Spring cacheable annotations do not cache null values

Today, when annotated with cacheable, null values are found and cached. The next time another system updates the value, from the cache, or the null value, there is a problem. So on the one hand, you want the other system to update, to clear the cache, on the other hand do not want to cache too much junk data.

Reference http://stackoverflow.com/questions/12113725/ How-do-i-tell-spring-cache-not-to-cache-null-value-in-cacheable-annotation the procedure and make changes to the program

   @Cacheable(key = "''+#id", unless="#result == null")
    public XXXPO get(int id) {
       //get from db
    }

This way, when a method returns a null value, it is not cached. See unless explanation:

/**
 * Spring Expression Language (SpEL) attribute used to veto method caching.
 * <p>Unlike {@link #condition()}, this expression is evaluated after the method
 * has been called and can therefore refer to the {@code result}. Default is "",
 * meaning that caching is never vetoed.
 * @since 3.2
 */

The effect is to use the value of result to decide whether to negate the method cache. So it can be used to make conditional judgments.

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