Java开发框架spring实现自定义缓存标签

Z时代
2024-01-10
分类：IT

自从spring3.1之后，spring引入了抽象缓存，可以通过在方法上添加@Cacheable等标签对方法返回的数据进行缓存。但是它到底是怎么实现的呢，我们通过一个例子来看一下。首先我们定义一个@MyCacheable


package caching.springaop; 
import java.lang.annotation.Retention; 
import java.lang.annotation.RetentionPolicy; 
import java.lang.annotation.Target; 
import java.lang.annotation.ElementType; 
/** 
 * 使用@MyCacheable注解方法 
 */ 
@Retention(RetentionPolicy.RUNTIME) 
@Target(ElementType.METHOD) 
public @interface MyCacheable{ 
}

然后定义处理MyCacheable的切面


package caching.springaop; 
import java.util.HashMap; 
import java.util.Map; 
import org.apache.log4j.Logger; 
import org.aspectj.lang.ProceedingJoinPoint; 
import org.aspectj.lang.annotation.Around; 
import org.aspectj.lang.annotation.Aspect; 
import org.aspectj.lang.annotation.Pointcut; 
/** 
 * 处理MyCacheable方法的切面 
 */ 
@Aspect 
public class CacheAspect { 
  private Logger logger = Logger.getLogger(CacheAspect.class); 
  private Map<String, Object> cache; 
  public CacheAspect() { 
    cache = new HashMap<String, Object>(); 
  } 
  /** 
   * 所有标注了@Cacheable标签的方法切入点 
   */ 
  @Pointcut("execution(@MyCacheable * *.*(..))") 
  @SuppressWarnings("unused") 
  private void cache() { 
  } 
  @Around("cache()") 
  public Object aroundCachedMethods(ProceedingJoinPoint thisJoinPoint) 
      throws Throwable { 
    logger.debug("Execution of Cacheable method catched"); 
    //产生缓存数据的key值，像是这个样子caching.aspectj.Calculator.sum(Integer=1;Integer=2;) 
    StringBuilder keyBuff = new StringBuilder(); 
    //增加类的名字 
    keyBuff.append(thisJoinPoint.getTarget().getClass().getName()); 
    //加上方法的名字 
    keyBuff.append(".").append(thisJoinPoint.getSignature().getName()); 
    keyBuff.append("("); 
    //循环出cacheable方法的参数 
    for (final Object arg : thisJoinPoint.getArgs()) { 
      //增加参数的类型和值 
      keyBuff.append(arg.getClass().getSimpleName() + "=" + arg + ";"); 
    } 
    keyBuff.append(")"); 
    String key = keyBuff.toString(); 
    logger.debug("Key = " + key); 
    Object result = cache.get(key); 
    if (result == null) { 
      logger.debug("Result not yet cached. Must be calculated..."); 
      result = thisJoinPoint.proceed(); 
      logger.info("Storing calculated value '" + result + "' to cache"); 
      cache.put(key, result); 
    } else { 
      logger.debug("Result '" + result + "' was found in cache"); 
    return result; 
  } 
}

上述代码展示了如何处理MyCacheable自定义的标签，以及默认情况下产生key值的规则。最后生成的key值大概是这个样子：caching.aspectj.Calculator.sum(Integer=1;Integer=2;)

下边这段代码在方法上添加了MyCacheable标签


package caching.springaop; 
import org.apache.log4j.Logger; 
public class Calculator { 
  private Logger logger = Logger.getLogger(Calculator.class); 
  @MyCacheable 
  public int sum(int a, int b) { 
    logger.info("Calculating " + a + " + " + b); 
    try { 
      //假设这是代价非常高的计算 
      Thread.sleep(3000); 
    } catch (InterruptedException e) { 
      logger.error("Something went wrong...", e); 
    } 
    return a + b; 
  } 
}

在方法上加了MyCacheable标签，当key值相同的情况下会直接在缓存中获取数据，如果没有相同的key值，则会重新计算，因为这里只是一个加和操作，耗时非常的短暂。我们在这里让其睡眠3秒钟。

我们在spring-config.xml配置如下：


<?xml version="1.0" encoding="UTF-8"?> 
<beans xmlns="http://www.springframework.org/schema/beans" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:aop="http://www.springframework.org/schema/aop" 
  xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd 
    http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> 
  <aop:aspectj-autoproxy /> 
  <bean class="caching.springaop.CacheAspect" /> 
  <bean id="calc" class="caching.springaop.Calculator" /> 
</beans>

测试类：


package caching.springaop; 
import org.apache.log4j.Logger; 
import org.springframework.context.ApplicationContext; 
import org.springframework.context.support.ClassPathXmlApplicationContext; 
/** 
 * 使用SpringAOP缓存的简单例子 
 * @author txxs 
 */ 
public class App { 
  private static Logger logger = Logger.getLogger(App.class); 
  public static void main(String[] args) { 
    logger.debug("Starting..."); 
    ApplicationContext ctx = new ClassPathXmlApplicationContext("spring-config.xml"); 
    Calculator calc = (Calculator) ctx.getBean("calc"); 
    //计算出来的结果将会被存储在cache 
    logger.info("1 + 2 = " + calc.sum(1, 2)); 
    //从缓存中获取结果 
    logger.info("1 + 2 = " + calc.sum(1, 2)); 
    logger.debug("Finished!"); 
  } 
}