JSON+AJAX的应用
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主要内容：
- JSON数据格式
- AJAX异步请求
- 利用JSON+AJAX进行用户名的判断
- 利用JSON＋AJAX进行省、市、区信息联动
详细记录：
1 JSON数据格式
JS中的JSON
JAVA中的JSON：
引入JAR包：
commons-beanutils-1.7.0.jar
commons-collections-3.1.jar
commons-httpclient-3.1.jar
commons-lang-2.5.jar
commons-logging-1.0.4.jar
ezmorph-1.0.3.jar
json-lib-2.1-jdk15.jar
测试类：
（1）自定义JSON类对象
import net.sf.json.JSONObject;public class TestJSON { public static void main(String[] args) { JSONObject obj=new JSONObject(); obj.put("name", "zb"); obj.put("age", 20); obj.put("birth", "1998-11-1"); System.out.println(obj); }}执行：{“birth”:”1998-11-1”,”age”:20,”name”:”zb”}
（2）由MAP生成JSON类对象
public class TestJSON { public static void main(String[] args) { Map obj=new HashMap(); obj.put("name", "zb"); obj.put("age", 20); obj.put("birth", "1998-11-1"); JSONObject objJSON=JSONObject.fromObject(obj); System.out.println(objJSON); }}执行结果：{“birth”:”1998-11-1”,”name”:”zb”,”age”:20}
（3）由JAVA集合生成JSON数组对象
public class TestJSON { public static void main(String[] args) { List<Map> list=new ArrayList<Map>(); Map obj1=new HashMap(); obj1.put("name", "zb"); obj1.put("age", 20); obj1.put("birth", "1998-11-1"); list.add(obj1); Map obj2=new HashMap(); obj2.put("name", "zb2"); obj2.put("age", 22); obj2.put("birth", "1996-1-1"); list.add(obj2); JSONArray array=JSONArray.fromObject(list); System.out.println(array); }}执行结果：[{“birth”:”1998-11-1”,”age”:20,”name”:”zb”},{“birth”:”1996-1-1”,”age”:22,”name”:”zb2”}]
（4）由JavaBean生成JSON类对象
User类的定义：
package cn.sdut.po;public class User { private int id; private String name; private String password; private String sex; private String birthday; private String hobby; private String telephone; private String address; private int type; public User() { super(); } public User(int id, String name, String password, String sex, String birthday, String hobby, String telephone, String address, int type) { super(); this.id = id; this.name = name; this.password = password; this.sex = sex; this.birthday = birthday; this.hobby = hobby; this.telephone = telephone; this.address = address; this.type = type; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public String getBirthday() { return birthday; } public void setBirthday(String birthday) { this.birthday = birthday; } public String getHobby() { return hobby; } public void setHobby(String hobby) { this.hobby = hobby; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public int getType() { return type; } public void setType(int type) { this.type = type; } @Override public String toString() { return "User [id=" + id + ", name=" + name + ", password=" + password + ", sex=" + sex + ", birthday=" + birthday + ", hobby=" + hobby + ", telephone=" + telephone + ", address=" + address + ", type=" + type + "]"; }}测试类：
package cn.sdut.po;import net.sf.json.JSONObject;public class TestJSON { public static void main(String[] args) { User user=new User(1,"李华","1111","女","1999-1-1","体育","122342","淄博",1); JSONObject userJson=JSONObject.fromObject(user); System.out.println(userJson.toString()); }}执行：{“id”:1,”birthday”:”1999-1-1”,”sex”:”女”,”address”:”淄博”,”name”:”李华”,”hobby”:”体育”,”type”:1,”telephone”:”122342”,”password”:”1111”}
2 AJAX异步请求
3 利用JSON+AJAX进行用户名的判断
过程分析：
（1）数据库层面的支持——根据用户名查询用户对象
（2）JSP页面的支持——“姓名”文本框内容改变时，需要响应onchange事件（或者onblur事件），另外，在姓名输入框后加个提示信息的控件，用于显示用户名是否可用。
（3）Servlet的处理——获得用户名，根据用户名查询用户，若查到，就返回页面“true”，否则返回“false”
（4）JSP页面根据返回值“true”还是“false”，进行不同的处理。 详细代码：
（1）数据库层面的支持——根据用户名查询用户对象（UserDao.java）
DBUtilsBaseDao.java
