day28
今日内容
- JDBC基本概念
- 快速入门
- 对JDBC中个接口和类详解
JDBC
- 概念:Java数据库连接,(Java Database Connectivity,简称JDBC)是Java语言中用来规范客户端程序如何来访问数据库的应用程序接口,提供了诸如查询和更新数据库中数据的方法。JDBC也是Sun Microsystems的商标。我们通常说的JDBC是面向关系型数据库的。
- 快速入门:
步骤:
1.导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
1.复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
2.右键-->Add As Library
2.注册驱动
3.获取数据库连接对象Connection
4.定义sql
5.获取执行sql语句的对象Statement
6.执行sql,接受返回结果
7.处理结果
8.释放资源
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class JdbcDemo01 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3", "root", "root");
String sql = "update account set balance = 500 where id = 1";
Statement statement = conn.createStatement();
int count = statement.executeUpdate(sql);
System.out.println(count);
statement.close();
conn.close();
}
}
- 详解各个对象:
- DriverManager:驱动管理对象,类
- 功能:
- 注册驱动:告诉程序该使用哪一个数据库驱动jar
static void registerDriver(Driver driver) 注册与给定的驱动程序 DriverManager 。
写代码使用:Class.forName("com.mysql.jdbc.Driver");
通过查看源码发现:在com.mysql.jdbc.Driver类中存在静态代码块
static {
try {
DriverManager.registerDriver(new Driver());
} catch (SQLException var1) {
throw new RuntimeException("Can't register driver!");
}
}
注意:mysql 5 之后的驱动jar包可以省略注册驱动的步骤
Class.forName("com.mysql.jdbc.Driver");
- 获取数据库连接
方法:static Connection getConnection(String url, String user, String password) 尝试建立与给定数据库URL的连接。
参数:
url:指定连接的路径
语法:jdbc:mysql://ip地址(域名):端口号/数据库名称
例子:jdbc:mysql://localhost:3306/db3
细节:乳如果连接的是本机mysql服务器,并且mysql服务默认端口是3306,则url可以简写为:jdbc:mysql:/
user:用户名
password:密码
1. 获取执行sql的对象
Statement createStatement()创建一个 Statement对象,用于将SQL语句发送到数据库。
PreparedStatement prepareStatement(String sql)创建一个 PreparedStatement对象,用于将参数化的SQL语句发送到数据库。
2. 管理事务:
开启事务:void setAutoCommit(boolean autoCommit)将此连接的自动提交模式设置为给定状态。调用该方法设置参数为false,即开启事务
提交事务:void commit()使自上次提交/回滚以来所做的所有更改都将永久性,并释放此 Connection对象当前持有的任何数据库锁。
回滚事务:void rollback()撤消在当前事务中所做的所有更改,并释放此 Connection对象当前持有的任何数据库锁。
- Statement:用于执行静态SQL语句并返回其生成的结果的对象,接口
boolean execute(String sql)执行给定的SQL语句,这可能会返回多个结果。(了解)
返回值:
true表示第一个结果是一个ResultSet对象;
false表示更新计数或没有结果。
int executeUpdate(String sql)执行给定的SQL语句(DML),这可能是INSERT,UPDATE,或DELETE语句,或者不返回任何内容,如DDL语句的SQL语句(create,alter,drop)。
返回值:
(1)返回值>0表示sql语句影响了多少行记录,可以通过这个影响的行数判断DML语句是否执行成功,返回值>0的则执行成功,反之,则失败。
(2)0不返回的SQL语句,如DDL语句
ResultSet executeQuery(String sql)执行给定的SQL语句,该语句返回单个ResultSet对象。
一个ResultSet对象,其中包含给定查询产生的数据; 从不null
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBCDemo02 {
public static void main(String[] args) {
Statement statement = null;
Connection connection = null;
try {
Class.forName("com.mysql.jdbc.Driver");
String sql = "insert into account values(null, '王五', 3000)";
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3", "root", "root");
statement = connection.createStatement();
int count = statement.executeUpdate(sql);
System.out.println(count);
if (count > 0){
System.out.println("添加成功");
}else{
System.out.println("添加失败");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (statement != null) {
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
- Resultset:结构集对象,接口,表示数据库结果集的数据表,通常通过执行查询数据库的语句生成。
boolean next()将光标从当前位置向前移动一行。
返回值:
true表示新的当前行有效;
false表示没有更多的行;
getXxx(参数)获取数据
Xxx:代表数据类型 如:int getInt() 、String getString()
参数:
1. int:代表列的编号,从1开始 如:getString(1)
2. String:代表列名称 如:getDouble("balance")
注意:
使用步骤:
1. 游标向下移动一行
2. 判断是否有数据
3. 获取数据
while (resultSet.next()){
int id = resultSet.getInt(1);
String name = resultSet.getString("name");
double balance = resultSet.getDouble(3);
System.out.println(id + "------" + name + "------" + balance);
}
package cn.itcast.domain;
import java.util.Date;
public class Emp {
private int id;
private String name;
private int job_id;
private int mgr;
private Date joindate;
private double salary;
private double bonus;
private int dept_id;
public Emp() {
}
public Emp(int id, String name, int job_id, int mgr, Date joindate, double salary, double bonus, int dept_id) {
this.id = id;
this.name = name;
