JDBC
一、JDBC基本概念
①Java DataBase Connectivity 用java来操作数据库连接
②用统一的一套java代码操作所有的关系型数据库的一个规则(接口)
二、JDBC快速入门
1.步骤
-
导入jar包
-
注册数据库驱动
-
获取数据库连接对象
-
定义sql语句
-
获取执行sql语句的对象 Statement
-
执行sql语句，接收返回的结果
-
对结果进行处理
-
资源的释放
2.代码案例
public class demo1 {
public static void main(String[] args) throws Exception {
//2.注册数据库驱动
Class.forName("com.mysql.jdbc.Driver");
//3. 获取数据库连接对象 Connection
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mystudy","root","root");
//4. 定义sql语句
String sql = "update mytest set spwd = 111111 where id=1";
//5. 获取执行sql语句的对象 Statement
Statement statement = conn.createStatement();
//6. 执行sql语句，接收返回的结果
int i = statement.executeUpdate(sql);
//7. 对结果进行处理
System.out.println(i);
//8.资源的释放
statement.close();
conn.close();
}
}
三、JDBC各个接口和类的详解
1.DriverManager
注册数据库驱动
Class.forName("com.mysql.jdbc.Driver");//mysql 5以后可以省略
//源码
static {
try {
DriverManager.registerDriver(new Driver());
} catch (SQLException var1) {
throw new RuntimeException("Can't register driver!");
}
}
获取数据库连接
Connection conn = DriverManager.getConnection(url,user,paassword);
url格式:jdbc:mysql://ip地址:端口号/数据库名
user格式:数据库用户名
password:密码
2. Connection
获取执行sql的语句
Statement statement = conn.createStatement();//不安全
PreparedStatement preparedStatement = conn.prepareStatement(sql);//比较安全
创建一个 PreparedStatement 对象来将参数化的 SQL 语句发送到数据库。
管理事务
//开启事务的方法---autoCommit -为 false开启事务
void setAutoCommit(boolean autoCommit)
//提交事务
void commit();
//回滚事务
void rollback();
/**
* 事务管理
*/
public class demo7 {
//修改密码的方法，同时修改赵四和admin的密码
public static boolean update_pass(String pass){
Connection connection = null;
PreparedStatement preparedStatement1 = null;
PreparedStatement preparedStatement2 = null;
if(pass==null){
System.out.println("输入的密码不能为空！");
return false;
}
try {
connection = jdbcUtiles.getConnection();
connection.setAutoCommit(false); //事务已经开启
String sql1 = "update mytest set spwd = ? where id = ?";
String sql2 = "update mytest set spwd = ? where id = ?";
preparedStatement1 = connection.prepareStatement(sql1);
preparedStatement2 = connection.prepareStatement(sql2);
preparedStatement1.setString(1,pass);
preparedStatement1.setInt(2,1);
preparedStatement2.setString(1,pass);
preparedStatement2.setInt(2,2);
int i = preparedStatement1.executeUpdate();
//人为添加异常，测试事务隔离
int k = 3/0;
int j = preparedStatement2.executeUpdate();
System.out.println(i);
System.out.println(j);
connection.commit();//提交事务
return true;
} catch (Exception throwables) {
try {
connection.rollback();//回滚
} catch (SQLException e) {
e.printStackTrace();
}
throwables.printStackTrace();
}finally {
jdbcUtiles.close(preparedStatement1,connection);
jdbcUtiles.close(preparedStatement2,null);
}
return false;
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("请输入密码：");
String pass = input.next();
boolean b = update_pass(pass);
if(b){
System.out.println("成功");
}else {
System.out.println("失败");
}
}
}
3.Statement
执行静态的sql语句
boolean execute(String sql)
//可以执行任意sql语句，了解一下即可
int i = statement.executeUpdate(sql);
//DML语句增删改、DDL语句 创建表和库
//i代表我们的操作影响的数据库行数，可以通过i判断语句是否执行成功
ResultSet executeQuery(String sql)
//执行给定的 SQL 语句，该语句返回单个 ResultSet 对象。
4.练习题1
//对数据库中的表进行增删改操作----完整版
public class demo2 {
public static void main(String[] args) {
Connection connection = null;
Statement statement = null;
try {
//获取数据库连接对象 Connection
connection = DriverManager.getConnection("jdbc:mysql://ip地址:端口号/数据库名", "用户名", "用户密码");
//定义sql语句
String sql = "insert into mytest values(4,'jack',12312)";
String sql2 = "update mytest set spwd=22222 where id=2";
String sql3 = "delete from mytest where id = 3";
//执行sql语句的对象 Statement
statement = connection.createStatement();
//执行sql语句，接收返回的结果
int i = statement.executeUpdate(sql);
int i2 = statement.executeUpdate(sql2);
int i3 = statement.executeUpdate(sql3);
System.out.println(i+i2+i3);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
if(statement!=null) {
try {
statement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(connection!=null) {
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
5.ResultSet
//方法
boolean next(); 将光标从当前位置向下移动一个
getXXX(参数); //xxx代表数据类型，参数可以是int类型，也可以string 列名
//案例 查询数据库表中信息
public class demo3 {
public static void main(String[] args) {
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
try {
//获取数据库连接对象 Connection
connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/mystudy","root","root");
//定义sql语句
String sql = "select * from mytest where id=1";
//执行sql语句的对象 Statement
statement = connection.createStatement();
//执行sql语句，接收返回的结果
resultSet = statement.executeQuery(sql);
//判断
if(resultSet.next()){
int id = resultSet.getInt(1);
String name = resultSet.getString("sname");
String pass = resultSet.getString(3);
System.out.println(id+"---"+name+"---"+pass);
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}
finally {
try {
connection.close();
statement.close();
