JavaWeb之JDBC

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1.概念

  • 概念:Java DataBase Connectivity Java 数据库连接, Java语言操作数据库
  • JDBC本质:其实是官方(sun公司)定义的一套操作所有关系型数据库的规则,即接口。各个数据库厂商去实现这套接口,提供数据库驱动jar包。我们可以使用这套接口(JDBC)编程,真正执行的代码是驱动jar包中的实现类。

2. 快速入门:

2.1 步骤:

  • 导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
    • 复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
    • 右键–>Add As Library
  • 注册驱动
  • 获取数据库连接对象 Connection
  • 定义sql
  • 获取执行sql语句的对象 Statement
  • 执行sql,接受返回结果
  • 处理结果
  • 释放资源

2.2 代码实现

//1. 导入驱动jar包
 //2.注册驱动
 Class.forName("com.mysql.jdbc.Driver");
 //3.获取数据库连接对象
 Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3", "root", "root");
 //4.定义sql语句
 String sql = "update account set balance = 500 where id = 1";
 //5.获取执行sql的对象 Statement
 Statement stmt = conn.createStatement();
 //6.执行sql
 int count = stmt.executeUpdate(sql);
 //7.处理结果
 System.out.println(count);
 //8.释放资源
 stmt.close();
 conn.close();
package com.weeks.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;

/**
 * JDBC 的快速入门
 */
public class JDBCDemo 
    public static void main(String[] args) throws Exception 
        //1.注册驱动
        Class.forName("com.mysql.jdbc.Driver");

        //2.获取链接
        String url = "jdbc:mysql://localhost:3306/javaweb";
        String username = "root";
        String password = "root123";
        Connection conn = DriverManager.getConnection(url, username, password);

        //3.定义sql
        String sql = "update user set name='rising' where id=202101";

        //4.获取执行sql的对象
        Statement statement = conn.createStatement();

        //5.执行sql语句
        int i = statement.executeUpdate(sql);

        //6.处理结果
        System.out.println(i);

        //8.释放资源
        statement.close();
        conn.close();
    

3.详解各个对象

3.1 DriverManager:驱动管理对象

  • 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 
       java.sql.DriverManager.registerDriver(new Driver());
    catch (SQLException E) 
       throw new RuntimeException("Can't register driver!");
   

注意:mysql5之后的驱动jar包可以省略注册驱动的步骤。
  • 获取数据库连接:
    • 方法:static Connection getConnection(String url, String user, String password)
    • 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: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:///数据库名称
    • user:用户名
    • password:密码

3.2 Connection:数据库连接对象

  • 功能:
    • 获取执行sql 的对象
      • Statement createStatement()
      • PreparedStatement prepareStatement(String sql)
  • 管理事务:
    • 开启事务:setAutoCommit(boolean autoCommit) :调用该方法设置参数为false,即开启事务
    • 提交事务:commit()
    • 回滚事务:rollback()

3.3 Statement:执行sql的对象

  • 执行sql
    • boolean execute(String sql) :可以执行任意的sql 了解
    • int executeUpdate(String sql) :执行DML(insert、update、delete)语句、DDL(create,alter、drop)语句
      • 返回值:影响的行数,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。
    • ResultSet executeQuery(String sql) :执行DQL(select)语句
  • 练习:
    1. account表 添加一条记录
    2. account表 修改记录
    3. account表 删除一条记录
package com.weeks.jdbc;

import org.junit.Test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * jdbc增删改测试
 */
public class JDBCDemo2 
    @Test
    public void testInsert()
        Statement stmt = null;
        Connection conn = null;
        try 
            //1.导入驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db2", "root", "root123");
            //3.定义sql语句
            String sql = "insert into account (name, balance) values ('wangwu', 2000)";
            //4.定义执行sql的对象
            stmt = conn.createStatement();
            //5.执行sql语句
            int count = stmt.executeUpdate(sql);
            //6.处理结果
            System.out.println(count);

         catch (ClassNotFoundException | SQLException e) 
            e.printStackTrace();
         finally 
            //7.关闭资源
            if(stmt != null)//防止空指针异常
                try 
                    stmt.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            

            if(conn != null)
                try 
                    conn.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            
        
    

    @Test
    public void testUpdate()
        Statement stmt = null;
        Connection conn = null;
        try 
            //1.导入驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db2", "root", "root123");
            //3.定义sql语句
            String sql = "update account set balance='1000' where id=3";
            //4.定义执行sql的对象
            stmt = conn.createStatement();
            //5.执行sql语句
            int count = stmt.executeUpdate(sql);
            //6.处理结果
            System.out.println(count);

         catch (ClassNotFoundException | SQLException e) 
            e.printStackTrace();
         finally 
            //7.关闭资源
            if(stmt != null)//防止空指针异常
                try 
                    stmt.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            

            if(conn != null)
                try 
                    conn.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            
        
    

