Spring Cacheable Key Generator Example

In most cases you can convert a pull-start engine to an electric-start. It specifically depends on the type of engine you have. Looking at your engine and performing a little research will let you know if it is both cost effective and feasible to convert your motor to electric-start. Conversion Requirements. Modify pull generator to key start car. Dec 24, 2009 (Patent Pending) The Pull Start Eliminator prevents you from having to use the pull cord with your lawn mowers, snow blowers, and other gasoline driven tools with a pull cord. It may be possible to convert your pull-start lawn mower, generator outboard engine to electric start. To make a small engine electric start conversion, the engine must have mounting bosses for the starter and the manufacturer or a third party must provide a starter that will fit your machine. Sep 27, 2018 A typical electric start kit that provides the power for your generator consists of the starter motor, the push button device or a key switch, bolts, the plug and the installation instructions. Be sure to get the starter kit volt that can supply the right power to your generator to prevent burnout. Mar 03, 2016 This post and attached video shows how I did a DIY pull start to electric start conversion on my generator. Converting a Generator to Electric Start Is Not Hard. In this case, it was really about finding a generator that had a toothed flywheel. I’ve thought about converting a generator to electric start.

From the spring documentation :

Spring Cacheable Key Generator Example For Kids
Spring Boot Cacheable Key

Aug 23, 2018 We are also going to cover the option to create a custom key generator with Spring Cache. Spring Cache API uses a simple KeyGenerator for generating a key to store caching data. The default key generators for Spring Cache SimpleKeyGenerator.This default implementation uses the method parameters to generate the key. Here is the high-level overview for the default key generation algorithm. The default key generators for Spring Cache SimpleKeyGenerator and SimpleKey only consider the argument types of a method and not the method itself. This means that if you have two different methods with the same argument types (eg. Integer or String) and the arguments themselves are equal then Spring Cache. This allows for customizing the strategy for cache key generation, per Spring's KeyGenerator SPI. Normally, @EnableCaching will configure Spring's SimpleKeyGenerator for this purpose, but when implementing CachingConfigurer, a key generator must be provided explicitly. If you first call #getModel1 with 1 and then call #getModel2 with 1 then Spring Cache will return the value that #getModel1 returned because all the method arguments are equal. This is almost certainly not what you want. The following key generator solves this issue. Sep 15, 2015 We have earlier written few interesting articles on caching in spring and another good article on @Cacheable and @CacheEvict annotations for caching in spring. This is another comprehensive tutorial for spring caching using Spring 4.Spring caching is available since 3.1, but spring 4.1 has added lot of cool features with the existing spring caching framework. Oct 09, 2019 Learn how to implement a custom Spring Cache KeyGenerator. This is responsible for generating every key for each data item in the cache, which would be used to lookup the data item on retrieval.

How can I specify @Cachable to use isbn and checkWarehouse as key?

Answers:

Update: Current Spring cache implementation uses all method parameters as the cache key if not specified otherwise. If you want to use selected keys, refer to Arjan’s answer which uses SpEL list {#isbn, #includeUsed} which is the simplest way to create unique keys.

From Spring Documentation

Spring has a built-in EhCache cache manager, org.springframework.cache.ehcache.EhCacheManagerFactoryBean. This is suitable for most caching situations, but I have found defining a custom cache manager to be useful because it allows me to control the cache either programmatically, or with annotations, using the same cache.

The default key generation strategy changed with the release of Spring
4.0. Earlier versions of Spring used a key generation strategy that, for multiple key parameters, only considered the hashCode() of
parameters and not equals(); this could cause unexpected key
collisions (see SPR-10237 for background). The new
‘SimpleKeyGenerator’ uses a compound key for such scenarios.

Before Spring 4.0

I suggest you to concat the values of the parameters in Spel expression with something like key='#checkWarehouse.toString() + #isbn.toString()'), I believe this should work as org.springframework.cache.interceptor.ExpressionEvaluator returns Object, which is later used as the key so you don’t have to provide an int in your SPEL expression.

As for the hash code with a high collision probability – you can’t use it as the key.

Someone in this thread has suggested to use T(java.util.Objects).hash(#p0,#p1, #p2) but it WILL NOT WORK and this approach is easy to break, for example I’ve used the data from SPR-9377 :

Both lines print -636517714 on my environment.

P.S. Actually in the reference documentation we have

I think that this example is WRONG and misleading and should be removed from the documentation, as the keys should be unique.

P.P.S. also see https://jira.springsource.org/browse/SPR-9036 for some interesting ideas regarding the default key generation.

I’d like to add for the sake of correctness and as an entertaining fact that using a secure cryptographic hash function like SHA256, due to the properties of such function IS possible for this task, but to compute it every time may be too expensive.

Answers:

After some limited testing with Spring 3.2, it seems one can use a SpEL list: {.., .., ..}. This can also include null values. Spring passes the list as the key to the actual cache implementation. When using Ehcache, such will at some point invoke List#hashCode(), which takes all its items into account. (I am not sure if Ehcache only relies on the hash code.)

I use this for a shared cache, in which I include the method name in the key as well, which the Spring default key generator does not include. This way I can easily wipe the (single) cache, without (too much…) risking matching keys for different methods. Like:

Of course, if many methods need this and you’re always using all parameters for your key, then one can also define a custom key generator that includes the class and method name: