Spring boot cacheable源码及默认配置

一. Spring boot cache原理

第一步. 自动配置类

  • ​自动启动类:CacheAutoConfiguration
  • 属性配置:CacheProperties
  • 主启动类添加:@EnableCaching注解

cache  POM添加:


   org.springframework.boot
   spring-boot-starter-cache

第二步. 从缓存的配置类 中获取 多个cache

CacheConfigurationImportSelector.selectImports()方法获取

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;
     }
}

获取结果:SimpleCacheConfiguration 默认cache

   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.GuavaCacheConfiguration
   org.springframework.boot.autoconfigure.cache.SimpleCacheConfiguration【默认】
   org.springframework.boot.autoconfigure.cache.NoOpCacheConfiguration

第三步. SimpleCacheConfiguration.cacheManager()

 此方法中给容器中注册了一个CacheManager组件:类型为ConcurrentMapCacheManager

@Bean
public ConcurrentMapCacheManager cacheManager() {
   ConcurrentMapCacheManager cacheManager = new ConcurrentMapCacheManager();
   List cacheNames = this.cacheProperties.getCacheNames();
   if (!cacheNames.isEmpty()) {
      cacheManager.setCacheNames(cacheNames);
   }
   return this.customizerInvoker.customize(cacheManager);
}

第四步. 查看获取缓存方法getCache()

ConcurrentMapCacheManager 类里,数据都存储到为ConcurrentMap 中

public Cache getCache(String name) {
   Cache cache = this.cacheMap.get(name); //cacheMap 为ConcurrentMap  类型,获取一个cache组件
   if (cache == null && this.dynamic) {
      synchronized (this.cacheMap) {
         cache = this.cacheMap.get(name); //cahceMap不为空获取
         if (cache == null) {
            //可以获取或者创建ConcurrentMapCache类型的缓存组件;他的作用将数据保存在ConcurrentMap中;
            cache = createConcurrentMapCache(name);   
            this.cacheMap.put(name, cache); //ConcurrentMapCache.lookup();
         }
      }
   }
   return cache;
}

二. Cacheable运行流程

@Cacheable:        

  1. 方法运行之前,先去查询Cache(缓存组件),按照cacheNames指定的名字获取;(CacheManager先获取相应的缓存),第一次获取缓存如果没有Cache组件会自动创建。
  2. 去Cache中查找缓存的内容(ConcurrentMapCache.lookup()方法中去查找),使用一个key,默认就是方法的参数; key是按照某种策略生成的;默认是使用keyGenerator生成的,默认使用SimpleKeyGenerator生成key;

SimpleKeyGenerator生成key的默认策略:

  • 如果没有参数;key=new SimpleKey();                      
  • 如果有一个参数:key=参数的值                      
  • 如果有多个参数:key=new SimpleKey(params);
//这个方法  SimpleKeyGenerator.generateKey()    方法生成key
public static Object generateKey(Object... params) {
   if (params.length == 0) {
      return SimpleKey.EMPTY;
   }
   if (params.length == 1) {  //如果只有一个参数,直接返回这个参数为key
      Object param = params[0];
      if (param != null && !param.getClass().isArray()) {
         return param;
      }
   }
   return new SimpleKey(params);
}
public class SimpleKey implements Serializable {
    public static final SimpleKey EMPTY = new SimpleKey(new Object[0]);
    private final Object[] params;
    private final int hashCode;

    public SimpleKey(Object... elements) {
        Assert.notNull(elements, "Elements must not be null");
        this.params = new Object[elements.length];
        System.arraycopy(elements, 0, this.params, 0, elements.length);
        this.hashCode = Arrays.deepHashCode(this.params);
    }

    public boolean equals(Object obj) {
        return this == obj || obj instanceof SimpleKey && Arrays.deepEquals(this.params, ((SimpleKey)obj).params);
    }

    public final int hashCode() {
        return this.hashCode;
    }

    public String toString() {
        return this.getClass().getSimpleName() + " [" + StringUtils.arrayToCommaDelimitedString(this.params) + "]";
    }
}
public static int hashCode(Object a[]) {
    if (a == null)
        return 0;
    int result = 1;
    for (Object element : a)
        result = 31 * result + (element == null ? 0 : element.hashCode());
    return result;
}

public static int deepHashCode(Object a[]) {
    if (a == null)
        return 0;
    int result = 1;
    for (Object element : a) {
        int elementHash = 0;
        if (element instanceof Object[])
            elementHash = deepHashCode((Object[]) element);
        else if (element instanceof byte[])
            elementHash = hashCode((byte[]) element);
        else if (element instanceof short[])
            elementHash = hashCode((short[]) element);
        else if (element instanceof int[])
            elementHash = hashCode((int[]) element);
        else if (element instanceof long[])
            elementHash = hashCode((long[]) element);
        else if (element instanceof char[])
            elementHash = hashCode((char[]) element);
        else if (element instanceof float[])
            elementHash = hashCode((float[]) element);
        else if (element instanceof double[])
            elementHash = hashCode((double[]) element);
        else if (element instanceof boolean[])
            elementHash = hashCode((boolean[]) element);
        else if (element != null)
            elementHash = element.hashCode();

        result = 31 * result + elementHash;
    }
    return result;
}

       3. 没有查到缓存就调用目标方法;        

