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Java - 非著名Java程序员
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<h1>Spring Boot 增加缓存功能</h1>
<div class="a-content">
<div class="a-content-text">
<pre class="line-numbers"><code class="language-plain_text">spring.jpa.properties.hibernate.show_sql=true，开启hibernate对sql语句的打印
</code></pre>
<p>单元测试中，用userRepository 查询两次相同内容。</p>
<p><img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15373729123926.jpg" alt="" /><br />
运行一下，会看到在控制台打出了两条sql，说明是查了两次库。</p>
<p><img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15373729221221.jpg" alt="" /></p>
<p>增加缓存：<br />
pom中添加依赖：</p>
<pre class="line-numbers"><code class="language-plain_text"><dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-cache</artifactId>
</dependency>
</code></pre>
<p>SpringBoot主类中添加注解 <code>@EnableCaching</code><br />
UserRepository 类添加注解<code>@CacheConfig(cacheNames = "users")</code><br />
findByName方法添加注解<code>@Cacheable</code></p>
<p>org.springframework.data.redis.serializer.SerializationException:?</p>
<p>缓存对象需要实现序列化接口.<code>UserDO implements Serializable</code></p>
<p>在次运行就会出现</p>
<p><img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15374555362360.jpg" alt="" style="width:1076px;" />可以看到，第二次请求的时候就没有打印出sql语句。</p>
<p>注解：</p>
<ul>
<li>
<p>@CacheConfig：<br />
主要配置该类中会用到的一些公用的缓存配置。<br />
cacheNames 配置了数据访问对象中返回的内容将存储于名为users的数组中。<br />
<img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15374561374912.jpg" alt="" /></p>
</li>
<li>
<p>@Cacheable：<br />
配置了findByName的函数返回值将会被加入到缓存。同时在查询时，会先查询缓存，若不存在才会查询数据库。<br />
<img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15374562984908.jpg" alt="" /></p>
</li>
<li>
<p><code>cacheNames</code>、<code>value</code>：用于指定缓存存储的集合名。两个参数等效。</p>
</li>
<li>
<p><code>key</code>：缓存对象存储在Map集合中的key值，非必需，缺省按照函数的所有参数组合作为key值，若自己配置需使用SpEL表达式，比如：@Cacheable(key = "#p0")：使用函数第一个参数作为缓存的key值，更多关于SpEL表达式的详细内容可参考<a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/integration.html#cache">官方文档</a></p>
</li>
<li>
<p><code>condition</code>:缓存对象的条件，非必需，也需使用SpEL表达式，只有满足表达式条件的内容才会被缓存，比如：@Cacheable(key = "#p0", condition = "#p0.length() < 3")，表示只有当第一个参数的长度小于3的时候才会被缓存，若做此配置上面的AAA用户就不会被缓存，读者可自行实验尝试。</p>
</li>
<li>
<p><code>unless</code>:另外一个缓存条件参数，非必需，需使用SpEL表达式。它不同于condition参数的地方在于它的判断时机，该条件是在函数被调用之后才做判断的，所以它可以通过对result进行判断。</p>
</li>
<li>
<p><code>keyGenerator</code>:用于指定key生成器，非必需。若需要指定一个自定义的key生成器，我们需要去实现org.springframework.cache.interceptor.KeyGenerator接口，并使用该参数来指定。需要注意的是：该参数与key是互斥的</p>
</li>
<li>
<p><code>cacheManager</code>:用于指定使用哪个缓存管理器，非必需。只有当有多个时才需要使用</p>
</li>
<li>
<p><code>cacheResolver</code>:用于指定使用那个缓存解析器，非必需。需通过org.springframework.cache.interceptor.CacheResolver接口来实现自己的缓存解析器，并用该参数指定。</p>
</li>
</ul>
<p>CacheManager</p>
<p><img src="http://hitol.blog.cdn.updev.cn/2020-07-05-15374571943253.jpg" alt="" /></p>
<p>在Spring Boot中通过@EnableCaching注解自动化配置合适的缓存管理器（CacheManager），Spring Boot根据下面的顺序去侦测缓存提供者：</p>
<ul>
<li>Generic</li>
<li>JCache (JSR-107)</li>
<li>EhCache 2.x</li>
<li>Hazelcast</li>
<li>Infinispan</li>
<li>Redis</li>
<li>Guava</li>
<li>Simple</li>
</ul>
<p>可以通过配置属性spring.cache.type来强制指定</p>
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<span class="date">2020/10/21 20:17 下午</span>
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