Question

如何实现省市区三级联动的效果

Answer 1

1、在做这个小项目前的准备工作：
1.1、分析：
由于省、市、县城（区）这些数据是存储到了MySQL数据库中的，我们要通过后台servlet获取数据库中的数据，然后再通过转发或者重定向的方式将数据呈现到前台页面中。
1.2、需要导入的jar包有:
mysql驱动包：mysql-connector-Java-5.1.7-bin.jar
c3p0数据库连接池：c3p0-0.9.2.1.jar、mysql-connector-java-5.1.7-bin.jar（c3p0依赖包）
前台c标签（需要通过遍历的方式呈现——c:forEach）：jstl-1.0.2.jar、standard-1.0.1.jar（jstl依赖包）
将集合或者数组转换成json数据格式（Jackson包）：jackson-annotations-2.2.1.jar、jackson-core-2.2.1.jar、jackson-databind-2.2.1.jar
前台页面需要用到jQuery，故还需要导入jquery-1.7.2.js库文件
1.3、该小项目用到的技术：
jdbc的知识、servlet的知识、jquery的知识、Ajax的知识（局部刷新）、标签的知识、EL表达式的知识、JSP的知识
2、开发过程：
2.1、准备数据源
创建一个数据库，命名为thereaction并创建三个表——province（省）、city（市）、county（县/区）
2.2后台开发
创建三个Javabean分别是Province、City、County。（由于太过简单，这里就不粘代码了）
创建Java类和c3p0连接池实现与数据库的连接：DAO.java(实现获取数据库数据的功能)、jdbctools.java（实现获取数据库连接、释放连接的功能）、c3p0-config.xml
jdbctools.java代码如下：
[java] view plain copy
package com.xiaojie.dao;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class Jdbctools {
private static DataSource ds=null;
//数据库连接池应只被初始化一次
static{
ds=new ComboPooledDataSource("helloc3p0");
}
//获取数据库连接
public static Connection getConnection() throws ClassNotFoundException, SQLException, IOException{
return ds.getConnection();
}
public static void shifanglianjie(Connection ct, PreparedStatement ps,ResultSet rs) {
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(ps!=null){
try {
ps.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(ct!=null){
try {
ct.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

}

DAO.java的代码如下
[java] view plain copy
package com.xiaojie.dao;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import com.xiaojie.beans.City;
import com.xiaojie.beans.County;
import com.xiaojie.beans.Province;

public class DAO {
public List<Province> getprovince(String sql ,Object...args) throws ClassNotFoundException, SQLException, IOException{
List<Province> provinces=new ArrayList<Province>();
//准备去查数据库
Connection ct=null;
ct=Jdbctools.getConnection();
System.out.println("获取到数据库的连接了");
PreparedStatement ps=null;
ResultSet rs=null;
ps=ct.prepareStatement(sql);
for(int i=0;i<args.length;i++){
ps.setObject(i+1, args[i]);
}
rs=ps.executeQuery();
while(rs.next()){
provinces.add(new Province(rs.getInt("province_id"),rs.getString("province_name")));
}
Jdbctools.shifanglianjie(ct, ps, rs);
return provinces;

}
public List<City> getcity(String sql ,Object...args) throws SQLException, ClassNotFoundException, IOException{
List<City> cities=new ArrayList<City>();
//准备去查数据库
Jdbctools jt=new Jdbctools();
Connection ct=null;
ct=jt.getConnection();
PreparedStatement ps=null;
ResultSet rs=null;
ps=ct.prepareStatement(sql);
for(int i=0;i<args.length;i++){
ps.setObject(i+1, args[i]);
}
rs=ps.executeQuery();
while(rs.next()){
cities.add(new City(rs.getInt("city_id"),rs.getString("city_name")));
}
jt.shifanglianjie(ct, ps, rs);
return cities;

