Shiro的subject实质上是当前执行用户的特定视图。
通过org.apache.shiro.SecurityUtils可以查询当前执行用户：
Subject currentUser = SecurityUtils.getSubject();
获取当前执行用户的session：
（在非web、非EJB的情况下，Shiro自动使用自带session；如果是web或者EJB应用，则Shiro自动使用HttpSession，不需要人为改变。）
Session session = currentUser.getSession();
session.setAttribute( "someKey", "aValue" );
案例一：
验证用户是否为认证用户：
if ( !currentUser.isAuthenticated() ) {
//collect user principals and credentials in a gui specific manner
//such as username/password html form, X509 certificate, OpenID, etc.
//We'll use the username/password example here since it is the most common.
//(do you know what movie this is from? ;)
UsernamePasswordToken token = new UsernamePasswordToken("lonestarr", "vespa");
//this is all you have to do to support 'remember me' (no config - built in!):
token.setRememberMe(true);
currentUser.login(token);
}
验证失败，提示信息：
ry {
currentUser.login( token );
//if no exception, that's it, we're done!
} catch ( UnknownAccountException uae ) {
//username wasn't in the system, show them an error message?
} catch ( IncorrectCredentialsException ice ) {
//password didn't match, try again?
} catch ( LockedAccountException lae ) {
//account for that username is locked - can't login. Show them a message?
}
... more types exceptions to check if you want ...
} catch ( AuthenticationException ae ) {
//unexpected condition - error?
}
案例二（展示当前用户信息）：
//print their identifying principal (in this case, a username):
log.info( "User [" + currentUser.getPrincipal() + "] logged in successfully." );
案例三（判断当前用户角色）：
if ( currentUser.hasRole( "schwartz" ) ) {
log.info("May the Schwartz be with you!" );
} else {
log.info( "Hello, mere mortal." );
}
案例四（验证当前用户权限）：
if ( currentUser.isPermitted( "lightsaber:weild" ) ) {
log.info("You may use a lightsaber ring. Use it wisely.");
} else {
log.info("Sorry, lightsaber rings are for schwartz masters only.");
}
案例五（退出登录）：
currentUser.logout(); //removes all identifying information and invalidates their session too.
Shiro支持创建subject的实例，但不推荐。因为我们平常可以直接通过getSubject来获取当前执行用户。个别情况需要创建subject：
1.当前没有用户可以与系统进行交互，但是为保持系统的运行，需要假设一个用户，此时可以创建一个subject，比如admin用户。
2.集成测试时，需要创建一个临时的subject用以进入下一步的测试。
3.应用的后台进程运行的时候，需要一个subject。
（如果已经拥有了一个subject，但是需要和其他线程共享的话，需要调用Subject.associateWith*方法。）
subject的创建
案例六（Subject.Builder，创建subject，而无需知道其中细节，会访问到SecurityManager的SecurityUtils.getSecurityManager()方法。）：
Subject subject = new Subject.Builder().buildSubject()
案例七（自建securityManager）：
SecurityManager securityManager = //acquired from somewhere
Subject subject = new Subject.Builder(securityManager).buildSubject();
案例八（利用session创建新的subject）：
Serializable sessionId = //acquired from somewhere
Subject subject = new Subject.Builder().sessionId(sessionId).buildSubject();
案例九（创建subject，并将其属性映射到验证属性中）：
Object userIdentity = //a long ID or String username, or whatever the "myRealm" requires
String realmName = "myRealm";
PrincipalCollection principals = new SimplePrincipalCollection(userIdentity, realmName);
Subject subject = new Subject.Builder().principals(principals).buildSubject();
将自建的subject与线程进行绑定：
1.系统的自动绑定，Subject.execute*方法的调用。
2.手动的绑定。
3.利用已绑定的线程来绑定到新的线程，Subject.associateWith*方法的调用。
（subject与线程绑定，则可以在线程执行过程中取到信息；subject与线程取消绑定，则线程可以被回收。）
案例十（调用execute方法，参数为runable实例，实现subject的自动绑定与拆除）：
Subject subject = //build or acquire subject
subject.execute( new Runnable() {
public void run() {
//subject is 'bound' to the current thread now
//any SecurityUtils.getSubject() calls in any
//code called from here will work
}
});
//At this point, the Subject is no longer associated
//with the current thread and everything is as it was before
案例十一（调用execute方法，参数为callable实例，实现subject的自动绑定与拆除）：
Subject subject = //build or acquire subject
MyResult result = subject.execute( new Callable<MyResult>() {
public MyResult call() throws Exception {
//subject is 'bound' to the current thread now
//any SecurityUtils.getSubject() calls in any
//code called from here will work
...
//finish logic as this Subject
...
return myResult;
}
});
//At this point, the Subject is no longer associated
//with the current thread and everything is as it was before
案例十二（spring远程调用subject）：
Subject.Builder builder = new Subject.Builder();
//populate the builder's attributes based on the incoming RemoteInvocation
...
Subject subject = builder.buildSubject();
return subject.execute(new Callable() {
public Object call() throws Exception {
return invoke(invocation, targetObject);
}
});
线程池的清理：
Subject subject = new Subject.Builder()...
ThreadState threadState = new SubjectThreadState(subject);
threadState.bind();
try {
//execute work as the built Subject
} finally {
//ensure any state is cleaned so the thread won't be
//corrupt in a reusable or pooled thread environment
threadState.clear();
}
案例十三（callable）：
Subject subject = new Subject.Builder()...
Callable work = //build/acquire a Callable instance.
//associate the work with the built subject so SecurityUtils.getSubject() calls works properly:
work = subject.associateWith(work);
ExecutorService executorService = new java.util.concurrent.Executors.newCachedThreadPool();
//execute the work on a different thread as the built Subject:
executor.execute(work);
案例十四（runable）：
Subject subject = new Subject.Builder()...
Runnable work = //build/acquire a Runnable instance.
//associate the work with the built subject so SecurityUtils.getSubject() calls works properly:
work = subject.associateWith(work);
Executor executor = new java.util.concurrent.Executors.newCachedThreadPool();
//execute the work on a different thread as the built Subject:
executor.execute(work);