从上一篇的实例中可以看出，用字符串类型存储对象有一些不足，在存储/读取时需要进行序列化/反序列化，即时只想修改一项内容，如价格，也必须修改整个键值。不仅增大开发的复杂度，也增加了不必要的性能开销。

一个更好的选择是使用散列类型，或称为Hash表。散列类型与Java中的HashMap相似，是一组键值对的集合，且支持单独对其中一个键进行增删改查操作。使用散列类型存储前面示例中的商品对象，结构如下图所示：

下面先通过示例代码来看散列类型常用的操作命令

一、常用命令

HashExample.java

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;import redis.clients.jedis.Jedis;public class HashExample {public static void main(String[] args) {Jedis jedis = JedisProvider.getJedis();jedis.flushDB();// 为了避免混淆,下文中对Hash表中的键统称为fieldString key = "goods";// hset 仅当操作在hash中创建新field时返回1Long hset = jedis.hset(key, "id", "1");print("hset id 1=" + hset + "; value=" + jedis.hget(key, "id"));// 如果field已存在则执行修改,并返回0hset = jedis.hset(key, "id", "2");print("hset id 2=" + hset + "; value=" + jedis.hget(key, "id"));// hexists 判断field是否存在boolean hexists = jedis.hexists(key, "id");print("hexists id=" + hexists);hexists = jedis.hexists(key, "title");print("hexists title=" + hexists);// hsetex 如果field不存在则添加, 已存在则不会修改值, 可用来添加要求不重复的fieldLong hsetnx = jedis.hsetnx(key, "id", "3");print("hsetnx id 3=" + hsetnx + "; value=" + jedis.hget(key, "id"));hsetnx = jedis.hsetnx(key, "title", "商品001");print("hsetnx title 商品001=" + hsetnx + "; value=" + jedis.hget(key, "title"));// hmset 设置多个fieldMap<String, String> msets = new HashMap<>();msets.put("color", "red");msets.put("width", "100");msets.put("height", "80");String hmset = jedis.hmset(key, msets);print("hmset color,width,height=" + hmset);// hincr 新增整数类型的键值对或增加值long hincr = jedis.hincrBy(key, "price", 4l);print("hincrBy price 4=" + hincr + "; value=" + jedis.hget(key, "price"));// hlen 读取field数量print("hlen=" + jedis.hlen(key));// hkeys 读取所有fieldSet<String> sets = jedis.hkeys(key);print("hkeys=" + Arrays.toString(sets.toArray()));// hvals 读取所有值List<String> list = jedis.hvals(key);print("hvals=" + Arrays.toString(list.toArray()));// hgetAll 读取所有键值对System.out.println("hgetAll 读取所有键值对");Map<String, String> maps = jedis.hgetAll(key);for (String field : maps.keySet()) {System.out.println("hget " + field + "=" + maps.get(field));}System.out.println("------------------------------------------------------");System.out.println();// hdel 删除fieldLong hdel = jedis.hdel(key, "id");print("hdel id=" + hdel);// 删除多个fieldhdel = jedis.hdel(key, "color", "width", "height");print("hdel color,width,height=" + hdel);// hincrBy 在整数类型值上增加, 返回修改后的值Long hincrBy = jedis.hincrBy(key, "price", 100l);print("hincrBy price 100=" + hincrBy);// hget 读取单个field的值String hget = jedis.hget(key, "title");print("hget title=" + hget);// hmget 批量读取field的值jedis.hmget(key, "title", "price");list = jedis.hvals(key);print("hmget title,price=" + Arrays.toString(list.toArray()));jedis.close();}private static void print(String info) {System.out.println(info);System.out.println("------------------------------------------------------");System.out.println();}}

二、实践练习

对前一篇基于字符串类型的商品管理示例改造，以散列类型存储商品，并增加单独修改标题和修改价格的接口。

首先是添加商品代码

    /*** 添加一个商品* @param goods* @return*/public boolean addGoods(Goods goods) {long id = getIncrementId();Map<String, String> map = new HashMap<>();map.put("id", String.valueOf(id));map.put("title", goods.getTitle());map.put("price", String.valueOf(goods.getPrice()));String key = "goods:" + id;return jedis.hmset(key, map).equals("OK");}

然后增加两个单独修改属性的方法

   /*** 修改商品标题* @param goods* @return*/public boolean updateTitle(long id, String title) {String key = "goods:" + id;return jedis.hset(key, "title", title) == 0;}/*** 修改商品价格* @param id* @param price* @return*/public boolean updatePrice(long id, float price) {String key = "goods:" + id;return jedis.hset(key, "price", String.valueOf(price)) == 0;}

最后还需要修改读取商品列表的方法

  /*** 读取用于分页的商品列表* @param pageIndex 页数* @param pageSize 每页显示行数* @return*/public List<Goods> getGoodsList(int pageIndex, int pageSize) {int totals = (int)getTotalCount();int from = (pageIndex - 1) * pageSize;if(from < 0) {from = 0;}else if(from > totals) {from = (totals / pageSize) * pageSize;}int to = from + pageSize;if(to > totals) {to = totals;}List<Goods> goodsList = new ArrayList<>();for(int i = from; i < to; i++) {String key = "goods:" + (i + 1);Map<String, String> maps = jedis.hgetAll(key);Goods goods = new Goods();goods.setId(NumberUtils.toLong(maps.get("id")));goods.setTitle(maps.get("title"));goods.setPrice(NumberUtils.toFloat(maps.get("price")));goodsList.add(goods);}return goodsList;}

测试代码

 public static void main(String[] args) {HashLession hl = new HashLession();hl.clear();//添加一批商品for(int i = 0; i< 41; i++) {Goods goods = new Goods(0, "goods" + String.format("%05d", i), i);hl.addGoods(goods);}//读取商品总数System.out.println("商品总数: " + hl.getTotalCount());//修改商品价格for(int i = 1; i <= hl.getTotalCount(); i++) {hl.updatePrice(i, new Random().nextFloat());}//分页显示List<Goods> list = hl.getGoodsList(2, 20);System.out.println("第二页商品:");for(Goods goods : list) {System.out.println(goods);}}

到目前为止，此示例仍然不能支持删除商品的功能，这是因为商品总数是以一个自增数字记录的，且关联了新商品key的生成，删除商品后不能直接减小总数，进而影响到分页的计算。一个比较低效的办法遍历数据库并累加符合规则的key总数，但是更好的做法是以链表保存所有存活的id，这将在下一篇介绍。

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