概述

前不久刚学会使用权限注解()，开始思索了一番。最开始猜测实现方式是注解@Aspect，具体实现方式类似如下所示(切面记录审计日志)。后来发现并非如此，所以特地分析一下源码。

@Component
@Aspect
public class AuditLogAspectConfig {
    @Pointcut("@annotation(com.ygsoft.ecp.mapp.basic.audit.annotation.AuditLog) || @annotation(com.ygsoft.ecp.mapp.basic.audit.annotation.AuditLogs)")
    public void pointcut() {        
    }

    @After(value="pointcut()")
    public void after(JoinPoint joinPoint) {
        //执行的逻辑
    }
    ...
}

权限注解的源码分析

DefaultAdvisorAutoProxyCreator这个类实现了BeanProcessor接口,当ApplicationContext读取所有的Bean配置信息后，这个类将扫描上下文，寻找所有的Advistor(一个Advisor是一个切入点和一个通知的组成)，将这些Advisor应用到所有符合切入点的Bean中。

@Configuration
public class ShiroAnnotationProcessorConfiguration extends AbstractShiroAnnotationProcessorConfiguration{
    @Bean
    @DependsOn("lifecycleBeanPostProcessor")
    protected DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator() {
        return super.defaultAdvisorAutoProxyCreator();
    }

    @Bean
    protected AuthorizationAttributeSourceAdvisor authorizationAttributeSourceAdvisor(SecurityManager securityManager) {
        return super.authorizationAttributeSourceAdvisor(securityManager);
    }

}

AuthorizationAttributeSourceAdvisor继承了StaticMethodMatcherPointcutAdvisor，如下代码所示，只匹配五个注解，也就是说只对这五个注解标注的类或者方法增强。StaticMethodMatcherPointcutAdvisor是静态方法切点的抽象基类，默认情况下它匹配所有的类。StaticMethodMatcherPointcut包括两个主要的子类分别是NameMatchMethodPointcut和AbstractRegexpMethodPointcut，前者提供简单字符串匹配方法前面，而后者使用正则表达式匹配方法前面。动态方法切点：DynamicMethodMatcerPointcut是动态方法切点的抽象基类，默认情况下它匹配所有的类，而且也已经过时，建议使用DefaultPointcutAdvisor和DynamicMethodMatcherPointcut动态方法代替。另外还需关注构造器中的传入的AopAllianceAnnotationsAuthorizingMethodInterceptor。

public class AuthorizationAttributeSourceAdvisor extends StaticMethodMatcherPointcutAdvisor {

    private static final Logger log = LoggerFactory.getLogger(AuthorizationAttributeSourceAdvisor.class);

    private static final Class<? extends Annotation>[] AUTHZ_ANNOTATION_CLASSES =
            new Class[] {
                    RequiresPermissions.class, RequiresRoles.class,
                    RequiresUser.class, RequiresGuest.class, RequiresAuthentication.class
            };

    protected SecurityManager securityManager = null;

    public AuthorizationAttributeSourceAdvisor() {
        setAdvice(new AopAllianceAnnotationsAuthorizingMethodInterceptor());
    }

    public SecurityManager getSecurityManager() {
        return securityManager;
    }

    public void setSecurityManager(org.apache.shiro.mgt.SecurityManager securityManager) {
        this.securityManager = securityManager;
    }

    public boolean matches(Method method, Class targetClass) {
        Method m = method;

        if ( isAuthzAnnotationPresent(m) ) {
            return true;
        }
        
        if ( targetClass != null) {
            try {
                m = targetClass.getMethod(m.getName(), m.getParameterTypes());
                if ( isAuthzAnnotationPresent(m) ) {
                    return true;
                }
            } catch (NoSuchMethodException ignored) {
                
            }
        }

        return false;
    }

    private boolean isAuthzAnnotationPresent(Method method) {
        for( Class<? extends Annotation> annClass : AUTHZ_ANNOTATION_CLASSES ) {
            Annotation a = AnnotationUtils.findAnnotation(method, annClass);
            if ( a != null ) {
                return true;
            }
        }
        return false;
    }

