背景与问题

在 《一个略复杂的数据映射聚合例子及代码重构》 一文中，将一个JSON字符串转成了所需要的订单信息Map。尽管做了代码重构和配置化，过程式的代码仍然显得晦涩难懂，并且客户端使用Map也非常难受。

能不能把这个JSON串转成相应的对象，昆山软件开发，更易于使用呢？ 为了方便讲解，这里重复写下JSON串。

{
    "item:s_id:18006666": "1024",
    "item:s_id:18008888": "1024",
    "item:g_id:18006666": "6666",
    "item:g_id:18008888": "8888",
    "item:num:18008888": "8",
    "item:num:18006666": "6",
    "item:item_core_id:18006666": "9876666",
    "item:item_core_id:18008888": "9878888",
    "item:order_no:18006666": "E20171013174712025",
    "item:order_no:18008888": "E20171013174712025",
    "item:id:18008888": "18008888",
    "item:id:18006666": "18006666",

    "item_core:num:9878888": "8",
    "item_core:num:9876666": "6",
    "item_core:id:9876666": "9876666",
    "item_core:id:9878888": "9878888",

    "item_price:item_id:1000": "9876666",
    "item_price:item_id:2000": "9878888",
    "item_price:price:1000": "100",
    "item_price:price:2000": "200",
    "item_price:id:2000": "2000",
    "item_price:id:1000": "1000",

    "item_price_change_log:id:1111": "1111",
    "item_price_change_log:id:2222": "2222",
    "item_price_change_log:item_id:1111": "9876666",
    "item_price_change_log:item_id:2222": "9878888",
    "item_price_change_log:detail:1111": "haha1111",
    "item_price_change_log:detail:2222": "haha2222",
    "item_price_change_log:id:3333": "3333",
    "item_price_change_log:id:4444": "4444",
    "item_price_change_log:item_id:3333": "9876666",
    "item_price_change_log:item_id:4444": "9878888",
    "item_price_change_log:detail:3333": "haha3333",
    "item_price_change_log:detail:4444": "haha4444"
}

思路与实现

要解决这个问题，需要有一个清晰的思路。

推断目标对象

仔细观察可知，每个 key 都是 tablename:field:id 组成，其中 table:id 相同的可以构成一个对象的数据； 此外，不同的tablename 对应不同的对象，而这些对象之间可以通过相同的 itemId 关联。

根据对JSON字符串的仔细分析（尤其是字段的关联性），可以知道： 目标对象应该类似如下嵌套对象：

@Getter
@Setter
public class ItemCore {
  private String id;
  private String num;

  private Item item;

  private ItemPrice itemPrice;

  private List<ItemPriceChangeLog> itemPriceChangeLogs;

}

@Getter
@Setter
public class Item {
  private String sId;
  private String gId;
  private String num;
  private String orderNo;
  private String id;
  private String itemCoreId;

}

@Getter
@Setter
public class ItemPrice {
  private String itemId;
  private String price;
  private String id;
}

@Getter
@Setter
public class ItemPriceChangeLog {
  private String id;
  private String itemId;
  private String detail;
}

注意到，劳务派遣管理系统，对象里的属性是驼峰式，JSON串里的字段是下划线，遵循各自领域内的命名惯例。这里需要用到一个函数，将Map的key从下划线转成驼峰。这个方法在 《Java实现递归将嵌套Map里的字段名由驼峰转为下划线》 给出。

明确了目标对象，就成功了 30%。 接下来，需要找到一种方法，从指定字符串转换到这个对象。

算法设计

由于 JSON 并不是与对象结构对应的嵌套结构。需要先转成容易处理的Map对象。这里的一种思路是，

STEP1: 将 table:id 相同的字段及值分组聚合，得到 Map[tablename:id, mapForKey[field, value]]；

STEP2: 将每个 mapForKey[field, value] 转成 tablename 对应的单个对象 Item, ItemCore, ItemPrice, ItemPriceChangeLog；

STEP3: 然后根据 itemId 来关联这些对象，组成最终对象。

代码实现

package zzz.study.algorithm.object;

import com.alibaba.fastjson.JSON;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

import zzz.study.datastructure.map.TransferUtil;
import static zzz.study.utils.BeanUtil.map2Bean;

public class MapToObject {

  private static final String json = "{\n"
             + "    \"item:s_id:18006666\": \"1024\",\n"
             + "    \"item:s_id:18008888\": \"1024\",\n"
             + "    \"item:g_id:18006666\": \"6666\",\n"
             + "    \"item:g_id:18008888\": \"8888\",\n"
             + "    \"item:num:18008888\": \"8\",\n"
             + "    \"item:num:18006666\": \"6\",\n"
             + "    \"item:item_core_id:18006666\": \"9876666\",\n"
             + "    \"item:item_core_id:18008888\": \"9878888\",\n"
             + "    \"item:order_no:18006666\": \"E20171013174712025\",\n"
             + "    \"item:order_no:18008888\": \"E20171013174712025\",\n"
             + "    \"item:id:18008888\": \"18008888\",\n"
             + "    \"item:id:18006666\": \"18006666\",\n"
             + "    \n"
             + "    \"item_core:num:9878888\": \"8\",\n"
             + "    \"item_core:num:9876666\": \"6\",\n"
             + "    \"item_core:id:9876666\": \"9876666\",\n"
             + "    \"item_core:id:9878888\": \"9878888\",\n"
             + "\n"
             + "    \"item_price:item_id:1000\": \"9876666\",\n"
             + "    \"item_price:item_id:2000\": \"9878888\",\n"
             + "    \"item_price:price:1000\": \"100\",\n"
             + "    \"item_price:price:2000\": \"200\",\n"
             + "    \"item_price:id:2000\": \"2000\",\n"
             + "    \"item_price:id:1000\": \"1000\",\n"
             + "\n"
             + "    \"item_price_change_log:id:1111\": \"1111\",\n"
             + "    \"item_price_change_log:id:2222\": \"2222\",\n"
             + "    \"item_price_change_log:item_id:1111\": \"9876666\",\n"
             + "    \"item_price_change_log:item_id:2222\": \"9878888\",\n"
             + "    \"item_price_change_log:detail:1111\": \"haha1111\",\n"
             + "    \"item_price_change_log:detail:2222\": \"haha2222\",\n"
             + "    \"item_price_change_log:id:3333\": \"3333\",\n"
             + "    \"item_price_change_log:id:4444\": \"4444\",\n"
             + "    \"item_price_change_log:item_id:3333\": \"9876666\",\n"
             + "    \"item_price_change_log:item_id:4444\": \"9878888\",\n"
             + "    \"item_price_change_log:detail:3333\": \"haha3333\",\n"
             + "    \"item_price_change_log:detail:4444\": \"haha4444\"\n"
             + "}";

