How to connect to database with jdbc? (with code)-javaTutorial-php.cn

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Introduction to JDBC

The full name of JDBC is: Java Data Base Connectivity (java database connection), which can provide unified access to a variety of databases . JDBC is a set of database access programming interfaces developed by sun. It is a SQL-level API. It is written in Java language, so it has good cross-platform characteristics. Database applications written using JDBC can run on any platform that supports Java without having to write different applications on different platforms. [Video tutorial recommendation: Java tutorial]

JDBC programming steps

(1) Load the driver:

Download the driver package: http://dev.mysql.com/downloads/connector/j/

Unzip and get the jar file. Copy this file to the Java project directory Java Resources/Libraries/, → buildpath.

(2) Obtain database connection

(3) Create Statement object:

(4) Send SQL command to database

(5 ) Process the returned results from the database (ResultSet class)

package com.baidu.emp.jdbcTest;

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

import com.mysql.jdbc.Driver;
/**
 * 开始使用jdbc连接数据库
 * @author Admin
 *
 */
public class Test001 {

    public static void main(String[] args) throws Exception {

        /**
         * 加载驱动
         */
        // 方法一：
        /*
         * import java.sql.DriverManager; import com.mysql.jdbc.Driver;
         */
        // Driver driver = new Driver();
        // DriverManager.registerDriver(driver);

        // 方法二：(推荐使用)
        Class.forName("com.mysql.jdbc.Driver");

        /**
         * 创建链接
         */
        String url = "jdbc:mysql://localhost:3306/testjdbc";
        String user = "root";
        String password = "root";
        Connection connection = DriverManager.getConnection(url, user, password);

        // 创建statement对象
        Statement statement = connection.createStatement();

        /**
         * 执行SQL，获取结果集
         */
        String sql = "select * from test01";
        ResultSet result = statement.executeQuery(sql);

        // 遍历结果集
        while (result.next()) {
            String name = result.getString("name");
            int id = result.getInt("id");
            System.out.println(name + "\t" + id);
        }

        /**
         * 关闭链接，释放资源
         */
        result.close();
        statement.close();
        connection.close();
    }
}

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Prevent SQL injection and use prepareStatement

package com.boya.emp.jdbcTest;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
/**
 * SQL注入，使用prepareStatement对象进行预编译
 * @author Admin
 *
 */
public class Test002 {

    public static void main(String[] args) throws Exception {

        /**
         * 加载驱动
         */
        Class.forName("com.mysql.jdbc.Driver");

        /**
         * 创建链接
         */
        String url = "jdbc:mysql://localhost:3306/testjdbc";
        String user = "root";
        String password = "root";
        Connection connection = DriverManager.getConnection(url, user, password);

        // 写SQL 
        String sql = "select * from test01 where id = ?";
        //创建statement对象，预编译
        PreparedStatement statement = connection.prepareStatement(sql);
        //设置参数
        statement.setInt(1, 2);
        /**
         * 执行SQL，获取结果集
         */
        ResultSet result = statement.executeQuery();

        // 遍历结果集
        while (result.next()) {
            String name = result.getString("name");
            int id = result.getInt("id");
            System.out.println(name + "\t" + id);
        }

        /**
         * 关闭链接，释放资源
         */
        result.close();
        statement.close();
        connection.close();
    }
}

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to code Optimize, set configuration files, tool classes, and implement additions and deletions.

Add configuration files to facilitate database modification and user login. . .

jdbc.properties (configuration file name)

driverName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/testjdbc
userName=root
password=root

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Note that when writing the configuration file, there cannot be spaces or quotation marks in the middle.

Tool class: Enhanced code complexity Usability

package com.baidu.emp.utils;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

import org.junit.Test;



public class JdbcUtils {

    static String driverClassName;
    static String url;
    static String user;
    static String password;

    static {
        // 创建配置文件对象
        Properties properties = new Properties();
        // 加载配置文件输入流
        InputStream inputStream = JdbcUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
        // 重新加载配置文件
        try {
            properties.load(inputStream);
            // 获取配置文件的值
            driverClassName = properties.getProperty("driverName");
            url = properties.getProperty("url");
            user = properties.getProperty("userName");
            password = properties.getProperty("password");
            Class.forName(driverClassName);

        } catch (Exception e) {
            // 抛出异常
            throw new RuntimeException(e);
        }
    }

    /**
     * 获取连接
     */
    @Test
    public void testName() throws Exception {
        
        System.out.println(driverClassName);
    }
    public static Connection getConnection() {
        Connection connection = null;
        try {
            connection = DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            // 抛出异常
            throw new RuntimeException(e);
        }
        return connection;
    }

    /**
     * 关闭链接，释放资源
     */
    public static void close(Connection connection, PreparedStatement statement, ResultSet resultSet) {

        try {
            if (resultSet != null) {
                resultSet.close();
            }
            resultSet = null; // 垃圾及时清除
            //注意，不要弄成死循环
            close(connection, statement);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }

    }

    /**
     * 增删改释放资源
     */
    public static void close(Connection connection, PreparedStatement statement) {

        try {
            if (connection != null) {
                connection.close();
            }
                
            connection = null;
            if (statement != null) {
                statement.close();
            }
            statement = null;

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }

    }

}

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Test additions, deletions, modifications and checks:

package com.baidu.emp.jdbcTest;

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

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.baidu.emp.utils.JdbcUtils;

/**
 * 使用jdbcUtils连接数据库进行增删改查
 * 
 * @author Admin
 *
 */
public class Test003 {

    // 初始化值
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet result = null;

    @Before
    public void start() throws Exception {
        // 创建链接
        connection = JdbcUtils.getConnection();
        System.out.println("创建链接");
    }

    @After
    public void end() throws Exception {
        // 关闭链接
        JdbcUtils.close(connection, statement, result);
        System.out.println("关闭链接");
    }
    
    /**
     *插入数据
     * @throws Exception
     */
    @Test
    public void add() throws Exception {
        String sql = "insert into test01 values(null,?)";
        statement = connection.prepareStatement(sql);
        statement.setString(1, "李四");
        int result = statement.executeUpdate();
        if (result!=0) {
            System.out.println("添加成功");
        }
    }
    /**
     * 删除数据
     * @throws Exception
     */
    @Test
    public void del() throws Exception {
        String sql = "delete from test01 where id =?";
        statement = connection.prepareStatement(sql);
        statement.setInt(1,3);
        int result = statement.executeUpdate();
        if (result!=0) {
            System.out.println("删除成功");
        }
    }
    /**
     * 修改数据
     * @throws Exception
     */
    @Test
    public void change() throws Exception {
        String sql = "update test01 set name = ? where id = ?";
        statement = connection.prepareStatement(sql);
        statement.setString(1, "张飞");
        statement.setInt(2, 2);
        int result = statement.executeUpdate();
        if (result!=0) {
            System.out.println("修改成功");
        }
    }
    
    /**
     * 查询全部数据
     * @throws Exception
     */
    @Test
    public void findAll() throws Exception {
        String sql = "select id , name from test01";
        statement = connection.prepareStatement(sql);
        result = statement.executeQuery();
        if (result.next()) {
            System.out.println("查询成功");
        }
    }
    
    /**
     * 条件查询数据
     * @throws Exception
     */
    @Test
    public void findOne() throws Exception {
        String sql = "select id , name from test01 where id = ?";
        statement = connection.prepareStatement(sql);
        statement.setInt(1, 2);
        result = statement.executeQuery();
        if (result.next()) {
            System.out.println("查询成功");
        }
    }

}

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There are errors. Colleagues pointed out, thank you very much

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