假设您想使用@LogExecTime 注释记录一些带注释的方法所花费的时间。
我先创建一个注解LogExecTime：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface LogExecTime {
}
然后我定义一个方面：
@Component // For Spring AOP
@Aspect
public class LogTimeAspect {
@Around(value = "@annotation(annotation)")
public Object LogExecutionTime(final ProceedingJoinPoint joinPoint, final LogExecTime annotation) throws Throwable {
final long startMillis = System.currentTimeMillis();
try {
System.out.println("Starting timed operation");
final Object retVal = joinPoint.proceed();
return retVal;
} finally {
final long duration = System.currentTimeMillis() - startMillis;
System.out.println("Call to " + joinPoint.getSignature() + " took " + duration + " ms");
}
}
}
我创建了一个带有 LogExecTime 注释的类：
@Component
public class Operator {
@LogExecTime
public void operate() throws InterruptedException {
System.out.println("Performing operation");
Thread.sleep(1000);
}
}
还有一个主要使用Spring AOP：
public class SpringMain {
public static void main(String[] args) throws InterruptedException {
ApplicationContext context = new GenericXmlApplicationContext("applicationContext.xml");
final Operator bean = context.getBean(Operator.class);
bean.operate();
}
}
如果我运行这个类，我会在标准输出上得到以下输出：
Starting timed operation
Performing operation
Call to void testaop.Operator.Operate() took 1044 ms
现在有了魔法。正如我确实使用 Spring AOP 而不是 AspectJ weaver 一样，神奇之处在于使用代理机制在运行时发生。所以.class 文件保持不变。例如，如果我调试这个程序并在operate 中放置一个断点，您将看到 Spring 是如何发挥作用的：
由于 Spring AOP 实现是非侵入式并使用 Spring 机制，您需要添加 @Component 注释并使用 Spring 上下文而不是普通的 new 创建对象。
另一边的AspectJ 将更改.class 文件。我用 AspectJ 尝试了这个项目，并用 jad 反编译了 Operator 类。这导致：
public void operate()
throws InterruptedException
{
JoinPoint joinpoint = Factory.makeJP(ajc$tjp_0, this, this);
operate_aroundBody1$advice(this, joinpoint, LogTimeAspect.aspectOf(), (ProceedingJoinPoint)joinpoint, (LogExecTime)(ajc$anno$0 == null && (ajc$anno$0 = testaop/Operator.getDeclaredMethod("operate", new Class[0]).getAnnotation(testaop/LogExecTime)) == null ? ajc$anno$0 : ajc$anno$0));
}
private static final void operate_aroundBody0(Operator ajc$this, JoinPoint joinpoint)
{
System.out.println("Performing operation");
Thread.sleep(1000L);
}
private static final Object operate_aroundBody1$advice(Operator ajc$this, JoinPoint thisJoinPoint, LogTimeAspect ajc$aspectInstance, ProceedingJoinPoint joinPoint, LogExecTime annotation)
{
long startMillis = System.currentTimeMillis();
Object obj;
System.out.println("Starting timed operation");
ProceedingJoinPoint proceedingjoinpoint = joinPoint;
operate_aroundBody0(ajc$this, proceedingjoinpoint);
Object retVal = null;
obj = retVal;
long duration = System.currentTimeMillis() - startMillis;
System.out.println((new StringBuilder("Call to ")).append(joinPoint.getSignature()).append(" took ").append(duration).append(" ms").toString());
return obj;
Exception exception;
exception;
long duration = System.currentTimeMillis() - startMillis;
System.out.println((new StringBuilder("Call to ")).append(joinPoint.getSignature()).append(" took ").append(duration).append(" ms").toString());
throw exception;
}
private static void ajc$preClinit()
{
Factory factory = new Factory("Operator.java", testaop/Operator);
ajc$tjp_0 = factory.makeSJP("method-execution", factory.makeMethodSig("1", "operate", "testaop.Operator", "", "", "java.lang.InterruptedException", "void"), 5);
}
private static final org.aspectj.lang.JoinPoint.StaticPart ajc$tjp_0; /* synthetic field */
private static Annotation ajc$anno$0; /* synthetic field */
static
{
ajc$preClinit();
}