}

AopAllianceAnnotationsAuthorizingMethodInterceptor在初始化时，interceptors添加了5个方法拦截器(都继承自AuthorizingAnnotationMethodInterceptor)，这5个拦截器分别对5种权限验证的方法进行拦截，执行invoke方法。

public class AopAllianceAnnotationsAuthorizingMethodInterceptor
        extends AnnotationsAuthorizingMethodInterceptor implements MethodInterceptor {

    public AopAllianceAnnotationsAuthorizingMethodInterceptor() {
        List<AuthorizingAnnotationMethodInterceptor> interceptors =
                new ArrayList<AuthorizingAnnotationMethodInterceptor>(5);
        AnnotationResolver resolver = new SpringAnnotationResolver();
        
        interceptors.add(new RoleAnnotationMethodInterceptor(resolver));
        interceptors.add(new PermissionAnnotationMethodInterceptor(resolver));
        interceptors.add(new AuthenticatedAnnotationMethodInterceptor(resolver));
        interceptors.add(new UserAnnotationMethodInterceptor(resolver));
        interceptors.add(new GuestAnnotationMethodInterceptor(resolver));
        setMethodInterceptors(interceptors);
    }
    
    public Object invoke(MethodInvocation methodInvocation) throws Throwable {
        org.apache.shiro.aop.MethodInvocation mi = createMethodInvocation(methodInvocation);
        return super.invoke(mi);
    }
    ...
}

AopAllianceAnnotationsAuthorizingMethodInterceptor的invoke方法，又会调用超类AuthorizingMethodInterceptor的invoke方法，在该方法中先执行assertAuthorized方法，进行权限校验，校验不通过，抛出AuthorizationException异常，中断方法；校验通过，则执行methodInvocation.proceed()，该方法也就是被拦截并且需要权限校验的方法。

public abstract class AuthorizingMethodInterceptor extends MethodInterceptorSupport {

    public Object invoke(MethodInvocation methodInvocation) throws Throwable {
        assertAuthorized(methodInvocation);
        return methodInvocation.proceed();
    }

    protected abstract void assertAuthorized(MethodInvocation methodInvocation) throws AuthorizationException;
}

assertAuthorized方法最终执行的还是AuthorizingAnnotationMethodInterceptor.assertAuthorized，而AuthorizingAnnotationMethodInterceptor有5中的具体的实现类(RoleAnnotationMethodInterceptor, PermissionAnnotationMethodInterceptor, AuthenticatedAnnotationMethodInterceptor, UserAnnotationMethodInterceptor, GuestAnnotationMethodInterceptor)。

public abstract class AnnotationsAuthorizingMethodInterceptor extends   AuthorizingMethodInterceptor {
  
    protected void assertAuthorized(MethodInvocation methodInvocation) throws AuthorizationException {
        //default implementation just ensures no deny votes are cast:
        Collection<AuthorizingAnnotationMethodInterceptor> aamis = getMethodInterceptors();
        if (aamis != null && !aamis.isEmpty()) {
            for (AuthorizingAnnotationMethodInterceptor aami : aamis) {
                if (aami.supports(methodInvocation)) {
                    aami.assertAuthorized(methodInvocation);
                }
            }
        }
    }
    ...
}

AuthorizingAnnotationMethodInterceptor的assertAuthorized，首先从子类获取AuthorizingAnnotationHandler，再调用该实现类的assertAuthorized方法。

public abstract class AuthorizingAnnotationMethodInterceptor extends AnnotationMethodInterceptor
{

    public AuthorizingAnnotationMethodInterceptor( AuthorizingAnnotationHandler handler ) {
        super(handler);
    }

    public AuthorizingAnnotationMethodInterceptor( AuthorizingAnnotationHandler handler,
                                                   AnnotationResolver resolver) {
        super(handler, resolver);
    }

    public Object invoke(MethodInvocation methodInvocation) throws Throwable {
        assertAuthorized(methodInvocation);
        return methodInvocation.proceed();
    }

    public void assertAuthorized(MethodInvocation mi) throws AuthorizationException {
        try {
            ((AuthorizingAnnotationHandler)getHandler()).assertAuthorized(getAnnotation(mi));
        }
        catch(AuthorizationException ae) {
            if (ae.getCause() == null) ae.initCause(new AuthorizationException("Not authorized to invoke method: " + mi.getMethod()));
            throw ae;
        }         
    }
}

