69期-Java SE-037_JDBC-1

時間 2019-11-09

標籤 java jdbc 欄目 Java 简体版

原文原文鏈接

### JDBC

Java Database Connectivity 是一個獨立於特定數據庫的管理系統，通用的 SQL 數據庫存取和操做的公共接口。

定義了一組標準，爲訪問不一樣數據庫提供了統一途徑。

JDBC 體系結構

兩個層面：

- 面向應用的 API，供開發人員調用。
- 面向數據庫的 API，供數據庫開發廠商開發數據庫驅動程序。

JDBC API

提供者：Java 官方

內容：供開發者調用的接口

java.sql 或者 javax.sql 包中

DriverManager 類：管理數據庫驅動

Connection 接口：鏈接數據庫

Statement 接口：執行 SQL 

ResultSet 接口：封裝結果集



Driver Manager

提供者：Java 官方

做用：爲不一樣的數據庫產品提供統一的接入標準。



JDBC 驅動

提供者：數據庫廠商

做用：讓 Java 完成與特定數據庫的對接。



### 使用 JDBC 原理

1、加載數據庫驅動，Java Application 和 數據庫的橋樑。

2、獲取 Connection，一次鏈接。

3、經過 Connection 對象產生 Statement，執行 SQL 語句。

4、ResultSet 保存 Statment 執行後所產生的結果。



```java
package com.southwind.test;

import com.southwind.entity.User;

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

public class Test {
    public static void main(String[] args) {
        delete();
    }

    public static void save(){
        try {
            Connection connection = getConn();
            //三、定義 SQL
            String sql = "insert into t_user(username,password,age) values('conn','000',18)";
            //四、執行 SQL
            Statement statement = connection.createStatement();
            int result = statement.executeUpdate(sql);
            System.out.println(result);
            statement.close();
            connection.close();
        } catch (SQLException e){
            e.printStackTrace();
        }
    }

    public static void find(){
        try {
            Connection connection = getConn();
            String sql = "select * from t_user where id = 2";
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);
            User user = new User();
            if(resultSet.next()){
                long id = resultSet.getLong(1);
                String username = resultSet.getString(2);
                String password2 = resultSet.getString(3);
                int age = resultSet.getInt(4);
                user.setId(id);
                user.setUsername(username);
                user.setPassword(password2);
                user.setAge(age);
            }
            System.out.println(user);
            statement.close();
            connection.close();
        } catch (SQLException e){
            e.printStackTrace();
        }
    }

    public static void findAll(){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            connection = getConn();
            String sql = "select * from t_user";
            statement = connection.createStatement();
            resultSet = statement.executeQuery(sql);
            List<User> list = new ArrayList<>();
            User user = null;
            while(resultSet.next()){
                long id = resultSet.getLong(1);
                String username = resultSet.getString(2);
                String password2 = resultSet.getString(3);
                int age = resultSet.getInt(4);
                user = new User(id,username,password2,age);
                list.add(user);
            }
            for(User user1 :list){
                System.out.println(user1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if(connection != null){
                    connection.close();
                }
                if(statement != null){
                    statement.close();
                }
                if(resultSet != null){
                    resultSet.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static void update(){
        Connection connection = null;
        Statement statement = null;
        try {
            connection = getConn();
            String sql = "update t_user set username = 'tom',password = '100',age = 16";
            statement = connection.createStatement();
            System.out.println(statement.executeUpdate(sql));
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                if(connection!=null){
                    connection.close();
                }
                if(statement!=null){
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

    }

    public static void delete(){
        Connection connection = null;
        Statement statement = null;
        try{
            connection = getConn();
            String sql = "delete from t_user where id = 2";
            statement = connection.createStatement();
            System.out.println(statement.executeUpdate(sql));
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if(connection != null){
                    connection.close();
                }
                if(statement != null){
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static Connection getConn(){
        Connection connection = null;
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/mbtest?useUnicode=true&characterEncoding=UTF-8";
            String user = "root";
            String password = "root";
            connection = DriverManager.getConnection(url,user,password);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }
}
```



根據數據表建立相應的類，叫作實體類。

```java
package com.southwind.entity;

public class User {
    private Long id;
    private String username;
    private String password;
    private Integer age;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", age=" + age +
                '}';
    }

    public User(Long id, String username, String password, Integer age) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
    }

    public User() {
    }
}
```



