Spring Security實現原理剖析（一）：filter的構造和初始化

前言

我們知道Spring Security的核心實現原理都是從filter開始的，Spring Security通過構造層層filter來實現登錄跳轉、權限驗證，角色管理等功能。本章通過剖析Spring Security的核心源碼來說明Spring Security的filter是如何開始構造並運行的。

從最初開始

往往我們定義一個Spring Security程序都是通過配置一個WebSecurityConfig類開始的，簡單代碼如下：

@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();
    }
    
}

通過以上代碼一個簡單的Spring Security應用程序就能成功執行了，該程序能攔截除了/login路徑以外的所有請求到登錄頁面。
我們可以看到以上代碼並沒有任何顯示聲明filter的語句，那麼Spring Security是如何通過上述代碼生成filter的呢？下面就由我來一層層解剖Spring Security的源碼來說明。

@EnableWebSecurity註解

我們注意到如上代碼有個@EnableWebSecurity註解,進入該註解查看

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

WebSecurityConfiguration類

我們可以看到如上該註解導入了WebSecurityConfiguration類，進入該類查看：

@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類是作爲一個Spring配置源，同時定義了許多bean，這裏重點看如下這個方法：

    
     @Autowired(
        required = false
    )
    public void setFilterChainProxySecurityConfigurer(ObjectPostProcessor<Object> objectPostProcessor, 
    @Value("#{@autowiredWebSecurityConfigurersIgnoreParents.getWebSecurityConfigurers()}") 
    List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers) throws Exception {
    
        // 這段代碼初始化webSecurity
        this.webSecurity = (WebSecurity)objectPostProcessor.postProcess(new WebSecurity(objectPostProcessor));
        if (this.debugEnabled != null) {
            this.webSecurity.debug(this.debugEnabled);
        }
        
        // webSecurityConfigurers該屬性是通過@Value註解注入的
        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;
        }
        
        // 將webSecurityConfigurers依次放入webSecurity
        var5 = webSecurityConfigurers.iterator();
        while(var5.hasNext()) {
            config = (SecurityConfigurer)var5.next();
            this.webSecurity.apply(config);
        }

        this.webSecurityConfigurers = webSecurityConfigurers;
    }

總結下該方法所做的主要操作：

首先初始化了webSecurity屬性，該屬性對應WebSecurity類
注入了webSecurityConfigurers屬性，該屬性是一個List<SecurityConfigurer>集合
遍歷webSecurityConfigurers集合，調用webSecurity的apply方法，該方法參數爲SecurityConfigurer接口

這裏有一個重要的接口SecurityConfigurer接口，該接口代碼如下：

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

    void configure(B var1) throws Exception;
}

回顧上面我們編寫的WebSecurityConfig配置類，也有一個configure方法，那麼我們猜測WebSecurityConfig類是不是也實現了SecurityConfigurer接口呢？答案是是的，我們可以看WebSecurityConfig類的類圖

可以看到WebSecurityConfig類實現了SecurityConfigurer接口。
因此webSecurityConfigurers屬性通過依賴注入包含了WebSecurityConfig類，通過上述第3條操作將我們配置的WebSecurityConfig類和WebSecurity類關聯起來。

WebSecurity類

到這裏我們知道了WebSecurityConfiguration類調用上述方法將我們配置的WebSecurityConfig類用WebSecurity類的apply方法關聯起來，那麼我們詳細看看WebSecurity類的apply方法：

public <C extends SecurityConfigurerAdapter<O, B>> C apply(C configurer) throws Exception {
        configurer.addObjectPostProcessor(this.objectPostProcessor);
        configurer.setBuilder(this);
        // 繼續調用該類的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");
        // 獲取class屬性
        Class<? extends SecurityConfigurer<O, B>> clazz = configurer.getClass();
        // 獲取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);
                // 將configurer放入一個LinkedHashMap中
                this.configurers.put(clazz, configs);
                if (this.buildState.isInitializing()) {
                    this.configurersAddedInInitializing.add(configurer);
                }

