JDBC (IV)

1. Concept Overview

## JDBC:
	1.  Concept ： Java Database Connectivity. java Database connection ,java Language operation database .
	* JDBC The essence ：  official （sun company ） Defined set of operations all   Relational type   Database rules , Interface . Each database manufacturer to implement this set of interface , Provide database driver jar package . We can use this interface (jdbc) Programming , The code that actually executes is the driver jar The implementation class in the package .

	2.  Quick start ：
		*  step ：
			1.  Import driver jar package   mysql-connector-java-5.1.37-bin.jar
				1.  Copy mysql-connector-java-5.1.37-bin.jar To the project libs Under the table of contents 
				2.  Right click -->Add as Library
			2.  Registration drive 
			3.  Get database connection object Connection
			4.  Definition sql
			5.  Access to perform sql Object of statement  Statement
			6.  perform sql, Accept the return result 
			7.  Processing results 
			8.  Release resources 
		*  Code implementation ：
			//1. Import driver jar package 
		        //2. Registration drive 
        		Class.forName("com.mysql.jdbc.Driver");
		        //3. Get database connection object 
        		Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3", "root", "root");
        		//4. Definition sql sentence 
        		String sql = "UPDATE  account set balance = 500 where id = 1";
			//5. Access to perform sql The object of statement
        		Statement stmt = conn.createStatement();
        		//6. perform sql
        		int conunt = stmt.executeUpdate(sql);
        		//7. Processing results 
        		System.out.println(conunt);
        		//8. Release resources 
        		stmt.close();
        		conn.close();
	3.  Explain the objects in detail 
		1. DriverManager:  Drive management objects 
			*  function ：
			1.  Registration drive ： Tell the program which database driver to use jar
				static void registerDriver(Driver driver) : Register with given driver  DriverManager . 
				 Write code using ：  Class.forName("com.mysql.jdbc.Driver");
				 Discover by looking at the source code ： stay com.mysql.jdbc.Driver Class has static code blocks 
				 static {
				        try {
				            java.sql.DriverManager.registerDriver(new Driver());
				        } catch (SQLException E) {
				            throw new RuntimeException("Can't register driver!");
				        }
					}

				 Be careful ：mysql5 After the drive jar Packages can omit the steps of registering drivers .
			2.  Get database connection ：
				*  Method ： static connection getConnection(String url, String user, String password);
				*  Parameters ：
					* url：  Specify the path of the connection 
						*  grammar ： jdbc:mysql://ip Address （ domain name ）： Port number / Database name 
					* user:  user name 
					* password:  password 
		2. Connection:  Database connection object 
			1.  function ：		
				1.  Access to perform sql The object of 
					* Statement createStatement()
					* PreparedStatement prepareStatement(String sql)
				2.  Manage affairs ：
					*  Open transaction ： setAutoCommit(boolean autoCommit):  Call this method to set parameters false, That is, start the transaction .
					*  Commit transaction ： commit()
					*  Roll back the transaction ： rollback()
		3. Statement:  perform SQL The object of 
			1.  perform SQL
				1. boolean execute(String sql):  You can do whatever you want sql （ understand ）
				2. int executeUpdate(String sql):  perform DML（insert,update,delete） sentence 、DDL（create,alter,drop） sentence .
					*  Return value ：  Number of rows affected , It can be judged by the number of rows affected DML Is the statement executed successfully , Return value >0 Is successful , conversely , Failure .
				3. ResultSet executeQuery(String sql):  perform DQL(select) sentence .

			2.  practice ：  Additions and deletions 
				 Template code ：
package cn.itcast.jdbc;
import com.mysql.jdbc.Driver;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class jdbcDemo2 {
    public static void main(String[] args) {
        Statement stmt = null;
        Connection conn = null;
        try {
            //1. Registration drive 
            Class.forName("com.mysql.jdbc.Driver");
            //2. Definition sql
            String sql = "insert into account values(2,'zhang3',3000)";
            //3. obtain Connection object 
            conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
            //4. Access to perform sql object  statement
            stmt = conn.createStatement();
            //5. perform sql
            int count = stmt.executeUpdate(sql);
            System.out.println(count);
            if (count > 0){
                System.out.println("successful");
            }else{
                System.out.println("fail");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            // Avoid null pointer release exceptions 
            if (stmt!=null){
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(conn != null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}
				
		4. ResultSet:  Result set object , Encapsulate query results .
			* boolean next():  Move the cursor down one line , Determine whether the current line is the end of the last line （ Is there any data ）, If it is , Then return to false, If not, return true.
			* getXXX( Parameters )：  get data 
				* XXX：  Representative data type 	 Such as ： int getInit()
				*  Parameters ：
					1. int:  Represents the number of the column , from 1 Start . 
					2. String:  Represents the name of the column .
			
			*  Be careful ：
				*  Use steps ：
					1.  Move the cursor down one line 
					2.  Judge whether there is data 
					3.  get data 
		5. PreparedStatement：  perform SQL object 
			1. SQL Injection problem ：  In splicing sql when , Somewhat sql Special keywords participate in string splicing . It will cause safety problems .

			2.  solve sql Injection problem ：  Use PreparedStatement Object to solve .
			3.  precompile SQL：  Parameters use ？ As   Place holder .
			4.  step ：
				1.  Import driver jar package   mysql-connector-java-5.1.37-bin.jar
						1.  Copy mysql-connector-java-5.1.37-bin.jar To the project libs Under the table of contents 
						2.  Right click -->Add as Library
				2.  Registration drive 
				3.  Get database connection object Connection
				4.  Definition sql
					*  Be careful ： sql Parameter usage of ？ As placeholder .  Such as ： select * from user where user = ? and passwd = ?;
				5.  Access to perform sql Object of statement :  PreparedStatement Connection.preparedStatement(String sql);
				6.  to ？ assignment ：
					*  Method ： setXXX( Parameters 1, Parameters 2)
						*  Parameters 1： ? Location number of , from 1 Start .
						*  Parameters 2： ? Value .
				7.  perform sql, Accept the return result , There is no need to pass on sql sentence 
				8.  Processing results 
				9.  Release resources 
			5.  Be careful ：  It will be used later PreparedStatement To complete all operations of addition, deletion, modification and query 
				1.  Can prevent SQL Inject 
				2.  More efficient 
 
##  extract JDBC Tool class ： JDBCUtils
	*  Purpose ：  Simplify writing 
	*  analysis ：
		1.  Registration drivers also extract 
		2.  Extract a method to get the connection object 
			*  demand ：  Don't want to pass parameters （ trouble ）,  We also need to ensure the universality of tool class .
			*  solve ：  The configuration file 
				jdbc.properties
					url=
					user=
					password=
		3.  Extract a method to release resources 
	*  Code implementation ：

import com.mysql.jdbc.Driver;

import java.sql.*;

public class jdbcDemo4 {
    public static void main(String[] args) {
        Statement stmt = null;
        Connection conn = null;
        ResultSet rs =null;
        try {
            //1. Registration drive 
            Class.forName("com.mysql.jdbc.Driver");
            //2. Definition sql
            String sql = "select * from account";
            //3. obtain Connection object 
            conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
            //4. Access to perform sql object  statement
            stmt = conn.createStatement();
            //5. perform sql
            rs = stmt.executeQuery(sql);
           rs.next();
           int id = rs.getInt(1);
           String name = rs.getString("name");
            int balance = rs.getInt(3);
            System.out.println(id+ name+ balance);

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            // Avoid null pointer release exceptions 
            if (rs !=null){
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(conn != null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

	*  practice 
		*  demand ：
                 1.  Enter the user name and password through the keyboard 
                 2.  Determine whether the user has successfully logged in 
package cn.itcast.jdbc;

import cn.itcast.utils.JDBCUtils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;

/**
 *  practice 
 *      *  demand ：
 *              1.  Enter the user name and password through the keyboard 
 *              2.  Determine whether the user has successfully logged in 
 */
	*  step ：
		1.  Create database tables 
 create table user(
       id int primary key auto_increment,
       username varchar(32),
       password varchar(32));
		2. Realization 
public class JDBCDemo9 {
    public static void main(String[] args) {
    //1. Keyboard Entry ,  Accept user name and password 
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter a user name ");
        String username = sc.nextLine();
        System.out.println(" Please input a password ");
        String password = sc.nextLine();
        //2. Calling method 
        boolean flag = new JDBCDemo9().login(username, password);
        //3. Judge the result 
        if (flag){
            System.out.println("successful");
        }else{
            System.out.println("fail...");
        }
    }

