一、前言

中国省市区还是不少的，省有34个，市有391个，区有1101个，这是以小编的库里的，可能不是最新的，但是个数也差不了多少。

当一次返回所有的数据，并且还要组装成一个三级树，一般的for，会循环34*391*1101次。这样就是千万级的，加上与数据库交互，你跑半天也跑不完。

最后的处理是组长提供的思路，果然很快。

二、思路

首先：小编的省市区是三张表

第一：我们通过三次IO从数据库中查询出所有省市区的数据，下面在进行for循环组装树形效率就很快了！

第二：为了减少IO交互，我们把刚刚取出来的市和区构建为map<provinceCode,List<City>>，map<districtCode,List<District>>，这样效率就上来了！

三、数据库表设计

1. 省

CREATE TABLE `address_province`  (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `name` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `short_name` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `new_code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `is_latest` tinyint(3) NULL DEFAULT 1 COMMENT '是否是最新地址，0否1是',
  `remarks` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `created_at` datetime(0) NULL DEFAULT NULL COMMENT '创建时间',
  `created_by` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `updated_at` datetime(0) NULL DEFAULT NULL COMMENT '更新时间',
  `updated_by` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `is_deleted` tinyint(3) UNSIGNED NOT NULL DEFAULT 0 COMMENT '删除标记，0：正常；1：删除',
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `uk_code`(`code`) USING BTREE,
  INDEX `idx_address_province_name`(`name`) USING BTREE,
  INDEX `idx_address_province_short_name`(`short_name`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 35 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '地址省' ROW_FORMAT = Dynamic;

2. 市：

CREATE TABLE `address_city`  (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `name` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `new_code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `province_code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `is_latest` tinyint(3) NULL DEFAULT 1 COMMENT '是否是最新地址，0否1是',
  `remarks` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `created_at` datetime(0) NULL DEFAULT NULL COMMENT '创建时间',
  `created_by` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `updated_at` datetime(0) NULL DEFAULT NULL COMMENT '更新时间',
  `updated_by` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `is_deleted` tinyint(3) NULL DEFAULT 0 COMMENT '删除标记，0正常1删除',
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `uk_code`(`code`) USING BTREE,
  INDEX `idx_address_city_name`(`name`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 392 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '地址市' ROW_FORMAT = Dynamic;

3. 区

CREATE TABLE `address_district`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `name` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `new_code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `city_code` char(6) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT