

总结下该方法所做的主要操作：

1. 首先初始化了webSecurity属性，该属性对应WebSecurity类
2. 注入了webSecurityConfigurers属性，该属性是一个List<SecurityConfigurer>集合
3. 遍历webSecurityConfigurers集合，调用webSecurity的apply方法，该方法参数为SecurityConfigurer接口

这里有一个重要的接口SecurityConfigurer接口，该接口代码如下：

public interface SecurityConfigurer<O, B extends SecurityBuilder<O>> {
    void init(B var1) throws Exception;

    void configure(B var1) throws Exception;
}

回顾上面我们编写的WebSecurityConfig配置类，也有一个configure方法，那么我们猜测WebSecurityConfig类是不是也实现了SecurityConfigurer接口呢？答案是是的，我们可以看WebSecurityConfig类的类图

可以看到WebSecurityConfig类实现了SecurityConfigurer接口。

因此webSecurityConfigurers属性通过依赖注入包含了WebSecurityConfig类，通过上述第3条操作将我们配置的WebSecurityConfig类和WebSecurity类关联起来。

WebSecurity类

到这里我们知道了WebSecurityConfiguration类调用上述方法将我们配置的WebSecurityConfig类用WebSecurity类的apply方法关联起来，那么我们详细看看WebSecurity类的apply方法：

public <C extends SecurityConfigurerAdapter<O, B>> C apply(C configurer) throws Exception {
        configurer.addObjectPostProcessor(this.objectPostProcessor);
        configurer.setBuilder(this);
        #继续调用该类的add方法
        this.add(configurer);
        return configurer;
    }
    
private <C extends SecurityConfigurer<O, B>> void add(C configurer) throws Exception {
        Assert.notNull(configurer, "configurer cannot be null");
        #获取class属性
        Class<? extends SecurityConfigurer<O, B>> clazz = configurer.getClass();
        #获取LinkedHashMap
        LinkedHashMap var3 = this.configurers;
        synchronized(this.configurers) {
            if (this.buildState.isConfigured()) {
                throw new IllegalStateException("Cannot apply " + configurer + " to already built object");
            } else {
                List<SecurityConfigurer<O, B>> configs = this.allowConfigurersOfSameType ? (List)this.configurers.get(clazz) : null;
                if (configs == null) {
                    configs = new ArrayList(1);
                }

                ((List)configs).add(configurer);
                #将configurer放入一个LinkedHashMap中
                this.configurers.put(clazz, configs);
                if (this.buildState.isInitializing()) {
                    this.configurersAddedInInitializing.add(configurer);
                }

            }
        }
    }

从上述代码可知，实际上就是将WebSecurityConfig类放入了WebSecurity类的一个LinkedHashMap中，该LinkedHashMap在WebSecurity中属性名为configurers。

我们继续回到WebSecurityConfiguration类，查看它的另外一个重要的方法：

@Bean(
        name = {"springSecurityFilterChain"}
    )
    public Filter springSecurityFilterChain() throws Exception {
        boolean hasConfigurers = this.webSecurityConfigurers != null && !this.webSecurityConfigurers.isEmpty();
        if (!hasConfigurers) {
            WebSecurityConfigurerAdapter adapter = (WebSecurityConfigurerAdapter)this.objectObjectPostProcessor.postProcess(new WebSecurityConfigurerAdapter() {
            });
            this.webSecurity.apply(adapter);
        }

        return (Filter)this.webSecurity.build();
    }

该方法即为Spring Security构建Filter的核心方法，通过webSecurity的build方法构建了Spring Security的Filter。

我们继续查看WebSecurity类的build方法：

public final O build() throws Exception {
        if (this.building.compareAndSet(false, true)) {
            this.object = this.doBuild();
            return this.object;
        } else {
            throw new AlreadyBuiltException("This object has already been built");
        }
    }

