Java 为什么Spring对@Cacheable注释方法的一次调用执行@Cacheable keyGenerator两次

为什么Spring在一次调用带注释的@Cacheable方法时会执行我的自定义@Cacheable键生成器两次，为什么不执行一次呢

我的密钥生成器实现

package com.example.demo;

import org.springframework.cache.interceptor.KeyGenerator;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;
import java.util.ArrayList;

/**
 * Custom key generator
 */
@Component(value = "customerKeyGenerator")
public class CustomerKeyGen implements KeyGenerator
{
    @Override
    public Object generate(Object target, Method method, Object... params)
    {
        System.out.println("Generating a key");
        ArrayList<String> customerNames = (ArrayList<String>) params[0];
        return customerNames.hashCode();
    }
}

curl http://127.0.0.1:8080/countCustomers
 % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    18  100    18    0     0     18      0  0:00:01 --:--:--  0:00:01    
76countOfCustomers=2

日志 我在应用程序属性中有以下设置来启用缓存跟踪

logging.level.org.springframework.cache=TRACE

...
2018-08-27 11:56:53.753  INFO 18756 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-08-27 11:56:53.757  INFO 18756 --- [           main] c.example.demo.TestCacheableApplication  : Started TestCacheableApplication in 3.543 seconds (JVM running for 5.137)
2018-08-27 11:56:58.411  INFO 18756 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2018-08-27 11:56:58.411  INFO 18756 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2018-08-27 11:56:58.446  INFO 18756 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 35 ms
Generating a key
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : Computed cache key '104328221' for operation Builder[public int com.example.demo.CustomerService.getCountOfCustomers(java.util.ArrayList)] caches=[customersCache] | key='' | keyGenerator='customerKeyGenerator' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : No cache entry for key '104328221' in cache(s) [customersCache]
Generating a key
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : Computed cache key '104328221' for operation Builder[public int com.example.demo.CustomerService.getCountOfCustomers(java.util.ArrayList)] caches=[customersCache] | key='' | keyGenerator='customerKeyGenerator' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'

从概念上讲，我认为Spring只需要运行一次keyGenerator，首先使用它查找缓存，如果找不到，当方法完成时，使用相同的键放入缓存。所以我不明白为什么我两次看到这个

我的问题是：

我对它的工作原理和原因感到困惑

日志记录和调试变得混乱

潜在的性能影响，即使keyGeneration实现应该很便宜，为什么要多次这么做呢

---

我想我知道为什么，密钥生成一次用于在缓存中查找，一次用于放入缓存。不知道为什么会这样，但似乎是发生了什么。

你能发布关于如何调用getCountOfCustomers（list）方法的代码吗？@jay，我已经发布了用于调用的代码，并注意到我调用了两次。现在我调用\@Cacheable注释的方法一次，但看到keyGenerator运行了两次。我想我知道为什么，一次生成一个密钥用于在缓存中查找，一次用于放入缓存。我认为您的密钥不是唯一的，这可能是原因之一，您可能希望尝试更改不同的generate（）方法。有人发现这是“正常”行为吗？我注意到了同样的行为，我的钥匙绝对是独一无二的。

curl http://127.0.0.1:8080/countCustomers
 % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    18  100    18    0     0     18      0  0:00:01 --:--:--  0:00:01    
76countOfCustomers=2

...
2018-08-27 11:56:53.753  INFO 18756 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-08-27 11:56:53.757  INFO 18756 --- [           main] c.example.demo.TestCacheableApplication  : Started TestCacheableApplication in 3.543 seconds (JVM running for 5.137)
2018-08-27 11:56:58.411  INFO 18756 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2018-08-27 11:56:58.411  INFO 18756 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2018-08-27 11:56:58.446  INFO 18756 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 35 ms
Generating a key
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : Computed cache key '104328221' for operation Builder[public int com.example.demo.CustomerService.getCountOfCustomers(java.util.ArrayList)] caches=[customersCache] | key='' | keyGenerator='customerKeyGenerator' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : No cache entry for key '104328221' in cache(s) [customersCache]
Generating a key
2018-08-27 11:56:58.480 TRACE 18756 --- [nio-8080-exec-1] o.s.cache.interceptor.CacheInterceptor   : Computed cache key '104328221' for operation Builder[public int com.example.demo.CustomerService.getCountOfCustomers(java.util.ArrayList)] caches=[customersCache] | key='' | keyGenerator='customerKeyGenerator' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'