redis-cache中的callback

这个是mybatis/redis-cache中关键类  RedisCache  的源码

/**
 *    Copyright 2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.mybatis.caches.redis;

import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;

import org.apache.ibatis.cache.Cache;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;

/**
 * Cache adapter for Redis.
 *
 * @author Eduardo Macarron
 */
public final class RedisCache implements Cache {

  private final ReadWriteLock readWriteLock = new DummyReadWriteLock();

  private String id;

  private static JedisPool pool;

  public RedisCache(final String id) {
    if (id == null) {
      throw new IllegalArgumentException("Cache instances require an ID");
    }
    this.id = id;
    RedisConfig redisConfig = RedisConfigurationBuilder.getInstance().parseConfiguration();
    pool = new JedisPool(redisConfig, redisConfig.getHost(), redisConfig.getPort(),
            redisConfig.getConnectionTimeout(), redisConfig.getSoTimeout(), redisConfig.getPassword(),
            redisConfig.getDatabase(), redisConfig.getClientName());
  }

  private Object execute(RedisCallback callback) {
    Jedis jedis = pool.getResource();
    try {
      return callback.doWithRedis(jedis);
    } finally {
      jedis.close();
    }
  }

  @Override
  public String getId() {
    return this.id;
  }

  @Override
  public int getSize() {
    return (Integer) execute(new RedisCallback() {
      @Override
      public Object doWithRedis(Jedis jedis) {
        Map<byte[], byte[]> result = jedis.hgetAll(id.toString().getBytes());
        return result.size();
      }
    });
  }

  @Override
  public void putObject(final Object key, final Object value) {
    execute(new RedisCallback() {
      @Override
      public Object doWithRedis(Jedis jedis) {
        jedis.hset(id.toString().getBytes(), key.toString().getBytes(), SerializeUtil.serialize(value));
        return null;
      }
    });
  }

  @Override
  public Object getObject(final Object key) {
    return execute(new RedisCallback() {
      @Override
      public Object doWithRedis(Jedis jedis) {
        return SerializeUtil.unserialize(jedis.hget(id.toString().getBytes(), key.toString().getBytes()));
      }
    });
  }

  @Override
  public Object removeObject(final Object key) {
    return execute(new RedisCallback() {
      @Override
      public Object doWithRedis(Jedis jedis) {
        return jedis.hdel(id.toString(), key.toString());
      }
    });
  }

  @Override
  public void clear() {
    execute(new RedisCallback() {
      @Override
      public Object doWithRedis(Jedis jedis) {
        jedis.del(id.toString());
        return null;
      }
    });

  }

  @Override
  public ReadWriteLock getReadWriteLock() {
    return readWriteLock;
  }

  @Override
  public String toString() {
    return "Redis {" + id + "}";
  }

}

可以看到其中大量使用了callback方法来操作redis, 但是调用本身是同步的, 其中能想到的唯一好处, 就是省下了每次调用之后的close() - 不知道是否还有别的优点.

MyBatis使用Redis作为Cache

如果将MyBatis内建Cache换为Redis, 需要在重启MyBatis所在服务时, 同时对Redis所在的db进行flushdb, 在部署脚本中增加一句

echo 'Cleaning Redis cache'
redis-cli -h 192.168.1.18 -p  -a foobar -n  flushdb
# -h 服务器地址
# -p 端口
# -a 口令
# -n db编号