Subject

毫无疑问，Subject是Shiro最重要的一个概念。

“Subject”只是一个安全术语，意味着应用程序用户的特定于安全性的“视图”。Shiro Subject实例代表单个应用程序用户的安全状态和相关操作。

创建

初次创建是在AbstractShiroFilter#doFilterInternal方法中：

final Subject subject = createSubject(request, response);

protected WebSubject createSubject(ServletRequest request, ServletResponse response) {return new WebSubject.Builder(getSecurityManager(), request, response).buildWebSubject();
}

创建的时候传入安全管理器，Subject.Builder是这样操作的：

public Builder(SecurityManager securityManager) {if (securityManager == null) {throw new NullPointerException("SecurityManager method argument cannot be null.");}this.securityManager = securityManager;this.subjectContext = newSubjectContextInstance();if (this.subjectContext == null) {throw new IllegalStateException("Subject instance returned from 'newSubjectContextInstance' " +"cannot be null.");}this.subjectContext.setSecurityManager(securityManager);
}public Subject buildSubject() {return this.securityManager.createSubject(this.subjectContext);
}

这个安全管理器还是我们指定的那个DefaultWebSecurityManager，一路传过去的。这个subjectContext参数是一个DefaultSubjectContext，子接口中的Builder覆盖了父类的方法，实际赋予的是一个DefaultWebSubjectContext。

protected Subject doCreateSubject(SubjectContext context) {return getSubjectFactory().createSubject(context);
}

subjectFactory是安全管理器DefaultWebSecurityManager中默认的DefaultWebSubjectFactory：

public DefaultWebSecurityManager() {super();((DefaultSubjectDAO) this.subjectDAO).setSessionStorageEvaluator(new DefaultWebSessionStorageEvaluator());this.sessionMode = HTTP_SESSION_MODE;setSubjectFactory(new DefaultWebSubjectFactory());setRememberMeManager(new CookieRememberMeManager());setSessionManager(new ServletContainerSessionManager());
}

最终的创建又回到：

public class DefaultWebSubjectFactory extends DefaultSubjectFactory {public DefaultWebSubjectFactory() {super();}public Subject createSubject(SubjectContext context) {if (!(context instanceof WebSubjectContext)) {return super.createSubject(context);}WebSubjectContext wsc = (WebSubjectContext) context;SecurityManager securityManager = wsc.resolveSecurityManager();Session session = wsc.resolveSession();boolean sessionEnabled = wsc.isSessionCreationEnabled();PrincipalCollection principals = wsc.resolvePrincipals();boolean authenticated = wsc.resolveAuthenticated();String host = wsc.resolveHost();ServletRequest request = wsc.resolveServletRequest();ServletResponse response = wsc.resolveServletResponse();return new WebDelegatingSubject(principals, authenticated, host, session, sessionEnabled,request, response, securityManager);}//......
}

根据相关属性new出来一个WebDelegatingSubject。

shiro中很多都是这样的继承和组合关系：

DefaultSecurityManager -> DefaultSubjectFactory -> DelegatingSubject

DefaultWebSecurityManager -> DefaultWebSubjectFactory -> WebDelegatingSubject

再回到创建的方法：

final Subject subject = createSubject(request, response);//noinspection unchecked
subject.execute(new Callable() {public Object call() throws Exception {updateSessionLastAccessTime(request, response);executeChain(request, response, chain);return null;}
});

这个execute方法是在DelegatingSubject中实现的：

public <V> V execute(Callable<V> callable) throws ExecutionException {Callable<V> associated = associateWith(callable);try {return associated.call();} catch (Throwable t) {throw new ExecutionException(t);}
}public <V> Callable<V> associateWith(Callable<V> callable) {return new SubjectCallable<V>(this, callable);
}

SubjectCallable首先构造了一个ThreadState：

public SubjectCallable(Subject subject, Callable<V> delegate) {this(new SubjectThreadState(subject), delegate);
}

associated.call()调用ThreadState.bind():

public V call() throws Exception {try {threadState.bind();return doCall(this.callable);} finally {threadState.restore();}
}

SubjectThreadState的bind方法：

public void bind() {SecurityManager securityManager = this.securityManager;if ( securityManager == null ) {//try just in case the constructor didn't find one at the time:securityManager = ThreadContext.getSecurityManager();}this.originalResources = ThreadContext.getResources();ThreadContext.remove();ThreadContext.bind(this.subject);if (securityManager != null) {ThreadContext.bind(securityManager);}
}