}
public List<County> getcounty(String sql,Object...args ) throws SQLException, ClassNotFoundException, IOException{
List<County> counties=new ArrayList<County>();
//准备去查数据库
Jdbctools jt=new Jdbctools();
Connection ct=null;
ct=jt.getConnection();
PreparedStatement ps=null;
ResultSet rs=null;
ps=ct.prepareStatement(sql);
for(int i=0;i<args.length;i++){
ps.setObject(i+1, args[i]);
}
rs=ps.executeQuery();
while(rs.next()){
counties.add(new County(rs.getInt("county_id"),rs.getString("county_name")));
}
jt.shifanglianjie(ct, ps, rs);
return counties;

}
}
c3p0-config.xml的代码如下：
[html] view plain copy
<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
<named-config name="helloc3p0">
<!-- 连接数据源的基本属性 -->
<property name="user">root</property>
<property name="password"></property>
<property name="driverClass">com.mysql.jdbc.Driver</property>
<property name="jdbcUrl">jdbc:mysql:///thereaction</property>

<!-- 若数据库中连接数不足时，一次向数据库服务器申请多少个连接 -->
<property name="acquireIncrement">5</property>
<!-- 初始化数据库连接池时连接的数量 -->
<property name="initialPoolSize">5</property>
<!-- 数据库连接池中的最小的数据库连接数 -->
<property name="minPoolSize">5</property>
<!-- 数据库连接池中的最大的数据库连接数 -->
<property name="maxPoolSize">10</property>
<!-- c3p0数据库连接可以维护的statement的个数 -->
<property name="maxStatements">20</property>
<!-- 每个连接同时可以使用的statement对象的个数 -->
<property name="maxStatementsPerConnection">5</property>
</named-config>
</c3p0-config>

创建servlet.java 文件
[java] view plain copy
package com.xiaojie.servlet;

import java.io.IOException;
import java.lang.reflect.Method;
import java.sql.SQLException;
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 com.fasterxml.jackson.databind.ObjectMapper;
import com.xiaojie.beans.City;
import com.xiaojie.beans.County;
import com.xiaojie.beans.Province;
import com.xiaojie.dao.DAO;
/**
* Servlet implementation class ThreeactiondServlet
*/
@WebServlet("/threeactiondServlet")
public class ThreeactiondServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String methodname=request.getParameter("method");
try {
Method method=getClass().getDeclaredMethod(methodname,HttpServletRequest.class,HttpServletResponse.class);
method.invoke(this, request,response);//调用各自的方法
} catch (Exception e) {
e.printStackTrace();
}
}
private DAO dao=new DAO();
protected void province(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, ClassNotFoundException, SQLException {
System.out.println("province的servlet进入了");
String sql="select province_id,province_name from province";
List<Province> provinces=dao.getprovince(sql);
request.setAttribute("provinces", provinces);
System.out.println(provinces);
//注意：这里不能用重定向的形式，因为我们好不容易在request请求域中存储了省的信息，目的是在前台页面中能够从请求域中获取到我们存在数据库中的值
//故这里只能用转发的方式
request.getRequestDispatcher("/index2.jsp").forward(request, response);
}
protected void city(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, ClassNotFoundException, SQLException {
System.out.println("city的servlet进入了");
String province_id=request.getParameter("province_id");
String sql="select city_id,city_name from city where province_id=?";
List<City> cities=dao.getcity(sql,Integer.parseInt(province_id));
ObjectMapper mapper=new ObjectMapper();
String result=mapper.writeValueAsString(cities);
System.out.println(result);
response.setContentType("text/javascript");
response.getWriter().print(result);
}
protected void county(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, ClassNotFoundException, SQLException {
System.out.println("county的servlet进入了");
String city_id=request.getParameter("city_id");
String sql="select county_id,county_name from county where city_id=?";
List<County> counties=dao.getcounty(sql,Integer.parseInt(city_id));
ObjectMapper mapper=new ObjectMapper();
String result=mapper.writeValueAsString(counties);
System.out.println(result);
response.setContentType("text/javascript");
response.getWriter().print(result);
}
}