this.job_id = job_id;
this.mgr = mgr;
this.joindate = joindate;
this.salary = salary;
this.bonus = bonus;
this.dept_id = dept_id;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getJob_id() {
return job_id;
}
public void setJob_id(int job_id) {
this.job_id = job_id;
}
public int getMgr() {
return mgr;
}
public void setMgr(int mgr) {
this.mgr = mgr;
}
public Date getJoindate() {
return joindate;
}
public void setJoindate(Date joindate) {
this.joindate = joindate;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public double getBonus() {
return bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
public int getDept_id() {
return dept_id;
}
public void setDept_id(int dept_id) {
this.dept_id = dept_id;
}
@Override
public String toString() {
return "Emp{" +
"id=" + id +
", name='" + name + '\'' +
", job_id=" + job_id +
", mgr=" + mgr +
", joindate=" + joindate +
", salary=" + salary +
", bonus=" + bonus +
", dept_id=" + dept_id +
'}';
}
}
package cn.itcast.jdbc;
import cn.itcast.domain.Emp;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
public class JDBCDemo08 {
public static void main(String[] args) {
List<Emp> all = new JDBCDemo08().findAll();
System.out.println(all);
System.out.println(all.size());
}
public List<Emp> findAll(){
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
List<Emp> list = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3","root","root");
String sql = "select * from emp";
statement = connection.createStatement();
resultSet = statement.executeQuery(sql);
Emp emp = null;
list = new ArrayList<>();
while (resultSet.next()){
int id = resultSet.getInt("id");
String ename = resultSet.getString("ename");
int job_id = resultSet.getInt("job_id");
int mgr = resultSet.getInt("mgr");
Date joindate = resultSet.getDate("joindate");
double salary = resultSet.getDouble("salary");
double bonus = resultSet.getDouble("bonus");
int dept_id = resultSet.getInt("dept_id");
emp = new Emp(id, ename, job_id, mgr, joindate, salary, bonus, dept_id);
list.add(emp);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (statement != null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return list;
}
}
需求:
1.通过键盘录入用户名和密码
2.判断用户是否登录成功
-- 创建数据库
CREATE DATABASE db4;
USE db4;
CREATE TABLE USER(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(32),
PASSWORD VARCHAR(32)
);
INSERT INTO USER VALUE
(NULL, 'zhangsan', '123'),
(NULL, 'lisi', '234');
package cn.itcast.jdbc;
import cn.itcast.util.JDBCUtils;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
public class JDBCDemo09 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("请输入用户名:");
String username = sc.nextLine();
System.out.println("请输入密码:");
String password = sc.nextLine();
boolean flag = new JDBCDemo09().login(username, password);
if(flag){
System.out.println("登录成功!");
}else{
System.out.println("用户名或密码错误!");
}
}
public boolean login(String username, String password){
if (username == null || password == null){
return false;
}
Connection conn = null;
Statement statement = null;
ResultSet resultSet = null;
try {
conn = JDBCUtils.getConnection();
String sql = "select * from user where username = '" + username + "'and password = '" + password + "'";
statement = conn.createStatement();
resultSet = statement.executeQuery(sql);
return resultSet.next();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.close(resultSet, statement, conn);
}
return false;
}
}
- PreparedStatement:执行sql的对象,接口,表示预编译的SQL语句的对象。
* SQL注入问题:在拼接sql时,有一些sql的特殊关键字参与字符串的拼接。会造成安全性问题
1. 输入用户随便,输入密码:a' or 'a' = 'a
2. sql : select * from user where username = 'fhdsjkf' and password = 'a' or 'a' = 'a'
* 解决sql注入问题:使用PreparedStatement对象来解决
* 预编译的sql:参数使用?作为占位符
* 步骤:
1.导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
1.复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
2.右键-->Add As Library
2.注册驱动
3.获取数据库连接对象Connection
4.定义sql
* 注意:sql的参数使用?作为占位符。如:select * from user where username = ? and password = ?