    @Test
    public void testDelete()
        Statement stmt = null;
        Connection conn = null;
        try 
            //1.导入驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db2", "root", "root123");
            //3.定义sql语句
            String sql = "delete from account where id = 4";
            //4.定义执行sql的对象
            stmt = conn.createStatement();
            //5.执行sql语句
            int count = stmt.executeUpdate(sql);
            //6.处理结果
            System.out.println(count);

         catch (ClassNotFoundException | SQLException e) 
            e.printStackTrace();
         finally 
            //7.关闭资源
            if(stmt != null)//防止空指针异常
                try 
                    stmt.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            

            if(conn != null)
                try 
                    conn.close();
                 catch (SQLException throwables) 
                    throwables.printStackTrace();
                
            
        
    


3.4 ResultSet:结果集对象,封装查询结果

  • boolean next(): 游标向下移动一行,判断当前行是否是最后一行末尾(是否有数据),如果是,则返回false,如果不是则返回true

  • getXxx(参数):获取数据

    • Xxx:代表数据类型 如: int getInt() , String getString()

    • 参数:

      • int:代表列的编号,从1开始 如: getString(1)
      • String:代表列名称。 如: getDouble(“balance”)
      • 注意:
        • 使用步骤:
          • 游标向下移动一行
          • 判断是否有数据
          • 获取数据
  • 练习:

    • 定义一个方法,查询emp表的数据将其封装为对象,然后装载集合,返回。
      1. 定义Emp类
      2. 定义方法 public List findAll()
      3. 实现方法 select * from emp;
create table emp(
	id int primary key,
	ename varchar(50),
	job_id int,
	mgr int,
	joindate date,
	salary decimal(7, 2),
	bonus decimal(7, 2),
	dept_id int,
);

INSERT INTO emp(id,ename,job_id,mgr,joindate,salary,bonus,dept_id) VALUES 
(1001,'孙悟空',4,1004,'2000-12-17','8000.00',NULL,20),
(1002,'卢俊义',3,1006,'2001-02-20','16000.00','3000.00',30),
(1003,'林冲',3,1006,'2001-02-22','12500.00','5000.00',30),
(1004,'唐僧',2,1009,'2001-04-02','29750.00',NULL,20),
(1005,'李逵',4,1006,'2001-09-28','12500.00','14000.00',30),
(1006,'宋江',2,1009,'2001-05-01','28500.00',NULL,30),
(1007,'刘备',2,1009,'2001-09-01','24500.00',NULL,10),
(1008,'猪八戒',4,1004,'2007-04-19','30000.00',NULL,20),
(1009,'罗贯中',1,NULL,'2001-11-17','50000.00',NULL,10),
(1010,'吴用',3,1006,'2001-09-08','15000.00','0.00',30),
(1011,'沙僧',4,1004,'2007-05-23','11000.00',NULL,20),
(1012,'李逵',4,1006,'2001-12-03','9500.00',NULL,30),
(1013,'小白龙',4,1004,'2001-12-03','30000.00',NULL,20),
(1014,'关羽',4,1007,'2002-01-23','13000.00',NULL,10);
package com.weeks.domain;

import java.util.Date;

public class Emp 
    private Integer id;
    private String name;
    private Integer jobId;
    private Integer manager;
    private Date joinDate;
    private double salary;
    private double bonus;
    private Integer deptId;

    public Integer getId() 
        return id;
    

    public void setId(Integer id) 
        this.id = id;
    

    public String getName() 
        return name;
    

    public void setName(String name) 
        this.name = name;
    

    public Integer getJobId() 
        return jobId;
    

    public void setJobId(Integer jobId) 
        this.jobId = jobId;
    

    public Integer getManager() 
        return manager;
    

    public void setManager(Integer manager) 
        this.manager = manager;
    

    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 Integer getDeptId() 
        return deptId;
    

    public void setDeptId(Integer deptId) 
        this.deptId = deptId;
    

    @Override
    public String toString() 
        return "Emp" +
                "id=" + id +
                ", name='" + name + '\\'' +
                ", jobId=" + jobId +
                ", manager=" + manager +
                ", joinDate=" + joinDate +
                ", salary=" + salary +
                ", bonus=" + bonus +
                ", deptId=" + deptId +
                '';
    

package com.weeks.jdbc;

import com.weeks.domain.Emp;
import org.junit.Test;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * jdbc ResultSet测试
 */
public class JDBCDemo4 
    @Test
    public void testResultSet()
        ResultSet resultSet = null;
        Statement stmt = null;
        Connection conn = null;
        try 
            //1.导入驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3", "root", "root123");
            //3.定义sql语句
            String sql = "select * from emp";
            //4.定义执行sql的对象
            stmt = conn.createStatement();
            //5.执行sql语句
            resultSet = stmt.executeQuery(sql);
            //6.处理结果
            Emp emp = null;
            List<Emp> emps = new ArrayList<>();
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