package cn.sdut.dao;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.util.List;import org.apache.commons.dbutils.DbUtils;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanListHandler;public class DBUtilsBaseDao { //得到数据库连接 public Connection getConn() { Connection conn=null; DbUtils.loadDriver("com.mysql.jdbc.Driver"); try { conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/shopping?useUnicode=true&characterEncoding=utf-8","root","usbw"); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return conn; } //增、删、改数据库的方法 public int update(String sql,Object... param) { int result=0; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { result=runner.update(conn, sql, param); //进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } return result; } //数据库查询 public List query(String sql,Class clazz,Object... param) { List list=null; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { list=runner.query(conn,sql,new BeanListHandler(clazz),param); //进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } return list; } //批量操作数据库的方法 public boolean bactchUpdate(String sql,Object[][] param) { int[] result=new int[param.length]; int r=1; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { result=runner.batch(conn,sql,param);// 批量进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } //对返回数据进行加工，将整型数组转化为布尔类型 for(int i=0;i<result.length;i++) { r*=result[i]; } return r>0?true:false; }}UserDao.java
package cn.sdut.dao;import java.util.List;import cn.sdut.po.User;public class UserDao extends DBUtilsBaseDao { // …………. //用户注册或增加用户时根据用户名查询用户（是否存在） public User findUserByName(String name) { User user=null; String sql="select * from users where name=?"; Object[] param=new Object[]{name}; List<User> users=query(sql, User.class, param); if(users!=null&&users.size()>0) { user=users.get(0); } return user; }}（2）JSP页面的支持——“姓名”文本框内容改变时，需要响应onchange事件（或者onblur事件），另外，在姓名输入框后加个提示信息的控件，用于显示用户名是否可用。（m_addUser.jsp）
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP ’addUser.jsp’ starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> <script src="js/calendar.js"></script> <style type="text/css"> body { text-align: center;} </style> <script> function checkUser() { var name=document.getElementById("name").value; var httpRequest=new XMLHttpRequest(); httpRequest.open("GET","<%=path%>/UserServlet?method=byname&name="+name,true); httpRequest.onreadystatechange=function() { if(httpRequest.status==200&&httpRequest.readyState==4) { var response=httpRequest.responseText; if(response=="true") { document.getElementById("info").innerHTML="用户名已存在"; document.getElementById("name").value=""; } else { document.getElementById("info").innerHTML="用户名可用";} } } httpRequest.send(); } </script> </head> <body> <br> <form name="form1" method="post" action="<%=path%>/UserServlet?method=add"> <table width="496" border="1"> <caption>用户添加</caption> <tr> <td width="92" height="38" align="center">用户名：</td> <td width="157"><input type="text" name="name" id="name" onblur="checkUser()"> <span id="info" style="color:red"></span> </td> </tr> <tr> <td height="41" align="center">密码：</td> <td><input type="text" name="password" id="password"></td> </tr> <tr> <td height="41" align="center">出生日期：</td> <td><input type="text" name="birthday" id="birthday" onclick="new Calendar().show(this)"></td> </tr> <tr> <td height="44" align="center">性别：</td> <td><input type="radio" name="sex" id="sex" value="男">男 <input type="radio" name="sex" id="sex2" value="女"> 女 </td> </tr> <tr> <td align="center">爱好：</td> <td><p> <label> <input type="checkbox" name="hobby" value="运动" id="hobby_0">运动</label> <label> <input type="checkbox" name="hobby" value="音乐" id="hobby_1">音乐</label> <label> <input type="checkbox" name="hobby" value="阅读" id="hobby_2">阅读</label> <br> </p></td> </tr> <tr> <td align="center">地址：</td> <td><textarea name="address" id="address" cols="45" rows="5"></textarea></td> </tr> <tr> <td height="42" align="center">联系电话：</td> <td><input type="text" name="telephone" id="telephone"></td> </tr> <tr> <td height="64" colspan="2" align="center"> <input type="submit" name="submit" id="submit" value="提交"> <input type="reset" name="button" id="button" value="取消"></td> </tr> </table> </form> </body></html>（3）Servlet的处理——获得用户名，根据用户名查询用户，若查到，就返回页面“true”，否则返回“false”。（UserServlet.java）
