一、JDBC基本概念

概念：Java DataBase Connectivity

JDBC是Java DataBase Connectivity的縮寫，Java數據庫連接，也就是Java語言操作數據庫。
JDBC的本質：是sun公司定義的一套操作所有關係型數據庫的規則，即接口。各個數據庫廠商去實現這套藉口提供數據庫驅動jar包。我們可以使用這套接口（JDBC）編程，真正執行的代碼是jar包當中的實現類。

二、快速入門

步驟

1、導入驅動jar包

在項目當中創建libs目錄，並將mysql-connector-java-5.1.48-bin.jar文件複製到libs目錄下
右鍵libs文件夾，選擇add as library

2、註冊驅動

	Class.forName("com.mysql.jdbc.Driver"); //調用靜態代碼塊

3、獲取數據庫連接對象 Connection

/**
 *url:指明數據庫的名稱
 *user:用戶名
 *password:密碼
 */
Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/city", "root", "root");

4、定義sql

//同sql語句
String sql = "UPDATE employee SET age = 22 WHERE NAME = '張三'";

5、獲取執行sql語句的對象 statement

Statement statement = connection.createStatement();

6、執行sql，接收返回結果

//結果是整型
int count = statement.executeUpdate(sql);

7、處理結果

//僅僅是代表一個步驟,實際上不是光打印count這麼簡單
System.out.println(count);

8、釋放資源

//close()方法釋放資源
statement.close();
connection.close();

整體代碼段

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

public class JDBCDemo {
    public static void main(String[] args) throws Exception {
        // 1.導入驅動jar包 mysql-connector-java-5.1.48-bin.jar
        // 2.註冊驅動
        Class.forName("com.mysql.jdbc.Driver");
        // 3.獲取數據庫連接對象
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/city", "root", "cjd510510");
        // 4.定義sql語句
        String sql = "UPDATE employee SET age = 22 WHERE NAME = '張三'";
        // 5.獲取執行sql的對象
        Statement statement = connection.createStatement();
        // 6.執行sql
        int count = statement.executeUpdate(sql);
        // 7.處理結果
        System.out.println(count);
        // 8.釋放資源
        statement.close();
        connection.close();
    }
}

三、對JDBC中各個接口和類的詳細解析

DriverManager：驅動管理對象

1、註冊驅動

	// DriverManager當中的註冊驅動的方法
	public static synchronized void registerDriver(java.sql.Driver driver)
	       throws SQLException {
	
	       registerDriver(driver, null);
	}
	// 在com.mysql.jdbc.Driver類當中存在靜態代碼塊
	// 靜態塊當中的代碼將會調用DriverManager的registerDriver方法
	public class Driver extends NonRegisteringDriver implements java.sql.Driver {
	    public Driver() throws SQLException {
	    }
	
	    static {
	        try {
	            DriverManager.registerDriver(new Driver());
	        } catch (SQLException var1) {
	            throw new RuntimeException("Can't register driver!");
	        }
	    }
	}

2、獲取數據庫連接

/**
 *url:指定連接的路徑
 *jdbc:mysql://ip地址(域名):端口號/數據庫名稱
 *user:用戶名
 *password:密碼
 */
public static Connection getConnection(String url, String user, String password) 
	throws SQLException {}

Connection：數據庫連接對象

/**
 *功能:獲取執行sql語句的對象
 *createStatement()
 *preparedStatement()
 *=============================
 *功能:管理實務
 *開啓事務:setAutoCommit(boolean autoCommit)
 *autoCommit=false->開啓事務
 *提交事務:commit()
 *回滾事務:rollback()
 */
Statement createStatement() throws SQLException;
PreparedStatement prepareStatement(String sql) throws SQLException;

void setAutoCommit(boolean autoCommit) throws SQLException;
void commit() throws SQLException;
void rollback() throws SQLException;

Statement：執行sql對象

/**
 *功能:執行靜態sql語句並返回其生成的結果對象
 *執行任意sql語句:execute(String sql)
 *執行DDL,DML語句:executeUpdate(String sql)
 *return->影響的行數
 *執行DQL語句:executeQuery(String sql)
 *return->ResultSet
 */
boolean execute(String sql) throws SQLException;
int executeUpdate(String sql) throws SQLException;
ResultSet executeQuery(String sql) throws SQLException;

