最近项目需要用到Spring Security的权限控制,故花了点时间简单的去看了一下其权限控制相关的源码(版本为4.2)。

AccessDecisionManager

spring security是通过AccessDecisionManager进行授权管理的,先来张官方图镇楼。

权限

AccessDecisionManager

AccessDecisionManager 接口定义了如下方法:

//调用AccessDecisionVoter进行投票(关键方法)
void decide(Authentication authentication, Object object,
		Collection<ConfigAttribute> configAttributes) throws AccessDeniedException,
		InsufficientAuthenticationException;

boolean supports(ConfigAttribute attribute);
boolean supports(Class clazz);

接下来看看它的实现类的具体实现:

AffirmativeBased

public void decide(Authentication authentication, Object object,
		Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
	int deny = 0;

	for (AccessDecisionVoter voter : getDecisionVoters()) {
		//调用AccessDecisionVoter进行vote(我们姑且称之为投票吧),后面再看vote的源码。
		int result = voter.vote(authentication, object, configAttributes);

		if (logger.isDebugEnabled()) {
			logger.debug("Voter: " + voter + ", returned: " + result);
		}
		
		switch (result) {
		case AccessDecisionVoter.ACCESS_GRANTED://值为1
			//只要有voter投票为ACCESS_GRANTED,则通过
			return;

		case AccessDecisionVoter.ACCESS_DENIED://值为-1
			deny++;

			break;

		default:
			break;
		}
	}

	if (deny > 0) {
		//如果有两个及以上AccessDecisionVoter(姑且称之为投票者吧)都投ACCESS_DENIED,则直接就不通过了
		throw new AccessDeniedException(messages.getMessage(
				"AbstractAccessDecisionManager.accessDenied", "Access is denied"));
	}

	// To get this far, every AccessDecisionVoter abstained
	checkAllowIfAllAbstainDecisions();
}

源码中,有个Collection configAttributes 参数,ConfigAttribute是什么? 这个其实是一个很灵活的东西,不同的情况代表不同的语义,比如在使用了角色控制的时候,传入的则可能是ROLE__XXX之类的,以便ROLE_VOTER使用。具体的后面在细说。

通过以上代码可直接看到AffirmativeBased的策略:

  • 只要有投通过(ACCESS_GRANTED)票,则直接判为通过。
  • 如果没有投通过票且反对(ACCESS_DENIED)票在两个及其以上的,则直接判为不通过。

UnanimousBased

public void decide(Authentication authentication, Object object,
		Collection<ConfigAttribute> attributes) throws AccessDeniedException {

	int grant = 0;
	int abstain = 0;

	List<ConfigAttribute> singleAttributeList = new ArrayList<ConfigAttribute>(1);
	singleAttributeList.add(null);

	for (ConfigAttribute attribute : attributes) {
		singleAttributeList.set(0, attribute);

		for (AccessDecisionVoter voter : getDecisionVoters()) {
			//配置的投票者进行投票
			int result = voter.vote(authentication, object, singleAttributeList);

			if (logger.isDebugEnabled()) {
				logger.debug("Voter: " + voter + ", returned: " + result);
			}

			switch (result) {
			case AccessDecisionVoter.ACCESS_GRANTED:
				grant++;

				break;

			case AccessDecisionVoter.ACCESS_DENIED:
				//只要有投票者投反对票就立马判为无权访问
				throw new AccessDeniedException(messages.getMessage(
						"AbstractAccessDecisionManager.accessDenied",
						"Access is denied"));

			default:
				abstain++;

				break;
			}
		}
	}

	// To get this far, there were no deny votes
	if (grant > 0) {
		//如果没反对票且有通过票,那么就判为通过
		return;
	}

	// To get this far, every AccessDecisionVoter abstained
	checkAllowIfAllAbstainDecisions();
}

由此可见UnanimousBased的策略:

  • 无论多少投票者投了多少通过(ACCESS_GRANTED)票,只要有反对票(ACCESS_DENIED),那都判为不通过。
  • 如果没有反对票且有投票者投了通过票,那么就判为通过。

ConsensusBased

public void decide(Authentication authentication, Object object,
		Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
	int grant = 0;
	int deny = 0;
	int abstain = 0;

	for (AccessDecisionVoter voter : getDecisionVoters()) {
		//配置的投票者进行投票
		int result = voter.vote(authentication, object, configAttributes);

		if (logger.isDebugEnabled()) {
			logger.debug("Voter: " + voter + ", returned: " + result);
		}

		switch (result) {
		case AccessDecisionVoter.ACCESS_GRANTED:
			grant++;

			break;

		case AccessDecisionVoter.ACCESS_DENIED:
			deny++;

			break;

		default:
			abstain++;

			break;
		}
	}

	if (grant > deny) {
		//通过的票数大于反对的票数则判为通过
		return;
	}

	if (deny > grant) {
		//通过的票数小于反对的票数则判为不通过
		throw new AccessDeniedException(messages.getMessage(
				"AbstractAccessDecisionManager.accessDenied", "Access is denied"));
	}

	if ((grant == deny) && (grant != 0)) {
		//this.allowIfEqualGrantedDeniedDecisions默认为true
		//通过的票数和反对的票数相等,则可根据配置allowIfEqualGrantedDeniedDecisions进行判断是否通过
		if (this.allowIfEqualGrantedDeniedDecisions) {
			return;
		}
		else {
			throw new AccessDeniedException(messages.getMessage(
					"AbstractAccessDecisionManager.accessDenied", "Access is denied"));
		}
	}

	// To get this far, every AccessDecisionVoter abstained
	checkAllowIfAllAbstainDecisions();
}