这样就妥妥地把当前subject和线程绑定到了一起（还有securityManager）。

在这里遇到一个问题，记录下：
https://www.oschina.net/question/2275855_2273492

其实这只是每次进入核心过滤器时默认为我们创建的一个Subject，当调用subject.login方法之后会再次创建一个Subject，后面登录部分会做详细介绍。

获取

Subject subject = SecurityUtils.getSubject();

public static Subject getSubject() {Subject subject = ThreadContext.getSubject();if (subject == null) {subject = (new Subject.Builder()).buildSubject();ThreadContext.bind(subject);}return subject;
}

绑定是通过ThreadContext，获取当然也是从其取。

public abstract class ThreadContext {private static final Logger log = LoggerFactory.getLogger(ThreadContext.class);public static final String SECURITY_MANAGER_KEY = ThreadContext.class.getName() + "_SECURITY_MANAGER_KEY";public static final String SUBJECT_KEY = ThreadContext.class.getName() + "_SUBJECT_KEY";private static final ThreadLocal<Map<Object, Object>> resources = new InheritableThreadLocalMap<Map<Object, Object>>();private static Object getValue(Object key) {return resources.get().get(key);}public static Object get(Object key) {Object value = getValue(key);return value;}public static Subject getSubject() {return (Subject) get(SUBJECT_KEY);}}

最终是到ThreadLocal中拿，不过这个ThreadLocal是 InheritableThreadLocalMap 类型的（继承自InheritableThreadLocal）。

每个线程都有一个Map

SecurityManager

<!-- 安全管理器 -->
<bean id="securityManager" class="org.apache.shiro.web.mgt.DefaultWebSecurityManager">  <property name="realm" ref="casRealm" />  <property name="sessionManager" ref="sessionManager" /><property name="cacheManager" ref="shiroCacheManager" />  <!-- <property name="rememberMeManager" ref="rememberMeManager" />  -->
</bean>
<bean id="sessionManager" class="org.apache.shiro.web.session.mgt.ServletContainerSessionManager"/>

public interface SecurityManager extends Authenticator, Authorizer, SessionManager {Subject login(Subject subject, AuthenticationToken authenticationToken) throws AuthenticationException;void logout(Subject subject);Subject createSubject(SubjectContext context);}

安全管理器继承了Authenticator, Authorizer, SessionManager三个接口。自顶向下第一个抽象类是CachingSecurityManager，接着是RealmSecurityManager，后面是AuthenticatingSecurityManager，AuthorizingSecurityManager，SessionsSecurityManager。

然后才是DefaultSecurityManager，DefaultWebSecurityManager。

由于是web项目，我们指定了DefaultWebSecurityManager，在构造器中会为我们设置相匹配的属性（都是和web相关的）：

public DefaultWebSecurityManager() {super();((DefaultSubjectDAO) this.subjectDAO).setSessionStorageEvaluator(new DefaultWebSessionStorageEvaluator());this.sessionMode = HTTP_SESSION_MODE;setSubjectFactory(new DefaultWebSubjectFactory());setRememberMeManager(new CookieRememberMeManager());setSessionManager(new ServletContainerSessionManager());
}

SessionsSecurityManager持有一个sessionManager对象，对sessionManager接口的实现是转移到这个对象上来的：

public abstract class SessionsSecurityManager extends AuthorizingSecurityManager {private SessionManager sessionManager;public SessionsSecurityManager() {super();this.sessionManager = new DefaultSessionManager();applyCacheManagerToSessionManager();}
}

AuthenticatingSecurityManager，AuthorizingSecurityManager类似，这两个抽象管理器在无参构造函数中创建了默认的对象：

public abstract class AuthorizingSecurityManager extends AuthenticatingSecurityManager {private Authorizer authorizer;public AuthorizingSecurityManager() {super();this.authorizer = new ModularRealmAuthorizer();}}public abstract class AuthenticatingSecurityManager extends RealmSecurityManager {private Authenticator authenticator;public AuthenticatingSecurityManager() {super();this.authenticator = new ModularRealmAuthenticator();}
}

所以这个安全管理器几乎承担了所有的操作，然后转移到具体的对象。它的层次结构非常清晰，职责分明。对Subject所有操作最终都会转移到SecurityManager。