话说Spring Security权限管理（源码详解）

//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);

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();
}

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();
}

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();
}

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);

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;
}  

...
//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();

...
//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);
  }
}