package cn.sdut.servlet;import java.io.IOException;import java.util.List;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 javax.servlet.http.HttpSession;import cn.sdut.dao.UserDao;import cn.sdut.po.User;@WebServlet("/UserServlet")public class UserServlet extends HttpServlet { private static final long serialVersionUID = 1L; UserDao userDao = new UserDao(); public UserServlet() { super(); // TODO Auto-generated constructor stub } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); String method = request.getParameter("method"); switch (method) { //……… case "byname": queryUserByName(request,response); break; } } private void queryUserByName(HttpServletRequest request, HttpServletResponse response) throws IOException { String result="false"; String name = request.getParameter("name"); User user = userDao.findUserByName(name); if(user!=null) { result="true"; } response.getWriter().write(result); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}（4）JSP页面根据返回值“true”还是“false”，进行不同的处理。（m_addUser.jsp）
var response=httpRequest.responseText; if(response=="true") { document.getElementById("info").innerHTML="用户名已存在"; document.getElementById("name").value=""; }else { document.getElementById("info").innerHTML="用户名可用";}（5）程序执行：
http://localhost:8080/adduser/m_addUser.jsp
4 利用JSON＋AJAX进行省、市、区信息联动
过程分析：
（0）创建表syscode，向里面加入省、市、区的数据，建立与该表对应的实体类
/*Navicat MySQL Data TransferSource Server : 127.0.0.1_3306Source Server Version : 50621Source Host : 127.0.0.1:3306Source Database : procitydisTarget Server Type : MYSQLTarget Server Version : 50621File Encoding : 65001Date: 2016-08-05 11:37:55*/SET FOREIGN_KEY_CHECKS=0;-- ------------------------------ Table structure for syscode-- ----------------------------DROP TABLE IF EXISTS `syscode`;CREATE TABLE `syscode` ( `pid` int(11) NOT NULL AUTO_INCREMENT, `pname` varchar(20) NOT NULL, `pcode` varchar(20) NOT NULL, `pvalue` varchar(20) NOT NULL, `fcode` varchar(20) NOT NULL, PRIMARY KEY (`pid`)) ENGINE=InnoDB AUTO_INCREMENT=47 DEFAULT CHARSET=utf8;-- ------------------------------ Records of syscode-- ----------------------------INSERT INTO `syscode` VALUES (’1’, ’省市’, ’01’, ’北京’, ’0’);INSERT INTO `syscode` VALUES (’2’, ’省市’, ’02’, ’上海’, ’0’);INSERT INTO `syscode` VALUES (’3’, ’省市’, ’03’, ’广州’, ’0’);INSERT INTO `syscode` VALUES (’4’, ’省市’, ’04’, ’山东’, ’0’);INSERT INTO `syscode` VALUES (’5’, ’省市’, ’0101’, ’东城区’, ’01’);INSERT INTO `syscode` VALUES (’6’, ’省市’, ’010101’, ’东华门街道’, ’0101’);INSERT INTO `syscode` VALUES (’7’, ’省市’, ’010102’, ’景山街道’, ’0101 ’);INSERT INTO `syscode` VALUES (’8’, ’省市’, ’0102’, ’西城区’, ’01’);INSERT INTO `syscode` VALUES (’9’, ’省市’, ’010201’, ’西长安街街道’, ’0102’);INSERT INTO `syscode` VALUES (’10’, ’省市’, ’010202’, ’广安门内街道’, ’0102 ’);INSERT INTO `syscode` VALUES (’11’, ’省市’, ’0103’, ’朝阳区’, ’01’);INSERT INTO `syscode` VALUES (’12’, ’省市’, ’010301’, ’南磨房地区’, ’0103’);INSERT INTO `syscode` VALUES (’13’, ’省市’, ’010302’, ’高碑店地区’, ’0103 ’);INSERT INTO `syscode` VALUES (’14’, ’省市’, ’0201’, ’黄浦’, ’02’);INSERT INTO `syscode` VALUES (’15’, ’省市’, ’020101’, ’黄浦1’, ’0201’);INSERT INTO `syscode` VALUES (’16’, ’省市’, ’020102’, ’黄浦2’, ’0201’);INSERT INTO `syscode` VALUES (’17’, ’省市’, ’0202’, ’徐汇’, ’02’);INSERT INTO `syscode` VALUES (’18’, ’省市’, ’020201’, ’徐汇1’, ’0202’);INSERT INTO `syscode` VALUES (’19’, ’省市’, ’020201’, ’徐汇2’, ’0202’);INSERT INTO `syscode` VALUES (’20’, ’省市’, ’0203’, ’长宁’, ’02’);INSERT INTO `syscode` VALUES (’21’, ’省市’, ’020301’, ’长宁1’, ’0203’);INSERT INTO `syscode` VALUES (’22’, ’省市’, ’020302’, ’长宁2’, ’0203’);INSERT INTO `syscode` VALUES (’23’, ’省市’, ’0301’, ’越秀区’, ’03’);INSERT INTO `syscode` VALUES (’24’, ’省市’, ’030101’, ’越秀1’, ’0301’);INSERT INTO `syscode` VALUES (’25’, ’省市’, ’030102’, ’越秀2’, ’0301’);INSERT INTO `syscode` VALUES (’26’, ’省市’, ’0302’, ’天河区’, ’03’);INSERT INTO `syscode` VALUES (’27’, ’省市’, ’030201’, ’天河1’, ’0302’);INSERT INTO `syscode` VALUES (’28’, ’省市’, ’030201’, ’天河2’, ’0302’);INSERT INTO `syscode` VALUES (’29’, ’省市’, ’0303’, ’白云区’, ’03’);INSERT INTO `syscode` VALUES (’30’, ’省市’, ’030301’, ’白云1’, ’0303’);INSERT INTO `syscode` VALUES (’31’, ’省市’, ’030201’, ’白云2’, ’0303’);INSERT INTO `syscode` VALUES (’32’, ’省市’, ’0401’, ’济南’, ’04’);INSERT INTO `syscode` VALUES (’33’, ’省市’, ’040101’, ’历下’, ’0401’);INSERT INTO `syscode` VALUES (’34’, ’省市’, ’030202’, ’槐荫’, ’0302’);INSERT INTO `syscode` VALUES (’35’, ’省市’, ’0402’, ’青岛’, ’04’);INSERT INTO `syscode` VALUES (’36’, ’省市’, ’040201’, ’市南’, ’0402’);INSERT INTO `syscode` VALUES (’37’, ’省市’, ’040201’, ’黄岛’, ’0402’);INSERT INTO `syscode` VALUES (’38’, ’省市’, ’0403’, ’烟台’, ’04’);INSERT INTO `syscode` VALUES (’39’, ’省市’, ’040301’, ’荣成 ’, ’0403’);INSERT INTO `syscode` VALUES (’40’, ’省市’, ’040302’, ’文登’, ’0403’);INSERT INTO `syscode` VALUES (’41’, ’省市’, ’0405’, ’淄博’, ’04’);INSERT INTO `syscode` VALUES (’42’, ’省市’, ’040501’, ’张店’, ’0405’);INSERT INTO `syscode` VALUES (’43’, ’省市’, ’040502’, ’淄川’, ’0405’);INSERT INTO `syscode` VALUES (’44’, ’省市’, ’040503’, ’周村’, ’0405’);INSERT INTO `syscode` VALUES (’45’, ’省市’, ’040504’, ’临淄’, ’0405’);INSERT INTO `syscode` VALUES (’46’, ’省市’, ’040505’, ’博山’, ’0405’);Syscode.java
package cn.sdut.po;public class Syscode { private int id; private String pname; private String pcode; private String pvalue; private String fcode; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getPname() { return pname; } public void setPname(String pname) { this.pname = pname; } public String getPcode() { return pcode; } public void setPcode(String pcode) { this.pcode = pcode; } public String getPvalue() { return pvalue; } public void setPvalue(String pvalue) { this.pvalue = pvalue; } public String getFcode() { return fcode; } public void setFcode(String fcode) { this.fcode = fcode; } }（1）数据库层面，提供查询省、市、区的方法
package cn.sdut.dao;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.util.List;import org.apache.commons.dbutils.DbUtils;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanListHandler;public class DBUtilsBaseDao { //得到数据库连接 public Connection getConn() { Connection conn=null; DbUtils.loadDriver("com.mysql.jdbc.Driver"); try { conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/shopping?useUnicode=true&characterEncoding=utf-8","root","usbw"); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return conn; } //增、删、改数据库的方法 public int update(String sql,Object... param) { int result=0; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { result=runner.update(conn, sql, param); //进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } return result; } //数据库查询 public List query(String sql,Class clazz,Object... param) { List list=null; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { list=runner.query(conn,sql,new BeanListHandler(clazz),param); //进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } return list; } //批量操作数据库的方法 public boolean bactchUpdate(String sql,Object[][] param) { int[] result=new int[param.length]; int r=1; Connection conn=getConn(); //得到连接 QueryRunner runner=new QueryRunner(); //得到运行对象 try { result=runner.batch(conn,sql,param);// 批量进行数据库操作 } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(conn); //关闭数据库连接 } //对返回数据进行加工，将整型数组转化为布尔类型 for(int i=0;i<result.length;i++) { r*=result[i]; } return r>0?true:false; }}package cn.sdut.dao;
