·按照地市统计最受欢迎的Top10课程 (ip)

Dao层

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package echart;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
 
public class barDAO {
    public ArrayList<barBean> select_all() {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rst = null;
        try {
            conn = DBUtil.getConnection();
            stmt = conn.createStatement();
            String sql = "select * from abc limit 10";
            rst = stmt.executeQuery(sql);
            ArrayList<barBean> array = new ArrayList<barBean>();
            while (rst.next()) {
                barBean bar = new barBean();
                bar.setName(rst.getString("name"));
                bar.setNum(rst.getInt("num"));
                array.add(bar);
            }
            stmt.close();
            rst.close();
            return array;
 
        } catch (SQLException e) {
            System.out.println("Error occured at barDAO->select_all()");
            return new ArrayList<barBean>();
        }
    }
}

  servlet层

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package echart;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import net.sf.json.JSONArray;
 
public class helloBar extends HttpServlet {
 
     
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
 
        //创建了一个bardao的对象,barDAO主要是对数据库的连接和对数据库的操作
        barDAO bardao=new barDAO();
        //调用bardao的select_all()方法把从数据库中读取所有的数据返回的是一个ArrayList,ArrayList里面放的是一个barBean
        ArrayList<barBean> array = bardao.select_all();
        //设置返回时的编码格式
        response.setContentType("text/html; charset=utf-8");
        //调用JSONArray.fromObject方法把array中的对象转化为JSON格式的数组
        JSONArray json=JSONArray.fromObject(array);
        System.out.println(array.toString());
        //返回给前段页面
        PrintWriter out = response.getWriter(); 
        out.println(json); 
        out.flush(); 
        out.close();  
         
    }
}

  配置xml文件:

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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>echart</display-name>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>helloBar</servlet-name>
    <servlet-class>echart.helloBar</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>helloBar</servlet-name>
    <url-pattern>/bar.do</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

  截图: