JDBC tool class jdbcconutil gets the connection to the database

  One 、JDBC Tool class for connecting to database

package com.jdbc.utils;

/*  Connect to database tool 
	1、 Registration drive 
	2、 Connect to database 
	3、 Close the connection 
*/
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JdbcConUtil {
	private static String driver;
	private static String url=null;
	private static String username=null;
	private static String password=null;
	// These are all to be used by the whole website in the future , All static variables or static code blocks , Once loaded , Global use 
  private static Properties pro=new Properties(); // Ready to read the configuration file , Creating configuration objects 
	static {
		FileInputStream is=null;
	 try {   
		  
//		 is=new FileInputStream(new File("D:\\【1】 School professional courses \\ Junior year \\Web Back end development technology \\workspace\\Jdbc\\src\\com\\jdbc\\utils\\jdbc.properties"));
		 is=new FileInputStream(new File("jdbc.properties"));
		// is=class.getResourceAsStream(new File("jdbc.properties"));
	 }
	 catch (FileNotFoundException e) { System.out.println(e.toString()); e.printStackTrace();
		// TODO: handle exception
	}
	 try {   pro.load(is); // Load files from disk , It should be set according to the specific folder where your configuration file is stored , If you're confused, use the absolute path 		 
	 }
	 catch (IOException e) {System.out.println(e.toString()); e.printStackTrace();
		// TODO: handle exception
	}
	 // See if you can read the parameters in the file 
	 driver=pro.getProperty("driverClass");
	 url=pro.getProperty("url");
	 username=pro.getProperty("username");
	 password=pro.getProperty("password");
//	 System.out.println(" from mysql Data obtained from the configuration file "+driver+url+username+password);
	 try {
	  Class.forName(driver);// take mysql Driver registered to DriverManager In the middle 
	  
	 }
	 catch (ClassNotFoundException e) {System.out.println(e.toString());e.printStackTrace();
	 
		// TODO: handle exception
	}	}
	// The following is the connection method for external access 
public static   java.sql.Connection   getConnection() { // notes , It can't be mysql Of , yes java.sql Of 
		java.sql.Connection con1=null; // The parent class is wrong , You can't go back 		  
		  try {
			  con1=DriverManager.getConnection(url, username, password);// get mysql The connection of 
		  }
		  catch (SQLException e) { System.out.println(e.toString());e.printStackTrace();
			// TODO: handle exception
		}
		  return con1;
		
	}
	// Release resources 
	public static void close(ResultSet rs,Statement st,Connection conn)// When querying, use 
	{ if(rs!=null) try {rs.close();}catch (SQLException e) {
		// TODO: handle exception
	}
	 if(st!=null) try {st.close();}catch (SQLException e) {
		// TODO: handle exception
	}
	 if(conn!=null) try {conn.close();}catch (SQLException e) {
		// TODO: handle exception
	}		
	}
	public static void close(Statement st,Connection conn) // Use... In non query mode 
	{  	 if(st!=null) try {st.close();}catch (SQLException e) {
		// TODO: handle exception
	}
	 if(conn!=null) try {conn.close();}catch (SQLException e) {
		// TODO: handle exception
	}		
	}
	}

Two 、 The configuration file jdbc.properties

username=root
password=123456
url=jdbc:mysql://localhost:3306/xs
driverClass=com.mysql.jdbc.Driver

3、 ... and 、MySQL Driver download of connector

https://pan.baidu.com/s/1ygZ5H9gospSXItc4xqEQag?pwd=6666 
Extraction code ：6666

Four 、 stay servlet Demonstrate the use of this tool class

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// The unified code is set to utf-8		
        request.setCharacterEncoding("UTF-8");
	    response.setContentType("text/html;Charset=UTF-8");
// Get the student number or gender from the front end 
	    String frontdata=request.getParameter("querydata");
	    System.out.println(" The data to be queried "+frontdata);
		
		String sql0="select * from student";
		Connection con1=(Connection) JdbcUtil.getConnection();
		ResultSet rs1=null;
		Statement st1 = null;
		try {
				st1 = (Statement) con1.prepareStatement(sql0);
			} catch (SQLException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
		try {
				rs1=st1.executeQuery(sql0);
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

// Output data test 
		try {	
			    while(rs1.next()) 
               // As long as you haven't finished reading . You can also navigate to a certain line . Use for It's OK to cycle 
			{  // Start outputting student data information 
					 String xs = ""; 
					 String xh=rs1.getString(1);
					//1=== If you query the student number and the rs The first data pointed to is the same , The query is successful   
					 if (frontdata.equals(xh)) {
						 for(int i=1;i<=rs1.getMetaData().getColumnCount();i++)
						 {// A loop outputs a student information  System.out.print(rs1.getString(i)+"  ");
							if(i==5) {
								 xs=xs+rs1.getString(i)+"*"; 
								 }
							else {
									 xs=xs+rs1.getString(i)+"|";
								}
							  } 
							System.out.println(" The student ID is :"+frontdata+" Of the students ------"+xs); 
							PrintWriter out1=response.getWriter();
							out1.println(xs); 
							out1.close();
						}
						 String xb=rs1.getString(5);
						 //2=== If gender equals male, output the student 
						 if(frontdata.equals(xb)) {
							for(int i=1;i<=rs1.getMetaData().getColumnCount();i++)
							  {// A loop outputs a student information  System.out.print(rs1.getString(i)+"  ");
								 if(i==5) {
									 xs=xs+rs1.getString(i)+"*"; 
								 }
								 else {
									 xs=xs+rs1.getString(i)+"|";
								} 
							  } 
								System.out.println(" The query gender is :"+frontdata+" Of the students -----"+xs); 
								PrintWriter out1=response.getWriter();
								out1.println(xs); 		 
						 }
					   }
				} catch (SQLException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			JdbcUtil.close(rs1,st1,con1);

	}