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2_JDBC

作者：互联网

目录

一. 引言

1.1 如何操作数据库

1.2 实际开发中, 会采用客户端操作数据库吗?

二. JDBC

2.1 什么是JDBC?

2.2 JDBC核心思想

2.2.1 MySQL数据库驱动
2.2.2 JDBC API
类型 权限定名 简介
class java.sql.DriverManager 管理多个数据库驱动类, 提供了获取数据库连接的方法
interface java.sql.Connection 代表一个数据库连接(当Connection不是null时, 表示已连接数据库)
interface java.sql.Statement 发送SQL语句到数据库工具
interface java.sql.ResultSet 保存SQL查询语句的结果数据(结果集)
class java.sql.SQLException 处理数据库应用程序时所发生的异常

2.3 环境搭建

  1. 在项目下新建lib文件夹,用于存放jar文件
  2. 将mysql驱动mysql-connector-java-5.1.X-bin.jar复制到项目中的lib文件夹中
  3. 选中lib文件夹右键Add as Library, 点击OK

三. JDBC开发步骤[重点]

3.1 注册驱动

Class.forName("com.mysql.jdbc.Driver");//加载驱动

3.2 连接数据库

Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database?useUnicode=true&characterEncoding=utf8", "root", "root");

3.3 获取发送SQL的对象

Statement statement = conn.createStatement();

3.4 执行SQL语句

String sql = "insert into t_jobs(job_id,job_title,min_salary,max_salary) values('JAVA_Mgr','JAVA_Manager',4000,10000)";

int result = statement.executeUpdate(sql);//执行SQL语句并接收结果

3.5 处理结果

if(result == 1) {
    System.out.println("Success");
}

3.6 释放资源

statement.close();
conn.close();

3.7 综合案例

public class DeleteJDBC {

    public static void main(String[] args) throws Exception{

        //1. 加载驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2. 获得连接对象
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root", "root");
        //3. 获得执行SQL的对象
        Statement statement = conn.createStatement();
        //4. 执行SQL语句, 并接收结果
        int result = statement.executeUpdate("delete from t_jobs where job_id = 'JAVA_Mgr'");
        //5. 处理结果
        if (result == 1) {
            System.out.println("删除成功!");
        }else{
            System.out.println("删除失败!");
        }
        //6. 释放资源
        statement.close();
        conn.close();
    }
}

四. ResultSet(结果集)

4.1 接收结果集

ResultSet rs = statement.executeQuery("select * from t_employees");

4.2 遍历ResultSet中的数据

boolean next() throws SQLException //判断 rs 的结果集中 下一行是否存在数据
4.2.1 遍历方法
int getInt(int columnIndex) throws SQLException //获得当前行第N列的int值
int getInt(String columnLabel) throws SQLException //获得当前行columnLabel列的int值
    
double getDouble(int columnIndex) throws SQLException //获得当前行第N列的double值
double getDouble(String columnLabel) throws SQLException //获得当前行columnLabel列的double值
    
String getString(int columnIndex) throws SQLException //获得当前行第N列的String值
String getString(String columnLabel) throws SQLException //获得当前行columnLabel列的String值

4.3 综合案例

4.3.1 根据列的名称获取
public class QueryJdbc {

    public static void main(String[] args) throws Exception{

        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2. 获取连接对象
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root","root");
        //3. 获取执行SQL的对象
        Statement statement = conn.createStatement();
        //4. 执行SQL语句,接收结果
        ResultSet resultSet = statement.executeQuery("select * from t_jobs");
        //5. 处理结果
        while (resultSet.next()) {
            //对当前行每列数据进行获取, 根据列的编号
            String job_id = resultSet.getString("job_id");
            String job_title = resultSet.getString("job_title");
            String min_salary = resultSet.getString("min_salary");
            String max_salary = resultSet.getString("max_salary");
            System.out.println(job_id+"\t"+job_title+"\t"+min_salary+"\t"+max_salary);
        }
        //6. 释放资源
        resultSet.close();
        statement.close();
        conn.close();
    }
}
4.3.2根据列的编号获取
public class QueryJdbc2 {

