Java个人总结——JDBC工具类封装

工具类封装

在前面的JDBC案例中我们不难发现，每次操纵数据库都需要进行数据库的注册、连接等大量重复的操作，是的代码变得十分的臃肿，所以此时我们应该考虑如何把重复代码提取出来，随时需要随时拿来用。
这就是工具类的封装。

案例实现：实现emp表的查询、添加、删除、修改

封装DbUtils

由于多个地方都需要使用数据库连接和释放，所以把功能封装到工具类中DbUtils
四个功能：

1. 注册驱动
2. 获取连接
3. 释放资源
4. 执行命令

db.properties信息文件

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/emp
user=root
password=root

自定义DbUtils工具类

public class DBUtils {

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

    static {
        // 使用信息文件进行赋值
        // 使用类加载器加载信息文件
        InputStream is = DBUtils.class.getClassLoader().getResourceAsStream("db.properties");
        Properties pro = new Properties();
        try {
            // 读取文件信息并赋值
            pro.load(is);
            driver = pro.getProperty("driver");
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            // 注册驱动
            Class.forName(driver);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 获取数据库连接
    public static Connection getConnection() {
        Connection conn = null;
        try {
            // 获取数据库连接
            conn = DriverManager.getConnection(url, user, password);
            return conn;
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

    // 更新数据库
    public static int update(String sql, Object... params) {// 接收SQL语句和数据完成数据库的操作
        Connection conn = getConnection();
        PreparedStatement ps = null;
        try {
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < params.length; i++) {
                ps.setObject(i + 1, params[i]);
            }
            int len = ps.executeUpdate();
            return len;
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll(conn, ps, null);
        }
        return 0;
    }

    // 查询所有
    public static List getAll() {
        List list = new ArrayList();
        String sql = "SELECT * FROM emp;";
        Connection conn = getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = conn.prepareStatement(sql);
            rs = ps.executeQuery();
            while (rs.next()) {
                int empno = rs.getInt(1);
                String ename = rs.getString(2);
                String job = rs.getString(3);
                int mgr = rs.getInt(4);
                Date hiredate = rs.getDate(5);
                double sal = rs.getDouble(6);
                double comm = rs.getDouble(7);
                int deptno = rs.getInt(8);
                Employee emp = new Employee(empno, ename, job, mgr, hiredate, sal, comm, deptno);
                list.add(emp);
            }
            return list;
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

    // 根据ID查询
    public static Employee getById(int empno) {
        String sql = "SELECT * FROM emp WHERE empno=?";
        Connection conn = getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        Employee emp = null;
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, empno);
            rs = ps.executeQuery();
            if (rs.next()) {
                String ename = rs.getString(2);
                String job = rs.getString(3);
                int mgr = rs.getInt(4);
                Date hiredate = rs.getDate(5);
                double sal = rs.getDouble(6);
                double comm = rs.getDouble(7);
                int deptno = rs.getInt(8);
                emp = new Employee(empno, ename, job, mgr, hiredate, sal, comm, deptno);
            }
            return emp;
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

    // 关闭数据库连接
    public static void closeAll(Connection conn, PreparedStatement ps, ResultSet rs) {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (ps != null) {
                ps.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}