實例練習


import java.sql.*;

public class JDBCDemo {
    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/city","root", "root");
            statement = connection.createStatement();

            String insertSQL = "INSERT INTO STUDENT (ID, NAME, AGE, SEX, ADDRESS, MATH, ENGLISH) VALUES (9, '陳', 20, '男', '山東', 100, 99)";
            String updateSQL = "UPDATE STUDENT SET ENGLISH = 100 WHERE NAME = '陳'";
            String deleteSQL = "DELETE FROM STUDENT WHERE NAME = '馬德'";

            System.out.println(statement.executeUpdate(insertSQL));
            System.out.println(statement.executeUpdate(updateSQL));
            System.out.println(statement.executeUpdate(deleteSQL));

        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {

            if(statement != null) {
                try {
                    statement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

            if(connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

        }

    }
}

ResultSet：結果集對象

/**
 *遊標向下移動一行:next()
 *獲取數據:getXxx(),只能一行按列獲取
 *獲取某一列的數據:getXxx(int columnIndex),getXxx(String columnLabel)
 *columnIndex從1開始
 */
boolean next() throws SQLException;
double getDouble(String columnLabel) throws SQLException;
int getInt(int columnIndex) throws SQLException;

簡單實例練習

import java.sql.*;

public class JDBCDemo {
    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/city","root", "cjd510510");
            statement = connection.createStatement();

            String  querySQL = "SELECT * FROM STUDENT WHERE NAME LIKE '___'";
            resultSet = statement.executeQuery(querySQL);

            System.out.println("id    name    age    sex    address    math    english");

            while(resultSet.next()) {
                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                int age = resultSet.getInt(3);
                String sex = resultSet.getString(4);
                String address = resultSet.getString(5);
                int math = resultSet.getInt(6);
                int english = resultSet.getInt(7);
                System.out.println(" " + id + "    " + name + "    " + age + "      " + sex + "      " + address + "       " + math + "      " + english);
            }

        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {

            if(statement != null) {
                try {
                    statement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

            if(resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

            if(connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

        }

    }
}

PreparedStatement：執行sql對象（後期全部使用該類來完成增刪改查的所有操作）

sql注入問題

在拼接sql時有一些sql特殊關鍵字參與字符串的拼接，造成安全性的問題

使用PreparedStatement類解決sql注入問題

/*
 * 預編譯SQL:參數作爲佔位符
 * 步驟:
 * 1.在定義sql時參數使用佔位符
 * "select * from ？ where name = ?"
 * 2.給佔位符賦值
 * setXxx(int parameterIndex, typedef x)
 * parameterIndex:問號的位置
 * typedef:數據類型
 * 3.執行sql語句
 * executeUpdate(),executeQuery()
 */
import java.sql.*;
import java.util.Scanner;

public class JDBCDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Connection connection = JDBCUtil.getConnection();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            String sql = "SELECT password FROM users WHERE name = ?";
            preparedStatement = connection.prepareStatement(sql);

            String user, password;
            while(scanner.hasNext()) {
                user = scanner.next();
                password = scanner.next();

                preparedStatement.setString(1, user);
                resultSet = preparedStatement.executeQuery();
                if(!resultSet.next()) {
                    System.out.println("賬號不存在!");
                    continue;
                }

                if(password.trim().equals(resultSet.getString("password").trim())) {
                    System.out.println("登陸成功!");
                } else {
                    System.out.println("登陸失敗!");
                }
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }

        JDBCUtil.close(connection, preparedStatement, resultSet);
        scanner.close();
    }
}

JDBC

一、JDBC基本概念

概念：Java DataBase Connectivity

二、快速入門

步驟

整體代碼段

三、對JDBC中各個接口和類的詳細解析

DriverManager：驅動管理對象

Connection：數據庫連接對象

Statement：執行sql對象

ResultSet：結果集對象

PreparedStatement：執行sql對象（後期全部使用該類來完成增刪改查的所有操作）

sql注入問題

使用PreparedStatement類解決sql注入問題

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