    public static void main(String[] args) throws Exception{

        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2. 获取连接对象
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root","root");
        //3. 获取执行SQL的对象
        Statement statement = conn.createStatement();
        //4. 执行SQL语句,接收结果
        ResultSet resultSet = statement.executeQuery("select * from t_jobs");
        //5. 处理结果
        while (resultSet.next()) { //判断下一行是否有数据
            //对当前行每列数据进行获取, 根据列的编号
            String job_id = resultSet.getString(1);
            String job_title = resultSet.getString(2);
            String min_salary = resultSet.getString(3);
            String max_salary = resultSet.getString(3);
            System.out.println(job_id+"\t"+job_title+"\t"+min_salary+"\t"+max_salary);
        }
        //6. 释放资源
        resultSet.close();
        statement.close();
        conn.close();
    }
}

五. 常见错误

六. 综合案例[登陆]

6.1 创建表

CREATE TABLE users(
	id INT PRIMARY KEY AUTO_INCREMENT,
	username VARCHAR(18) UNIQUE NOT NULL,
	`password` VARCHAR(18) NOT NULL,
	phone VARCHAR(11)
)CHARSET=utf8;

INSERT INTO users(username,`password`,phone) VALUES('zhangsan','123','12345678901'); 
INSERT INTO users(username,`password`,phone) VALUES('lisi','321','12345678902');

6.2 实现登录

public class LoginJdbc {
    public static void main(String[] args) throws Exception{
        Scanner input = new Scanner(System.in);
        System.out.println("请输入用户名: ");
        String username = input.next();
        System.out.println("请输入密码: ");
        String password = input.next();

        Class.forName("com.mysql.jdbc.Driver");

        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb","root","root");

        Statement statement = conn.createStatement();

        ResultSet resultSet = statement.executeQuery("select username,password from users where username = '"+username+"' and password = '"+password+"'");

        if (resultSet.next()) { //查询到了数据
            System.out.println("登陆成功!");
        }else{
            System.out.println("登陆失败!");
        }

        resultSet.close();
        statement.close();
        conn.close();
    }
}

七. SQL注入问题

7.1 什么是SQL注入

7.2 如何避免SQL注入

八. PreparedStatement[重点]

8.1 PreparedStatement的应用

8.1.1 参数标记
//1. 预编译 SQL 语句
PreparedStatement ps = conn.preparedStatement("select * from users where username=? and password=?");
8.1.2 动态参数绑定
//2. 为参数下标赋值
ps.setString(1,username);
ps.setString(2,password);

public class LoginJdbc2 {
    public static void main(String[] args) throws Exception{
        Scanner input = new Scanner(System.in);
        System.out.println("请输入用户名: ");
        String username = input.nextLine();
        System.out.println("请输入密码: ");
        String password = input.nextLine();

        Class.forName("com.mysql.jdbc.Driver");

        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root", "root");

        //获得PreparedStatement对象,预编译SQL语句
        PreparedStatement ps = conn.prepareStatement("select * from users where username = ? and password = ?");
        //为?占位符赋值
        ps.setString(1,username);
        ps.setString(2,password);
        ResultSet resultSet = ps.executeQuery();

        if (resultSet.next()) {
            System.out.println("登陆成功!");
        }else{
            System.out.println("登陆失败");
        }

        resultSet.close();
        ps.close();
        conn.close();
    }
}

九. 封装工具类

9.1 重用性方案

9.1.1 重用工具类实现
public class JdbcUtils {

    static{//类加载,只执行一次
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    //1. 获取连接
    public static Connection getConnection(){
        Connection conn = null;
        try {
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb","root","root");
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return conn;
    }
    //2. 释放资源
    public static void closeAll(Connection conn, Statement statement, ResultSet resultSet){
        try {
            if (resultSet != null){
                resultSet.close();
            }
            if (statement != null){
                statement.close();
            }
            if (conn != null){
                conn.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }

}

9.2 跨平台方案

9.2.1 跨平台工具类实现

(1) 在src目录下新建jdbc.properties配置文件

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/companydb?useUnicode=true&characterEncoding=utf8
username=root
password=root

(2) 工具类的封装

public class JdbcUtils2 {
    private static final Properties PROPERTIES = new Properties();//存储配置文件的map
    static {
        InputStream is = JdbcUtils2.class.getResourceAsStream("/jdbc.properties");//通过复用本类自带流, 读取jdbc.properties配置文件
        try {
            PROPERTIES.load(is);//通过流,将配置文件内容加载到properties集合
            Class.forName(PROPERTIES.getProperty("driver"));//通过键"driver"得到值"com.mysql.jdbc.Driver"
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() {
        Connection conn = null;
        try {
            conn = DriverManager.getConnection(PROPERTIES.getProperty("url"), PROPERTIES.getProperty("username"), PROPERTIES.getProperty("password"));//通过键"url"得到值"jdbc:mysql://localhost:3306/companydb",通过键"username"得到值"root",通过键"password"得到值"root"
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return conn;
    }

    public static void closeAll(Connection conn, Statement statement, ResultSet resultSet) {
        try {
            if (resultSet != null) {
                resultSet.close();
            }
            if (statement != null) {
                statement.close();
            }
            if (conn != null) {//先开后关
                conn.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }

}
折叠

十. ORM 对象关系映射

10.1 实体类(entity): 零散数据的载体

10.1.1 ORM应用
public class T_Jobs {
    private String job_id;
    private String job_title;
    private String min_salary;
    private String max_salary;

    public T_Jobs() {
    }

    public String getJob_id() {
        return job_id;
    }

    public void setJob_id(String job_id) {
        this.job_id = job_id;
    }

    public String getJob_title() {
        return job_title;
    }

    public void setJob_title(String job_title) {
        this.job_title = job_title;
    }

    public String getMin_salary() {
        return min_salary;
    }

    public void setMin_salary(String min_salary) {
        this.min_salary = min_salary;
    }

    public String getMax_salary() {
        return max_salary;
    }

    public void setMax_salary(String max_salary) {
        this.max_salary = max_salary;
    }

    @Override
    public String toString() {
        return "T_Jobs{" +
                "job_id='" + job_id + '\'' +
                ", job_title='" + job_title + '\'' +
                ", min_salary='" + min_salary + '\'' +
                ", max_salary='" + max_salary + '\'' +
                '}';
    }
}
折叠 

public class TestORM {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        List<T_Jobs> t_jobsList = new ArrayList<>();
        try {
            conn = JdbcUtils2.getConnection();
            ps = conn.prepareStatement("select * from t_jobs");
            resultSet = ps.executeQuery();
            while (resultSet.next()) {
                String job_id = resultSet.getString("job_id");
                String job_title = resultSet.getString("job_title");
                String min_salary = resultSet.getString("min_salary");
                String max_salary = resultSet.getString("max_salary");

                //创建对象, 封装查询到的零散数据
                T_Jobs t_jobs = new T_Jobs();

                t_jobs.setJob_id(job_id);
                t_jobs.setJob_title(job_title);
                t_jobs.setMin_salary(min_salary);
                t_jobs.setMax_salary(max_salary);
                //每遍历一次得到一个对象, 把对象存到集合里, 方便后续的使用
                t_jobsList.add(t_jobs);
            }
            //集合遍历
            for (T_Jobs t_jobs : t_jobsList) {
                System.out.println(t_jobs);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            JdbcUtils2.closeAll(conn,ps,resultSet);
        }
    }
}

十一. DAO 数据访问对象

11.1 创建数据库

CREATE TABLE person(
	id INT PRIMARY KEY AUTO_INCREMENT,
	`name` VARCHAR(20) NOT NULL,
	age INT NOT NULL,
	birthday DATE,
	email VARCHAR(20),
	address VARCHAR(20)
)CHARSET=utf8;