       4. 将目标方法返回的结果,放进缓存中ConcurrentMapCache.put();     

详细执行流程:ConcurrentMapCache.lookup()上断点查看,执行过程

//第一步 CacheAspectSupport  中execute()
private Object execute(final CacheOperationInvoker invoker, Method method, CacheOperationContexts contexts) 
//第二步  CacheAspectSupport
private Cache.ValueWrapper findCachedItem(Collection contexts) {
    Object result = CacheOperationExpressionEvaluator.NO_RESULT;
    for (CacheOperationContext context : contexts) {
        if (isConditionPassing(context, result)) {
            Object key = generateKey(context, result);  //获取key
            Cache.ValueWrapper cached = findInCaches(context, key);
            if (cached != null) {
                return cached;
            }
            else {
                if (logger.isTraceEnabled()) {
                    logger.trace("No cache entry for key '" + key + "' in cache(s) " + context.getCacheNames());
                }
            }
        }
    }
    return null;
}
//第三步:CacheAspectSupport.findInCaches()
//第四步:AbstractCacheInvoker.doGet()
//第五步:AbstractValueAdaptingCache.get();
@Override
public ValueWrapper get(Object key) {
        Object value = lookup(key);
        return toValueWrapper(value);
}
// 第六步:ConcurrentMapCache.lookup();  从ConcurrentMap 中根据key获取值
@Override
protected Object lookup(Object key) {
        return this.store.get(key);
}

三. Cacheable  注解的几个属性

  • cacheNames/value:指定缓存组件的名字;将方法的返回结果放在哪个缓存中,是数组的方式,可以指定 多个缓存;
  • key:缓存数据使用的key;可以用它来指定。
  • keyGenerator:key的生成器;可以自己指定key的生成器的组件id
  • cacheManager:指定缓存管理器;或者cacheResolver指定获取解析器
  • ​condition:指定符合条件的情况下才缓存:如 condition = "#a0>1":第一个参数的值>1的时候才进行缓存
  • unless: 否定缓存;当unless指定的条件为true,方法的返回值就不会被缓存;如 unless = "#a0==2":如果第一个参数的值是2,结果不缓存;
  • ​sync:是否使用异步模式;异步模式的情况下unless不支持

四. Cache使用

1.Cacheable的使用

@Cacheable(value = {"emp"}/*,keyGenerator = "myKeyGenerator",condition = "#a0>1",unless = "#a0==2"*/)
public Employee getEmp(Integer id){
    System.out.println("查询"+id+"号员工");
    Employee emp = employeeMapper.getEmpById(id);
    return emp;
}

2. 自定义keyGenerator:

@Bean("myKeyGenerator")
public KeyGenerator keyGenerator(){
    return new KeyGenerator(){
​
        @Override
        public Object generate(Object target, Method method, Object... params) {
            return method.getName()+"["+ Arrays.asList(params).toString()+"]";
        }
    };
}

3. CachePut的使用:更新缓存

/**
     * @CachePut:既调用方法,又更新缓存数据;同步更新缓存
     * 修改了数据库的某个数据,同时更新缓存;
     * 运行时机:
     *  1、先调用目标方法
     *  2、将目标方法的结果缓存起来
     *
     * 测试步骤:
     *  1、查询1号员工;查到的结果会放在缓存中;
     *          key:1  value:lastName:张三
     *  2、以后查询还是之前的结果
     *  3、更新1号员工;【lastName:zhangsan;gender:0】
     *          将方法的返回值也放进缓存了;
     *          key:传入的employee对象  值:返回的employee对象;
     *  4、查询1号员工?
     *      应该是更新后的员工;
     *          key = "#employee.id":使用传入的参数的员工id;
     *          key = "#result.id":使用返回后的id
     *             @Cacheable的key是不能用#result
     *      为什么是没更新前的?【1号员工没有在缓存中更新】
     *
     */
    @CachePut(value = "emp",key = "#result.id")
    public Employee updateEmp(Employee employee){
        System.out.println("updateEmp:"+employee);
        employeeMapper.updateEmp(employee);
        return employee;
    }

4. CacheEvict 缓存清除

/**
 * @CacheEvict:缓存清除
 *  key:指定要清除的数据
 *  allEntries = true:指定清除这个缓存中所有的数据
 *  beforeInvocation = false:缓存的清除是否在方法之前执行
 *      默认代表缓存清除操作是在方法执行之后执行;如果出现异常缓存就不会清除
 *
 *  beforeInvocation = true:
 *      代表清除缓存操作是在方法运行之前执行,无论方法是否出现异常,缓存都清除
 *
 *
 */
@CacheEvict(value="emp",beforeInvocation = true,key = "#id")
public void deleteEmp(Integer id){
    System.out.println("deleteEmp:"+id);
    //employeeMapper.deleteEmpById(id);
    int i = 10/0;
}

5. Caching 复杂配置

// @Caching 定义复杂的缓存规则
@Caching(
     cacheable = {
         @Cacheable(/*value="emp",*/key = "#lastName")
     },
     put = {
         @CachePut(/*value="emp",*/key = "#result.id"),
         @CachePut(/*value="emp",*/key = "#result.email")
     }
)
public Employee getEmpByLastName(String lastName){
    return employeeMapper.getEmpByLastName(lastName);
}

转载自:https://blog.csdn.net/yangliuhbhd/article/details/80626468

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