前言：
利用Ajax来实现一个地区的三级联动，用Java代码来读json文件，先eclipse做一个简单的，最基础的。（json我用的jackson来解析，也可用fastjson-阿里巴巴的等还有很多）提供代码，思路之类的，注释也没有自己去想去琢磨出来的思路好
first：首先先要熟悉json文件，并要想好利用什么类型去解析，这是最难的，最好找一个没人的地方戴上耳机（对于初学）我是用maven来做的用到的jar坐标 ：
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：首先创建一个html文件 three.html
加了一个字体居中和大小的样式以至于不会太难看，太原生
首先来实现–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>
然后来写对应的ProvinceController.class的代码（主要是逻辑，为什么我要用ListMapString,Object>>类型）
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可在前端标注也可在后端 看自己习惯 我前后都加了
ObjectMapper om = new ObjectMapper(); //jackson核心类
String path = req.getServletContext().getRealPath("/WEB-INF/classes/city_code.json");//利用servletContext(也有叫appliaction)来拿到文件的真实路径，也可以利用加载器拿都一样
FileInputStream fi = new FileInputStream(path);//流
ListMapString, Object>> province = om.readValue(fi, new TypeReferenceListMapString,Object>>>() {});//jackson解析的方法，为什么是这个方法，百度学的 利用TypeReference可解析你想要得到的类型
ListMapString,Object>> list = new ArrayList>();
IteratorMapString, Object>> iterator = province.iterator();//我用的迭代器遍历的 foreach等 也可以
while(iterator.hasNext()) {
MapString, Object> map2 = iterator.next();
map2.remove("city");//可写也可不写
list.add(map2);
}
om.writeValue(resp.getWriter(), list);
}
}
在three.html添加改变事件
代码比较简单，就是跟简单的清空 赋值 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");
});
再写对应的CityController.class(代码类似)我为什么还会强转ListMapString,Object>>类型
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);
ListMapString, Object>> province = om.readValue(fi, new TypeReferenceListMapString,Object>>>() {});
ListMapString,Object>> list = new ArrayList>();
IteratorMapString, Object>> iterator = province.iterator();
while(iterator.hasNext()) {
MapString, Object> map2 = iterator.next();
if(map2.get("code").equals(code)) {
map2.remove("code");
map2.remove("name");
list=(ListMapString,Object>>) map2.get("city");
break;
}
}
ListMapString,Object>> list1 = new ArrayList>();
IteratorMapString,Object>> iterator2 = list.iterator();
while(iterator2.hasNext()) {
MapString,Object> next = iterator2.next();
next.remove("area");
list1.add(next);
}
om.writeValue(resp.getWriter(), list1);
}
}
不懂的话，可以先看一看city_code.json文件，多想一想
继续来three.html
$("#city").on("change", function(){
let code = $(this).find(":selected").val();
$.post("village",{"code":code}, function(data){
$("#village").empty();
$("#village").append("option>---县---/option>");
$.each(data, function(){
$("#village").append("option value="+this.code+">"+this.name+"/option>");
})
},"json");
代码雷同以至于VillageController.class也是雷同，加了一些判断而已多了一个循环，
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);
ListMapString, Object>> province = om.readValue(fi, new TypeReferenceListMapString,Object>>>() {});
ListMapString,Object>> list = new ArrayList>();
IteratorMapString, Object>> iterator = province.iterator();
while(iterator.hasNext()) {
MapString, Object> map2 = iterator.next();
if(map2.get("code").equals(cityCode)) {
map2.remove("code");
map2.remove("name");
list=(ListMapString,Object>>) map2.get("city");
break;
}
}
ListMapString,Object>> list1 = new ArrayList>();
IteratorMapString,Object>> iterator2 = list.iterator();
while(iterator2.hasNext()) {
MapString,Object> next = iterator2.next();
if(next.get("code").equals(code)) {
next.remove("code");
next.remove("name");
list1 = (ListMapString,Object>>)next.get("area");
}
}
om.writeValue(resp.getWriter(), list1);
}
}
完结：只提供了代码，但是为什么这样何不自己去想一想？
json地区文件下载：
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思考？可不可以用xml文件来代替json文件？将jackson换成jsoup来解析？
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