11.2 封装实体类

public class Person {//根据表名person, 创建Person类
    private int id;//根据表的列名编写类的各个属性(私有)
    private String name;
    private int age;
    private Date birthday;
    private String email;
    private String address;

    public Person() {
    }

    public Person(String name, int age, Date birthday, String email, String address) {
        this.name = name;
        this.age = age;
        this.birthday = birthday;
        this.email = email;
        this.address = address;
    }

    public Person(int id, String name, int age, Date birthday, String email, String address) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.birthday = birthday;
        this.email = email;
        this.address = address;
    }

    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 getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", birthday=" + birthday +
                ", email='" + email + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}
折叠

11.3 编写DaoImpl类

public class PersonDaoImpl {
    //1. 新增
    public int insert(Person person) {
        Connection conn = null;
        PreparedStatement ps = null;
        String sql = "insert into person(name,age,birthday,email,address) values(?,?,?,?,?)";//往person表里新增一条数据
        try {
            conn = DBUtils.getConnection();//调用跨平台工具类获取数据库连接对象
            ps = conn.prepareStatement(sql);//获取执行SQL语句的对象
            //为指定的参数下标赋值
            ps.setString(1,person.getName());
            ps.setInt(2,person.getAge());
            ps.setDate(3,null);
            ps.setString(4,person.getEmail());
            ps.setString(5,person.getAddress());
            int result = ps.executeUpdate();
            return result;//返回执行结果,result为1则成功,0则失败
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DBUtils.closeAll(conn,ps,null);//最后调用跨平台工具类释放资源
        }

        return 0;
    }
    //2. 修改
    public int update(Person person) {
        Connection conn = null;
        PreparedStatement ps = null;
        String sql = "update person set name=?,age=?,birthday=?,email=?,address=? where id = ?";
        try {
            conn = DBUtils.getConnection();
            ps = conn.prepareStatement(sql);
            ps.setString(1,person.getName());
            ps.setInt(2,person.getAge());
            ps.setDate(3,null);
            ps.setString(4,person.getEmail());
            ps.setString(5,person.getAddress());
            ps.setInt(6,person.getId());
            int result = ps.executeUpdate();
            return result;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DBUtils.closeAll(conn,ps,null);
        }
        return 0;
    }
    //3. 删除
    public int delete(int id) {
        Connection conn = null;
        PreparedStatement ps = null;
        String sql = "delete from person where id = ?";
        try {
            conn = DBUtils.getConnection();
            ps = conn.prepareStatement(sql);
            ps.setInt(1,id);
            int result = ps.executeUpdate();
            return result;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DBUtils.closeAll(conn,ps,null);
        }
        return 0;
    }
    //4. 查单条数据
    public Person select(int id) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        String sql = "select * from person where id = ?";
        Person person = null;
        try {
            conn = DBUtils.getConnection();
            ps = conn.prepareStatement(sql);
            ps.setInt(1,id);
            resultSet = ps.executeQuery();
            if (resultSet.next()) {//如果查到数据
                person = new Person();//则创建一个对象
                int pid = resultSet.getInt("id");
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                Date birthday = resultSet.getDate("birthday");
                String email = resultSet.getString("email");
                String address = resultSet.getString("address");
                //通过set方法为属性赋值
                person.setId(pid);
                person.setName(name);
                person.setAge(age);
                person.setBirthday(birthday);
                person.setEmail(email);
                person.setAddress(address);
            }
            return person;

        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DBUtils.closeAll(conn,ps,resultSet);
        }
        return null;
    }
    //5. 查所有数据
    public List<Person> selectAll() {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        String sql = "select * from person";
        Person person = null;
        List<Person> personList = new ArrayList<>();//创建一个集合,用来存放Person对象
        try {
            conn = DBUtils.getConnection();
            ps = conn.prepareStatement(sql);
            resultSet = ps.executeQuery();
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                Date birthday = resultSet.getDate("birthday");
                String email = resultSet.getString("email");
                String address = resultSet.getString("address");
                person = new Person(id,name,age,birthday,email,address);//通过构造方法为属性赋值
                personList.add(person);
            }
            return personList;