5.获取执行sql语句的对象PreparedStatement
PreparedStatement prepareStatement(String sql)
创建一个 PreparedStatement对象,用于将参数化的SQL语句发送到数据库。
6.给?赋值:
方法:setXxx(参数1, 参数2)
* 参数1: ?的位置编号,从1开始
* 参数2:?的值
7.执行sql,接受返回结果,不需要传递sql语句
8.处理结果
9.释放资源
* 注意:后期都会使用Preparedstatement来完成增删改查的所有操作
1.可以防止SQL注入
2.效率更高
public boolean login2(String username, String password){
if (username == null || password == null){
return false;
}
Connection conn = null;
ResultSet resultSet = null;
PreparedStatement preparedStatement = null;
try {
conn = JDBCUtils.getConnection();
String sql = "select * from user where username = ? and password = ?";
preparedStatement = conn.prepareStatement(sql);
preparedStatement.setString(1, username);
preparedStatement.setString(2, password);
resultSet = preparedStatement.executeQuery();
return resultSet.next();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.close(resultSet, preparedStatement, conn);
}
return false;
}
抽JDBC工具类:JDBCUtils
目的:简化书写
分析:
1. 注册驱动也抽取
2. 抽取一个方法获取连接对象
需求:不想传递参数,还想保证工具类的通用性。
解决:配置文件
jdbc_properties
url =
user =
password
3. 抽取一个方法释放资源
url = jdbc:mysql://localhost:3306/db3
user = root
password = root
driver = com.mysql.jdbc.Driver
package cn.itcast.util;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;
public class JDBCUtils {
private static String url;
private static String user;
private static String password;
private static String driver;
static {
try {
Properties properties = new Properties();
ClassLoader classLoader = JDBCUtils.class.getClassLoader();
URL res = classLoader.getResource("jdbc_properties");
String path = res.getPath();
properties.load(new FileReader(path));
url = properties.getProperty("url");
user = properties.getProperty("user");
password = properties.getProperty("password");
driver = properties.getProperty("driver");
Class.forName(driver);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url, user, password);
}
public static void close(Statement statement, Connection connection){
if (statement != null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void close(ResultSet resultSet, Statement statement, Connection connection){
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (statement != null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
JDBC控制事务:
- 事务:一个包含多个步骤的业务操作。如果这个业务操作被事物管理,则这多个步骤要么同时成功,要么同时失败
- 操作:
1.开启事务
2.提交事务
3.回滚事务 - 使用Connection对象来管理事务
- 开启事务:void setAutoCommit(boolean autoCommit)将此连接的自动提交模式设置为给定状态。调用该方法设置参数为false,即开启事务
- 提交事务:void commit()使自上次提交/回滚以来所做的所有更改都将永久性,并释放此 Connection对象当前持有的任何数据库锁。
- 回滚事务:void rollback()撤消在当前事务中所做的所有更改,并释放此 Connection对象当前持有的任何数据库锁。
import cn.itcast.util.JDBCUtils;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class JDBCDemo10 {
public static void main(String[] args) {
Connection connection = null;
PreparedStatement preparedStatement1 = null;
PreparedStatement preparedStatement2 = null;
try {
connection = JDBCUtils.getConnection();
connection.setAutoCommit(false);
String sql1 = "update account set balance = balance - ? where id = ?";
String sql2 = "update account set balance = balance + ? where id = ?";
preparedStatement1 = connection.prepareStatement(sql1);
preparedStatement2 = connection.prepareStatement(sql2);
preparedStatement1.setDouble(1, 500);
preparedStatement1.setInt(2, 1);
preparedStatement2.setDouble(1, 500);
preparedStatement2.setInt(2, 2);
preparedStatement1.executeUpdate();
int i = 3/0;
preparedStatement2.executeUpdate();
connection.commit();
} catch (Exception e) {
try {
if (connection != null)
connection.rollback();
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
} finally {
JDBCUtils.close(preparedStatement1,connection);
JDBCUtils.close(preparedStatement2,null);
}
}
}