现在分析其中一种实现类PermissionAnnotationMethodInterceptor，也是用的最多的，但是这个类的实际代码很少，很明显上述分析的getHandler在PermissionAnnotationMethodInterceptor中返回值为PermissionAnnotationHandler。

public class PermissionAnnotationMethodInterceptor extends AuthorizingAnnotationMethodInterceptor {

    public PermissionAnnotationMethodInterceptor() {
        super( new PermissionAnnotationHandler() );
    }

 
    public PermissionAnnotationMethodInterceptor(AnnotationResolver resolver) {
        super( new PermissionAnnotationHandler(), resolver);
    }
}

在PermissionAnnotationHandler类中，终于发现实际的检验逻辑，还是调用的Subject.checkPermission()进行校验。

public class PermissionAnnotationHandler extends AuthorizingAnnotationHandler {

    public PermissionAnnotationHandler() {
        super(RequiresPermissions.class);
    }

    protected String[] getAnnotationValue(Annotation a) {
        RequiresPermissions rpAnnotation = (RequiresPermissions) a;
        return rpAnnotation.value();
    }

    public void assertAuthorized(Annotation a) throws AuthorizationException {
        if (!(a instanceof RequiresPermissions)) return;

        RequiresPermissions rpAnnotation = (RequiresPermissions) a;
        String[] perms = getAnnotationValue(a);
        Subject subject = getSubject();

        if (perms.length == 1) {
            subject.checkPermission(perms[0]);
            return;
        }
        if (Logical.AND.equals(rpAnnotation.logical())) {
            getSubject().checkPermissions(perms);
            return;
        }
        if (Logical.OR.equals(rpAnnotation.logical())) {
            boolean hasAtLeastOnePermission = false;
            for (String permission : perms) if (getSubject().isPermitted(permission)) hasAtLeastOnePermission = true;
            if (!hasAtLeastOnePermission) getSubject().checkPermission(perms[0]);
            
        }
    }
}

实现类似编程式AOP

定义一个注解

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Log {
    String value() default "";
}

继承StaticMethodMatcherPointcutAdvisor类，并实现相关的方法。

@SuppressWarnings("serial")
@Component
public class HelloAdvisor extends StaticMethodMatcherPointcutAdvisor{
    
    public HelloAdvisor() {
        setAdvice(new LogMethodInterceptor());
    }

    public boolean matches(Method method, Class targetClass) {
        Method m = method;
        if ( isAuthzAnnotationPresent(m) ) {
            return true;
        }

        if ( targetClass != null) {
            try {
                m = targetClass.getMethod(m.getName(), m.getParameterTypes());
                return isAuthzAnnotationPresent(m);
            } catch (NoSuchMethodException ignored) {
               
            }
        }
        return false;
    }

    private boolean isAuthzAnnotationPresent(Method method) {
        Annotation a = AnnotationUtils.findAnnotation(method, Log.class);
        return a!= null;
    }
}

实现MethodInterceptor接口，定义切面处理的逻辑

public class LogMethodInterceptor implements MethodInterceptor{

    public Object invoke(MethodInvocation invocation) throws Throwable {
        Log log = invocation.getMethod().getAnnotation(Log.class);
        System.out.println("log: "+log.value());
        return invocation.proceed();    
    }
}

定义一个测试类，并添加Log注解

@Component
public class TestHello {

    @Log("test log")
    public String say() {
        return "ss";
    }
}

编写启动类，并且配置DefaultAdvisorAutoProxyCreator

@Configuration
public class TestBoot {

    public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext("com.fzsyw.test");  
        TestHello th = ctx.getBean(TestHello.class);
        System.out.println(th.say());
    }
    
    @Bean
    public DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator(){
        DefaultAdvisorAutoProxyCreator da = new DefaultAdvisorAutoProxyCreator();
        da.setProxyTargetClass(true);
        return da;
    }
}

最终打印的结果如下，证明编程式的AOP生效。

log: test log
ss

总结与思考

Shiro的注解式权限，使用确实方便，通过源码也分析了它的实现原理，比较核心的是配置DefaultAdvisorAutoProxyCreator和继承StaticMethodMatcherPointcutAdvisor。其中的5中权限注解，使用了统一一套代码架构，用到了的模板模式，方便扩展。最后自己也简单做了一个小例子，加深对编程式AOP的理解。