        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DBUtils.closeAll(conn,ps,resultSet);
        }
        return null;
    }
}
折叠

十二. Date工具类

12.1 java.util.Date

12.2 java.sql.Date

12.3 SimpleDateFormat

12.3.1 SimpleDateFormat应用
public class TestTimes {
    public static void main(String[] args) throws Exception{
        //格式化
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        //将字符串转日期 parse
        Date date = sdf.parse("2021-03-22");
        System.out.println(date);
        //将日期转字符串 format
        String str = sdf.format(date);
        System.out.println(str);

        //sql.Date 不支持字符串转换, 只支持毫秒值创建
        //通过util.Date拿到指定日期的毫秒值, 转换为sql.Date
        java.sql.Date sqlDate = new java.sql.Date(date.getTime());
        System.out.println(sqlDate);

    }
}

12.4 封装DateUtils工具类

public class DateUtils {

    private static final SimpleDateFormat sdf = new SimpleDateFormat("yy-MM-dd");
    //1. 字符串转为util.Date
    public static java.util.Date strToUtil(String str) {
        try {
            return sdf.parse(str);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return null;
    }

    //2. util.Date转sql.Date
    public static java.sql.Date utilToSql(java.util.Date date) {
        return new java.sql.Date(date.getTime());
    }

    //3. util.Date转字符串
    public static String utilToString(java.util.Date date) {
        return sdf.format(date);
    }
}

十三. Service业务逻辑

13.1 什么是业务?

(软件所提供的一个功能就叫业务)

service层核心思想

站在用户角度, 一个功能即是一个业务,可能需要多个DAO组成

AccountServiceImpl{
transfer(){
saveMoney();
takeMoney();
}
}

AccountDaoImpl{
saveMoney();
takeMoney();
}

ProductServiceImpl{
showProduct(){
hostProduct();
salesProduct();
newProduct();
}
}

ProductDaoImpl{
hostProduct();
salesProduct();
newProduct();
}

13.2 Service开发流程

client
int result = AccountServiceImpl.transfer();

if (result > 0) {
//成功
}else {
//失败
}

AccountServiceImpl {
public int transfer(){
//1.验证卡号密码
//2.验证金额是否充足
//3.验证对方卡号
//4.A账户扣钱
//5.B账户加钱
return 0/1;
}
}

AccountDaoImpl{
//1.验证卡号密码
//2.验证金额是否充足
//3.验证对方卡号
//4.A账户扣钱
//5.B账户加钱
}

13.2.1 编写service实现转账功能
/**
 * @description: 转账业务
 * @param: fromNo 转账卡号
 * @param: pwd    转账卡的密码
 * @param: toNo   收钱卡号
 * @param: money  转账金额
 */

public class AccountsServiceImpl {

    public String transfer(String fromNo,String pwd,String toNo,double money) {//1. 收参
        String result = "转账失败!"
        //2. 组织完善业务功能
        AccountsDaoImpl accountsDao = new AccountsDaoImpl();
        try {                       
            //2.1 验证fromNo是否存在
            Accounts account = accountsDao.select(fromNo);
            if (account == null) {
                throw new RuntimeException("您的卡号不存在!");
            }

            //2.2 验证fromNo的密码是否正确
            if (!account.getPassword().equals(pwd)) {
                throw new RuntimeException("您的密码错误!");
            }

            //2.3 验证fromNo的余额是否充足
            if (account.getBalance() < money) {
                throw new RuntimeException("您的余额不足!");
            }

            //2.4 验证toNo的卡号是否存在
            Accounts toAccount = accountsDao.select(toNo);
            if (toAccount == null) {
                throw new RuntimeException("抱歉,对方卡号不存在!");
            }