import java.util.List;import cn.sdut.po.Syscode;public class SyscodeDao extends DBUtilsBaseDao { public List<Syscode> findPCD(String pname, String fcode) { List<Syscode> pcd = null; String sql = "select * from syscode where pname=? and fcode=?"; pcd=query(sql, Syscode.class, new String[] { pname, fcode }); System.out.println(pcd); return pcd; }}（2）页面层提供省、市、区3个下拉列表框，实现信息联动。
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP ’index.jsp’ starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> <script type="text/javascript"> function showCity() { //显示市 var value=document.getElementById("province").value; var httpRequest=new XMLHttpRequest(); httpRequest.open("GET","<%=path%>/SyscodeServlet?method=city&fcode="+value,true); httpRequest.onreadystatechange=function(){ if(httpRequest.status==200 && httpRequest.readyState==4) { var cities=httpRequest.responseText; var jsonCities=eval("("+cities+")"); var obj=document.getElementById("city"); obj.options.length=0; for(var i=0;i<jsonCities.length;i++) { obj.add(new Option(jsonCities[i].pvalue,jsonCities[i].pcode)); } showDist(); } }; httpRequest.send(); } function showDist() { //显示区 var value=document.getElementById("city").value; var httpRequest=new XMLHttpRequest(); httpRequest.open("GET","<%=path%>/SyscodeServlet?method=city&fcode="+value,true); httpRequest.onreadystatechange=function(){ if(httpRequest.status==200 && httpRequest.readyState==4) { var cities=httpRequest.responseText; var jsonCities=eval("("+cities+")"); var obj=document.getElementById("dist"); obj.options.length=0; for(var i=0;i<jsonCities.length;i++) { obj.add(new Option(jsonCities[i].pvalue,jsonCities[i].pcode)); } } }; httpRequest.send(); } </script> </head> <body onload="showCity()"> <select id="province" name="province" onchange="showCity()"> <c:forEach items="${provinceList }" var="province"> <option value="${province.pcode }">${province.pvalue }</option> </c:forEach> </select> <select id="city" name="city" onchange="showDist()"> </select> <select id="dist" name="dist"> </select> </body></html>（3）Servlet层面——完成2个任务：
l 页面加载时显示所有省的信息； l 异步请求显示市和区的信息
package cn.sdut.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import net.sf.json.JSONArray;import net.sf.json.JSONObject;import cn.sdut.dao.SyscodeDao;import cn.sdut.po.Syscode;public class SyscodeServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); String method=request.getParameter("method"); switch(method) { case "province": queryProvince(request,response); break; case "city": queryCity(request,response); break; case "dist": queryCity(request,response); break; } } private void queryProvince(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { SyscodeDao dao=new SyscodeDao(); List<Syscode> provinceList = dao.findPCD("省市", "0"); //System.out.println(provinceList); request.setAttribute("provinceList", provinceList); request.getRequestDispatcher("/index.jsp").forward(request, response); } private void queryCity(HttpServletRequest request, HttpServletResponse response) throws IOException { System.out.println(11); String fcode=request.getParameter("fcode"); SyscodeDao dao=new SyscodeDao(); List<Syscode> provinceList = dao.findPCD("省市", fcode); JSONArray cities=JSONArray.fromObject(provinceList); System.out.println(provinceList); response.getWriter().write(cities.toString()); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); }}（4）执行：
http://localhost:8080/PCD/SyscodeServlet?method=province
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