实际上调用了上层的doBuild：

protected final O doBuild() throws Exception {
        LinkedHashMap var1 = this.configurers;
        synchronized(this.configurers) {
            this.buildState = AbstractConfiguredSecurityBuilder.BuildState.INITIALIZING;
            this.beforeInit();
            this.init();
            this.buildState = AbstractConfiguredSecurityBuilder.BuildState.CONFIGURING;
            this.beforeConfigure();
            this.configure();
            this.buildState = AbstractConfiguredSecurityBuilder.BuildState.BUILDING;
            O result = this.performBuild();
            this.buildState = AbstractConfiguredSecurityBuilder.BuildState.BUILT;
            return result;
        }
    }

这里主要看WebSecurity的init方法和performBuild方法,首先看init方法

private void init() throws Exception {
        #this.getConfigurers()该方法实际上获取WebSecurity中LinkedHashMap中的Value值集合
        Collection<SecurityConfigurer<O, B>> configurers = this.getConfigurers();
        Iterator var2 = configurers.iterator();

        SecurityConfigurer configurer;
        while(var2.hasNext()) {
            configurer = (SecurityConfigurer)var2.next();
            #调用SecurityConfigurer的init方法
            configurer.init(this);
        }

        var2 = this.configurersAddedInInitializing.iterator();

        while(var2.hasNext()) {
            configurer = (SecurityConfigurer)var2.next();
            configurer.init(this);
        }

    }

通过该代码可知，该方法首先获取WebSecurity中的LinkedHashMap中的Value值集合，再对Value值进行遍历并执行其中的init方法，从上面的代码分析我们知道WebSecurity中的LinkedHashMap实际存的就是WebSecurityConfig，这段代码将会调用WebSecurityConfig的init方法，而WebSecurityConfig的init方法来自于它的父类WebSecurityConfigurerAdapter，该init方法代码如下：

public abstract class WebSecurityConfigurerAdapter implements WebSecurityConfigurer<WebSecurity> {
        public void init(final WebSecurity web) throws Exception {
        #获取HttpSecurity
        final HttpSecurity http = this.getHttp();
        #将HttpSecurity放入WebSecurity中
        web.addSecurityFilterChainBuilder(http).postBuildAction(new Runnable() {
            public void run() {
                FilterSecurityInterceptor securityInterceptor =
                 (FilterSecurityInterceptor)http.getSharedObject(FilterSecurityInterceptor.class);
                web.securityInterceptor(securityInterceptor);
            }
        });
       }
       
       protected final HttpSecurity getHttp() throws Exception {
        if (this.http != null) {
            return this.http;
        } else {
            DefaultAuthenticationEventPublisher eventPublisher = (DefaultAuthenticationEventPublisher)this.objectPostProcessor.postProcess(new DefaultAuthenticationEventPublisher());
            this.localConfigureAuthenticationBldr.authenticationEventPublisher(eventPublisher);
            AuthenticationManager authenticationManager = this.authenticationManager();
            this.authenticationBuilder.parentAuthenticationManager(authenticationManager);
            this.authenticationBuilder.authenticationEventPublisher(eventPublisher);
            Map<Class<? extends Object>, Object> sharedObjects = this.createSharedObjects();
            this.http = new HttpSecurity(this.objectPostProcessor, this.authenticationBuilder, sharedObjects);
            if (!this.disableDefaults) {
                ((HttpSecurity)((DefaultLoginPageConfigurer)((HttpSecurity)((HttpSecurity)((HttpSecurity)((HttpSecurity)((HttpSecurity)((HttpSecurity)((HttpSecurity)((HttpSecurity)this.http.csrf().and()).addFilter(new WebAsyncManagerIntegrationFilter()).exceptionHandling().and()).headers().and()).sessionManagement().and()).securityContext().and()).requestCache().and()).anonymous().and()).servletApi().and()).apply(new DefaultLoginPageConfigurer())).and()).logout();
                ClassLoader classLoader = this.context.getClassLoader();
                List<AbstractHttpConfigurer> defaultHttpConfigurers = SpringFactoriesLoader.loadFactories(AbstractHttpConfigurer.class, classLoader);
                Iterator var6 = defaultHttpConfigurers.iterator();

                while(var6.hasNext()) {
                    AbstractHttpConfigurer configurer = (AbstractHttpConfigurer)var6.next();
                    this.http.apply(configurer);
                }
            }
            #调用本类的configure方法
            this.configure(this.http);
            return this.http;
        }
    }
    
