Shiro源码分析----登录流程

在Shiro中，登录操作是由Subject的login()方法完成的，Subject是个接口，在Web环境中，实现类为WebDelegatingSubject，login方法从DeletatingSubject继承而来：

public void login(AuthenticationToken token) throws AuthenticationException {clearRunAsIdentitiesInternal();    Subject subject = securityManager.login(this, token);// 省略一些代码...}

由上可见，Subject.login()方法委托给了SecurityManager对象，在Web环境中，SecurityManager实现类为DefaultWebSecurityManager，其login方法从DefaultSecurityManager继承而来：

public Subject login(Subject subject, AuthenticationToken token) throws AuthenticationException {AuthenticationInfo info;try {// 对提交的AuthenticationToken进行认证info = authenticate(token);} catch (AuthenticationException ae) {try {// 如果认证失败onFailedLogin(token, ae, subject);} catch (Exception e) {if (log.isInfoEnabled()) {log.info("onFailedLogin method threw an " +"exception.  Logging and propagating original AuthenticationException.", e);}}throw ae; //propagate，如果认证失败，使异常继续向上传播，从而返回至登录页面(见上篇)}// 如果认证成功则重新创建Subject对象Subject loggedIn = createSubject(token, info, subject);// 登录成功，主要处理RememberMe操作，即将登录信息存储在cookie中onSuccessfulLogin(token, info, loggedIn);return loggedIn;}

最关键的authenticate方法：

public AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {return this.authenticator.authenticate(token);}

SecurityManager把认证方法委托给认证器Authenticator的authenticate方法，Authenticator的实现类为：ModularRealmAuthenticator，其可以实现多认证信息源综合认证。ModularRealmAuthenticator实现使用了模版方法模式，随后执行doAuthenticate方法：

protected AuthenticationInfo doAuthenticate(AuthenticationToken authenticationToken) throws AuthenticationException {assertRealmsConfigured();// Realm集合在为SecurityManager设置Realm时就会设置给Authenticator// 至于Realm代表什么，请参看：http://jinnianshilongnian.iteye.com/blog/2018936Collection<Realm> realms = getRealms();if (realms.size() == 1) {// 如果Realm只有一个return doSingleRealmAuthentication(realms.iterator().next(), authenticationToken);} else {// 如果Realm有多个return doMultiRealmAuthentication(realms, authenticationToken);}}

单一Realm认证：

protected AuthenticationInfo doSingleRealmAuthentication(Realm realm, AuthenticationToken token) {// 该Realm是否支持此种Token，因为并不是任何一种Realm与AuthenticationToken都是相互匹配的if (!realm.supports(token)) {String msg = "Realm [" + realm + "] does not support authentication token [" +token + "].  Please ensure that the appropriate Realm implementation is " +"configured correctly or that the realm accepts AuthenticationTokens of this type.";throw new UnsupportedTokenException(msg);}// 根据AuthenticationToken获取认证信息// Realm一般是由自己实现的，虽然说Shiro有一些自己的实现，但是在实际项目中，Shiro的实现直接就能使用的情况很少// 比较将认证信息(用户名密码等)存在数据库，则该getAuthenticationInfo方法就是根据Token中的信息去数据库中查找、// 匹配，如果匹配上了则返回相应认证后的认证信息AuthenticationInfo info = realm.getAuthenticationInfo(token);// 如果没有获取到则认证失败if (info == null) {String msg = "Realm [" + realm + "] was unable to find account data for the " +"submitted AuthenticationToken [" + token + "].";throw new UnknownAccountException(msg);}return info;}

一般来说，自定义实现的Realm会继承自AuthenticatingRealm，所以会执行至：

public final AuthenticationInfo getAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {// 先去缓存中查找，如果你使用了缓存，则不用每次都去文件或数据库中查找AuthenticationInfo info = getCachedAuthenticationInfo(token);if (info == null) {//otherwise not cached, perform the lookup:// 使用模版方法模式，进行直正的认证信息查找info = doGetAuthenticationInfo(token);log.debug("Looked up AuthenticationInfo [{}] from doGetAuthenticationInfo", info);if (token != null && info != null) {cacheAuthenticationInfoIfPossible(token, info);}} else {log.debug("Using cached authentication info [{}] to perform credentials matching.", info);}if (info != null) {// 断言AuthenticationToken与AuthenticationInfo是匹配的，简单点来说就是判断密码是否正确，不正确则抛异常// doGetAuthenticationInfo方法主要判断账户是否存在assertCredentialsMatch(token, info);} else {log.debug("No AuthenticationInfo found for submitted AuthenticationToken [{}].  Returning null.", token);}return info;}

