[부스트코스 SQL] JDBC

JDBC (JAVA Database Connectivity)

• 자바를 이용한 데이터베이스 접속과 SQL 문장의 실행, 그리고 실행 결과로 얻어진 데이터의 핸들링을 제공하는 방법과 절차에 관한 규약
  -자바 프로그램내에서 SQL문을 실행하기 위한 자바 API

<dependency>
  <groupId)mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.45</version>
</dependency>

JDBC를 이용한 프로그래밍 방법

1. import java.sql.*;
2. 드라이버를 로드한다.
3. Connection 객체 생성
4. Statement 객체를 생성 및 질의 수행
5. SQL문에 결과물이 잇다면 ResultSet 객체 생성
6. 모든 객체를 닫는다

1. import

import java.sql.*;

2. 드라이버 로드

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

3. Connection 얻기

1. String dburl = "jdbc:mysql://localhost/dbName";
2. Connection con = DriverManager.getConnection(dburl, ID, PWD);

4. Statement 생성

Statement stmt = con.createStatement();

5. 질의 수행

ResultSet rs = stmt.executeQuery("select no from user");

6. ResultSet으로 결과 받기

while(rs.next())
    System.out.println(rs.getInt("no"));

7. Close

rs.close();
stmt.close();
con.close();

실습 1

실습 자료 링크

File -> New -> Other -> Maven Project

pom.xml 수정

plugins에 하위 코드 추가

		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-compiler-plugin</artifactId>
			<version>3.6.1</version>
			<configuration>
				<source>1.8</source>
				<target>1.8</target>
			</configuration>
		</plugin>

dependencies에 하위 코드 추가

    <dependency>
		<groupId>mysql</groupId>
		<artifactId>mysql-connector-java</artifactId>
		<version>5.1.45</version>
	</dependency>

구조

1. Role 클래스 생성

package kr.or.connect.jdbcexam.dto;

public class Role {
	private Integer roleId;
	private String description;
	
	public Role() {
		
	}
	
	public Role(Integer roleId, String description) {
		super();
		this.roleId = roleId;
		this.description = description;
	}
	
	public Integer getRoleId() {
		return roleId;
	}
	
	public void setRoleId(Integer roleId) {
		this.roleId = roleId;
	}
	
	public String getDescription() {
		return description;
	}
	
	public void setDescription(String description) {
		this.description = description;
	}
	
	@Override
	public String toString() {
		return "Role [roleId=" + roleId + ", description=" + description + "]";
	}
}

2. RoleDao 클래스 생성

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import kr.or.connect.jdbcexam.dto.Role;

public class RoleDao {
	private static String dburl = "jdbc:mysql://localhost:3306/connectdb?useSSL=false";
	private static String dbUser = "connectuser";
	private static String dbpasswd = "connect123!@#";
	
	public Role getRole(Integer roleId) {
		Role role = null; //
		Connection conn = null; //연결 객체
		PreparedStatement ps = null; //명령 선언 객체
		ResultSet rs = null; //결과값 담을 객체
		
		try {
			Class.forName("com.mysql.jdbc.Driver"); //드라이버가 로딩됨
			conn = DriverManager.getConnection(dburl,dbUser, dbpasswd);
			String sql = "SELECT role_id, description FROM role WHERE role_id = ?";
			ps = conn.prepareStatement(sql);
			ps.setInt(1, roleId);
			rs = ps.executeQuery();
			
			if (rs.next()) {
				String description = rs.getString("description"); //첫번째 컬럼
				int id = rs.getInt("role_id");
				role = new Role(id, description);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if (rs != null) {
				try {
					rs.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
			if (ps != null) {
				try {
					ps.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
			if (conn != null) {
				try {
					conn.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
		
		return role;
	}
  }

3. JDBCExam1 클래스 생성

package kr.or.connect.jdbcexam;

import kr.or.connect.jdbcexam.dao.RoleDao;
import kr.or.connect.jdbcexam.dto.Role;

public class JDBCExam1 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		RoleDao dao = new RoleDao();
		Role role = dao.getRole(100);
		System.out.println(role);
	}

}

실행결과:

Role [roleId=100, description=Developer]

실습 2

INSERT 하기

	public int addRole(Role role) {
		int insertCount = 0;
		
		Connection conn = null;
		PreparedStatement ps = null;
		
		try {
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager.getConnection(dburl, dbUser, dbpasswd);
			String sql = "INSERT INTO role (role_id, description) VALUES (?, ?)";
			
			ps = conn.prepareStatement(sql);
			ps.setInt(1,  role.getRoleId());
			ps.setString(2,  role.getDescription());
			
			insertCount = ps.executeUpdate();
		} catch (Exception ex) {
			ex.printStackTrace();
		} finally {
			if (ps != null) {
				try {
					ps.close();
				}catch (Exception ex) {
					
				}
			}
			
			if (conn != null) {
				try {
					conn.close();
				} catch (Exception ex) {
					
				}
			}
		}
		return insertCount;
	}

package kr.or.connect.jdbcexam;

import kr.or.connect.jdbcexam.dao.RoleDao;
import kr.or.connect.jdbcexam.dto.Role;

public class JDBCExam2 {

	public static void main(String[] args) {
		int roleId = 500;
		String description = "CTO";
		
		Role role = new Role(roleId, description);
		
		RoleDao dao = new RoleDao();
		int insertCount = dao.addRole(role);
		
		System.out.println(insertCount);

	}

}

실습 3

모두 조회하기

try-with-resource 사용

	public List<Role> getRoles() {
		List<Role> list = new ArrayList<>();
		
		try {
			Class.forName("com.mysql.jdbc.Driver");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
		
		String sql = "SELECT description, role_id FROM role ORDER BY role_id DESC";
		
		try (Connection conn = DriverManager.getConnection(dburl, dbUser, dbpasswd);
				PreparedStatement ps = conn.prepareStatement(sql)) {
					try (ResultSet rs = ps.executeQuery()) {
						while (rs.next()) {
							String description = rs.getString("description");
							int id = rs.getInt("role_id");
							Role role = new Role(id, description);
							list.add(role);
						}
					} catch (Exception e) {
						e.printStackTrace();
					}
		} catch (Exception ex) {
			ex.printStackTrace();
		}
		return list;
	}

package kr.or.connect.jdbcexam;

import java.util.List;

import kr.or.connect.jdbcexam.dao.RoleDao;
import kr.or.connect.jdbcexam.dto.Role;

public class JDBCExam3 {
	public static void main(String[] args) {
		RoleDao dao = new RoleDao();
		
		List<Role> list = dao.getRoles();
		
		for (Role role : list) {
			System.out.println(role);
		}
	}
}