            //2.5 减少fromNo的余额
            //修改自己的金额,将余额减去转账金额 替换原有的属性
            account.setBalance(account.getBalance() - money);
            accountsDao.update(account);

            //2.6 增加toNo的余额
            toAccount.setBalance(toAccount.getBalance() + money);
            accountsDao.update(toAccount);

            result = "转账成功!";
            
        } catch (Exception e) {
            e.printStackTrace();              
        } finally {
            DBUtils.closeAll(conn,null,null);
        }
        return result;
    }
}
折叠

十四. 事务

14.1 service层控制事务

public class AccountsServiceImpl {

    public String transfer(String fromNo,String pwd,String toNo,double money) {//1. 收参
        String result = "转账失败!";
        //2. 组织完善业务功能
        AccountsDaoImpl accountsDao = new AccountsDaoImpl();

        //拿一个连接
        Connection conn = null;

        try {
            //建立了一个数据库连接
            conn = DBUtils.getConnection();
            System.out.println("service: "+conn);
            //开启事务,并关闭事务的自动提交
            conn.setAutoCommit(false);

            //2.1 验证fromNo是否存在
            Accounts account = accountsDao.select(fromNo);
            if (account == null) {
                throw new RuntimeException("您的卡号不存在!");
            }

            //2.2 验证fromNo的密码是否正确
            if (!account.getPassword().equals(pwd)) {
                throw new RuntimeException("您的密码错误!");
            }

            //2.3 验证fromNo的余额是否充足
            if (account.getBalance() < money) {
                throw new RuntimeException("您的余额不足!");
            }

            //2.4 验证toNo的卡号是否存在
            Accounts toAccount = accountsDao.select(toNo);
            if (toAccount == null) {
                throw new RuntimeException("抱歉,对方卡号不存在!");
            }

            //2.5 减少fromNo的余额
            //修改自己的金额,将余额减去转账金额 替换原有的属性
            account.setBalance(account.getBalance() - money);
            accountsDao.update(account);

            //2.6 增加toNo的余额
            toAccount.setBalance(toAccount.getBalance() + money);
            accountsDao.update(toAccount);

            result = "转账成功!";
            //执行到这里,没有异常,则提交事务
            conn.commit();
        } catch (RuntimeException | SQLException e) {
            e.printStackTrace();
            //转账失败,则整个事务回滚
            try {
                //出现异常,回滚
                System.out.println("出现了异常,回滚整个事务!");
                conn.rollback();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }

        } finally {
            DBUtils.closeAll(conn,null,null);
        }
        return result;
    }
}
折叠

14.2 解决方案1: 传递Connection

14.2.1 传递的问题

14.3 解决方案2: ThreadLocal

14.4 ThreadLocal应用

14.4.1 参数绑定
public class DBUtils {

    private static final Properties PROPERTIES = new Properties();

    private static ThreadLocal<Connection> threadLocal = new ThreadLocal<>();
    static {
        InputStream is = DBUtils.class.getResourceAsStream("/jdbc.properties");

        try {
            PROPERTIES.load(is);
            Class.forName(PROPERTIES.getProperty("driver"));
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() {
        Connection conn = threadLocal.get();//获取当前线程中存储的Connection对象,赋值给conn

        try {
            if (conn == null) {
                conn = DriverManager.getConnection(PROPERTIES.getProperty("url"), PROPERTIES.getProperty("username"), PROPERTIES.getProperty("password"));
                threadLocal.set(conn);//把连接存储到当前线程共享中
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }

        return conn;
    }

    //关闭所有连接 增加 threadLocal.remove(); 移除
    public static void closeAll(Connection conn, Statement statement, ResultSet resultSet) {
        try {
            if (resultSet != null) {
                resultSet.close();
            }
            if (statement != null) {
                statement.close();
            }
            if (conn != null) {
                conn.close();
                threadLocal.remove();//将conn移除
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
}
折叠

