1.引入RedisTemplate

据以前的情况，我们在Java中使用Redis时一般是使用Jedis来操作的，大致的一段代码如下所示

    @Override
    public User findUserById(Integer id) {
        User user = null;
        Jedis jedis = null;
        try {
            jedis = jedisPool.getResource();
            String userStr = jedis.get("user_" + id); // 尝试获取数据
            if (userStr != null && !userStr.isEmpty()) { // 如果获取到有效数据，则转换后返回
                user = JSONObject.parseObject(userStr, User.class);
            } else {// 如果没有获取到数据，则查询数据库返回
                user = userMapper.findUserById(id);
                if (user != null) jedis.set("user_" + id, JSONObject.toJSONString(user)); // 设置到redis中
            }
        } finally {
            // 记得关闭Jedis，因为这里使用的是JedisPool，所以这里的关闭并不是直接关闭连接，而是释放，以供其他的业务使用
            if (jedis != null) jedis.close();
        }
        return user;
    }

上边的这样的一段代码其实是有些臃肿的，但是如果我们引入RedisTemplate，其实会简化不少。

• maven 引入 spring-data-redis

  <dependency>
    <groupId>redis.clients</groupId>
    <artifactId>jedis</artifactId>
    <version>3.9.0</version>
  </dependency>
  <dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-redis</artifactId>
    <version>2.2.13.RELEASE</version>
  </dependency>

• 将RedisTemplate 加入Bean容器中，让Spring进行管理。

  @Bean
  public RedisConnectionFactory redisConnectionFactory() {
      RedisStandaloneConfiguration redisStandaloneConfiguration = new RedisStandaloneConfiguration();
      redisStandaloneConfiguration.setHostName(host);
      redisStandaloneConfiguration.setPort(port);

      RedisConnectionFactory redisConnectionFactory = new JedisConnectionFactory(redisStandaloneConfiguration);
      return redisConnectionFactory;
  }

  @Bean
  public RedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) {
      RedisTemplate redisTemplate = new RedisTemplate();
      redisTemplate.setConnectionFactory(redisConnectionFactory);
      //设置key值的序列化方式，默认是JDK的形式
      redisTemplate.setKeySerializer(StringRedisSerializer.UTF_8);
      return redisTemplate;
  }

• 如果使用RedisTemplate的替换的话，会简洁很多。

  @Autowired
  private RedisTemplate redisTemplate;

  @Override
  public User findUserById(Integer id) {
      Object result = redisTemplate.opsForValue().get("user_" + id);
      if (result != null) return (User) result;

      User user = userMapper.findUserById(id);
      // 设置到redis中
      if (user != null) redisTemplate.opsForValue().set("user_" + id, user);

      return user;
  }

• 大概看一下关于RedisTemplate的方法

看了以上的内容，可以看到引入了RedisTemplate其实已经很简洁了，但是明显还不够，下面我们将考虑引入 “注解”

---

2. 引入注解

• 开启缓存 @EnableCaching

  
@Configuration  
@EnableCaching  
public class AppConfig {
...
} 

• 引入@Cacheable，表示这个方法将会访问缓存，如果无法命中缓存的话，会将方法返回的值存入redis，假设有注解为 @Cacheable(value="user", key = "#id")，那么生成的key值为 user::{id}，即如果id为1 那么生成的 key就是 user::1

@Override
@Cacheable(value="user", key = "#id")
// 这里返回的值会被存放到redis，key-value格式，其中生成的key值(假设id为1)： user::1
public User findUserById(Integer id) {
User user = userMapper.findUserById(id);
return user;
}

但是这样还不够，因为Spring并不清楚缓存的方式是什么，这就涉及到CacheManager 了

• 设置CacheManager，在AppConfig中加入以下内容

@Bean
public RedisConnectionFactory redisConnectionFactory() {
    RedisStandaloneConfiguration redisStandaloneConfiguration = new RedisStandaloneConfiguration();
    redisStandaloneConfiguration.setHostName(host); // 这里是redis的ip
    redisStandaloneConfiguration.setPort(port);// 这里是redis的端口

    // 自适应集群变化
    RedisConnectionFactory redisConnectionFactory = new JedisConnectionFactory(redisStandaloneConfiguration);
    return redisConnectionFactory;
}

@Bean
public RedisCacheConfiguration redisCacheConfiguration() {
    RedisCacheConfiguration redisCacheConfiguration = RedisCacheConfiguration.defaultCacheConfig()
    .serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(RedisSerializer.string()))
    .serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(RedisSerializer.json()));
    return redisCacheConfiguration;
}

