我创建了一个Spring方面来处理Retry机制。我还创建了一个Retry注释。以下是重试注释的代码以及处理此注释的方面。

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Retry {
    /**
     * List of exceptions for which we need to retry method invocation.
     * 
     * @return Array of classes.
     */
    Class<?>[] exceptions();

    /**
     * Number of retries. Default is 3.
     * 
     * @return Number of retires.
     */
    int retries() default 3;

    /**
     * Back of period in ms. Default is 1000 ms.
     * 
     * @return Back off Period.
     */
    int backOffPeriod() default 1000;

}

@Aspect
public class RetryInterceptor implements Ordered {

    private static final RetryInterceptor   instance    = new RetryInterceptor();

    private RetryInterceptor() {
    }

    private static final Log    logger  = LogFactory.getLog(RetryInterceptor.class);
    private int                 order   = 100;

    @Around("@annotation(retry)")
    public Object performOperation(ProceedingJoinPoint pjp, Retry retry) throws Throwable {
        Class<?>[] exceptionClasses = retry.exceptions();
        Assert.notEmpty(exceptionClasses, "Exception classes cannot be empty.");
        int retries = retry.retries();
        if (logger.isInfoEnabled()) {
            logger.info("Attempting to call " + pjp.toShortString() + " with potential for " + getExceptionClasses(exceptionClasses)
                    + " with maximum " + retries + " retries");
        }
        int numAttempts = 0;
        do {
            try {
                return pjp.proceed();
            } catch (Throwable ex) {
                // if the exception is not what we're looking for, pass it through
                boolean canThrowException = true;
                for (Class<?> exceptionClass : exceptionClasses) {
                    if (exceptionClass.isAssignableFrom(ex.getClass())) {
                        canThrowException = false;
                        break;
                    }
                }
                // A non-configured exception was found.
                if (canThrowException) {
                    throw ex;
                }
                // we caught the configured exception, retry unless we've reached the maximum
                if (++numAttempts > retries) {
                    logger.warn("Caught " + ex.getClass().getCanonicalName() + " and exceeded maximum retries (" + retries
                            + "), rethrowing.");
                    throw ex;
                }
                if (logger.isInfoEnabled()) {
                    logger.info("Caught " + ex.getClass().getCanonicalName() + " and will retry, attempts: " + numAttempts);
                }
            }
            sleep(retry.backOffPeriod());
        } while (numAttempts <= retries);
        // this will never execute - we will have either successfully returned or re-thrown an
        // exception
        return null;
    }

    @Override
    public int getOrder() {
        return order;
    }

    private String getExceptionClasses(Class<?>[] classes) {
        StringBuilder builder = new StringBuilder();
        builder.append(classes[0].getCanonicalName());
        for (int i = 1; i < classes.length; i++) {
            builder.append(", ").append(classes[i].getCanonicalName());
        }
        return builder.toString();
    }

    public static RetryInterceptor getInstance() {
        return instance;
    }

    // Better than Thread.sleep().
    public void sleep(long backOffPeriod) throws InterruptedException {
        Object mutex = new Object();
        synchronized (mutex) {
            mutex.wait(backOffPeriod);
        }
    }
}

要启用注释，我需要实例化RetryInterceptor类。我要确保对于给定的上下文，只有该对象的一个​​实例。如果由于某种原因创建了多个对象，那么我的建议将被应用多次。我如何才能完全确保始终有1个实例？