二Spring Security基本原理

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一、Spring Security常见过滤器介绍

Spring Security 本质是一个过滤器链

从启动时，可以获取到过滤器链：

Spring Security中过滤器的介绍：

  1. org.springframework.security.web.context.SecurityContextPersistenceFilter
    首当其冲的一个过滤器，作用之重要，自不必多言。
    SecurityContextPersistenceFilter主要是使用SecurityContextRepository在session中保存或更新一个SecurityContext，并将SecurityContext给以后的过滤器使用，来为后续filter建立所需的上下文。
    SecurityContext中存储了当前用户的认证以及权限信息。
  2. org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter
    此过滤器用于集成SecurityContext到Spring异步执行机制中的WebAsyncManager
  3. org.springframework.security.web.header.HeaderWriterFilter
    向请求的Header中添加相应的信息,可在http标签内部使用security:headers来控制
  4. org.springframework.security.web.csrf.CsrfFilter
    csrf又称跨域请求伪造，SpringSecurity会对所有post请求验证是否包含系统生成的csrf的token信息，如果不包含，则报错。起到防止csrf攻击的效果。
  5. org.springframework.security.web.authentication.logout.LogoutFilter
    匹配URL为/logout的请求，实现用户退出,清除认证信息。
  6. org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter
    认证操作全靠这个过滤器，默认匹配URL为/login且必须为POST请求。
  7. org.springframework.security.web.authentication.ui.DefaultLoginPageGeneratingFilter
    如果没有在配置文件中指定认证页面，则由该过滤器生成一个默认认证页面。
  8. org.springframework.security.web.authentication.ui.DefaultLogoutPageGeneratingFilter
    由此过滤器可以生产一个默认的退出登录页面
  9. org.springframework.security.web.authentication.www.BasicAuthenticationFilter
    此过滤器会自动解析HTTP请求中头部名字为Authentication，且以Basic开头的头信息。
  10. org.springframework.security.web.savedrequest.RequestCacheAwareFilter
    通过HttpSessionRequestCache内部维护了一个RequestCache，用于缓存HttpServletRequest
  11. org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter
    针对ServletRequest进行了一次包装，使得request具有更加丰富的API
  12. org.springframework.security.web.authentication.AnonymousAuthenticationFilter
    当SecurityContextHolder中认证信息为空,则会创建一个匿名用户存入到SecurityContextHolder中。Spring Security为了兼容未登录的访问，也走了一套认证流程，只不过是一个匿名的身份。
  13. org.springframework.security.web.session.SessionManagementFilter
    SecurityContextRepository限制同一用户开启多个会话的数量
  14. org.springframework.security.web.access.ExceptionTranslationFilter
    异常转换过滤器位于整个springSecurityFilterChain的后方，用来转换整个链路中出现的异常
  15. org.springframework.security.web.access.intercept.FilterSecurityInterceptor
    获取所配置资源访问的授权信息，根据SecurityContextHolder中存储的用户信息来决定其是否有权限。

二、Spring Security过滤器链加载原理

通过前面15个过滤器功能的介绍，是不是有新的疑惑，我们并没有配置这些过滤器啊？它们都是怎么被加载出来的？

通过查看源码
FilterSecurityInterceptor：是一个方法级的权限过滤器，基本位于过滤链的最底部。
ExceptionTranslationFilter：是一个异常过滤器，用来处理在认证授权过程中抛出的异常。
UsernamePasswordAuthenticationFilter：对/login的post请求做拦截，校验表单中用户名、密码。

2.1、DelegatingFilterProxy

DelegatingFilterProxy源码里重要代码进行说明，其中删减掉了一些不重要的代码，大家注意我写的注释就行了。

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.web.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

public class DelegatingFilterProxy extends GenericFilterBean 
    @Nullable
    private String contextAttribute;
    @Nullable
    private WebApplicationContext webApplicationContext;
    @Nullable
    private String targetBeanName;
    private boolean targetFilterLifecycle;
    @Nullable
    private volatile Filter delegate; // 注:这个过滤器才是真正加载的过滤器
    private final Object delegateMonitor;

   
	// 注:doFilter才是过滤器的入口,直接从这看!
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException 
        Filter delegateToUse = this.delegate;
        if (delegateToUse == null) 
            synchronized(this.delegateMonitor) 
                delegateToUse = this.delegate;
                if (delegateToUse == null) 
                    WebApplicationContext wac = this.findWebApplicationContext();
                    if (wac == null) 
                        throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener or DispatcherServlet registered?");
                    
					// 第一步：doFilter中最重要的一步，初始化上面私有过滤器属性delegate
                    delegateToUse = this.initDelegate(wac);
                

                this.delegate = delegateToUse;
            
        
		
		//第三步：执行FilterChainProxy过滤器
        this.invokeDelegate(delegateToUse, request, response, filterChain);
    

    //第二步：直接看最终加载的过滤器到底是谁
    protected Filter initDelegate(WebApplicationContext wac) throws ServletException 
		//debug得知targetBeanName为：springSecurityFilterChain
        String targetBeanName = this.getTargetBeanName();
        Assert.state(targetBeanName != null, "No target bean name set");
		//debug得知delegate对象为：FilterChainProxy
        Filter delegate = (Filter)wac.getBean(targetBeanName, Filter.class);
        if (this.isTargetFilterLifecycle()) 
            delegate.init(this.getFilterConfig());
        

        return delegate;
    

    protected void invokeDelegate(Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException 
        delegate.doFilter(request, response, filterChain);