十五. 事务的封装

15.1 完善工具类

//开启事务
    public static void begin() {
        try {
            Connection conn = getConnection();
            conn.setAutoCommit(false);//开启事务,关闭自动提交
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }

    //提交事务
    public static void commit() {
        Connection conn = null;
        try {
            conn = getConnection();
            conn.commit();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            closeAll(conn,null,null);
        }
    }
    //回滚事务
    public static void rollback() {
        Connection conn = null;
        try {
            conn = getConnection();
            conn.rollback();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            closeAll(conn,null,null);
        }
    }

十六. 三层架构

16.1 什么是三层

  • 表示层(UI, Main)
    • 命名: XXXView
    • 职责:
      1. 收集用户输入数据
      2. 调用业务逻辑层, 完成业务方法
      3. 展示数据或展示操作结果
  • 业务逻辑层(service)
    • 命名: XXXServiceImpl
    • 职责:
      1. 开启事务
      2. 调用DAO层
      3. 处理数据
      4. 提交或回滚
  • 数据访问层(DAO)
    • 命名: XXXDaoImpl
    • 职责:
      1. 查询相关业务逻辑的数据
      2. 根据相关业务逻辑修改的数据

16.2 三层架构项目搭建(按开发步骤)

  • utils 存放工具类 (DBUtils)
  • entity 存放实体类 (Person)
  • dao 存放 DAO 接口 (PersonDao)
    • impl存放 DAO 接口实现类 (PersonDaoImpl)
  • service 存放 service 接口 (PersonServiceImpl)
    • impl存放 service 接口实现类 (PersonServiceImpl)
  • view 存放程序启动类 (main)
//1. 更自然的使用多态(父类接口引用指向子类对象)
//2. 更容易更换具体实现

public interface AccountsDao {

    int insert(Accounts accounts);
    int delete(String cardNo);
    int update(Accounts accounts);
    Accounts select(String cardNo);
    List<Accounts> selectAll();
    
}
public interface AccountsService {
    String transfer(String fromNo,String pwd,String toNo,double money);
}

十七. DaoUtils

17.1 commonUpdate

/*
* 公共处理增, 删, 改的方法
*
* @param sql 执行的sql语句
* @param args 参数列表,为占位符赋值
* @return  受影响的行数
*/
public class DaoUtils {

    public int commonUpdate(String sql,Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;

        conn = DbUtils.getConnection();
        try {
            ps = conn.prepareStatement(sql);

            for (int i = 0; i < args.length; i++) {
                ps.setObject(i+1,args[i]);
            }
            return ps.executeUpdate();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            DbUtils.closeAll(null,ps,null);
        }
        return 0;
    }
}

17.2 commonselect

/*
* 公共查询方法 (可查询单个对象, 也可以查询多个对象,可以查任何一张表)
*
* @param sql
* @param args
* @return 集合
*/
//	select * from t_account;
//	select * from t_student;
//  select * from person;
//	工具不知道查的是什么 调用者知道
//	封装对象,对象赋值 调用者清除
public List<T> commonSelect(String sql, RowMapper<T> rowMapper, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        List<T> list = new ArrayList<>();

        conn = DbUtils.getConnection();
        try {
            ps = conn.prepareStatement(sql);
            if (args != null) {
                for (int i = 0; i < args.length; i++) {
                    ps.setObject(i+1,args[i]);//为占位符赋值
                }
            }
            resultSet = ps.executeQuery();
            while (resultSet.next()) {
                // id.name,age,birthday,email,address
                // 如何根据查询结果完成ORM,如何进行对象的创建及赋值
                T t = rowMapper.getRow(resultSet);//回调--->调用者提供一个封装方法ORM
                list.add(t);
            }
            return list;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }

RowMapper接口

public interface RowMapper<T> {
    T getRow(ResultSet resultSet);
}

PersonRowMapper实现类

public class PersonRowMapper implements RowMapper<Person> {
    @Override
    public Person getRow(ResultSet resultSet) {
        Person person = null;
        try {
            int pid = resultSet.getInt("id");
            String name = resultSet.getString("name");
            int age = resultSet.getInt("age");
            Date birthday = resultSet.getDate("birthday");
            String email = resultSet.getString("email");
            String address = resultSet.getString("address");

            person = new Person(pid,name,age,birthday,email,address);
            return person;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }
}

