java 数据可视化（二）通过jdbc访问数据库，在servlet上获取数据库数据

想要通过servlet获取数据库数据，首先需要创建jdbc
因为数据是通过无线传感传到数据库的，因此jdbc里只有查询操作，增删改的同学可以自行添加。
代码中被注释掉的部分用于测试。

• main函数部分用于检测是否连接上数据库，并检测是否能读到数据，若是读得到就在后台打印
• 构造函数部分用于创建jdbc类后，检查是否能从数据库读到数据

package com.jdbc;

import com.jdbc.Data;
import java.sql.*;


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;

public class jdbc {

	final static String USERNAME = "root";
	final static String PASSWORD = "";
	final static String DRIVER = "com.mysql.jdbc.Driver";
	final static String URL = "jdbc:mysql://localhost:3306/test1";
	static Connection connection;
	/*public static void main(String[] args) throws SQLException {


	        try {
	            Class.forName(DRIVER);
	            System.out.println("Register driver success");
	        } catch (ClassNotFoundException e) {
	            // TODO Auto-generated catch block
	            System.out.println("Register driver failure");
	        }

            connection=getConnection();
	        String sql = "select * from testtable2t";
	        List<Data> result = getData(sql);
	        int i = 0;
	        for(Data a:result) {
	        	String aaa =(String)a.time;
	        	String bbb = (String)a.power;
	        	//*time[i] = aaa;*//*
	        	//*power1[i] = bbb;*//*
				System.out.println(aaa);
				System.out.println(bbb);
	        	i++;
	        }}*/

	public jdbc() throws SQLException {
		try {
			Class.forName("com.mysql.jdbc.Driver");
			System.out.println("Register driver success");
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			System.out.println("Register driver failure");
		}

		connection=getConnection();
		       /* String sql = "select * from testtable2t";
		        List<Data> result = getData(sql);
		        int i = 0;
		        for(Data a:result) {
		        	String aaa =(String)a.time;
		        	String bbb = (String)a.power1;

		        	System.out.println(time[i]);
		        	power1[i]= (String)bbb;
		        	i++;
		        }*/
	}

	public static Connection getConnection() {

		try {
			connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);

		} catch (Exception e) {
			// TODO: handle exception
			System.out.println("Connection exception !");
		}

		return connection;

	}
	public static ArrayList<Data> getData(String sql) throws SQLException{
		ArrayList<Data> result = new ArrayList<Data>();
		Statement statement=null;
		statement=connection.createStatement();
		ResultSet rs = statement.executeQuery(sql);
		Data time  = null;
		while(rs.next()) {
			time= new Data();
			time.time=rs.getString("time");
			time.power=rs.getString("pulse");

			result.add(time);
		}
		return result;
	}
}

其中用于接受数据的data类构造如下：

package com.jdbc;

public class Data {
    public String time;
    public String power;
    public void setTime(String time){
        this.time = time;
    }
    public String getTime(){
        return this.time;
    }
    public void setPower(String power){
        this.power = power;
    }
    public String getPower(){
        return this.power;
    }
}

jdbc创建好后，便可以在servlet中通过jdbc获取数据库数据了
servlet创建jdbc类获取数据并打印，代码段如下：

       request.setCharacterEncoding("utf-8");
       ArrayList<Data> result = null;
        jdbc DataBase = null;
        try {
            DataBase = new jdbc();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        String sql = "select * from testtable2t";
        try {
            result = DataBase.getData(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        System.out.println(result);
    ```
    若是连接成功变更在后台看到数据啦。