@Bean
public RedisCacheWriter redisCacheWriter(RedisConnectionFactory redisConnectionFactory) {
RedisCacheWriter redisCacheWriter = RedisCacheWriter.nonLockingRedisCacheWriter(redisConnectionFactory);
return redisCacheWriter;
}

@Bean
public CacheManager cacheManager(RedisCacheWriter redisCacheWriter, RedisCacheConfiguration redisCacheConfiguration) {
    CacheManager cacheManager = new RedisCacheManager(redisCacheWriter, redisCacheConfiguration);
    ((RedisCacheManager) cacheManager).isTransactionAware();
    return cacheManager;
}

---

3. 自行通过注解和AOP实现缓存

• 引入AOP相关的包

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-aop</artifactId>
  <version>5.3.22</version>
</dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-aspects</artifactId>
  <version>5.3.22</version>
</dependency>

<!-- Jackson JSON Processor -->
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-core</artifactId>
  <version>2.9.8</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.8</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-annotations</artifactId>
  <version>2.9.8</version>
</dependency>
<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>1.2.28</version>
</dependency>

• 创建@CustomCache

@Target(ElementType.METHOD)  
@Retention(RetentionPolicy.RUNTIME)
public @interface  CustomCache {  
    /**
   * key的规则，可以使用springEL表达式，可以使用方法执行的一些参数
   */
    String key();

    /**
   *  类似前缀
   * @return
   */
    String value();
}

• 修改AppConfig

@EnableAspectJAutoProxy // 开启AOP自动代理
public class AppConfig {
    @Bean  
    public RedisConnectionFactory redisConnectionFactory() {
        RedisStandaloneConfiguration redisStandaloneConfiguration = new RedisStandaloneConfiguration();
        redisStandaloneConfiguration.setHostName(host);
        redisStandaloneConfiguration.setPort(port); 
        // 自适应集群变化
        RedisConnectionFactory redisConnectionFactory = new JedisConnectionFactory(redisStandaloneConfiguration);
        return redisConnectionFactory;
    }

    @Bean
    public RedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) {
        RedisTemplate redisTemplate = new RedisTemplate();
        redisTemplate.setConnectionFactory(redisConnectionFactory);
        redisTemplate.setKeySerializer(StringRedisSerializer.UTF_8);
        redisTemplate.setValueSerializer(StringRedisSerializer.UTF_8);
        return redisTemplate;
    }
}

• 创建 CustomCacheAspect

@Component  
@Aspect  
public class CustomCacheAspect {
    @Autowired  
    private RedisTemplate redisTemplate;
    @Pointcut("@annotation(cn.lazyfennec.cache.redis.annotation.CustomCache)")
    public void cachePointcut() {
    }
    @Around("cachePointcut()")
    public Object doCache(ProceedingJoinPoint joinPoint) {
        Object obj = null;
        try {
            MethodSignature signature = (MethodSignature) joinPoint.getSignature();
            Method method = joinPoint.getTarget().getClass().getMethod(signature.getName(), signature.getMethod().getParameterTypes());
            CustomCache customCache = method.getAnnotation(CustomCache.class);
            String cacheKey = customCache.key();
            String cacheValue = customCache.value(); 
            // 创建解析器
            ExpressionParser parser = new SpelExpressionParser();
            Expression expression = parser.parseExpression(cacheKey);
            EvaluationContext context = new StandardEvaluationContext(); // 参数

            // 添加参数
            Object[] args = joinPoint.getArgs();
            DefaultParameterNameDiscoverer discover = new DefaultParameterNameDiscoverer();
            String[] parameterNames = discover.getParameterNames(method);
            for (int i = 0; i < parameterNames.length; i++) {
                context.setVariable(parameterNames[i], args[i].toString());
            }
            // 解析
            String key = cacheValue + "::" + expression.getValue(context).toString();
            // 1、 判定缓存中是否存在
            obj = redisTemplate.opsForValue().get(key);
            if (obj != null) return obj;
            // 2、不存在则继续行方法
            obj = joinPoint.proceed();
            // 3、 同步存储value到缓存。
            redisTemplate.opsForValue().set(key, obj);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }
        return obj;

    }
} 

• 新建方法 getUserNameById

@RequestMapping("/custom/name/{id}")
@ResponseBody
public String getUserNameById(@PathVariable Integer id) {
    return userService.getUserNameById(id);
}

• 实际实现方法 getUserNameById，使用方式

@Override
@CustomCache(value = "custom_user", key = "#id")
public String getUserNameById(Integer id) {
return userMapper.findUserNameById(id);
}

---