    // Login method 
    public boolean login(String username, String password){
        if(username == null || password == null){
            return false;
        }
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        // Connect to database , Judge success 
            //1. For a link 
        try {
            conn = JDBCUtils.getConnection();
            //2. Definition sql
            String sql = "select * from user where username = '"+ username +"' and password = '"+password+"'";
            //3. Access to perform sql The object of 
            stmt = conn.createStatement();
            //4. perform sql
            rs = stmt.executeQuery(sql);
            //5. Judge 
            return  rs.next();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs,stmt,conn);
        }
        return false;
    }
}

## JDBC Control the transaction ：
	1.  Business ：  A business operation with multiple steps .  If the business operation is managed by a transaction , Then these multiple steps will either succeed at the same time , Or fail at the same time .
	2、  operation ：
		1.  Open transaction 
		2.  Commit transaction 
		3.  Roll back the transaction 
	3.  Use Connection Object to manage affairs 
		*  Open transaction ： setAutoCommit(boolean autoCommit):  Call this method to set parameters false, That is, start the transaction .
			*  In execution sql Before opening the transaction 
		*  Commit transaction ： commit()
			*  When all sql All commit transactions are completed 
		*  Roll back the transaction ： rollback()
			*  stay catch Rollback transaction 
##  Database connection pool 
	1.  Concept ：  It's actually a container （ aggregate ）, Container for database connection .
		 When the system is initialized , Easy to create , Some connection objects will be applied for in easy , When the user comes to access the database , Get the connection object from the container , After the user visits , The connection object is returned to the container .
	2.  benefits ： 
		1.  Saving resource 
		2.  Efficient user access 
	3.  Realization ：
		1.  Standard interface ： DataSource	javax.sql Under bag 
			1.  Method ：
				*  Get the connection ： getConnection()
				*  Return connection ： Connection.close(). If the connection object Connection It's taken from the connection pool , So called Connection.close() Method , The connection will no longer be closed , But return the connection .

		2.  Generally we don't realize it ,  There are database vendors to implement .
			1. C3P0：  Database connection pool technology 
			2. Druid:  Database connection pool implementation technology ,  Provided by Alibaba 
			
	4. C3P0：  Database connection pool 
		*  step ：
			1.  Import jar package ： （ Two ）c3p0-0.9.5.2.jar、mchange-commons-java-0.2.12.jar
				*  Be careful ：  Don't forget to import database drivers jar package 
			2.  Define configuration file ：
				*  name ： c3p0.properties  Or  c3p0-config.xml
				*  route ：  Put the document directly in  src  Under the directory .
			3.  Create core objects   Database connection pool object  ComboPooledDataSource
			4.  Get the connection ： getConnection

 	5. Druid:  Database connection pool implementation technology ,  Provided by Alibaba 
		1.  step ：
			1.  Import jar package  druid-1.0.9.jar
				*  Be careful ：  Don't forget to import database drivers jar package 
			2.  Define configuration file ：
				*  yes properties Formal 
				*  You can call it anything , It can be placed in any directory 
			3.  Load profile .Properties
			4.  Get database connection pool object ：  Get through the factory class  DruidDataSourceFactory
			5.  Get the connection ： getConnection
		2.  Define a class 
			1.  Define a class JDBCUtils
			2.  Provide static code block loading configuration file , Initialize connection pool object 
			3.  Provide methods 
				1.  Get the connection method ：  Get the connection through the database connection pool 
				2.  Release resources 
				3.  How to get the connection pool 

## Spring JDBC
	* Spring Frame pair JDBC Simple encapsulation . Provides a JDBCTemplate Object simplification JDBC Development of 
	*  step ： 
		1.  Import jar package 
		2.  establish JDBCTemplate object . Depending on the data source DataSource
			* JdbcTemplate template = new JdbcTemplate(ds);
		3.  call JdbcTemplate To complete CRUD The operation of 
			* update():  perform DML sentence .  Add, delete, or change statements .
			* queryForMap():  Query results encapsulate the result set as map aggregate , Name as key, Take the value as value, Encapsulate this record as a map aggregate 
				*  Be careful ：  The result set length of this method query can only be 1
			* queryForList():  Query results encapsulate the results as List aggregate 
				*  Be careful ：  Encapsulate each record as a Map aggregate , then Map The collection is loaded into List Collection .
			* query():  Query results , Encapsulate the result as JavaBean object 
				* query Parameters of ： RowMapper
					*  Generally we use BeanPropertyRowMapper Implementation class . Can complete data to JavaBean Automatic encapsulation of .
					* new BeanPropertyRowMapper< type >( type .class)
			* queryForObject:  Query results ,  Encapsulate the results as objects 
				*  Commonly used in   Aggregate functions   Query for