            }
        }
    }

從上述代碼可知，實際上就是將WebSecurityConfig類放入了WebSecurity類的一個LinkedHashMap中，該LinkedHashMap在WebSecurity中屬性名爲configurers。

我們繼續回到WebSecurityConfiguration類，查看它的另外一個重要的方法：

 @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();
    }

該方法即爲Spring Security構建Filter的核心方法，通過webSecurity的build方法構建了Spring Security的Filter。
我們繼續查看WebSecurity類的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");
        }
    }

實際上調用了上層的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;
        }
    }

這裏主要看WebSecurity的init方法和performBuild方法,首先看init方法

 private void init() throws Exception {
        // this.getConfigurers()該方法實際上獲取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();
            // 調用SecurityConfigurer的init方法
            configurer.init(this);
        }

        var2 = this.configurersAddedInInitializing.iterator();

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

    }

通過該代碼可知，該方法首先獲取WebSecurity中的LinkedHashMap中的Value值集合，再對Value值進行遍歷並執行其中的init方法，從上面的代碼分析我們知道WebSecurity中的LinkedHashMap實際存的就是WebSecurityConfig，這段代碼將會調用WebSecurityConfig的init方法，而WebSecurityConfig的init方法來自於它的父類WebSecurityConfigurerAdapter，該init方法代碼如下：

public abstract class WebSecurityConfigurerAdapter implements WebSecurityConfigurer<WebSecurity> {
        public void init(final WebSecurity web) throws Exception {
        // 獲取HttpSecurity
        final HttpSecurity http = this.getHttp();
        // 將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);
                }
            }
            // 調用本類的configure方法
            this.configure(this.http);
            return this.http;
        }
    }
    
    // 模板方法設計模式，子類WebSecurityConfig將會覆蓋該方法
    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();
    }
       
}

以上代碼最終還是實際調用了我們寫的WebSecurityConfig類的configure方法。

仔細觀察以上代碼，我們發現有一條語句web.addSecurityFilterChainBuilder(http)，該語句將構建的HttpSecurity放入WebSecurity類中，以下是該方法源碼：

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

實際上就是將HttpSecurity放入了WebSecurity的一個list集合裏，該list集合屬性名爲securityFilterChainBuilders。

到目前爲止，我們終於知道我們編寫的WebSecurityConfig類的configure方法是如何被調用的了，但是仍有許多疑問沒解開，比如HttpSecurity類的作用，Spring Security是如何通過HttpSecurity類構建一條攔截器鏈等。

這裏我們先不分析HttpSecurity類的具體實現，再來看看WebSecurity的init方法執行後所執行的performBuild方法，該方法源碼如下：

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]));
        }
        
        / 遍歷securityFilterChainBuilders集合
        var3 = this.securityFilterChainBuilders.iterator();

        while(var3.hasNext()) {
            SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder = (SecurityBuilder)var3.next();
            // 執行securityFilterChainBuilders集合單位的build方法，返回一個SecurityFilterChain類，並加入List<SecurityFilterChain>中
            securityFilterChains.add(securityFilterChainBuilder.build());
        }
        
        // 將List<SecurityFilterChain>類構建成一個FilterChainProxy代理類
        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代理類
        return (Filter)result;
    }

該方法執行的操作主要如下：

遍歷securityFilterChainBuilders集合，並執行其中的build方法，從上面代碼分析可知，securityFilterChainBuilders集合裏存儲了HttpSecurity，所以這裏執行了HttpSecurity的build方法構建SecurityFilterChain類
將List<SecurityFilterChain>集合構建成一個FilterChainProxy代理類
返回這個FilterChainProxy代理類

到這裏總的過程就非常明瞭了，實際上Spring Security的頂層filter就是一個FilterChainProxy類，而HttpSecurity主要用於註冊和實例化各種filter

到這裏就分成了兩路，一路是HttpSecurity的build方法構建SecurityFilterChain類的原理，一路是FilterChainProxy類的作用，我們先從FilterChainProxy類開始

FilterChainProxy類

當請求到達的時候，FilterChainProxy會調用dofilter()方法，會遍歷所有的SecurityFilterChain，對匹配到的url，則一一調用SecurityFilterChain中的filter做認證授權。FilterChainProxy的dofilter()中調用了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);
    // 獲取請求對應的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);
    // 執行每個filter
    vfc.doFilter(fwRequest, fwResponse);
}

