Redis从基础命令到实战之列表类型(List)

经过上一篇基于Redis散列类型的改造后，实战练习中的商品管理已经具备了增加、修改整体、修改部分属性和分页查询功能，但仍然不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，进而会影响到分页的计算。

在本节中将完善这个功能，使用一个新的数据类型 - 列表类型(List)来保存所有商品ID，计算商品总量时通过计算列表类型长度获得，删除商品时也同时删除列表中的ID。

列表类型用于存储可重复的字符串列表，内部按照添加的先后保持顺序，在列表两端添加和取出元素非常高效，常见的应用场景是社交网站取出最新发表内容列表，也可以用于实现消息队列。先看常用的操作。

一、常用命令

import java.util.List;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.SortingParams;
import redis.clients.jedis.BinaryClient.LIST_POSITION;

public class ListExample {

    public static void main(String[] args) {
        Jedis jedis = JedisProvider.getJedis();
        jedis.flushDB();

        //lpush 在左边添加
        String fruitKey = "fruit";
        long lpush = jedis.lpush(fruitKey, "apple");
        print("lpush " + fruitKey + " apple=" + lpush);
        lpush = jedis.lpush(fruitKey, "banana");
        print("lpush " + fruitKey + " banana=" + lpush);
        jedis.lpush(fruitKey, "apple");
        jedis.lpush(fruitKey, "apple");
        jedis.lpush(fruitKey, "orange");
        jedis.lpush(fruitKey, "grape");
        jedis.lpush(fruitKey, "peach");
        jedis.lpush(fruitKey, "lemon");

        //rpush 在右边添加
        String numberKey = "numbers";
        jedis.rpush(numberKey, "5");
        jedis.rpush(numberKey, "4");
        jedis.rpush(numberKey, "2");
        jedis.rpush(numberKey, "1");

        //lrange 获得列表片段
        print("lrange " + fruitKey + " [0,-1]=" + jedis.lrange(fruitKey, 0, -1));
        print("lrange " + numberKey + " [0,-1]=" + jedis.lrange(numberKey, 0, -1));
        print("lrange " + fruitKey + " [1,3]=" + jedis.lrange(fruitKey, 1, 3));

        //删除列表指定的值,第二个参数为删除的个数(有重复时),后添加进去的值先被删,类似于出栈,返回删除个数
        Long del = jedis.lrem(fruitKey, 2, "apple");
        print("lrem " + fruitKey + " apple*2=" + del);
        print("after lrem, lrange " + fruitKey + " [0,-1]=" + jedis.lrange(fruitKey, 0, -1));

        //删除区间以外的数据, 成功返回 OK
        String ltrim = jedis.ltrim(fruitKey, 0, 3);
        print("ltrim " + fruitKey + " [0,3]=" + ltrim);
        print("after ltrim, lrange " + fruitKey + " [0,-1]=" + jedis.lrange(fruitKey, 0, -1));

        //列表元素出栈
        String lpop = jedis.lpop(fruitKey);
        print("lpop " + fruitKey + " =" + lpop);
        print("after lpop, lrange " + fruitKey + " [0,-1]=" + jedis.lrange(fruitKey, 0, -1));

        //修改列表中指定下标的值
        String lset = jedis.lset(fruitKey, 0, "mango");
        print("lset " + fruitKey + " 0=" + lset);
        print("after lset, lrange " + fruitKey + " [0,-1]=" + jedis.lrange(fruitKey, 0, -1));

        //数组长度
        print("llen " + fruitKey + " =" + jedis.llen(fruitKey));

        //排序
        SortingParams sortingParameters = new SortingParams();
        sortingParameters.alpha();
        sortingParameters.limit(0, 3);
        List<String> list = jedis.sort(fruitKey, sortingParameters);
        String sort = "";
        for(int i = 0; i < list.size(); i++) {
            sort += list.get(i) + " ";
        }
        print("sort " + fruitKey + " =" + sort);

        //获取列表指定下标的值, 不存在返回null
        int pos = 2;
        String lindex = jedis.lindex(fruitKey, pos);
        print("lindex " + fruitKey + " 2=" + lindex);

        //在指定元素前/后插入
        jedis.linsert(numberKey, LIST_POSITION.BEFORE, "2", "3");
        print("after linsert, lrange " + numberKey + " [0,-1]=" + jedis.lrange(numberKey, 0, -1));

        String value = jedis.rpoplpush(numberKey, "dst");
        while(value != null) {
            System.out.println("rpoplpush " + numberKey + " =" + value);
            value = jedis.rpoplpush(numberKey, "dst");
        }
        print("after rpoplpush, lrange dst [0,-1]=" + jedis.lrange("dst", 0, -1));

        jedis.close();
    }

    private static void print(String info) {
        System.out.println(info);
        System.out.println("------------------------------------------------------");
        System.out.println();
    }
}

二、实践练习

在上一篇商品管理示例的基础上，增加删除商品的功能。

修改添加商品的功能代码，增加了列表类型保存所有新加入的商品ID

/**
 * 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;
    boolean added = jedis.hmset(key, map).equals("OK");
    if(added) {
        jedis.rpush("goods:list", String.valueOf(id));
    }
    return added;
}

添加删除商品功能代码

/**
 * 删除商品
 * @param id
 * @return
 */
public boolean delGoods(long id) {
    long deleted = jedis.del("goods:" + id);
    if(deleted == 1) {
        jedis.lrem("goods:list", 1, String.valueOf(id));
    }
    return deleted == 1;
}

还需要修改获得商品总数和分页查询商品的代码，商品总数和ID列表改为从goods:list中获得

/**
 * 读取商品总数
 * @return
 */
public long getTotalCount() {
    String key = "goods:list";
    return jedis.llen(key);
}

/**
 * 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 - 1;
    if(to > totals) {
        to = totals;
    }
    List<Goods> goodsList = new ArrayList<>();
    List<String> idList = jedis.lrange("goods:list", from, to);
    for(String id : idList) {
        String key = "goods:" + id;
        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) {
    ListLession ll = new ListLession();
    ll.clear();

    //添加一批商品
    for(int i = 0; i< 42; i++) {
        Goods goods = new Goods(0, "goods" + String.format("%05d", (i + 1)), i);
        ll.addGoods(goods);
    }
    //读取商品总数
    System.out.println("商品总数: " + ll.getTotalCount());
    //删除第29件商品
    ll.delGoods(29);
    System.out.println("删除后商品总数: " + ll.getTotalCount());
    //分页显示
    List<Goods> list = ll.getGoodsList(2, 20);
    System.out.println("第二页商品:");
    for(Goods goods : list) {
        System.out.println(goods);
    }
}

现在，商品管理已经具备了增删改查功能，但是Redis还有两个数据类型没有被使用到，下一节将使用集合类型来实现为商品添加分类的功能。

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