resultSet.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
6.练习2：查询表中数据，并且封装代码
实体类
/**
* 实体类------对应数据库的表
*/
public class User {
private int id;
private String name;
private String pass;
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 String getPass() {
return pass;
}
public void setPass(String pass) {
this.pass = pass;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pass='" + pass + '\'' +
'}';
}
}
工具类
为了方便，我们可以提前编写工具类
//工具类
public class jdbcUtiles {
private static String url;
private static String user;
private static String password;
private static String driver;
static {
//读取资源文件，获取值，执行一次
Properties properties = new Properties();
try {
properties.load(new FileReader("D:\\桌面\\JDBC\\JDBC学习\\src\\jdbc.properties"));
//获取值
url = properties.getProperty("url");
user = properties.getProperty("user");
password = properties.getProperty("password");
driver = properties.getProperty("driver");
//注册驱动
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
} catch (IOException e) {
e.printStackTrace();
}
}
//获取连接对象的方法
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url,user,password);
}
// 关闭资源的方法
public static void close(Statement statement,Connection connection){
if(statement!=null){
try {
statement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(connection!=null){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
// 关闭资源的方法
public static void close(ResultSet resultSet, Statement statement, Connection connection){
if(statement!=null){
try {
statement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(connection!=null){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(resultSet!=null){
try {
resultSet.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
public static void close(PreparedStatement preparedStatement,Connection connection){
if(preparedStatement!=null){
try {
preparedStatement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(connection!=null){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
测试类
//数据库操作优化版
public class demo5 {
public static void main(String[] args) {
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
try {
List<User> list = new ArrayList<>();
connection = jdbcUtiles.getConnection();
statement = connection.createStatement();
String sql = "select * from mytest";
resultSet = statement.executeQuery(sql);
while (resultSet.next()){
User user = new User();
user.setId(resultSet.getInt(1));
user.setName(resultSet.getString(2));
user.setPass(resultSet.getString(3));
list.add(user);
}
for(int i=0;i<list.size();i++){
System.out.println(list.get(i));
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
jdbcUtiles.close(resultSet,statement,connection);
}
}
}
注册登录练习
public class demo登录注册 {
//登录的方法
public static boolean Login(String usename,String password){
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
if(usename==null||password==null){
System.out.println("用户名密码不能为空");
return false;
}
try {
connection = jdbcUtiles.getConnection();
statement = connection.createStatement();
String sql = "select * from mytest where sname='"+usename+"' and spwd='"+password+"'";
resultSet = statement.executeQuery(sql);
return resultSet.next();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return false;
}
//注册的方法
public static int regiest(String usename,String password){
Connection connection = null;
Statement statement = null;
if(usename==null||password==null){
System.out.println("用户名密码不能为空");
return 0;
}
try {
connection = jdbcUtiles.getConnection();
statement = connection.createStatement();
String sql = "insert into mytest values(null,'"+usename+"','"+password+"')";
int i = statement.executeUpdate(sql);
return i;
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return 0;
}
//测试
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("请输入用户名：");
String name = input.next();
System.out.println("请输入密码：");
String pass = input.next();
//登录
boolean login = Login(name, pass);
if(login){
System.out.println("登录成功！");
}else {
System.out.println("登录失败！");
}
//注册
int regiest = regiest(name, pass);
if(regiest==0){
System.out.println("注册失败！");
}else {
System.out.println("注册成功！");
}
}
}
7.PreparedStatement
步骤
Statement sql注入问题 非法恶意的sql操作数据库
sql预编译，用？占位符代替参数
- 导入jar包
- 注册驱动
- 获取数据库连接对象
- 定义sql 参数采用占位符
- 获取preparedstatement对象
- 给？赋值(setXXX(参数1，参数2)) 参数1：位置， 参数2：值
- 执行sql 接收返回的结果
- 结果处理
- 释放资源
代码案例
/**
* PreparedStatement
*/
public class demo6 {
public static void main(String[] args) {
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = jdbcUtiles.getConnection();
String sql="insert into mytest values(6,?,?)";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1,"jjj");
preparedStatement.setString(2,"789789");
int i = preparedStatement.executeUpdate();
System.out.println(i);
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
try {
preparedStatement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}