### 加載驅動

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

反射機制，獲取運行時類，什麼是運行時類？Java 程序是由類組成的，運行時，會將全部的類添加到 JVM 內存中，而且每一個類只有一份，保證在 JVM 內存中的類就叫作運行時類。

運行時類是一個動態概念，只有當程序運行的時候，纔有運行時類。



Statement 的方法，Statement 是經過 Connection 產生的，是用來執行 SQL 語句的，經常使用的方法：

- ResultSet executeQuery(String sql) 用來執行查詢操做。

- int executeUpdate(String sql) 用來執行新增，修改，刪除操做。

- boolean execute(String sql) 能夠執行任意的 CRUD 操做。

  true 表示返回結果是 ResultSet，執行的是查詢操做。

  false 表示返回結果不是 ResultSet，執行的是新增、修改、刪除操做。

/entity/User.javajava

package com.southwind.entity;

public class User {
    private Long id;
    private String username;
    private String password;
    private Integer age;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", age=" + age +
                '}';
    }

    public User(Long id, String username, String password, Integer age) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
    }

    public User() {
    }
}

test/Test.javamysql

package com.southwind.test;

import com.southwind.entity.User;

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

public class Test {
    public static void main(String[] args) {
        test();
    }

    public static void save(){
        try {
            Connection connection = getConn();
            //三、定義 SQL
            String sql = "insert into t_user(username,password,age) values('conn','000',18)";
            //四、執行 SQL
            Statement statement = connection.createStatement();
            int result = statement.executeUpdate(sql);
            System.out.println(result);
            statement.close();
            connection.close();
        } catch (SQLException e){
            e.printStackTrace();
        }
    }

    public static void find(){
        try {
            Connection connection = getConn();
            String sql = "select * from t_user where id = 2";
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);
            User user = new User();
            if(resultSet.next()){
                long id = resultSet.getLong(1);
                String username = resultSet.getString(2);
                String password2 = resultSet.getString(3);
                int age = resultSet.getInt(4);
                user.setId(id);
                user.setUsername(username);
                user.setPassword(password2);
                user.setAge(age);
            }
            System.out.println(user);
            statement.close();
            connection.close();
        } catch (SQLException e){
            e.printStackTrace();
        }
    }

    public static void findAll(){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            connection = getConn();
            String sql = "select * from t_user";
            statement = connection.createStatement();
            resultSet = statement.executeQuery(sql);
            List<User> list = new ArrayList<>();
            User user = null;
            while(resultSet.next()){
                long id = resultSet.getLong(1);
                String username = resultSet.getString(2);
                String password2 = resultSet.getString(3);
                int age = resultSet.getInt(4);
                user = new User(id,username,password2,age);
                list.add(user);
            }
            for(User user1 :list){
                System.out.println(user1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if(connection != null){
                    connection.close();
                }
                if(statement != null){
                    statement.close();
                }
                if(resultSet != null){
                    resultSet.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static void update(){
        Connection connection = null;
        Statement statement = null;
        try {
            connection = getConn();
            String sql = "update t_user set username = 'tom',password = '100',age = 16";
            statement = connection.createStatement();
            System.out.println(statement.executeUpdate(sql));
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                if(connection!=null){
                    connection.close();
                }
                if(statement!=null){
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

    }

    public static void delete(){
        Connection connection = null;
        Statement statement = null;
        try{
            connection = getConn();
            String sql = "delete from t_user where id = 2";
            statement = connection.createStatement();
            System.out.println(statement.executeUpdate(sql));
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if(connection != null){
                    connection.close();
                }
                if(statement != null){
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static Connection getConn(){
        Connection connection = null;
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/mbtest?useUnicode=true&characterEncoding=UTF-8";
            String user = "root";
            String password = "root";
            connection = DriverManager.getConnection(url,user,password);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }

    public static void test(){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try{
            connection = getConn();
//            String sql = "select * from t_user where id = 3";
//            String sql = "insert into t_user(username,password,age) values('aaa','111',22)";
//            String sql = "update t_user set username = 'aa',password='11',age=11";
            String sql = "delete from t_user";
            statement = connection.createStatement();
            boolean flag = statement.execute(sql);
            System.out.println(flag);
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if(connection!=null){
                    connection.close();
                }
                if(statement!=null){
                    statement.close();
                }
                if(resultSet!=null){
                    resultSet.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

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