/** 通过Java连接MySQL数据库。*/
package day23;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;public class ConnectionTest {public static void main(String[] args) {Connection con = null;Statement st = null;try {// 可以创建驱动类的对象来令驱动类初始化，只是创建// 的对象是多余的（根本不使用该对象）// new com.mysql.jdbc.Driver();// 加载并初始化驱动类。Class.forName("com.mysql.jdbc.Driver");// 获得数据库的连接，返回Connection接口类型的对象。con = DriverManager.getConnection("jdbc:mysql://000.0.0.0:3306/test?useSSL=false", "root", "");// System.out.println(con);// 创建可执行的sql语句。st = con.createStatement();// 执行更新语句。返回受影响的记录数。int count = st.executeUpdate("insert into student(id, name) values (8, '新增')");System.out.println(count);} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();} finally {// 资源释放的顺序：// 先创建的后释放，后创建的先释放。if (st != null) {try {st.close();} catch (SQLException e) {e.printStackTrace();}}if (con != null) {try {con.close();} catch (SQLException e) {e.printStackTrace();}}}}
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class TryWithResources {public static void main(String[] args) {try {Class.forName("com.mysql.jdbc.Driver");} catch (ClassNotFoundException e) {e.printStackTrace();}try (Connection con = DriverManager.getConnection("jdbc:mysql://***.0.0.1:3306/test?useSSL=false", "root", "");Statement st = con.createStatement();ResultSet rs = st.executeQuery("select id, name, age, sex from student");) {

// 判断是否有下一条记录，如果存在，返回true，同时
                                              // 移动游标（指针），使其指向下一条记录。如果不存在，
                                              // 返回false。

         while (rs.next()) {

// 根据字段的索引获得当前记录该字段的值。索引从1开始。
                                                  // int id = rs.getInt(1);
                                               // 根据字段的名字获得当前记录该字段的值。
                                                int id = rs.getInt("id");
                                                String name = rs.getString("name");
                                                 int age = rs.getInt("age");
                                                 String sex = rs.getString("sex");

            }} catch (SQLException e) {e.printStackTrace();}}}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class DBUtil {public static Connection getConnection() {Connection con = null;try {Class.forName("com.mysql.jdbc.Driver");con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test?useSSL=false", "root", "");} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}return con;}public static void release(ResultSet rs, Statement st, Connection con) {if (rs != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (st != null) {try {st.close();} catch (SQLException e) {e.printStackTrace();}}if (con != null) {try {con.close();} catch (SQLException e) {e.printStackTrace();}}}
}

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.Statement;public class PreparedTest {public static void main(String[] args) {}public void insert(int id, String name, int age, String sex) {try (Connection con = DBUtil.getConnection(); Statement st = con.createStatement();) {String sql = "insert into student(id, name, age, sex) values (" + id + ", '" + name + "'," + age + ",'"+ sex + "')";StringBuilder bu = new StringBuilder();bu.append("insert into student(id, name, age, sex) values (").append(id).append(",'").append(name).append("',").append(age).append(",'").append(sex).append("')");st.executeUpdate(sql);} catch (SQLException e) {e.printStackTrace();}}/** PreparedStatement与Statement* PreparedStatement是预处理的SQL语句对象，当重复* 执行时，PreparedStatement在性能上可能会好于* Statement（这要取决于底层数据库是否支持预处理）。* PreparedStatement在程序的可读性上，也好于* Statement，因此，我们应该总是有限的考虑使用* PreparedStatement。*/public void insert2(int id, String name, int age, String sex) {try (Connection con = DBUtil.getConnection();PreparedStatement ps = con.prepareStatement("insert into student(id, name, age, sex) values(?,?,?,?)")) {ps.setInt(1, id);ps.setString(2, name);ps.setInt(3, age);ps.setString(4, sex);ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();}}}

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;public class Transaction {public static void main(String[] args) {Connection con = DBUtil.getConnection();try (PreparedStatement ps1 = con.prepareStatement("update account set money = money - 100 where id = 1");PreparedStatement ps2 = con.prepareStatement("updatedd account set money = money + 100 where id = 2");) {// 将自动提交设置为假。con.setAutoCommit(false);ps1.executeUpdate();ps2.executeUpdate();// 事务执行完毕，没有异常，提交。con.commit();con.setAutoCommit(true);} catch (SQLException e) {try {// 失败，进行回滚操作。恢复到事务执行之前的// 状态。con.rollback();con.setAutoCommit(true);} catch (SQLException e1) {e1.printStackTrace();}e.printStackTrace();}}}