JDBC 万能模板

Update 2020-5-15：

我心态崩了，我把 JDBC 的原生用法摸透之后发现 Apache 提供了一个开源的 JDBC 工具类库叫 commons-dbutils，里面封装了针对于数据库的增删改查操作。需要使用原生 JDBC 的话使用这个库就行了，本文终结。

=====以下是原文章=====

users.sql:

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for users
-- ----------------------------
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL,
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

SET FOREIGN_KEY_CHECKS = 1;

User.java:

public class User {
    private int id;
    private String username;
    private String email;

    public User() {
    }

    public int getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

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

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public User(int id, String username, String email) {
        this.id = id;
        this.username = username;
        this.email = email;
    }

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

jdbc.properties:

driverClass=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/test?serverTimezone=GMT
user=root
password=root

JDBCUtils.java:

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

//操作数据库的工具类
public class JDBCUtils {
    //创建连接的操作
    public static Connection getConnection() throws IOException, ClassNotFoundException, SQLException {
        //读取配置文件中的4个基本信息
        InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
        Properties pros = new Properties();
        pros.load(is);
        String driverClass = pros.getProperty("driverClass");
        String url = pros.getProperty("url");
        String user = pros.getProperty("user");
        String password = pros.getProperty("password");
        //加载驱动
        Class.forName(driverClass);
        //获取连接
        Connection conn = DriverManager.getConnection(url, user, password);
        return conn;
    }

    //关闭连接和PreparedStatement的操作
    public static void closeResource(Connection conn, PreparedStatement ps) {
        try {
            if(ps != null)
                ps.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(conn != null)
                conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    //关闭资源操作
    public static void closeResource(Connection conn, PreparedStatement ps, ResultSet rs){
        try {
            if(ps != null)
                ps.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(conn != null)
                conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(rs != null)
                rs.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

JDBCTest.java:

import org.junit.Test;

import java.lang.reflect.Field;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JDBCTest {
    //通用的增删改操作
    public int update(String sql, Object... args) { //sql中占位符的个数与可变形参的长度相同
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            //获取数据库的连接
            conn = JDBCUtils.getConnection();
            //预编译sql语句，返回PreparedStatement的实例
            ps = conn.prepareStatement(sql);
            //填充占位符
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);//小心参数声明错误！
            }
            //执行
            return ps.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //资源的关闭
            JDBCUtils.closeResource(conn, ps);
        }
        return 0;
    }

    @Test
    public void testUpdate() {
        String sql = "UPDATE users SET username = ? WHERE id = ?";
        update(sql, "Alice", 1);
    }

    //通用的增删改操作（考虑上事务）
    public int update(Connection conn, String sql, Object... args) { //sql中占位符的个数与可变形参的长度相同
        PreparedStatement ps = null;
        try {
            //预编译sql语句，返回PreparedStatement的实例
            ps = conn.prepareStatement(sql);
            //填充占位符
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);//小心参数声明错误！
            }
            //执行
            return ps.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //资源的关闭
            JDBCUtils.closeResource(null, ps);
        }
        return 0;
    }

    @Test
    public void testTransactionUpdate() {
        Connection conn = null;
        try {
            conn = JDBCUtils.getConnection();
            //取消数据的自动提交
            conn.setAutoCommit(false);
            String sql1 = "update users set username = ? where id = 1";
            update(conn, sql1, "Alice Ma");
            String sql2 = "update users set username = ? where id = 2";
            update(conn, sql2, "Carlos Pi");
            //提交数据
            conn.commit();
        } catch (Exception e) {
            e.printStackTrace();
            //回滚数据
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
        } finally {
            JDBCUtils.closeResource(conn, null);
        }
    }

    //针对于不同的表的通用的查询操作，返回表中的一条记录
    public <T> T getInstance(Class<T> clazz, String sql, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery();
            //获取结果集的元数据：ResultSetMetaData
            ResultSetMetaData rsmd = rs.getMetaData();
            //通过ResultSetMetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();
            if (rs.next()) {
                T t = clazz.newInstance();
                //处理结果集一行数据中的每一个列
                for (int i = 0; i < columnCount; i++) {
                    //获取列值
                    Object columValue = rs.getObject(i + 1);
                    //获取每个列的列名
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    //给t对象指定的columnName属性，赋值为columnValue：通过反射
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columValue);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }
        return null;
    }

    @Test
    public void testGetInstance() {
        String sql = "select id,username,email from users where id = ?";
        User user = getInstance(User.class, sql, 1);
        System.out.println(user);
    }

    //通用的查询操作，用于返回数据表中的一条记录（考虑上事务）
    public <T> T getInstance(Connection conn, Class<T> clazz, String sql, Object... args) {
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery();
            //获取结果集的元数据 :ResultSetMetaData
            ResultSetMetaData rsmd = rs.getMetaData();
            //通过ResultSetMetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();
            if (rs.next()) {
                T t = clazz.newInstance();
                //处理结果集一行数据中的每一个列
                for (int i = 0; i < columnCount; i++) {
                    //获取列值
                    Object columnValue = rs.getObject(i + 1);
                    //获取每个列的列名
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    //给t对象指定的columnName属性，赋值为columnValue：通过反射
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columnValue);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(null, ps, rs);
        }
        return null;
    }

    @Test
    public void testTransactionSelect() throws Exception {
        Connection conn = JDBCUtils.getConnection();
        //获取当前连接的隔离级别
        System.out.println(conn.getTransactionIsolation());
        //设置数据库的隔离级别
        conn.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);
        //取消自动提交数据
        conn.setAutoCommit(false);
        String sql = "select id,username,email from users where id = ?";
        User user = getInstance(conn, User.class, sql, 1);
        System.out.println(user);
    }

    public <T> List<T> getForList(Class<T> clazz, String sql, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery();
            // 获取结果集的元数据 :ResultSetMetaData
            ResultSetMetaData rsmd = rs.getMetaData();
            // 通过ResultSetMetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();
            //创建集合对象
            ArrayList<T> list = new ArrayList<T>();
            while (rs.next()) {
                T t = clazz.newInstance();
                // 处理结果集一行数据中的每一个列:给t对象指定的属性赋值
                for (int i = 0; i < columnCount; i++) {
                    // 获取列值
                    Object columValue = rs.getObject(i + 1);
                    // 获取每个列的列名
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    // 给t对象指定的columnName属性，赋值为columValue：通过反射
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columValue);
                }
                list.add(t);
            }
            return list;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }
        return null;
    }

    @Test
    public void testGetForList() {
        String sql = "select id,username,email from users where id < ?";
        List<User> list = getForList(User.class, sql, 10);
        list.forEach(System.out::println);
    }
}