缓存-Ehcache

spring缓存很大程度上是围绕切面构建的。
在执行加有@Cacheable、@CachePut、@CacheEivt、@Caching等注解的方法（当然也可加在类上或者接口方法上，实现接口的方法都会执行缓存操作）。都会先进入CacheAspectSupport 类中。
执行getCache方法。
遍历所有配置的缓存（在指定的cache.xml中指定缓存名字）
然后查看是否存在这个缓存（不存在直接抛异常，这个要在xml中添加对应的缓存名字）。

具体步骤

1. 启用缓存
   在javaconfig中添加@EnableCaching
2. 配置EhCacheCacheManager
   配置EhCacheManagerFactoryBean bean（指定一个ConfigLocation，也就是Ehcache.xml的classpathresource），然后把这个bean注入到 EhCacheCacheManager
   FactoryBean接口
   EhCacheManagerFactoryBean 类实现了FactoryBean接口
   在查找上下文的时候，如果知道实现了FactoryBean接口就会调用getObject方法返回的对象注入到spring上下文。
   afterPropertiesSet方法，在EhCacheManagerFactoryBean对象构建成功后调用（因为实现了InitializingBean）在这个方法中根据classpathresource得到CacheManager

关于EhCacheManagerFactoryBean 和 FactoryBean

//源码中给本对象添加cacheManager   
//然后在查找上下文的时候就会调用getObject获取到这个cacheManager 
public void afterPropertiesSet() throws CacheException, IOException {
        logger.info("Initializing EhCache CacheManager");
        InputStream is = (this.configLocation != null ? this.configLocation.getInputStream() : null);
        try {
            Configuration configuration = (is != null ?
                    ConfigurationFactory.parseConfiguration(is) : ConfigurationFactory.parseConfiguration());
            if (this.cacheManagerName != null) {
                configuration.setName(this.cacheManagerName);
            }
            if (this.shared) {
                // Old-school EhCache singleton sharing...
                // No way to find out whether we actually created a new CacheManager
                // or just received an existing singleton reference.
                this.cacheManager = CacheManager.create(configuration);
            }
            else if (this.acceptExisting) {
                // EhCache 2.5+: Reusing an existing CacheManager of the same name.
                // Basically the same code as in CacheManager.getInstance(String),
                // just storing whether we're dealing with an existing instance.
                synchronized (CacheManager.class) {
                    this.cacheManager = CacheManager.getCacheManager(this.cacheManagerName);
                    if (this.cacheManager == null) {
                        this.cacheManager = new CacheManager(configuration);
                    }
                    else {
                        this.locallyManaged = false;
                    }
                }
            }
            else {
                // Throwing an exception if a CacheManager of the same name exists already...
                this.cacheManager = new CacheManager(configuration);
            }
        }
        finally {
            if (is != null) {
                is.close();
            }
        }
    }

配置EhcacheCacheManager

@Configuration
@EnableCaching 
public class CachingConfig {

  @Bean
  public EhCacheCacheManager cacheManager(CacheManager cm) {
//cm就是下面的 EhcacheManagerFactoryBean，上面关于FactoryBean是解释
    return new EhCacheCacheManager(cm);
  }

  @Bean
  public EhCacheManagerFactoryBean ehcache() {
    EhCacheManagerFactoryBean ehCacheFactoryBean = 
        new EhCacheManagerFactoryBean();
    ehCacheFactoryBean.setConfigLocation(
        new ClassPathResource("spittr/cache/ehcache.xml"));
    return ehCacheFactoryBean;
  }
  
}

使用缓存

//然后就可以使用这几个注解了  @Cacheable等  
//spitterCache在ehcache.xml中配置，一般缓存用户信息、系统信息
  @Cacheable(value = "spitterCache")
  public Spitter findOne(long id) {
//    try {
//        Thread.sleep(5000L);
//    } catch (InterruptedException e) {
//        e.printStackTrace();
//    }
      return jdbcTemplate.queryForObject(
            SELECT_SPITTER + " where id=?", new SpitterRowMapper(), id);
  }