Shiro中Subject对象的创建与绑定流程分析
bigfan 人气:0我们在平常使用Shrio进行身份认证时，经常通过获取Subject 对象中保存的Session、Principal等信息，来获取认证用户的信息，也就是说Shiro会把认证后的用户信息保存在Subject 中供程序使用
public static Subject getSubject()
{
return SecurityUtils.getSubject();
}
Subject 是Shiro中核心的也是我们经常用到的一个对象，那么Subject 对象是怎么构造创建，并如何存储绑定供程序调用的，下面我们就对其流程进行一下探究，首先是Subject 接口本身的继承与实现，这里我们需要特别关注下WebDelegatingSubject这个实现类，这个就是最终返回的具体实现类
一、Subject的创建
在Shiro中每个http请求都会经过SpringShiroFilter的父类AbstractShiroFilte中的doFilterInternal方法，我们看下具体代码
protected void doFilterInternal(ServletRequest servletRequest, ServletResponse servletResponse, final FilterChain chain)
throws ServletException, IOException {
Throwable t = null;
try {
final ServletRequest request = prepareServletRequest(servletRequest, servletResponse, chain);
final ServletResponse response = prepareServletResponse(request, servletResponse, chain);
//创建Subject
final Subject subject = createSubject(request, response);
//执行Subject绑定
//noinspection unchecked
subject.execute(new Callable() {
public Object call() throws Exception {
updateSessionLastAccessTime(request, response);
executeChain(request, response, chain);
return null;
}
});
} catch (ExecutionException ex) {
t = ex.getCause();
} catch (Throwable throwable) {
t = throwable;
}
if (t != null) {
if (t instanceof ServletException) {
throw (ServletException) t;
}
if (t instanceof IOException) {
throw (IOException) t;
}
//otherwise it's not one of the two exceptions expected by the filter method signature - wrap it in one:
String msg = "Filtered request failed.";
throw new ServletException(msg, t);
}
}
继续进入createSubject方法，也就是创建Subject对象的入口
protected WebSubject createSubject(ServletRequest request, ServletResponse response) {
return new WebSubject.Builder(getSecurityManager(), request, response).buildWebSubject();
}
这里使用了build的对象构建模式，进入WebSubject接口中查看Builder与buildWebSubject()的具体实现
Builder()中主要用于初始化SecurityManager 、ServletRequest 、ServletResponse 等对象，构建SubjectContext上下文关系对象
*/
public Builder(SecurityManager securityManager, ServletRequest request, ServletResponse response) {
super(securityManager);
if (request == null) {
throw new IllegalArgumentException("ServletRequest argument cannot be null.");
}
if (response == null) {
throw new IllegalArgumentException("ServletResponse argument cannot be null.");
}
setRequest(request);
setResponse(response);
}
buildWebSubject方法中开始构造Subject对象
public WebSubject buildWebSubject() {
Subject subject = super.buildSubject();//父类build方法
if (!(subject instanceof WebSubject)) {
String msg = "Subject implementation returned from the SecurityManager was not a " +
WebSubject.class.getName() + " implementation. Please ensure a Web-enabled SecurityManager " +
"has been configured and made available to this builder.";
throw new IllegalStateException(msg);
}
return (WebSubject) subject;
}
进入父类的buildSubject对象我们可以看到，具体实现是由SecurityManager来完成的
public Subject buildSubject() {
return this.securityManager.createSubject(this.subjectContext);
}
在createSubject方法中会根据你的配置从缓存、redis、数据库中获取Session、Principals等信息，并创建Subject对象
public Subject createSubject(SubjectContext subjectContext) {
//create a copy so we don't modify the argument's backing map:
SubjectContext context = copy(subjectContext); //复制一个SubjectContext对象
//ensure that the context has a SecurityManager instance, and if not, add one:
context = ensureSecurityManager(context); // 检查并初始化SecurityManager对象
//Resolve an associated Session (usually based on a referenced session ID), and place it in the context before
//sending to the SubjectFactory. The SubjectFactory should not need to know how to acquire sessions as the
//process is often environment specific - better to shield the SF from these details:
context = resolveSession(context);//解析获取Sesssion信息
//Similarly, the SubjectFactory should not require any concept of RememberMe - translate that here first
//if possible before handing off to the SubjectFactory:
context = resolvePrincipals(context);//解析获取resolvePrincipals信息
Subject subject = doCreateSubject(context);//创建Subject
//save this subject for future reference if necessary:
//(this is needed here in case rememberMe principals were resolved and they need to be stored in the
//session, so we don't constantly rehydrate the rememberMe PrincipalCollection on every operation).
//Added in 1.2:
save(subject);
return subject;
}
在doCreateSubject中通过SubjectFactory创建合成Subject对象
protected Subject doCreateSubject(SubjectContext context) {
return getSubjectFactory().createSubject(context);
}
我们可以看到最后返回的是具体实现类WebDelegatingSubject
public Subject createSubject(SubjectContext context) {
//SHIRO-646
//Check if the existing subject is NOT a WebSubject. If it isn't, then call super.createSubject instead.