第二步debug结果如下：

由此可知，DelegatingFilterProxy通过springSecurityFilterChain这个名称，得到了一个FilterChainProxy过滤器，
最终在第三步执行了这个过滤器。

2.2、FilterChainProxy

注意代码注释！注意代码注释！注意代码注释！

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.security.web;

import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import javax.servlet.Filter;
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 org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.web.firewall.FirewalledRequest;
import org.springframework.security.web.firewall.HttpFirewall;
import org.springframework.security.web.firewall.StrictHttpFirewall;
import org.springframework.security.web.util.UrlUtils;
import org.springframework.web.filter.GenericFilterBean;

public class FilterChainProxy extends GenericFilterBean 
    private static final Log logger = LogFactory.getLog(FilterChainProxy.class);
    private static final String FILTER_APPLIED = FilterChainProxy.class.getName().concat(".APPLIED");
    private List<SecurityFilterChain> filterChains;
    private FilterChainProxy.FilterChainValidator filterChainValidator;
    private HttpFirewall firewall;

    //可以通过一个叫SecurityFilterChain的对象实例化出一个FilterChainProxy对象
	//这FilterChainProxy又是何方神圣？会不会是真正的过滤器链对象呢？先留着这个疑问！
    public FilterChainProxy(SecurityFilterChain chain) 
        this(Arrays.asList(chain));
    
    //又是SecurityFilterChain这家伙！嫌疑更大了！
    public FilterChainProxy(List<SecurityFilterChain> filterChains) 
        this.filterChainValidator = new FilterChainProxy.NullFilterChainValidator();
        this.firewall = new StrictHttpFirewall();
        this.filterChains = filterChains;
    

    //注：直接从doFilter看
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException 
        boolean clearContext = request.getAttribute(FILTER_APPLIED) == null;
        if (clearContext) 
            try 
                request.setAttribute(FILTER_APPLIED, Boolean.TRUE);
                this.doFilterInternal(request, response, chain);
             finally 
                SecurityContextHolder.clearContext();
                request.removeAttribute(FILTER_APPLIED);
            
         else 
			//第一步：具体操作调用下面的doFilterInternal方法了
            this.doFilterInternal(request, response, chain);
        

    

    private void doFilterInternal(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException 
        FirewalledRequest fwRequest = this.firewall.getFirewalledRequest((HttpServletRequest)request);
        HttpServletResponse fwResponse = this.firewall.getFirewalledResponse((HttpServletResponse)response);
        //第二步：封装要执行的过滤器链，那么多过滤器就在这里被封装进去了！
		List<Filter> filters = this.getFilters((HttpServletRequest)fwRequest);
        if (filters != null && filters.size() != 0) 
            FilterChainProxy.VirtualFilterChain vfc = new FilterChainProxy.VirtualFilterChain(fwRequest, chain, filters);
            //第四步：加载过滤器链
			vfc.doFilter(fwRequest, fwResponse);
         else 
            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);
        
    

    private List<Filter> getFilters(HttpServletRequest request) 
        Iterator var2 = this.filterChains.iterator();
		//第三步：封装过滤器链到SecurityFilterChain中！
        SecurityFilterChain chain;
        do 
            if (!var2.hasNext()) 
                return null;
            

            chain = (SecurityFilterChain)var2.next();
         while(!chain.matches(request));

        return chain.getFilters();

第二步debug结果如下图所示，惊不惊喜？十五个过滤器都在这里了！

再看第三步，怀疑这么久！原来这些过滤器还真是都被封装进SecurityFilterChain中了。

2.3、SecurityFilterChain

最后看SecurityFilterChain，这是个接口，实现类也只有一个，这才是web.xml中配置的过滤器链对象！
接口：SecurityFilterChain.java

package org.springframework.security.web;

import java.util.List;
import javax.servlet.Filter;
import javax.servlet.http.HttpServletRequest;

public interface SecurityFilterChain 
    boolean matches(HttpServletRequest var1);

    List<Filter> getFilters();

实现类：DefaultSecurityFilterChain.java

package org.springframework.security.web;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.servlet.Filter;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.security.web.util.matcher.RequestMatcher;

public final class DefaultSecurityFilterChain implements SecurityFilterChain 
    private static final Log logger = LogFactory.getLog(DefaultSecurityFilterChain.class);
    private final RequestMatcher requestMatcher;
    private final List<Filter> filters;

    public DefaultSecurityFilterChain(RequestMatcher requestMatcher, Filter... filters) 
        this(requestMatcher, Arrays.asList(filters));
    

    public DefaultSecurityFilterChain(RequestMatcher requestMatcher, List<Filter> filters) 
        logger.info("Creating filter chain: " + requestMatcher + ", " + filters);
        this.requestMatcher = requestMatcher;
        this.filters = new ArrayList(filters);
    

    public RequestMatcher getRequestMatcher() 
        return this.requestMatcher;
    

    public List<Filter> getFilters() 
        return this.filters;
    

    public boolean matches(HttpServletRequest request) 
        return this.requestMatcher.matches(request);
    

    public String toString() 
        return "[ " + this.requestMatcher + ", " + this.filters + "]";

总结：对SpringSecurity工作原理有了一定的认识。但理论千万条，功能第一条，探寻底层，是为了更好的使用框架。

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