  public static void main(String[] args) {
    Order order = transferOrder(json);
    System.out.println(JSON.toJSONString(order));
  }

  public static Order transferOrder(String json) {
    return relate(underline2camelForMap(group(json)));
  }

  /**
   * 转换成 Map[tablename:id => Map["field": value]]
   */
  public static Map<String, Map<String,Object>> group(String json) {
    Map<String, Object> map = JSON.parseObject(json);
    Map<String, Map<String,Object>> groupedMaps = new HashMap();
    map.forEach(
        (keyInJson, value) -> {
          TableField tableField = TableField.buildFrom(keyInJson);
          String key = tableField.getTablename() + ":" + tableField.getId();
          Map<String,Object> mapForKey = groupedMaps.getOrDefault(key, new HashMap<>());
          mapForKey.put(tableField.getField(), value);
          groupedMaps.put(key, mapForKey);
        }
    );
    return groupedMaps;
  }

  public static Map<String, Map<String,Object>> underline2camelForMap(Map<String, Map<String,Object>> underlined) {
    Map<String, Map<String,Object>> groupedMapsCamel = new HashMap<>();
    Set<String> ignoreSets = new HashSet();
    underlined.forEach(
        (key, mapForKey) -> {
          Map<String,Object> keytoCamel = TransferUtil.generalMapProcess(mapForKey, TransferUtil::underlineToCamel, ignoreSets);
          groupedMapsCamel.put(key, keytoCamel);
        }
    );
    return groupedMapsCamel;
  }

  /**
   * 将分组后的子map先转成相应单个对象，再按照某个key值进行关联
   */
  public static Order relate(Map<String, Map<String,Object>> groupedMaps) {
    List<Item> items = new ArrayList<>();
    List<ItemCore> itemCores = new ArrayList<>();
    List<ItemPrice> itemPrices = new ArrayList<>();
    List<ItemPriceChangeLog> itemPriceChangeLogs = new ArrayList<>();
    groupedMaps.forEach(
        (key, mapForKey) -> {
          if (key.startsWith("item:")) {
            items.add(map2Bean(mapForKey, Item.class));
          }
          else if (key.startsWith("item_core:")) {
            itemCores.add(map2Bean(mapForKey, ItemCore.class));
          }
          else if (key.startsWith("item_price:")) {
            itemPrices.add(map2Bean(mapForKey, ItemPrice.class));
          }
          else if (key.startsWith("item_price_change_log:")) {
            itemPriceChangeLogs.add(map2Bean(mapForKey, ItemPriceChangeLog.class));
          }
        }
    );

    Map<String ,List<Item>> itemMap = items.stream().collect(Collectors.groupingBy(
        Item::getItemCoreId
    ));
    Map<String ,List<ItemPrice>> itemPriceMap = itemPrices.stream().collect(Collectors.groupingBy(
        ItemPrice::getItemId
    ));
    Map<String ,List<ItemPriceChangeLog>> itemPriceChangeLogMap = itemPriceChangeLogs.stream().collect(Collectors.groupingBy(
        ItemPriceChangeLog::getItemId
    ));
    itemCores.forEach(
        itemCore -> {
          String itemId = itemCore.getId();
          itemCore.setItem(itemMap.get(itemId).get(0));
          itemCore.setItemPrice(itemPriceMap.get(itemId).get(0));
          itemCore.setItemPriceChangeLogs(itemPriceChangeLogMap.get(itemId));
        }
    );
    Order order = new Order();
    order.setItemCores(itemCores);
    return order;
  }

}

@Data
public class TableField {

  String tablename;
  String field;
  String id;

  public TableField(String tablename, String field, String id) {
    this.tablename = tablename;
    this.field = field;
    this.id = id;
  }

  public static TableField buildFrom(String combined) {
    String[] parts = combined.split(":");
    if (parts != null && parts.length == 3) {
      return new TableField(parts[0], parts[1], parts[2]);
    }
    throw new IllegalArgumentException(combined);
  }

}

package zzz.study.utils;

import org.apache.commons.beanutils.BeanUtils;

import java.util.Map;

public class BeanUtil {

  public static <T> T map2Bean(Map map, Class<T> c) {
    try {
      T t = c.newInstance();
      BeanUtils.populate(t, map);
      return t;
    } catch (Exception ex) {
      throw new RuntimeException(ex.getCause());
    }
  }

}

代码重构

group的实现已经不涉及具体业务。这里重点说下 relate 实现的优化。在实现中看到了 if-elseif-elseif-else 条件分支语句。是否可以做成配置化呢？