十八. Druid连接池

18.1 Druid连接池使用步骤

18.1.1 database.properties配置文件
#<!-- 连接设置 -->
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/companydb?useUnicode=true&characterEncoding=utf8
username=root
password=root
#<!-- 初始化连接 -->
initialSize=10
#<!-- 最大连接数量 -->
maxActive=30
#<!-- 最小空闲连接 -->
minIdle=5
#<!-- 超时等待时间以毫秒为单位 60000毫秒/1000等于60秒 -->
maxWait=5000
18.1.2 连接池工具类
public class DbUtils {
    //声明连接池对象
    private static DruidDataSource ds;
    static {
        Properties properties = new Properties();
        InputStream is = DbUtils.class.getResourceAsStream("/database.properties");
        try {
            properties.load(is);
            //创建连接池
            ds = (DruidDataSource)DruidDataSourceFactory.createDataSource(properties);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() {
        try {
            return ds.getConnection();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }
}

十九. Apache的DbUtils的使用

19.1 DbUtils简介

19.1.1 DbUtils主要包含

19.2 DbUtils的使用步骤

19.2.1 DbUtils工具类
public class DbUtils {
    //声明连接池对象
    private static DruidDataSource ds;

    static {
        //实例化配置对象
        Properties properties = new Properties();
        InputStream is = DbUtils.class.getResourceAsStream("/database.properties");
        try {
            //加载配置文件内容
            properties.load(is);
            //创建连接池
            ds = (DruidDataSource)DruidDataSourceFactory.createDataSource(properties);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    //获取连接对象
    public static Connection getConnection() {
        try {
            return ds.getConnection();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }
    //返回一个数据源ds
    public static DataSource getDataSource() {
        return ds;
    }
    //释放资源
    //调用close()方法,实际调用的是DruidPooledConnection实现类里的close()
}
19.2.2 UserDaoImpl数据访问对象
public class UserDaoImpl implements UserDao {
    //创建QueryRunner对象,并传递一个数据源对象
    private QueryRunner queryRunner = new QueryRunner(DbUtils.getDataSource());
    @Override
    //1. 新增
    public int insert(User user) {
        Object[] params = {user.getUserId(),user.getUsername(),user.getPassword(),user.getAddress(),user.getPhone()};
        try {
            int result = queryRunner.update("insert into user(userId,username,password,address,phone) values(?,?,?,?,?)", params);
            return result;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return 0;
    }

    @Override
    //2. 删除
    public int delete(int userId) {
        try {
            int result = queryRunner.update("delete from user where userId=?", userId);
            return result;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return 0;
    }

    @Override
    //3. 修改
    public int update(User user) {
        Object[] params = {user.getUsername(),user.getPassword(),user.getAddress(),user.getPhone(),user.getUserId()};
        try {
            int result = queryRunner.update("update user set username=?,password=?,address=?,phone=? where userId=?", params);
            return result;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return 0;
    }

    @Override
    //4. 查单个
    public User select(int userId) {
        try {
            //把查询到的记录封装成 指定对象
            User user = queryRunner.query("select * from user where userId=?", new BeanHandler<User>(User.class), userId);
            return user;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }

    @Override
    //5. 查所有
    public List<User> selectAll() {
        try {
            List<User> userList = queryRunner.query("select * from user", new BeanListHandler<User>(User.class));
            return userList;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }

    @Override
    //6. 查数量(单行单列)
    public long selectUserNums() {
        try {
            long count = queryRunner.query("select count(*) from user", new ScalarHandler<>());
            return count;
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return 0;
    }
}

标签：JDBC,return,String,resultSet,null,public,conn
来源： https://www.cnblogs.com/spyX/p/16448012.html