我们在这一章中继续上一章的分析。我们在上一章中说到了获取到了切面类中所有不带@Pointcut注解的方法，我们看看Spring对我们获取到的这些方法进行了什么操作：
for (Method method : getAdvisorMethods(aspectClass)) {
//循环切面中所有不带@Pointcut注解的方法。
//method 切面中不带@Pointcut注解的方法
//lazySingletonAspectInstanceFactory中含有切面实例 是个单例
//advisors中的下标 切面的一个顺序
//aspectName 切面类的名字
//下面我们来看一下getAdvisor这个方法的内容
Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
if (advisor != null) {
advisors.add(advisor);
}
}
getAdvisor
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
int declarationOrderInAspect, String aspectName) {
//验证切面类 见我们上一章的分析
validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
//这里根据传入的方法和切面类获取 切点表达式
AspectJExpressionPointcut expressionPointcut = getPointcut(
candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
//没有获取到切点表达式 直接返回null
if (expressionPointcut == null) {
return null;
}
//返回一个Advisor的实例 这个实例中包含了 一下内容
//切点表达式 AspectJExpressionPointcut
//切点方法
//ReflectiveAspectJAdvisorFactory实例
//切面类实例
//切面类名字
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}
我们先来看一下AspectJExpressionPointcut这个类的UML类图：
private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
//方法上是否存在切面注解(通知类型注解) 即方法上是否有
//@Before, @Around, @After, @AfterReturning, @AfterThrowing, @Pointcut注解
//这里也提供了一种获取类上是否有我们想要的注解的一种方式
//返回一个AspectJAnnotation对象
//这里用了AnnotationUtils用来获取注解的相关信息
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}
//创建AspectJExpressionPointcut对象
AspectJExpressionPointcut ajexp =
new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
//设置切面表达式 在AspectJAnnotation中是可以获取到通知类型的，但是这里没有设置通知类型
ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
ajexp.setBeanFactory(this.beanFactory);
return ajexp;
}
在这里我们要看一下AspectJAnnotation这个类。这个类是AbstractAspectJAdvisorFactory中的内部类。从这个类中可以获取切点表达式和通知类型。
protected static class AspectJAnnotation<A extends Annotation> {
//切点表达式所在的属性 poincut会覆盖value的值
//其实这里指的是 通知类型注解中的属性
private static final String[] EXPRESSION_PROPERTIES = new String[] {"value", "pointcut"};
private static Map<Class<?>, AspectJAnnotationType> annotationTypes =
new HashMap<Class<?>, AspectJAnnotationType>();
static {
//初始化通知类型
annotationTypes.put(Pointcut.class,AspectJAnnotationType.AtPointcut);
annotationTypes.put(After.class,AspectJAnnotationType.AtAfter);
annotationTypes.put(AfterReturning.class,AspectJAnnotationType.AtAfterReturning);
annotationTypes.put(AfterThrowing.class,AspectJAnnotationType.AtAfterThrowing);
annotationTypes.put(Around.class,AspectJAnnotationType.AtAround);
annotationTypes.put(Before.class,AspectJAnnotationType.AtBefore);
}
.......
public AspectJAnnotation(A annotation) {
//注解信息
this.annotation = annotation;
//根据注解类型获取通知类型
this.annotationType = determineAnnotationType(annotation);
// We know these methods exist with the same name on each object,
// but need to invoke them reflectively as there isn't a common interface.
try {
//从通知类型注解上面获取切点表达式
this.pointcutExpression = resolveExpression(annotation);
//获取参数的名字
this.argumentNames = (String) annotation.getClass().getMethod("argNames").invoke(annotation);
}
catch (Exception ex) {
throw new IllegalArgumentException(annotation + " cannot be an AspectJ annotation", ex);
}
}
//从这个获取切点表达式的代码中我们可以看到 pointcut的属性会覆盖value的属性值
private String resolveExpression(A annotation) throws Exception {
String expression = null;
//循环上面的切点属性
for (String methodName : EXPRESSION_PROPERTIES) {
Method method;
try {
method = annotation.getClass().getDeclaredMethod(methodName);
}
catch (NoSuchMethodException ex) {
method = null;
}
if (method != null) {
//获取切点表达式！！！
String candidate = (String) method.invoke(annotation);
if (StringUtils.hasText(candidate)) {
expression = candidate;
}
}
}
return expression;
}
我们把上面获取Advisor的过程总结一下：循环切面类中的所有不带@Pointcut注解的方法，接着判断切面类的方法上是否有：@Before, @Around, @After, @AfterReturning, @AfterThrowing, @Pointcut注解。如果没有的话，循环下一个方法。如果有这些注解的话，则从这些注解中获取切点表达式存放到AspectJExpressionPointcut对象中，最后将获取到的切点表达式类封装到InstantiationModelAwarePointcutAdvisorImpl这个类中。从上面的分析我们知道InstantiationModelAwarePointcutAdvisorImpl类至少拥有：切点表达式类、切面对象、带有切点表达式的方法、ReflectiveAspectJAdvisorFactory实例。那么我们最后来分析一下InstantiationModelAwarePointcutAdvisorImpl这个类。
public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
//切点表达式类 AspectJExpressionPointcut
this.declaredPointcut = declaredPointcut;
//切面类
this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
//切点表达式方法所在的方法名 这里指的是@Before、@After这些通知类型所在的方法名
this.methodName = aspectJAdviceMethod.getName();
//通知参数类型
this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
//切面通知方法
this.aspectJAdviceMethod = aspectJAdviceMethod;
//ReflectiveAspectJAdvisorFactory实例
this.aspectJAdvisorFactory = aspectJAdvisorFactory;
//切面对象实例
this.aspectInstanceFactory = aspectInstanceFactory;
//切面顺序
this.declarationOrder = declarationOrder;
this.aspectName = aspectName;
//根据切面元数据判断是否要延迟实例化 一般为否
if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
// Static part of the pointcut is a lazy type.
Pointcut preInstantiationPointcut = Pointcuts.union(
aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);
this.pointcut = new PerTargetInstantiationModelPointcut(
this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
this.lazy = true;
}
else {
// A singleton aspect.
//切点表达式类
this.pointcut = this.declaredPointcut;
this.lazy = false;
//这里获取Advice实例 这里又拥有了Advice的实例！！！！
//不得不说InstantiationModelAwarePointcutAdvisorImpl这个类真的是太强大了
this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
}
}
OK下面我们的分析就到了如果从InstantiationModelAwarePointcutAdvisorImpl中获取Advice的内容。
