spring 3.1中的cache小结

spring 3.1中有cache了，下面结合目前网上的一些资料和手册的归纳总结下：

1 @cache注解
   在3.1中，都是用注解的了，
@Cacheable注解可以用在方法或者类级别。当他应用于方法级别的时候，就是如上所说的缓存返回值了。当应用在类级别的时候，这个类的所有方法的返回值都将被缓存。
 

@Cacheable(value = "employee")
public class EmployeeDAO {

  public Person findEmployee(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

  public Person findAnotherEmployee(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }
}

@Cacheable(value = "employee")
public class EmployeeDAO {

  public Person findEmployee(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

  public Person findAnotherEmployee(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }
}

   在上面的代码中，缓存了Person了，命名为employee，缓存的是方法的值，
@Cacheable注解有三个参数，value是必须的，还有key和condition。第一个参数，也就是value指明了缓存将被存到什么地方。
    在spring 3.1中，可以使用spel表达式去进行缓存的指定，比如：

 

@Cacheable(value = "employee", key = "#surname")
  public Person findEmployeeBySurname(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

@Cacheable(value = "employee", key = "#surname")
  public Person findEmployeeBySurname(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

  这里注意指定的缓存的是根据key=surename。也可以指定表达式

@Cacheable(value = "employee", condition = "#age < 25")
  public Person findEmployeeByAge(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

@Cacheable(value = "employee", condition = "#age < 25")
  public Person findEmployeeByAge(String firstName, String surname, int age) {

    return new Person(firstName, surname, age);
  }

   这里指定age<25的才缓存；
  接下来看下如何应用，比如：

@Test
  public void testCache() {

    Person employee1 = instance.findEmployee("John", "Smith", 22);
    Person employee2 = instance.findEmployee("John", "Smith", 22);

    assertEquals(employee1, employee2);
  }

@Test
  public void testCache() {

    Person employee1 = instance.findEmployee("John", "Smith", 22);
    Person employee2 = instance.findEmployee("John", "Smith", 22);

    assertEquals(employee1, employee2);
  }

     这个时候肯定是相等的了，因为用的是缓存。但是如果调用的是
findEmployeeBySurname方法的话，就一定有点不同了，

@Test
  public void testCacheOnSurnameAsKey() {

    Person employee1 = instance.findEmployeeBySurname("John", "Smith", 22);
    Person employee2 = instance.findEmployeeBySurname("Jack", "Smith", 55);

    assertEquals(employee1, employee2);
  }

@Test
  public void testCacheOnSurnameAsKey() {

    Person employee1 = instance.findEmployeeBySurname("John", "Smith", 22);
    Person employee2 = instance.findEmployeeBySurname("Jack", "Smith", 55);

    assertEquals(employee1, employee2);
  }

  但由于是缓存的是根据surename为key,所以上面结果两个对象却依然是相等的（尽管原本看上去是不同的对象了），所以key的选择一定要小心。

  继续单元测试：
 

@Test
  public void testCacheWithAgeAsCondition() {

    Person employee1 = instance.findEmployeeByAge("John", "Smith", 22);
    Person employee2 = instance.findEmployeeByAge("John", "Smith", 22);

    assertEquals(employee1, employee2);
  }

@Test
  public void testCacheWithAgeAsCondition() {

    Person employee1 = instance.findEmployeeByAge("John", "Smith", 22);
    Person employee2 = instance.findEmployeeByAge("John", "Smith", 22);

    assertEquals(employee1, employee2);
  }

    这两个就一样了，因为都是age<25的，都缓存了，指向同一个对象。


2 取消缓存
   下面看下如何取消缓存
  @CacheEvict

@CacheEvict(value = "employee", allEntries = true)
public void resetAllEntries() {

}

@CacheEvict(value = "employee", allEntries = true)
public void resetAllEntries() {

}

   使用@CacheEvict去取消缓存，

@CacheEvict支持如下几个参数：

value：缓存位置名称，不能为空，同上

key：缓存的key，默认为空，同上

condition：触发条件，只有满足条件的情况才会清除缓存，默认为空，支持SpEL

allEntries：true表示清除value中的全部缓存，默认为false
  当然，也可以@cahceable和@cacheEvict一起使用，比如：

@CacheEvict(value = "employee", beforeInvocation = true)
@Cacheable(value = "employee")
public Person evictAndFindEmployee(String firstName, String surname, int age) {

  return new Person(firstName, surname, age);
}

@CacheEvict(value = "employee", beforeInvocation = true)
@Cacheable(value = "employee")
public Person evictAndFindEmployee(String firstName, String surname, int age) {

  return new Person(firstName, surname, age);
}

  

@Test
public void testBeforeInvocation() {

  Person employee1 = instance.evictAndFindEmployee("John", "Smith", 22);
  Person employee2 = instance.evictAndFindEmployee("John", "Smith", 22);

  assertNotSame(employee1, employee2);
}

@Test
public void testBeforeInvocation() {

  Person employee1 = instance.evictAndFindEmployee("John", "Smith", 22);
  Person employee2 = instance.evictAndFindEmployee("John", "Smith", 22);

  assertNotSame(employee1, employee2);
}

   这里的话，先使用@CacheEvict(value = "employee", beforeInvocation = true)，
会先清掉所有缓存，所以asset的结果就不相等了；
 

3 如何配置
   .spring-cache

首先我们来看一下如何使用spring3.1自己的cache，

需要在命名空间中增加cache的配置

beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:cache="http://www.springframework.org/schema/cache"
   xsi:schemaLocation="
           http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
          http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-3.1.xsd">

beans xmlns="http://www.springframework.org/schema/beans"  
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"  
    xmlns:cache="http://www.springframework.org/schema/cache"  
   xsi:schemaLocation="  
           http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd  
          http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-3.1.xsd">  

 <!-- 启用缓存注解功能，这个是必须的，否则注解不会生效，另外，该注解一定要声明在spring主配置文件中才会生效 -->
<cache:annotation-driven cache-manager="cacheManager"/>


<!-- spring自己的换管理器，这里定义了两个缓存位置名称 ，既注解中的value -->
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
    <property name="caches">
       <set>
          <bean
               class="org.springframework.cache.concurrent.ConcurrentCacheFactoryBean"
                p:name="default" />
            <bean
                class="org.springframework.cache.concurrent.ConcurrentCacheFactoryBean"
                p:name="andCache" />
       </set>      </property>
</bean>

 <!-- 启用缓存注解功能，这个是必须的，否则注解不会生效，另外，该注解一定要声明在spring主配置文件中才会生效 -->  
<cache:annotation-driven cache-manager="cacheManager"/>  
  
  
<!-- spring自己的换管理器，这里定义了两个缓存位置名称 ，既注解中的value -->  
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">  
    <property name="caches">  
       <set>  
          <bean  
               class="org.springframework.cache.concurrent.ConcurrentCacheFactoryBean"  
                p:name="default" />  
            <bean  
                class="org.springframework.cache.concurrent.ConcurrentCacheFactoryBean"  
                p:name="andCache" />  
       </set>      </property>  
</bean>   

   spring对ehcache并没有很好的支持，不建议使用，可以参看http://hanqunfeng.iteye.com/blog/1204343