    #模板方法设计模式，子类WebSecurityConfig将会覆盖该方法
    protected void configure(HttpSecurity http) throws Exception {
        this.logger.debug("Using default configure(HttpSecurity). If subclassed this will potentially override subclass configure(HttpSecurity).");
        ((HttpSecurity)((HttpSecurity)((AuthorizedUrl)http.authorizeRequests().anyRequest()).authenticated().and()).formLogin().and()).httpBasic();
    }
       
}

以上代码最终还是实际调用了我们写的WebSecurityConfig类的configure方法。

仔细观察以上代码，我们发现有一条语句web.addSecurityFilterChainBuilder(http)，该语句将构建的HttpSecurity放入WebSecurity类中，以下是该方法源码：

public WebSecurity addSecurityFilterChainBuilder(SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder) {
        this.securityFilterChainBuilders.add(securityFilterChainBuilder);
        return this;
    }

实际上就是将HttpSecurity放入了WebSecurity的一个list集合里，该list集合属性名为securityFilterChainBuilders。

到目前为止，我们终于知道我们编写的WebSecurityConfig类的configure方法是如何被调用的了，但是仍有许多疑问没解开，比如HttpSecurity类的作用，Spring Security是如何通过HttpSecurity类构建一条拦截器链等。

这里我们先不分析HttpSecurity类的具体实现，再来看看WebSecurity的init方法执行后所执行的performBuild方法，该方法源码如下：

protected Filter performBuild() throws Exception {
        Assert.state(!this.securityFilterChainBuilders.isEmpty(), () -> {
            return "At least one SecurityBuilder<? extends SecurityFilterChain> needs to be specified. Typically this done by adding a @Configuration that extends WebSecurityConfigurerAdapter. More advanced users can invoke " + WebSecurity.class.getSimpleName() + ".addSecurityFilterChainBuilder directly";
        });
        int chainSize = this.ignoredRequests.size() + this.securityFilterChainBuilders.size();
        List<SecurityFilterChain> securityFilterChains = new ArrayList(chainSize);
        Iterator var3 = this.ignoredRequests.iterator();

        while(var3.hasNext()) {
            RequestMatcher ignoredRequest = (RequestMatcher)var3.next();
            securityFilterChains.add(new DefaultSecurityFilterChain(ignoredRequest, new Filter[0]));
        }
        
        #遍历securityFilterChainBuilders集合
        var3 = this.securityFilterChainBuilders.iterator();

        while(var3.hasNext()) {
            SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder = (SecurityBuilder)var3.next();
            #执行securityFilterChainBuilders集合单位的build方法，返回一个SecurityFilterChain类，并加入List<SecurityFilterChain>中
            securityFilterChains.add(securityFilterChainBuilder.build());
        }
        
        #将List<SecurityFilterChain>类构建成一个FilterChainProxy代理类
        FilterChainProxy filterChainProxy = new FilterChainProxy(securityFilterChains);
        if (this.httpFirewall != null) {
            filterChainProxy.setFirewall(this.httpFirewall);
        }

        filterChainProxy.afterPropertiesSet();
        Filter result = filterChainProxy;
        if (this.debugEnabled) {
            this.logger.warn("\n\n********************************************************************\n**********        Security debugging is enabled.       *************\n**********    This may include sensitive information.  *************\n**********      Do not use in a production system!     *************\n********************************************************************\n\n");
            result = new DebugFilter(filterChainProxy);
        }

        this.postBuildAction.run();
        #返回FilterChainProxy代理类
        return (Filter)result;
    }