由此可见,ConsensusBased的策略:

  • 通过的票数大于反对的票数则判为通过。
  • 通过的票数小于反对的票数则判为不通过。
  • 通过的票数和反对的票数相等,则可根据配置allowIfEqualGrantedDeniedDecisions(默认为true)进行判断是否通过。

到此,应该明白AffirmativeBased、UnanimousBased、ConsensusBased三者的区别了吧,spring security默认使用的是AffirmativeBased, 如果有需要,可配置为其它两个,也可自己去实现。

投票者

以上AccessDecisionManager的实现类都只是对权限(投票)进行管理(策略的实现),具体投票(vote)的逻辑是通过调用AccessDecisionVoter的子类(投票者)的vote方法实现的。spring security默认注册了RoleVoter和AuthenticatedVoter两个投票者。下面来看看其源码。

AccessDecisionManager

boolean supports(ConfigAttribute attribute);
boolean supports(Class<?> clazz);
//核心方法,此方法由上面介绍的的AccessDecisionManager调用,子类实现此方法进行投票。
int vote(Authentication authentication, S object,
		Collection<ConfigAttribute> attributes);

RoleVoter

private String rolePrefix = "ROLE_";

//只处理ROLE_开头的(可通过配置rolePrefix的值进行改变)
public boolean supports(ConfigAttribute attribute) {
	if ((attribute.getAttribute() != null)
			&& attribute.getAttribute().startsWith(getRolePrefix())) {
		return true;
	}
	else {
		return false;
	}
}

public int vote(Authentication authentication, Object object,
		Collection<ConfigAttribute> attributes) {
		
	if(authentication == null) {
		//用户没通过认证,则投反对票
		return ACCESS_DENIED;
	}
	int result = ACCESS_ABSTAIN;
	//获取用户实际的权限
	Collection<? extends GrantedAuthority> authorities = extractAuthorities(authentication);

	for (ConfigAttribute attribute : attributes) {
		if (this.supports(attribute)) {
			result = ACCESS_DENIED;

			// Attempt to find a matching granted authority
			for (GrantedAuthority authority : authorities) {
				if (attribute.getAttribute().equals(authority.getAuthority())) {
					//权限匹配则投通过票
					return ACCESS_GRANTED;
				}
			}
		}
	}
	//如果处理过,但没投通过票,则为反对票,如果没处理过,那么视为弃权(ACCESS_ABSTAIN)。
	return result;
}	

很简单吧,同时,我们还可以通过实现AccessDecisionManager来扩展自己的voter。但是,要实现这个,我们还必须得弄清楚attributes这个参数是从哪儿来的,这个是个很关键的参数啊。通过一张官方图能很清晰的看出这个问题来:

inceptor

接下来,就看看AccessDecisionManager的调用者AbstractSecurityInterceptor。

AbstractSecurityInterceptor

...
//上面说过默认是AffirmativeBased,可配置
private AccessDecisionManager accessDecisionManager;
...
protected InterceptorStatusToken beforeInvocation(Object object) {
	...
	//抽象方法,子类实现,但由此也可看出ConfigAttribute是由SecurityMetadataSource(实际上,默认是DefaultFilterInvocationSecurityMetadataSource)获取。
	Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource()
			.getAttributes(object);
	...
	//获取当前认证过的用户信息
	Authentication authenticated = authenticateIfRequired();

	try {
		//调用AccessDecisionManager
		this.accessDecisionManager.decide(authenticated, object, attributes);
	}
	catch (AccessDeniedException accessDeniedException) {
		publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated,
				accessDeniedException));

		throw accessDeniedException;
	}
	...		
}

public abstract SecurityMetadataSource obtainSecurityMetadataSource();

以上方法都是由AbstractSecurityInterceptor的子类(默认是FilterSecurityInterceptor)调用,那就再看看吧:

FilterSecurityInterceptor

...
//SecurityMetadataSource的实现类,由此可见,可通过外部配置。这也说明我们可以通过自定义SecurityMetadataSource的实现类来扩展出自己实际需要的ConfigAttribute
private FilterInvocationSecurityMetadataSource securityMetadataSource;	
...
//入口
public void doFilter(ServletRequest request, ServletResponse response,
		FilterChain chain) throws IOException, ServletException {
	FilterInvocation fi = new FilterInvocation(request, response, chain);
	//关键方法
	invoke(fi);
}

public void invoke(FilterInvocation fi) throws IOException, ServletException {
	if ((fi.getRequest() != null)
			&& (fi.getRequest().getAttribute(FILTER_APPLIED) != null)
			&& observeOncePerRequest) {
		// filter already applied to this request and user wants us to observe
		// once-per-request handling, so don't re-do security checking
		fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
	}
	else {
		// first time this request being called, so perform security checking
		if (fi.getRequest() != null) {
			fi.getRequest().setAttribute(FILTER_APPLIED, Boolean.TRUE);
		}
		//在这儿调用了父类(AbstractSecurityInterceptor)的方法, 也就调用了accessDecisionManager
		InterceptorStatusToken token = super.beforeInvocation(fi);

		try {
			fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
		}
		finally {
			super.finallyInvocation(token);
		}
		//完了再执行(父类的方法),一前一后,AOP无处不在啊
		super.afterInvocation(token, null);
	}
}

好啦,到此应该对于Spring Security的权限管理比较清楚了。看完这个,不知你是否能扩展出一套适合自己需求的权限需求来呢,如果还不太清楚,那也没关系,下篇就实战一下,根据它来开发一套自己的权限体系。

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