前言：

利用Ajax來實現一個地區的三級聯動，用Java代碼來讀json文件，先eclipse做一個簡單的，最基礎的。（json我用的jackson來解析，也可用fastjson-阿里巴巴的等還有很多）提供代碼，思路之類的，注釋也沒有自己去想去琢磨出來的思路好

first：首先先要熟悉json文件，并要想好利用什么類型去解析，這是最難的，最好找一個沒人的地方戴上耳機（對于初學）我是用maven來做的用到的jar坐標 ：

<dependency>			<groupId>redis.clients</groupId>			<artifactId>jedis</artifactId>			<version>2.9.0</version>			<scope>compile</scope>		</dependency>		<dependency>			<groupId>javax.servlet</groupId>			<artifactId>javax.servlet-api</artifactId>			<version>3.1.0</version>			<scope>provided</scope>		</dependency>		<dependency>			<groupId>com.fasterxml.jackson.core</groupId>			<artifactId>jackson-databind</artifactId>			<version>2.11.2</version>		</dependency>

文件位置：

second：首先創建一個html文件 three.html

加了一個字體居中和大小的樣式以至于不會太難看，太原生

首先來實現–省--的局部刷新，利用Ajax

<script type="text/javascript">	$(function(){		$.post("province",function(data){			$.each(data,function(){				$("#province").append("<option value="+this.code+">"+this.name+"</option>");			})		},"json")	})</script>

然后來寫對應的ProvinceController.class的代碼（主要是邏輯，為什么我要用List<Map<String,Object>>類型）

package com.daben.controller;import java.io.FileInputStream;import java.io.IOException;import java.util.ArrayList;import java.util.Iterator;import java.util.List;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.fasterxml.jackson.core.type.TypeReference;import com.fasterxml.jackson.databind.ObjectMapper;@WebServlet("/province")public class ProvinceController extends HttpServlet{	private static final long serialVersionUID = -6513954606070061277L;	@Override	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		this.doPost(req, resp);	}	@Override	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		resp.setContentType("appliaction/json;charset=utf-8");//可加可不加，json可在前端標注也可在后端 看自己習慣 我前后都加了		ObjectMapper om = new ObjectMapper(); //jackson核心類		String path = req.getServletContext().getRealPath("/WEB-INF/classes/city_code.json");//利用servletContext(也有叫appliaction)來拿到文件的真實路徑，也可以利用加載器拿都一樣		FileInputStream fi = new FileInputStream(path);//流		List<Map<String, Object>> province = om.readValue(fi, new TypeReference<List<Map<String,Object>>>() {});//jackson解析的方法，為什么是這個方法，百度學的 利用TypeReference可解析你想要得到的類型		List<Map<String,Object>> list = new ArrayList<>();		Iterator<Map<String, Object>> iterator = province.iterator();//我用的迭代器遍歷的 foreach等 也可以 		while(iterator.hasNext()) {			Map<String, Object> map2 = iterator.next();			map2.remove("city");//可寫也可不寫			list.add(map2);		}		om.writeValue(resp.getWriter(), list);	}	}

在three.html添加改變事件

代碼比較簡單，就是跟簡單的清空 賦值 取值

$("#province").on("change", function(){			let code = $(this).find(":selected").val();			$.post("city",{"code":code}, function(data){				$("#city").empty();				$("#city").append("<option>---市---</option>");				$.each(data, function(){					$("#city").append("<option value="+this.code+">"+this.name+"</option>");				})			},"json");		});

再寫對應的CityController.class(代碼類似)我為什么還會強轉List<Map<String,Object>>類型

package com.daben.controller;import java.io.FileInputStream;import java.io.IOException;import java.util.ArrayList;import java.util.Iterator;import java.util.List;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.fasterxml.jackson.core.type.TypeReference;import com.fasterxml.jackson.databind.ObjectMapper;@WebServlet("/city")public class CityController extends HttpServlet{	private static final long serialVersionUID = -6513954606070061277L;	@Override	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		this.doPost(req, resp);	}	@SuppressWarnings("unchecked")	@Override	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		resp.setContentType("appliaction/json;charset=utf-8");		String code = req.getParameter("code");		req.getSession().setAttribute("cityCode", code);		ObjectMapper om = new ObjectMapper();		String path = req.getServletContext().getRealPath("/WEB-INF/classes/city_code.json");		FileInputStream fi = new FileInputStream(path);		List<Map<String, Object>> province = om.readValue(fi, new TypeReference<List<Map<String,Object>>>() {});		List<Map<String,Object>> list = new ArrayList<>();		Iterator<Map<String, Object>> iterator = province.iterator();		while(iterator.hasNext()) {			Map<String, Object> map2 = iterator.next();			if(map2.get("code").equals(code)) {				map2.remove("code");				map2.remove("name");				list=(List<Map<String,Object>>) map2.get("city");				break;			}					}		List<Map<String,Object>> list1 = new ArrayList<>();		Iterator<Map<String,Object>> iterator2 = list.iterator();		while(iterator2.hasNext()) {			Map<String,Object> next = iterator2.next();			next.remove("area");			list1.add(next);					}		om.writeValue(resp.getWriter(), list1);	}	}

不懂的話，可以先看一看city_code.json文件，多想一想

繼續來three.html

$("#city").on("change", function(){			let code = $(this).find(":selected").val();			$.post("village",{"code":code}, function(data){				$("#village").empty();				$("#village").append("<option>---縣---</option>");				$.each(data, function(){					$("#village").append("<option value="+this.code+">"+this.name+"</option>");				})			},"json");

代碼雷同以至于VillageController.class也是雷同，加了一些判斷而已多了一個循環，

package com.daben.controller;import java.io.FileInputStream;import java.io.IOException;import java.util.ArrayList;import java.util.Iterator;import java.util.List;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.fasterxml.jackson.core.type.TypeReference;import com.fasterxml.jackson.databind.ObjectMapper;@WebServlet("/village")public class VillageController extends HttpServlet{	private static final long serialVersionUID = -6513954606070061277L;	@Override	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		this.doPost(req, resp);	}	@SuppressWarnings("unchecked")	@Override	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		resp.setContentType("appliaction/json;charset=utf-8");		String code = req.getParameter("code");		String cityCode = (String)req.getSession().getAttribute("cityCode");		ObjectMapper om = new ObjectMapper();		String path = req.getServletContext().getRealPath("/WEB-INF/classes/city_code.json");		FileInputStream fi = new FileInputStream(path);		List<Map<String, Object>> province = om.readValue(fi, new TypeReference<List<Map<String,Object>>>() {});		List<Map<String,Object>> list = new ArrayList<>();		Iterator<Map<String, Object>> iterator = province.iterator();		while(iterator.hasNext()) {			Map<String, Object> map2 = iterator.next();			if(map2.get("code").equals(cityCode)) {				map2.remove("code");				map2.remove("name");				list=(List<Map<String,Object>>) map2.get("city");				break;			}					}		List<Map<String,Object>> list1 = new ArrayList<>();		Iterator<Map<String,Object>> iterator2 = list.iterator();		while(iterator2.hasNext()) {			Map<String,Object> next = iterator2.next();				if(next.get("code").equals(code)) {					next.remove("code");					next.remove("name");					list1 = (List<Map<String,Object>>)next.get("area");				}		}		om.writeValue(resp.getWriter(), list1);			}	}

完結：只提供了代碼，但是為什么這樣何不自己去想一想？

json地區文件下載：

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思考？可不可以用xml文件來代替json文件？將jackson換成jsoup來解析？

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