spring-security-4 （3）spring security過濾器的創建與注冊原理

 　　spring security是通過一個過濾器鏈來保護你的web應用安全。在spring security中，該過濾鏈的名稱為springSecurityFilterChain，類型為FilterChainProxy。並通過DelegatingFilterProxy代理調用。對於這一點，這樣說可能更好理解：springSecurityFilterChain是spring中的bean，而過濾器要想起作用必須配置在web.xml中。為了使springSecurityFilterChain起到攔截作用，就必須讓web.xml意識到（其實應該是說讓servlet容器/Tomcat）。而DelegatingFilterChain就起到了該角色的作用。它將web.xml和springSecurityFilterChain聯系起來。接下來，我們用spring-security-4 （2）spring security 基於Java配置的搭建中的代碼為例，來講解spring security過濾器的創建和注冊原理。

一、Spring Security過濾器的創建原理

　　讓我們首先看下MySecurityConfig類

@EnableWebSecurity
@Configuration
public class MySecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Autowired
    public void configUser(AuthenticationManagerBuilder builder) throws Exception {
        builder
            .inMemoryAuthentication()
                //創建用戶名為user，密碼為password的用戶
                .withUser("user").password("password").roles("USER");
    }
}

 　　可以看到MySecurityConfig上的@EnableWebSecurity注解，查看該注解的源碼

@Retention(value = java.lang.annotation.RetentionPolicy.RUNTIME)
@Target(value = { java.lang.annotation.ElementType.TYPE })
@Documented
@Import({ WebSecurityConfiguration.class,
        SpringWebMvcImportSelector.class })
@EnableGlobalAuthentication
@Configuration
public @interface EnableWebSecurity {

    /**
     * Controls debugging support for Spring Security. Default is false.
     * @return if true, enables debug support with Spring Security
     */
    boolean debug() default false;
}

　　@EnableWebSecurity上的@Import注解引入了兩個類WebSecurityConfiguration和SpringWebMvcImportSelector，spring security的過濾器正是由WebSecurityConfiguration創建。讓我們看下WebSecurityConfiguration的部分源碼

...
    //查看AbstractSecurityWebApplicationInitializer的源碼可以看到
    //AbstractSecurityWebApplicationInitializer.DEFAULT_FILTER_NAME = "springSecurityFilterChain"
    @Bean(name = AbstractSecurityWebApplicationInitializer.DEFAULT_FILTER_NAME)
    public Filter springSecurityFilterChain() throws Exception {
        boolean hasConfigurers = webSecurityConfigurers != null
                && !webSecurityConfigurers.isEmpty();
        //如果沒有配置類那么就new一個WebSecurityConfigurerAdapter,也就是說我們沒有配置MySecurityConfig或者說其沒有被spring掃描到
        if (!hasConfigurers) {
            WebSecurityConfigurerAdapter adapter = objectObjectPostProcessor
                    .postProcess(new WebSecurityConfigurerAdapter() {
                    });
            webSecurity.apply(adapter);
        }
        //創建Filter
        return webSecurity.build();
    }
...

　　從源碼中可以看到通過WebSecurity.build()創建出名字為springSecurityFilterChain的Filter對象。（特別說明一下，一定要保證我們的MySecurityConfig類注解了@Configuration並可以被spring掃描到，如果沒有被sping掃描到，那么spring security會認為沒有配置類，就會新new 出一個WebSecurityConfigureAdapter對象，這會導致我們配置的用戶名和密碼失效。）那么該Filter的類型是什么呢？別着急，我們先來看下WeSecurity的繼承體系。

　　

　　build方法定義在AbstractSecurityBuilder中，源碼如下：

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

　　doBuild方法定義在AbstractConfiguredSecurityBuilder中，源碼如下：

...
protected final O doBuild() throws Exception {
        synchronized (configurers) {
            buildState = BuildState.INITIALIZING;

            beforeInit();
            init();

            buildState = BuildState.CONFIGURING;

            beforeConfigure();
            configure();

            buildState = BuildState.BUILDING;

            //performBuild方法創建
            O result = performBuild();

            buildState = BuildState.BUILT;

            return result;
        }
    }
...

　　performBuild()方法定義在WebSecurity中，源碼如下

...
protected Filter performBuild() throws Exception {
    Assert.state(
            !securityFilterChainBuilders.isEmpty(),
            "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 = ignoredRequests.size() + securityFilterChainBuilders.size();
    List<SecurityFilterChain> securityFilterChains = new ArrayList<SecurityFilterChain>(
            chainSize);
    for (RequestMatcher ignoredRequest : ignoredRequests) {
        securityFilterChains.add(new DefaultSecurityFilterChain(ignoredRequest));
    }
    for (SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder : securityFilterChainBuilders) {
        securityFilterChains.add(securityFilterChainBuilder.build());
    }

    //創建FilterChainProxy
    FilterChainProxy filterChainProxy = new FilterChainProxy(securityFilterChains);
    if (httpFirewall != null) {
        filterChainProxy.setFirewall(httpFirewall);
    }
    filterChainProxy.afterPropertiesSet();

    Filter result = filterChainProxy;
    if (debugEnabled) {
        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);
    }
    postBuildAction.run();
    return result;
}
...

