JDBC工具类_JdbcUtils

抽取JDBC工具类 ： JDBCUtils

• 目的：简化书写
  • 分析：

    1. 注册驱动也抽取

    2. 抽取一个方法获取连接对象
       需求：不想传递参数（麻烦），还得保证工具类的通用性。
       解决：配置文件
       jdbc.properties
       url=
       user=
       password=

    3. 抽取一个方法释放资源

抽取注册驱动，抽取一个方法释放资源

/**
 * JDBC工具类
 */
public class JDBCUtils {

    private static String url;
    private static String user;
    private static String password;
    private static String driver;

    /**
     * 文件的读取，只需要读取一次即可拿到这些值。使用静态代码块
     */
    static {
        try {
            //读取文件，获取值

            //1.创建Properties集合类
            Properties pro = new Properties();
            //获取src路径下的文件的方式 --->ClassLoader 类加载器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL res = classLoader.getResource("jdbc.properties");
            String path = res.getPath();
            System.out.println(path);
            //2.加载文件
            // pro.load(new FileReader("D:\\Learn\\IdeaProjects\\itcast\\day04_jdbc\\src\\jdbc.properties"));
            pro.load(new FileReader(path));

            //3.获取数据，赋值
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");

            //4.注册驱动
            try {
                Class.forName(driver);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }

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

    }


    /**
     * 获取连接
     *
     * @return 连接对象
     */
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, user, password);
    }

    /**
     * 释放资源
     *
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt, Connection conn) {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

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

    public static void close(ResultSet rs, Statement stmt, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

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

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

}

在src下创建jdbc.properties配置文件

url=jdbc:mysql:///db3?serverTimezone=UTC
user=root
password=123
driver=com.mysql.cj.jdbc.Driver

演示JDBC工具类：

public class JDBCDemo06 {

    public static void main(String[] args) {
        List<Emp> list = new JDBCDemo06().findAll2();
        for (Emp emp : list) {
            System.out.println(emp);
        }
    }

	/**
     * 演示JDBC工具类
     */
    public List<Emp> findAll2(){

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        List<Emp> list = null;

        try {
            //1.注册驱动
           /* Class.forName("com.mysql.cj.jdbc.Driver");
            //2.获取connection 对象
            conn = DriverManager.getConnection("jdbc:mysql:///db3?serverTimezone=UTC","root","123");
            */
            conn = JDBCUtils.getConnection();
            //3.定义sql
            String sql = "select * from emp";
            //4.获取执行sql语句的statement
            stmt = conn.createStatement();
            //5.执行sql
            rs = stmt.executeQuery(sql);
            //6.遍历结果集，封装对象，装载对象
            Emp emp = null;
            list = new ArrayList<Emp>();
            while(rs.next()){
                //获取数据
                int id = rs.getInt(1);
                String ename = rs.getString(2);
                int job_id = rs.getInt(3);
                int mgr = rs.getInt("mgr");
                Date joindate = rs.getDate("joindate");
                double salary = rs.getDouble(6);
                double bonus = rs.getDouble("bonus");
                int dept_id = rs.getInt("dept_id");

                //创建emp 对象，并赋值
                emp = new Emp();
                emp.setId(id);
                emp.setEname(ename);
                emp.setJob_id(job_id);
                emp.setMgr(mgr);
                emp.setJoindate(joindate);
                emp.setSalary(salary);
                emp.setBonus(bonus);
                emp.setDept_id(dept_id);

                //装载集合
                list.add(emp);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            //7.释放资源
            //注意避免空指针异常
           /* if (rs != null){
                try {
                    rs.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
            if (stmt != null){
                try {
                    stmt.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }

            if (conn != null){
                try {
                    conn.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }*/
            JDBCUtils.close(rs,stmt,conn);
        }
        return list;
    }
}

程序演示：

本文地址：https://blog.csdn.net/weixin_44664432/article/details/109573273