redis-jedis

jedis 事务

Transaction transaction = jedis.multi();

transaction.set("k4","v4");
transaction.set("k4","v4");

transaction.exec();
transaction.discard();

jedis锁-watch()标记一个key

watch命令标记一个键，在提交事务前如果键被别人修改过，那么事务就会失败，这种情况通常可以在程序中重新再尝试一次。

模拟银行转账的过程

127.0.0.1:6379>set balance 100
127.0.0.1:6379>set debt 0

public boolean transaction() throws InterrupttedException{
Jedis jedis = new Jedis("127.0.0.1",6379);
int balance;
int debt;
int amtToSubtract = 10;//实刷额度

jedis.watch("balance");
balance = Integer.parseInt(jedis.get("balance"));
if(balance < amtToSubtract ){
  jedis.unwatch();
  System.out.println("modify");
  return false;
}else{
  System.out.println("-------transaction");
  Transaction transaction = jedis.multi();
  transaction.decrBy("balance",amtToSubstract);
  transaction.incrBy("balance",amtToSubstract);
  transaction.exec();
  return true;
}
}

模拟在事务执行的时候balance的值发生改变的情况：
Thread.sleep(7000); // 线程休息7s，在redis的客户端修改balance的值。

jedisPool

多个connection连接:
为什么要有池:java的new gc需要消耗很多内存
线程的获得由线程池
数据库的连接有数据库连接池

JedisPool jedis = new JedisPool(poolConfig,”127.0.0.1”,6379);
JedisPoolConfig poolConfig = new JedisPoolConfig();
poolConfig.setMaxActive(1000);
poolConfig.setMaxIdle(32);//jedis不能变满
poolConfig.setMaxWait(100*1000);
poolConfig.setTestOnBorrow(true)；

使用单例模式

public class JedisPoolUtil{
 private static volatile JedisPool jedisPool = null;
 private JedisPoolUtil(){}

 public static JedisPool getJedisPoolInstance(){
    if(null == jedisPool){
      synchronized(JedisPoolUtil.class){
        if(null == jedisPool){
           JedisPool jedis = new JedisPool(poolConfig,"127.0.0.1",6379);
         } 
      }
    }
  }

  public static void release(JedisPool jedisPool,Jedis jedis){
    if(jedis != null){
       jedisPool.returnResourceObject(jedis)
     }
  }
}

jedisPool = JedisPoolUtil.getJedisPoolInstance();
jedis = jedisPool.getResource()

//在finally里面执行释放资源