作者:谭朝红

地址：www.ramostear.com/articles/spring_boot_ehcache.html

本次内容主要介绍基于Ehcache 3.0来快速实现Spring Boot应用程序的数据缓存功能。在Spring Boot应用程序中，我们可以通过Spring Caching来快速搞定数据缓存。

1. 创建一个Spring Boot工程

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">   <modelVersion>4.0.0</modelVersion>  <parent>  <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.3.RELEASE</version>    <relativePath/> <!-- lookup parent from repository -->  </parent> <groupId>com.ramostear</groupId>    <artifactId>cache</artifactId>  <version>0.0.1-SNAPSHOT</version>   <name>cache</name>  <description>Demo project for Spring Boot</description> <properties>  <java.version>1.8</java.version>    </properties> <dependencies>    <dependency>  <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-cache</artifactId>  </dependency> <dependency>  <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId>    </dependency> <dependency>  <groupId>org.ehcache</groupId>  <artifactId>ehcache</artifactId>    </dependency> <dependency>  <groupId>javax.cache</groupId>  <artifactId>cache-api</artifactId>  </dependency> <dependency>  <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId>   <scope>test</scope> </dependency> <dependency>  <groupId>org.projectlombok</groupId>    <artifactId>lombok</artifactId> </dependency> </dependencies>   <build>   <plugins> <plugin>  <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId>   </plugin> </plugins>    </build>
</project>

依赖说明：

• spring-boot-starter-cache为Spring Boot应用程序提供缓存支持

• ehcache提供了Ehcache的缓存实现

• cache-api 提供了基于JSR-107的缓存规范

2. 配置Ehcache缓存

spring.cache.jcache.config=classpath:ehcache.xml

然后使用@EnableCaching注解开启Spring Boot应用程序缓存功能，你可以在应用主类中进行操作：

package com.ramostear.cache;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;
@SpringBootApplication
@EnableCaching
public class CacheApplication { public static void main(String[] args) {    SpringApplication.run(CacheApplication.class, args);    }
}

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://www.ehcache.org/v3"    xmlns:jsr107="http://www.ehcache.org/v3/jsr107"  xsi:schemaLocation="  http://www.ehcache.org/v3 http://www.ehcache.org/schema/ehcache-core-3.0.xsd    http://www.ehcache.org/v3/jsr107 http://www.ehcache.org/schema/ehcache-107-ext-3.0.xsd">    <service> <jsr107:defaults enable-statistics="true"/>    </service>    <cache alias="person"> <key-type>java.lang.Long</key-type> <value-type>com.ramostear.cache.entity.Person</value-type>  <expiry>  <ttl unit="minutes">1</ttl>  </expiry> <listeners>   <listener>    <class>com.ramostear.cache.config.PersonCacheEventLogger</class>    <event-firing-mode>ASYNCHRONOUS</event-firing-mode> <event-ordering-mode>UNORDERED</event-ordering-mode>    <events-to-fire-on>CREATED</events-to-fire-on>  <events-to-fire-on>UPDATED</events-to-fire-on>  <events-to-fire-on>EXPIRED</events-to-fire-on>  <events-to-fire-on>REMOVED</events-to-fire-on>  <events-to-fire-on>EVICTED</events-to-fire-on>  </listener>   </listeners>  <resources>   <heap unit="entries">2000</heap> <offheap unit="MB">100</offheap> </resources>  </cache>
</config>

最后，还需要定义个缓存事件监听器，用于记录系统操作缓存数据的情况，最快的方法是实现CacheEventListener接口：

package com.ramostear.cache.config;
import org.ehcache.event.CacheEvent;
import org.ehcache.event.CacheEventListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/** * @author ramostear    * @create-time 2019/4/7 0007-0:48  * @modify by : * @since:  */
public class PersonCacheEventLogger implements CacheEventListener<Object,Object>{ private static final Logger logger = LoggerFactory.getLogger(PersonCacheEventLogger.class);    @Override  public void onEvent(CacheEvent cacheEvent) {    logger.info("person caching event {} {} {} {}",   cacheEvent.getType(),   cacheEvent.getKey(),    cacheEvent.getOldValue(),   cacheEvent.getNewValue());  }
}

3. 使用@Cacheable注解

要让Spring Boot能够缓存我们的数据，还需要使用@Cacheable注解对业务方法进行注释，告诉Spring Boot该方法中产生的数据需要加入到缓存中：

package com.ramostear.cache.service;
import com.ramostear.cache.entity.Person;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;
/** * @author ramostear    * @create-time 2019/4/7 0007-0:51  * @modify by : * @since:  */
@Service(value = "personService")
public class PersonService {    @Cacheable(cacheNames = "person",key = "#id")    public Person getPerson(Long id){   Person person = new Person(id,"ramostear","ramostear@163.com");   return person;  }
}

通过以上三个步骤，我们就完成了Spring Boot的缓存功能。接下来，我们将测试一下缓存的实际情况。

4. 缓存测试

package com.ramostear.cache.controller;
import com.ramostear.cache.entity.Person;
import com.ramostear.cache.service.PersonService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
/** * @author ramostear    * @create-time 2019/4/7 0007-0:54  * @modify by : * @since:  */
@RestController
@RequestMapping("/persons")
public class PersonController { @Autowired private PersonService personService;    @GetMapping("/{id}") public ResponseEntity<Person> person(@PathVariable(value = "id") Long id){    return new ResponseEntity<>(personService.getPerson(id), HttpStatus.OK);  }
}

package com.ramostear.cache.entity;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import java.io.Serializable;
/** * @author ramostear    * @create-time 2019/4/7 0007-0:45  * @modify by : * @since:  */
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Person implements Serializable{    private Long id;    private String username;    private String email;
}

以上准备工作都完成后，让我们编译并运行应用程序。项目成功启动后，使用浏览器打开：http://localhost:8080/persons/1 ,你将在浏览器页面中看到如下的信息：

{"id":1,"username":"ramostear","email":"ramostear@163.com"}

此时在观察控制台输出的日志信息：

2019-04-07 01:08:01.001  INFO 6704 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 5 ms
2019-04-07 01:08:01.054  INFO 6704 --- [e [_default_]-0] c.r.cache.config.PersonCacheEventLogger  : person caching event CREATED 1 null com.ramostear.cache.entity.Person@ba8a729

由于我们是第一次请求API，没有任何缓存数据。因此，Ehcache创建了一条缓存数据，可以通过CREATED看一了解到。

我们在ehcache.xml文件中将缓存过期时间设置成了1分钟（1），因此在一分钟之内我们刷新浏览器，不会看到有新的日志输出，一分钟之后，缓存过期，我们再次刷新浏览器，将看到如下的日志输出：

2019-04-07 01:09:28.612  INFO 6704 --- [e [_default_]-1] c.r.cache.config.PersonCacheEventLogger  : person caching event EXPIRED 1 com.ramostear.cache.entity.Person@a9f3c57 null
2019-04-07 01:09:28.612  INFO 6704 --- [e [_default_]-1] c.r.cache.config.PersonCacheEventLogger  : person caching event CREATED 1 null com.ramostear.cache.entity.Person@416900ce

第一条日志提示缓存已经过期，第二条日志提示Ehcache重新创建了一条缓存数据。

结束语