该方法执行的操作主要如下：

1. 遍历securityFilterChainBuilders集合，并执行其中的build方法，从上面代码分析可知，securityFilterChainBuilders集合里存储了HttpSecurity，所以这里执行了HttpSecurity的build方法构建SecurityFilterChain类
2. 将List<SecurityFilterChain>集合构建成一个FilterChainProxy代理类
3. 返回这个FilterChainProxy代理类

到这里总的过程就非常明了了，实际上Spring Security的顶层filter就是一个FilterChainProxy类，而HttpSecurity主要用于注册和实例化各种filter

到这里就分成了两路，一路是HttpSecurity的build方法构建SecurityFilterChain类的原理，一路是FilterChainProxy类的作用，我们先从FilterChainProxy类开始

FilterChainProxy类

当请求到达的时候，FilterChainProxy会调用dofilter()方法，会遍历所有的SecurityFilterChain，对匹配到的url，则一一调用SecurityFilterChain中的filter做认证授权。FilterChainProxy的dofilter()中调用了doFilterInternal()方法，如下：

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

    FirewalledRequest fwRequest = firewall
            .getFirewalledRequest((HttpServletRequest) request);
    HttpServletResponse fwResponse = firewall
            .getFirewalledResponse((HttpServletResponse) response);
    # 获取请求对应的filter列表
    List<Filter> filters = getFilters(fwRequest);

    if (filters == null || filters.size() == 0) {
        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);

        return;
    }

    VirtualFilterChain vfc = new VirtualFilterChain(fwRequest, chain, filters);
    # 执行每个filter
    vfc.doFilter(fwRequest, fwResponse);
}

# 通过遍历filterChains，调用SecurityFilterChain的matches方法，判断当前的请求对应哪些filter，返回匹配的filter列表
private List<Filter> getFilters(HttpServletRequest request) {
    for (SecurityFilterChain chain : filterChains) {
        if (chain.matches(request)) {
            return chain.getFilters();
        }
    }

    return null;
}

我们理清了FilterChainProxy类的作用，那么这些SecurityFilterChain是从哪来的呢？从上节可知SecurityFilterChain是由HttpSecurity的build方法生成的，下面我们分析下HttpSecurity类

HttpSecurity

HttpSecurity与WebSecurity一样，都继承了AbstractConfiguredSecurityBuilder类，而WebSecurity的build和doBuild方法和LinkedHashMap属性，均来自AbstractConfiguredSecurityBuilder，故HttpSecurity的build方法代码与WebSecurity的相同，区别在于LinkedHashMap存储的东西不同，HttpSecurity正是通过如此来生成SecurityFilterChain类的。

下面我们来看HttpSecurity构建filter的几个常见方法：

public ExpressionUrlAuthorizationConfigurer<HttpSecurity>.ExpressionInterceptUrlRegistry authorizeRequests() throws Exception {
        ApplicationContext context = this.getContext();
        return ((ExpressionUrlAuthorizationConfigurer)this.getOrApply(new ExpressionUrlAuthorizationConfigurer(context))).getRegistry();
    }


public FormLoginConfigurer<HttpSecurity> formLogin() throws Exception {
        return (FormLoginConfigurer)this.getOrApply(new FormLoginConfigurer());
    }

都调用了getOrApply方法，再来看getOrApply方法，又调用了其中的apply方法

private <C extends SecurityConfigurerAdapter<DefaultSecurityFilterChain, HttpSecurity>> C getOrApply(C configurer) throws Exception {
        C existingConfig = (SecurityConfigurerAdapter)this.getConfigurer(configurer.getClass());
        return existingConfig != null ? existingConfig : this.apply(configurer);
    }
    
public <C extends SecurityConfigurerAdapter<O, B>> C apply(C configurer) throws Exception {
        configurer.addObjectPostProcessor(this.objectPostProcessor);
        configurer.setBuilder(this);
        this.add(configurer);
        return configurer;
    }

apply方法又调用了add方法，这里的add方法最终还是将该configurer加入了linkedHashMap中

private <C extends SecurityConfigurer<O, B>> void add(C configurer) throws Exception {
        Assert.notNull(configurer, "configurer cannot be null");
        Class<? extends SecurityConfigurer<O, B>> clazz = configurer.getClass();
        LinkedHashMap var3 = this.configurers;
        synchronized(this.configurers) {
            if (this.buildState.isConfigured()) {
                throw new IllegalStateException("Cannot apply " + configurer + " to already built object");
            } else {
                List<SecurityConfigurer<O, B>> configs = this.allowConfigurersOfSameType ? (List)this.configurers.get(clazz) : null;
                if (configs == null) {
                    configs = new ArrayList(1);
                }

