深度理解springboot集成cache缓存之源码解析

原创

漫话人生 2022-07-08 17:36:51 博主文章分类：SpringBoot ©著作权

文章标签 spring boot spring 缓存 redis 数据 文章分类 后端开发

©著作权归作者所有：来自51CTO博客作者漫话人生的原创作品，请联系作者获取转载授权，否则将追究法律责任

一、案例准备

1.创建数据表(employee表)

深度理解springboot集成cache缓存之源码解析_spring

2.创建Employee实体类封装数据库中的数据

@AllArgsConstructor
@NoArgsConstructor
@Data
@ToString
public class Employee {

    private Integer id;
    private String lastName;
    private String email;
    private Integer gender;     //1.男   2.女
    private Integer dId;
}

3.编写EmployeeMapper接口(DAO测通)

@Mapper
public interface EmployeeMapper {

    @Select("select * from employee where id=#{id}")
    Employee getEmpById(Integer id);
}

4.编写EmployeeService接口及其EmployeeServiceImpl实现类

@Service
public class EmployeeServiceImpl implements EmployeeService {

    @Autowired
    private EmployeeMapper employeeMapper;
    
    @Override
    @Cacheable(cacheNames = "emp",key = "#id",condition = "#id>0")
    public Employee getEmp(Integer id) {
        System.out.println("正在查询id为"+id+"号的员工");
        Employee emp = employeeMapper.getEmpById(id);
        return emp;
    }
}

5.编写EmployeeController类

@RestController
public class EmpController {

    @Autowired
    private EmployeeService employeeService;

    @GetMapping("/emp/{id}")
    public Employee getEmployee(@PathVariable("id") Integer id){
        Employee emp = employeeService.getEmp(id);
        return emp;
    }
}

6.启动访问http://localhost:8080/emp/1

深度理解springboot集成cache缓存之源码解析_缓存_02

成功!

-----------------------------------------------分割线-------------------------------------------------------------

二、工作原理分析

1.查看springboot启动时，导入了哪些缓存组件

通过以往springboot相关的自动配置类可知与缓存相关的自动配置类为CacheAutoConfiguration

深度理解springboot集成cache缓存之源码解析_spring_03

@Import：向容器中导入一些组件(通常导入的选择器以ImportSelector结尾)

ctrl+右键查看CacheConfigurationImportSelector源码

static class CacheConfigurationImportSelector implements ImportSelector {

    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
      CacheType[] types = CacheType.values();
      String[] imports = new String[types.length];
      for (int i = 0; i < types.length; i++) {
        imports[i] = CacheConfigurations.getConfigurationClass(types[i]);
      }
      return imports;
    }

  }

}

打上断点，debug模式下运行

深度理解springboot集成cache缓存之源码解析_spring boot_04

放行,查看return imports的结果

深度理解springboot集成cache缓存之源码解析_数据_05

深度理解springboot集成cache缓存之源码解析_redis_06

导入的组件如下

* "org.springframework.boot.autoconfigure.cache.GenericCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.JCacheCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.EhCacheCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.HazelcastCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.InfinispanCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.CouchbaseCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.RedisCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.CaffeineCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.NoOpCacheConfiguration"
     * "org.springframework.boot.autoconfigure.cache.SimpleCacheConfiguration"

2.是哪个缓存配置类生效呢？根据当前的场景进行分析

有两种方法可以得出哪个缓存配置类生效

第一种：源码分析（该方法只做简单说明)
随便打开一个缓存配置类，例如第一个GenericCacheConfiguration,查看源码如下

@Configuration(proxyBeanMethods = false)
@ConditionalOnBean(Cache.class)
@ConditionalOnMissingBean(CacheManager.class)
@Conditional(CacheCondition.class)
class GenericCacheConfiguration {

  @Bean
  SimpleCacheManager cacheManager(CacheManagerCustomizers customizers, Collection<Cache> caches) {
    SimpleCacheManager cacheManager = new SimpleCacheManager();
    cacheManager.setCaches(caches);
    return customizers.customize(cacheManager);
  }

}

根据类上的
@ConditionalOnBean(Cache.class)
@ConditionalOnMissingBean(CacheManager.class)
@Conditional(CacheCondition.class)
注解进行判断该类是否生效
这些都是@Conditional注解的衍生注解，该注解是Spring4新推出的注解，判断是否满足某种条件，如果满足则给容器注册bean

第二种：查看自动配置报告
在application.properties配置文件中添加

debug=true

运行发现这几个组件中只有SimpleCacheConfiguration生效了

深度理解springboot集成cache缓存之源码解析_缓存_07

3.分析核心类的作用

进去查看SimpleCacheConfiguration的源码

@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(CacheManager.class)
@Conditional(CacheCondition.class)
class SimpleCacheConfiguration {

  @Bean
  ConcurrentMapCacheManager cacheManager(CacheProperties cacheProperties,
      CacheManagerCustomizers cacheManagerCustomizers) {
    ConcurrentMapCacheManager cacheManager = new ConcurrentMapCacheManager();
    List<String> cacheNames = cacheProperties.getCacheNames();
    if (!cacheNames.isEmpty()) {
      cacheManager.setCacheNames(cacheNames);
    }
    return cacheManagerCustomizers.customize(cacheManager);
  }

}

可以看出给容器中注册了一个ConcurrentMapCacheManager缓存管理器

查看源码分析创建Cache的具体细节

深度理解springboot集成cache缓存之源码解析_spring_08

这一段代码是创建Cache的核心

#首先通过该类中的cacheMap属性获取缓存，参数为缓存名字(key-value)

#然后进行判断，如果cache为null，则上锁；再次获取如果为null，则根据本类中的createConcurrentMapCache方法创建Cache，然后将其放到缓存中

深度理解springboot集成cache缓存之源码解析_缓存_09

protected Cache createConcurrentMapCache(String name) {
        SerializationDelegate actualSerialization = this.isStoreByValue() ? this.serialization : null;
        return new ConcurrentMapCache(name, new ConcurrentHashMap(256), this.isAllowNullValues(), actualSerialization);
    }
}