JDBC精解--java連接mysql數據庫

java與數據庫的連接

1.JDBC簡介

1.JDBC(Java Data Base Connectivity)是由java編程語言編寫的類及接口組成,
利用JDBC可以將JAVA代碼連接到oracle、DB2、SQLServer、MYSQL等數據庫
從而實現對數據庫中的數據操作的目的
2.JDBC是sun公司開發的一套數據庫訪問編程接口
3.JDBC四個核心類
 * DriverManager 創建連接
 * Connection    連接類
 * Statement     執行SQL語句-->執行查詢指令（executeQuery）
 * ResultSet     結果集

2.JDBC連接步驟

 * JDBC連接步驟
 * 1.註冊驅動
 * 2.獲取連接
 * 3.獲取SQL語句的執行對象 Statement
 * 4.執行SQL語句返回結果集 ResultSet
 * 5.處理結果集
 * 6.關閉資源

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

public class text1 {
     public static void main(String[] args) throws ClassNotFoundException, SQLException {
        //1.註冊一個驅動
            Class.forName("com.mysql.jdbc.Driver");//包名+類名
            //2.獲取連接對象
            String url = "jdbc:mysql://localhost:3306/myjdbc";//數據庫+主機地址+端口+數據庫名稱
            //3.連接數據庫(是個對象)
            Connection connection = DriverManager.getConnection(url, "root", "123456");//一個D..類的get..方法
            //4.獲取執行SQL語句的對象
            Statement statement = connection.createStatement();
            //5.執行sql語句 返回結果集
            String sql = "select * from users";
            ResultSet resultSet = statement.executeQuery(sql);
            //6.處理結果集-->輸出SQL語句讀取結果
            while(resultSet.next()) { //next()讀行指針          
                System.out.println(resultSet.getObject(1));//讀取第一個數據
                System.out.println(resultSet.getObject(2));
                System.out.println(resultSet.getObject(3));
                System.out.println(resultSet.getObject(4));
                System.out.println(resultSet.getObject(5));
                //注意:查詢數據庫時 索引是從1開始的
            }
            //7.關閉資源
            resultSet.close();
            statement.close();
            connection.close();

    }
}

3.JDBC增刪改查

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

import org.junit.jupiter.api.Test;

public class text2 {
-------------------1.增刪方法

      @Test //用於測試方法
      public void test() throws ClassNotFoundException, SQLException {
             //1.註冊驅動器
             Class.forName("com.mysql.jdbc.Driver");
             //2.連接數據庫(另一種方法)
             String url="jdbc:mysql://localhost:3306/myjdbc?"
                    + "user=root&password=123456";
             Connection connection = DriverManager.getConnection(url);
             //3.獲取SQL執行語句
             Statement statement = (Statement) connection.createStatement();
             //4.執行SQL語句,返回結果集
             //插入數據
             String sql = "insert into users values"
                    + "(5,'gl','123','[email protected]','2000-01-03')";   

             int row = statement.executeUpdate(sql);//executeUpdate 增刪改查使用
             System.out.println(row); //打印受影響的行數
             if (row > 0) {
                System.out.println("插入成功");
            }
             //5.關閉資源
             statement.close();
             connection.close();
         }
---------------------------------------------------------------------------------------
             2.查詢方法
           @Test
               public void testSelect()throws Exception {
                 //1.註冊驅動
                 Class.forName("com.mysql.jdbc.Driver");
                 //2.創建連接數據庫
                 String url="jdbc:mysql://localhost:3306/myjdbc?"
                        + "user=root&password=123456";
                 Connection connection = DriverManager.getConnection(url);
                 //3.獲取SQL語句執行方法
                 Statement statement = (Statement) connection.createStatement();
                 //4.執行SQL語句,返回結果集
                 //查詢
                 String sql = "select id,name,email from users";
                 ResultSet resultSet = statement.executeQuery(sql);
                 System.out.println(resultSet);//返回的是一個地址
                 //處理結果集
                 while(resultSet.next()) {//next()指針讀取器
                     System.out.println(resultSet.getObject("id"));
                     System.out.println(resultSet.getObject("name"));
                     System.out.println(resultSet.getObject("email"));
                 }
                 //5.關閉資源
                 resultSet.close();
                 statement.close();
                 connection.close();
          } 
 }

2.使用對象類打印查詢結果

2.1創建User類

package com.lanou3g.demo;

import java.sql.Date;

public class User {
        //對象中聲明的屬性名 儘量和數據庫中的字段相同
    private int id;
    public User() {
        super();

    }
    public User(int id, String name, String password, String email, Date birthday) {
            super();
            this.id = id;
            this.name = name;
            this.password = password;
            this.email = email;
            this.birthday = birthday;
        }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", password=" + password + ", email=" + email + ", birthday="
                + birthday + "]";
    }
    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 getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    private String name;
    private String password;
    private String email;
    private Date birthday;

}

2.2創建mysql查詢類

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

/*
 * 連接數據庫的異常處理
 */
public class DemoException {
  public static void main(String[] args) {
      ResultSet resultSet = null;
      Statement statement = null;
      Connection connection = null;
    try {
        //1.註冊驅動
        Class.forName("com.mysql.jdbc.Driver");
        //2.連接數據庫
        String url = "jdbc:mysql://localhost:3306/myjdbc";
        try {
            connection = DriverManager.getConnection(url, "root", "123456");
        //3.獲取SQL執行語句
            statement = connection.createStatement();
        //4.執行SQL語句,返回結果集
            String sql = "select * from users";
            resultSet = statement.executeQuery(sql);
        //5.創建ArrayLits集合讀取類型設爲User類
            ArrayList<User> list = new ArrayList<>();
            while(resultSet.next()) {
                //創建user對象
                User user = new User();
                user.setId(resultSet.getInt("id"));//user獲取返回結果集中的一條id信息
                user.setName(resultSet.getString("name"));//user獲取返回結果集中的一條name信息
                user.setPassword(resultSet.getString("password"));
                user.setBirthday(resultSet.getDate("birthday"));
                user.setEmail(resultSet.getString("email"));
                //6.將User類中的信息存入集合中
                list.add(user);
            }
            //遍歷查看
            for(User user : list) {
                System.out.println(user);
            }
        } catch (SQLException e) {
            throw new RuntimeException("獲取連接失敗");
        }finally {

            //關閉資源前判斷是否爲空 防止空指針出現
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (Exception e2) {
                    throw new RuntimeException("關閉失敗");
                }
                //加快系統回收速度
                resultSet = null;
            }
            if (statement != null) {
                try {
                    statement.close();
                } catch (Exception e2) {
                    throw new RuntimeException("關閉失敗");
                }
                //加快系統回收速度
                statement = null;
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (Exception e2) {
                    throw new RuntimeException("關閉失敗");
                }
                //加快系統回收速度
                connection = null;
            }
            //處理結果集(把數據的記錄封裝到對象中)
            //把對象保存到數組當中
        }
    } catch (ClassNotFoundException e) {
        //停止程序
        throw new RuntimeException("驅動加載失敗");
    }
}
}

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