Another: Preparations
Computer to install MySQL, MySQL installation visualization tools Workbench, create a good database.
A: connect to the database
Related jar package --1-- introduced mysql: mysql-connector-jar (manual procedure in another article package guide)
--2-- load the driver
By --3-- Connection class, fill the database to be connected to the basic information
package jdbc; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; /** * Created by Seadragon on 2019-12-26. */ public class JdbcConnect { public static void main(String[] args) throws ClassNotFoundException { Connection connection = null; Statement statement = null; try { //初始化驱动，加载驱动 Class.forName ( "com.mysql.jdbc.Driver" ); // Connection object's connection, fill in the information to be connected to the database. Connection-related database Connection = DriverManager.getConnection ( "? Jdbc: MySQL: //127.0.0.1: 3306 / ksea characterEncoding = UTF-8" , "root", "root" ); System.out.println ( "connection success: "+ connection.toString ()); // create sql statements related objects of statement of statement = Connection.createStatement (); System.out.println ( " get sql statement object: "+ of statement); // prepare the relevant sql statement // increment primary key positions can send NULL String sql = "; Int I = 100 ; the while (I = 0! ) { Statement.execute (SQL); I - ; } } the catch (SQLException E) { e.printStackTrace (); } the finally { // close the connection, the release of resources / / closed first statement, then off Connection IF (Statement =! null ) { the try { Statement.close (); } the catch (SQLException E) { e.printStackTrace (); } } if (connection!=null) { try { connection.close(); } catch (SQLException e) { e.printStackTrace(); } } System.out.println("关闭："+statement+"----"+connection); } } }
II: database operations
Connection object is used to connect the database
--1-- calling method to invoke mysql driver class, DriverManager.getConnection (url)
Statement object is used to operate the sql statement,
--1-- created: connection.createStatement
--2-- execution: executeQuery () [perform a query returns a ResultSet object]; execute [Update additions, can be queried by getResultSet, returns a Boolean]; executeUpdate [not query that returns the data is affected data several]
ps: sql statement from growth can be used instead of null
PreparedStatement Statement for the upgraded version, sql statement can be abbreviated, fast speed precompiled mechanism can prevent sql injection attacks
--1 - sql injection attacks: sql statement structure changes, for example: splicing "sql" + "or 1 = 1", that statement is executed unlimited
--2 - PreparedStatement only the set value, and perform pre-compiled into two phases, and can not be changed sql structure, it can inject the defense
package jdbc; import java.sql.*; /** * Created by Seadragon on 2019-12-26. */ public class JdbcPreparedStatemen { public static void main(String[] args) throws ClassNotFoundException, SQLException { Class.forName("com.mysql.jdbc.Driver"); Connection connection = null; Statement statement = null; String sql_preState = "insert into hero values(null,?,?)"; String sql_state = "insert into hero VALUES (null,"+"'提莫',"+12+")"; //执行sql语句的两种方式 connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/ksea?","root","root"); statement = connection.createStatement(); PreparedStatement preparedStatement = connection.prepareStatement(sql_preState); statement.execute(sql_state); preparedStatement.setString(1,"提莫pre"); preparedStatement.setInt(2,1233); preparedStatement.execute(); } }
Three: database metadata
That database name, which some basic data tables, which are to get through the DatabaseMetaData object, calls the method getMetaData
package jdbc; import java.sql.*; /** * Created by Seadragon on 2019-12-27. */ public class getMetaData { public static void main(String[] args) throws SQLException, ClassNotFoundException { Class.forName("com.mysql.jdbc.Driver"); Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/ksea?","root","root"); DatabaseMetaData databaseMetaData = connection.getMetaData(); System.out.println(databaseMetaData.getDatabaseProductName()); System.out.println(databaseMetaData.getDatabaseProductVersion()); } }
Four: Transaction
That is to perform several sql statements packaged together, if only all the successful implementation of the implementation, if not a whole fails to perform. Close approach of automatically submit to manual submission.
--1---
connection.setAutoCommit(false)
{sql}
connection.commit()
package jdbc; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; /** * Created by Seadragon on 2019-12-27. */ public class JdbcTransaction { public static void main(String[] args) throws ClassNotFoundException, SQLException { Class.forName("com.mysql.jdbc.Driver"); Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/ksea?","root","root"); Statement statement = connection.createStatement(); connection.setAutoCommit(false); String sql = "insert into user values(NULL,"+"'kkk',"+"'12345'"+")"; String sql_false = "insert into rrrr values(NULL,"+"'kkk',"+"'12345'"+")"; statement.execute(sql); statement.execute(sql_false); connection.commit(); System.out.println("你是否要删除该数据"); } }
Five: ORM
Object mapping data, i.e. to each of the data with a database object map database package I would be understood in java
package jdbc; import hero.Hero; import jdbc.*; import java.security.PublicKey; import java.sql.*; /** * Created by Seadragon on 2019-12-27. */ public class JdbcORM { public static void main(String[] args) throws ClassNotFoundException, SQLException { Hero hero = get(3); Hero hero_add = new Hero("男枪",12); add(hero_add); delete("男枪"); update(1); System.out.println(hero.getName()+":"+hero.getPrice()); } public static Connection connectMysql() throws ClassNotFoundException, SQLException { Class.forName("com.mysql.jdbc.Driver"); Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/ksea?","root","root"); return connection; } //ID查询 public static Hero get(int id) throws ClassNotFoundException, SQLException { Hero hero = null; Connection connection = connectMysql(); Statement statement = connection.createStatement(); String sql = "select * from hero where idHero = "+id; ResultSet resultSet = statement.executeQuery(sql); while (resultSet.next()){ hero = new Hero(); String name = resultSet.getString("name"); int price = resultSet.getInt("price"); hero.setName(name); hero.setPrice(price); } return hero; } //add方法 public static void add(Hero hero) throws ClassNotFoundException, SQLException { Connection connection = connectMysql(); String sql = "insert into hero values(null,?,?)"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1,hero.getName()); preparedStatement.setInt(2,hero.getPrice()); preparedStatement.execute(); } //delete方法 public static void delete(String heroname) throws SQLException, ClassNotFoundException { Connection connection = connectMysql(); String sql = "DELETE FROM hero WHERE NAME = ?"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1,heroname); preparedStatement.execute(); } //update public static void update(int id) throws SQLException, ClassNotFoundException { Connection connection = connectMysql(); String sql = "UPDATE hero SET name = ?,price = ? WHERE idHero = ?"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1,"修改的英雄名称"); preparedStatement.setInt(2,1234); preparedStatement.setInt(3,id); preparedStatement.execute(); } }
Six: Connection Pooling
Create a database to create a connection and reduce time to close connections, create a connection pool, which opened the n connection is never closed.
If desired connect to the database, the application to the connection pool, the pool has an idle connection if the connection is to it; but is not directly returned to the pool closed in the idle state after using the connection.
Involving multi-threaded related
package jdbc; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; /** * Created by Seadragon on 2019-12-28. */ public class JdbcConnectionPool { List<Connection> connections = new ArrayList<Connection>(); int size; public JdbcConnectionPool(int size) throws SQLException, ClassNotFoundException { this.size=size; init(); } public void init() throws ClassNotFoundException, SQLException { Class.forName("com.mysql.jdbc.Driver"); for (int i = 0;i<size;i++) { Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/ksea?", "root", "root"); connections.add(connection); } } public synchronized Connection getConnection() throws InterruptedException { while (connections.isEmpty()){ this.wait(); } Connection connection = connections.remove(0); return connection; } public synchronized void returnConnection(Connection connection){ connections.add(connection); this.notifyAll(); } }