// 通過遍歷filterChains，調用SecurityFilterChain的matches方法，判斷當前的請求對應哪些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;
}

我們理清了FilterChainProxy類的作用，那麼這些SecurityFilterChain是從哪來的呢？從上節可知SecurityFilterChain是由HttpSecurity的build方法生成的，下面我們分析下HttpSecurity類

HttpSecurity

HttpSecurity與WebSecurity一樣，都繼承了AbstractConfiguredSecurityBuilder類，而WebSecurity的build和doBuild方法和LinkedHashMap屬性，均來自AbstractConfiguredSecurityBuilder，故HttpSecurity的build方法代碼與WebSecurity的相同，區別在於LinkedHashMap存儲的東西不同，HttpSecurity正是通過如此來生成SecurityFilterChain類的。

下面我們來看HttpSecurity構建filter的幾個常見方法：

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());
    }

都調用了getOrApply方法，再來看getOrApply方法，又調用了其中的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方法又調用了add方法，這裏的add方法最終還是將該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在構建filter的過程中，本質還是將形如ExpressionUrlAuthorizationConfigurer、FormLoginConfigurer等類加入了它的LinkedHashMap中。

那麼將這些Configurer類存入LinkedHashMap的作用又是什麼？我們回憶上面WebSecurity類的doBuild方法，我們知道HttpSecurity類調用的doBuild方法與WebSecurity類一樣，而通過觀察WebSecurity類doBuild方法裏this.init();this.configure();這些語句的具體實現，實際就是調用其LinkedHashMap中的元素的init方法和configure方法。

我們現在來查看其中一個ExpressionUrlAuthorizationConfigurer類的configure方法的詳細代碼：

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);
            // 將Filter加入了HttpSecurity的Filters集合中
            http.addFilter(securityInterceptor);
            http.setSharedObject(FilterSecurityInterceptor.class, securityInterceptor);
        }
    }

最後來看看HttpSecruity的performBuild()方法：

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

實際上就是通過Filters集合構建了SecurityFilterChain。

從上面代碼可總結出，HttpSecurity內部維護一個Filter列表，而HttpSecurity調用形如authorizeRequests()，formLogin()等方法實際上就是將filter添加入它的列表當中，最後通過performBuild()方法構建出SecurityFilterChain，至此HttpSecurity構建filter的總過程就完成了。

總結

到目前爲止，我們終於知道Spring Security是如何一步步的構建和初始化filter的了，我們最後再來簡單總結下構建過程：

Spring Security啓動過程中通過WebSecurityConfiguration實例化WebSecurity
WebSecurityConfiguration會將使用者編寫的WebSecurityConfig類放入WebSecurity中的LinkedHashMap中
在構建WebSecurity的時候，會調用WebSecurity的doBuild()方法，這個方法是一個核心方法。
doBuild中的init方法將會調用LinkedHashMap中元素的init方法（這裏的元素是WebSecurityConfig），然後WebSecurityConfig的init方法會調用configure方法，調用configure方法後，將會初始化HttpSecurity構建各種Filter，這時HttpSecurity將會加入WebSecurity中。
doBuild中的init方法調用完後將會調用下一個performBuild()方法，該方法會獲取到HttpSecurity調用其doBuild方法構造SecurityFilterChain
將獲取到的SecurityFilterChain構建成一個FilterChainProxy類，作爲Spring Security的頂層filter
至此Spring Security的Filter構建完成

Spring Security實現原理剖析（一）：filter的構造和初始化

前言

從最初開始

@EnableWebSecurity註解

WebSecurityConfiguration類

WebSecurity類

FilterChainProxy類

HttpSecurity

總結

【JAVA集合知識集錦】LinkedList要點總結

【JAVA集合知識集錦】ArrayList要點總結

Spring Security實現原理剖析（一）：filter的構造和初始化

java併發實戰：連接池實現

https證書互信解決方案—創建私有CA並申請證書

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

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