                ((List)configs).add(configurer);
                this.configurers.put(clazz, configs);
                if (this.buildState.isInitializing()) {
                    this.configurersAddedInInitializing.add(configurer);
                }

            }
        }
    }

故HttpSecurity在构建filter的过程中，本质还是将形如ExpressionUrlAuthorizationConfigurer、FormLoginConfigurer等类加入了它的LinkedHashMap中。

那么将这些Configurer类存入LinkedHashMap的作用又是什么？我们回忆上面WebSecurity类的doBuild方法，我们知道HttpSecurity类调用的doBuild方法与WebSecurity类一样，而通过观察WebSecurity类doBuild方法里this.init();this.configure();这些语句的具体实现，实际就是调用其LinkedHashMap中的元素的init方法和configure方法。

我们现在来查看其中一个ExpressionUrlAuthorizationConfigurer类的configure方法的详细代码：

public void configure(H http) throws Exception {
        FilterInvocationSecurityMetadataSource metadataSource = this.createMetadataSource(http);
        if (metadataSource != null) {
            FilterSecurityInterceptor securityInterceptor = this.createFilterSecurityInterceptor(http, metadataSource, (AuthenticationManager)http.getSharedObject(AuthenticationManager.class));
            if (this.filterSecurityInterceptorOncePerRequest != null) {
                securityInterceptor.setObserveOncePerRequest(this.filterSecurityInterceptorOncePerRequest);
            }

            securityInterceptor = (FilterSecurityInterceptor)this.postProcess(securityInterceptor);
            #将Filter加入了HttpSecurity的Filters集合中
            http.addFilter(securityInterceptor);
            http.setSharedObject(FilterSecurityInterceptor.class, securityInterceptor);
        }
    }

最后来看看HttpSecruity的performBuild()方法：

protected DefaultSecurityFilterChain performBuild() throws Exception {
        Collections.sort(this.filters, this.comparator);
        return new DefaultSecurityFilterChain(this.requestMatcher, this.filters);
    }

实际上就是通过Filters集合构建了SecurityFilterChain。

从上面代码可总结出，HttpSecurity内部维护一个Filter列表，而HttpSecurity调用形如authorizeRequests()，formLogin()等方法实际上就是将filter添加入它的列表当中，最后通过performBuild()方法构建出SecurityFilterChain，至此HttpSecurity构建filter的总过程就完成了。

总结

到目前为止，我们终于知道Spring Security是如何一步步的构建和初始化filter的了，我们最后再来简单总结下构建过程：

1. Spring Security启动过程中通过WebSecurityConfiguration实例化WebSecurity
2. WebSecurityConfiguration会将使用者编写的WebSecurityConfig类放入WebSecurity中的LinkedHashMap中
3. 在构建WebSecurity的时候，会调用WebSecurity的doBuild()方法，这个方法是一个核心方法。
4. doBuild中的init方法将会调用LinkedHashMap中元素的init方法（这里的元素是WebSecurityConfig），然后WebSecurityConfig的init方法会调用configure方法，调用configure方法后，将会初始化HttpSecurity构建各种Filter，这时HttpSecurity将会加入WebSecurity中。
5. doBuild中的init方法调用完后将会调用下一个performBuild()方法，该方法会获取到HttpSecurity调用其doBuild方法构造SecurityFilterChain
6. 将获取到的SecurityFilterChain构建成一个FilterChainProxy类，作为Spring Security的顶层filter
7. 至此Spring Security的Filter构建完成