//Creating a WebSubject from a non-web Subject will cause the ServletRequest and ServletResponse to be null, which wil fail when creating a session.
boolean isNotBasedOnWebSubject = context.getSubject() != null && !(context.getSubject() instanceof WebSubject);
if (!(context instanceof WebSubjectContext) || isNotBasedOnWebSubject) {
return super.createSubject(context);
}
//获取上下文对象中的信息
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();
//构造返回WebDelegatingSubject对象
return new WebDelegatingSubject(principals, authenticated, host, session, sessionEnabled,
request, response, securityManager);
}
以上是Subject的创建过程，创建完成后我们还需要与当前请求线程进行绑定，这样才能通过SecurityUtils.getSubject()方法获取到Subject
二、Subject的绑定
Subject对象本质上是与请求所属的线程进行绑定，Shiro底层定义了一个ThreadContext对象，一个基于ThreadLocal的上下文管理容器，里面定义了一个InheritableThreadLocalMap<Map<Object, Object>>()，Subject最后就是被放到这个map当中，我们获取时也是从这个map中获取
首先我们看下绑定操作的入口，execuse是执行绑定，后续操作采用回调机制来实现
//执行Subject绑定
//noinspection unchecked
subject.execute(new Callable() {
public Object call() throws Exception {
updateSessionLastAccessTime(request, response);
executeChain(request, response, chain);
return null;
}
});
初始化一个SubjectCallable对象，并把回调方法传进去
public <V> V execute(Callable<V> callable) throws ExecutionException {
Callable<V> associated = associateWith(callable);//初始化一个SubjectCallable对象，并把回调方法传进去
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);
}
看下SubjectCallable类的具体实现
public class SubjectCallable<V> implements Callable<V> {
protected final ThreadState threadState;
private final Callable<V> callable;
public SubjectCallable(Subject subject, Callable<V> delegate) {
this(new SubjectThreadState(subject), delegate);//初始化构造方法
}
protected SubjectCallable(ThreadState threadState, Callable<V> delegate) {
if (threadState == null) {
throw new IllegalArgumentException("ThreadState argument cannot be null.");
}
this.threadState = threadState;//SubjectThreadState对象
if (delegate == null) {
throw new IllegalArgumentException("Callable delegate instance cannot be null.");
}
this.callable = delegate;//回调对象
}
public V call() throws Exception {
try {
threadState.bind();//执行绑定操作
return doCall(this.callable);//执行回调操作
} finally {
threadState.restore();
}
}
protected V doCall(Callable<V> target) throws Exception {
return target.call();
}
}
具体绑定的操作是通过threadState.bind()来实现的
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();//首先执行remove操作
ThreadContext.bind(this.subject);//执行绑定操作
if (securityManager != null) {
ThreadContext.bind(securityManager);
}
}
在上面bind方法中又会执行ThreadContext的bind方法，这里就是之前说到的shiro底层维护了的一个ThreadContext对象，一个基于ThreadLocal的上下文管理容器，bind操作本质上就是把创建的Subject对象维护到resources 这个InheritableThreadLocalMap中， SecurityUtils.getSubject()方法其实就是从InheritableThreadLocalMap中获取所属线程对应的Subject
private static final ThreadLocal<Map<Object, Object>> resources = new InheritableThreadLocalMap<Map<Object, Object>>();//定义一个InheritableThreadLocalMap
public static void bind(Subject subject) {
if (subject != null) {
put(SUBJECT_KEY, subject);//向InheritableThreadLocalMap中放入Subject对象
}
}
public static void put(Object key, Object value) {
if (key == null) {
throw new IllegalArgumentException("key cannot be null");
}
if (value == null) {
remove(key);
return;
}
ensureResourcesInitialized();
resources.get().put(key, value);
if (log.isTraceEnabled()) {
String msg = "Bound value of type [" + value.getClass().getName() + "] for key [" +
key + "] to thread " + "[" + Thread.currentThread().getName() + "]";
log.trace(msg);
}
}
三、总结
从以上对Shiro源码的分析，我们对Subject对象的创建与绑定进行了基本的梳理，Subject对象的创建是通过不断的对context上下文对象进行赋值与完善，并最终构造返回WebDelegatingSubject对象的过程；Subject对象创建后，会通过Shiro底层维护的一个基于ThreadLocal的上下文管理容器，即ThreadContext这个类，与请求所属的线程进行绑定，供后续访问使用。对Subject对象创建与绑定流程的分析，有助于理解Shiro底层的实现机制与方法，加深对Shiro的认识，从而在项目中能够正确使用。希望本文对大家能有所帮助，其中如有不足与不正确的地方还望指出与海涵。
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