　　不關心其具體實現，我們從源碼中看到spring security創建的過濾器類型為FilterChainProxy。由此完成過濾器的創建。

二、Spring Security過濾器的注冊原理

　　看下我們創建的SecurityInitializer類：

public class SecurityInitializer extends AbstractSecurityWebApplicationInitializer {

}

 　　這段代碼雖然很簡單，但卻是注冊過濾器所必須的。

　　根據Servlet3.0中，提供了ServletContainerInitializer接口，該接口提供了一個onStartup方法，用於在容器啟動時動態注冊Servlet,Filter,Listener等。因為我們建立的是web項目，那我們的依賴中肯定是由spring-web依賴的

　　根據Servlet 3.0規范，Servlet容器在啟動時，會負責創建圖中紅色箭頭所指的類，即SpringServletContainerInitializer，該類是ServletContainerInitializer的實現類。那么該類必有onStartup方法。讓我們看下它的源碼

package org.springframework.web;

import java.lang.reflect.Modifier;
import java.util.LinkedList;
import java.util.List;
import java.util.ServiceLoader;
import java.util.Set;
import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;

import org.springframework.core.annotation.AnnotationAwareOrderComparator;

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
    @Override
    public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
            throws ServletException {

        List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();

        if (webAppInitializerClasses != null) {
            for (Class<?> waiClass : webAppInitializerClasses) {
                //如果waiClass不為接口，抽象類，並且屬於WebApplicationInitializer類型
                //那么通過反射構造該接口的實例。
                if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                        WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
                    try {
                        initializers.add((WebApplicationInitializer) waiClass.newInstance());
                    }
                    catch (Throwable ex) {
                        throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                    }
                }
            }
        }

        if (initializers.isEmpty()) {
            servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
            return;
        }

        AnnotationAwareOrderComparator.sort(initializers);
        servletContext.log("Spring WebApplicationInitializers detected on classpath: " + initializers);

        for (WebApplicationInitializer initializer : initializers) {
            //調用所有WebApplicationInitializer實例的onStartup方法
            initializer.onStartup(servletContext);
        }
    }

}

　　請注意該類上的@HandlesTypes(WebApplicationInitializer.class)注解，根據Sevlet3.0規范，Servlet容器要負責以Set集合的方式注入指定類的子類（包括接口，抽象類）。其中AbstractSecurityWebApplicationInitializer是WebApplicationInitializer的抽象子類，我我們看下它的onStartup方法

...
public final void onStartup(ServletContext servletContext) throws ServletException {
        beforeSpringSecurityFilterChain(servletContext);
        if (this.configurationClasses != null) {
            AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
            rootAppContext.register(this.configurationClasses);
            servletContext.addListener(new ContextLoaderListener(rootAppContext));
        }
        if (enableHttpSessionEventPublisher()) {
            servletContext.addListener(
                    "org.springframework.security.web.session.HttpSessionEventPublisher");
        }
        servletContext.setSessionTrackingModes(getSessionTrackingModes());
        //注冊過濾器
        insertSpringSecurityFilterChain(servletContext);
        afterSpringSecurityFilterChain(servletContext);
}
...

　　該類中的insertSpringSecurityFilterChain(servletContext)就是在注冊過濾器。因為在過濾器創建中所說的springSecurityFilterChain，它其實是spring中的bean，而servletContext也必定可以獲取到該bean。我們接着看insertSpringSecurityFilterChain的源碼

...
public static final String DEFAULT_FILTER_NAME = "springSecurityFilterChain";

private void insertSpringSecurityFilterChain(ServletContext servletContext) {

    String filterName = DEFAULT_FILTER_NAME;
    //通過DelegatingFilterProxy代理
    DelegatingFilterProxy springSecurityFilterChain = new DelegatingFilterProxy(
            filterName);
    String contextAttribute = getWebApplicationContextAttribute();
    if (contextAttribute != null) {
        springSecurityFilterChain.setContextAttribute(contextAttribute);
    }
    //完成過濾器的注冊
    registerFilter(servletContext, true, filterName, springSecurityFilterChain);
}
...

　　一開始我們就提到了調用過濾器鏈springSecurityFilterChain需要DelegatingFilterProxy進行代理，將其與web.xml聯系起來。這段代碼就是很好的證明。DelegatingFilterProxy中維護了一個類型為String，名字叫做targetBeanName的字段，targetBeanName就是DelegatingFilterProxy所代理的類的名稱。最后通過registerFilter最終完成過濾器的注冊。

 

參考資料：http://www.tianshouzhi.com/api/tutorials/spring_security_4/250

　　　　　https://docs.spring.io/spring-security/site/docs/4.1.3.RELEASE/reference/htmlsingle/