单一Realm认证时，只需要判断一个Realm认证是否成功即可，但是当存在多个Realm时情况就有点复杂了。因为有可能有些Realm认证成功了，有些Realm又认证失败了，这时到底算是认证成功还是失败呢？所以这时Shiro使用了策略模式，用具体的策略类来处理这个问题。多个Realm认证时的doMultiRealmAuthentication方法如下：

protected AuthenticationInfo doMultiRealmAuthentication(Collection<Realm> realms, AuthenticationToken token) {// 首先就得获取认证策略，Shiro实现了三种：//1. AllSuccessfulStrategy: 必须所有Realm认证成功了才算是认证成功//2. AtLeastOneSuccessfulStrategy: 至少有一个Realm认证成功了就算是认证成功//3. FirstSuccessfulStrategy: 第一个Realm认证成功了就算是认证成功// 默认实现为AtLeastOneSuccessfulStrategyAuthenticationStrategy strategy = getAuthenticationStrategy();// 假设我们现在使用的就是AtLeastOneSuccessfulStrategy// 返回SimpleAuthenticationInfo，这是一个空认证信息，并不含有principal与credentialsAuthenticationInfo aggregate = strategy.beforeAllAttempts(realms, token);if (log.isTraceEnabled()) {log.trace("Iterating through {} realms for PAM authentication", realms.size());}for (Realm realm : realms) {// 直接返回aggregateaggregate = strategy.beforeAttempt(realm, token, aggregate);if (realm.supports(token)) {log.trace("Attempting to authenticate token [{}] using realm [{}]", token, realm);AuthenticationInfo info = null;Throwable t = null;try {info = realm.getAuthenticationInfo(token);} catch (Throwable throwable) {t = throwable;if (log.isDebugEnabled()) {String msg = "Realm [" + realm + "] threw an exception during a multi-realm authentication attempt:";log.debug(msg, t);}}//如果认证成功则info不为null，且包含有principal与credentials//afterAttempt方法会将info与aggregate合并，也就是将AuthenticationInfo的principal与credentials//分别用一集合存储aggregate = strategy.afterAttempt(realm, token, info, aggregate, t);} else {log.debug("Realm [{}] does not support token {}.  Skipping realm.", realm, token);}}// 检测合并后的AuthenticationInfo中是否含用principal，如果有则返回aggregate// 没有则抛出异常认证失败，由此可见只要有一个Realm认证成功则算是认证成功aggregate = strategy.afterAllAttempts(token, aggregate);return aggregate;}

上面只分析了AtLeastOneSuccessfulStrategy策略，其它两个请自行查看源码。


假设现在认证成功了，接下来执行DefaultSecurityManager.createSubject方法：

protected Subject createSubject(AuthenticationToken token, AuthenticationInfo info, Subject existing) {// 创建SubjectContext对象SubjectContext context = createSubjectContext();// 设置为已认证context.setAuthenticated(true);// 设置Tokencontext.setAuthenticationToken(token);// 设置认证通过后的认证信息context.setAuthenticationInfo(info);if (existing != null) {// 设置先前存在的Subjectcontext.setSubject(existing);}return createSubject(context);}public Subject createSubject(SubjectContext subjectContext) {// 复制SubjectContext，原SubjectContext信息得以保留SubjectContext context = copy(subjectContext);// 确保SubjectContext与SecurityManager关联context = ensureSecurityManager(context);// 解析会话，有可能使用Servlet中的Session实现，也可能使用Shiro自己实现的Sessioncontext = resolveSession(context);context = resolvePrincipals(context);// 交由DefaultWebSubjectFactory.createSubject重新创建SubjectSubject subject = doCreateSubject(context);// 将Subject中的principal与credentials存储在Session中save(subject);return subject;}

个人感觉createSubject重新创建是为了更新一些内部状态，至于为什么也没有去深入了解，望请高人指点一二。