JDBC练习select语句和JDBC工具类

JDBC练习-select语句

定义一个方法，查询emp表中的数据将其封装为对象，然后装载集合，然后打印

1.定义emp类

2.定义方法public List<Emp> findAll(){}

3.实现方法select * from emp;

Emp类

public class Emp {
    private int id;
    private String ename;
    private int job_id;
    private int mgr;
    private Date joindate;
    private double salary;
    private double bonus;
    private int dept_id;

    //toString
    @Override
    public String toString() {
        return "Emp{" +
                "id=" + id +
                ", ename='" + ename + '\'' +
                ", job_id=" + job_id +
                ", mgr=" + mgr +
                ", joindate=" + joindate +
                ", salary=" + salary +
                ", bonus=" + bonus +
                ", dept_id=" + dept_id +
                '}';
    }

    //get和set
    public int getId() {
        return id;
    }

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

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public int getJob_id() {
        return job_id;
    }

    public void setJob_id(int job_id) {
        this.job_id = job_id;
    }

    public int getMgr() {
        return mgr;
    }

    public void setMgr(int mgr) {
        this.mgr = mgr;
    }

    public Date getJoindate() {
        return joindate;
    }

    public void setJoindate(Date joindate) {
        this.joindate = joindate;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public double getBonus() {
        return bonus;
    }

    public void setBonus(double bonus) {
        this.bonus = bonus;
    }

    public int getDept_id() {
        return dept_id;
    }

    public void setDept_id(int dept_id) {
        this.dept_id = dept_id;
    }

测试类：

    public static void main(String[] args) {
        List<Emp> all = new JdbcPractice6().findAll();
        for (Emp emp : all) {
            System.out.println(emp);
        }
    }


    /**
     * 查询所有emp对象
     * @return
     */
    public List<Emp> findAll(){
        Connection conn = null;
        Statement state = null;
        ResultSet rs =null;
        List<Emp> list = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //2.获取连接
            conn = DriverManager.getConnection("jdbc:mysql:///db2", "root", "root");
            //3.定义sql
            String sql = "select * from emp";
            //4.获取执行sql对象
            state = conn.createStatement();
            //5.执行sql(结果集对象)
            rs = state.executeQuery(sql);
            //6.遍历结果集,封装对象,装载集合
            Emp emp= null;
            list = new ArrayList<>();
            while (rs.next()){
                //6.1获取数据
                int id = rs.getInt("id");
                String ename = rs.getString("ename");
                int job_id = rs.getInt("job_id");
                int mgr = rs.getInt("mgr");
                Date joindate = rs.getDate("joindate");
                double salary = rs.getDouble("salary");
                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 (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            if (rs != null){
                try {
                    rs.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }
            if (state != null){
                try {
                    state.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }
            if (conn != null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    throw new RuntimeException(e);
                }
            }
        }
        return list;
    }

 

 

JDBC工具类

 抽取工具类：JDBCUtils

　　目的：简化书写

　　分析：

　　　　1.注册驱动　　

　　　　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

 JDBCUtils工具类

/**
 * JDBC工具类
 *
 */
public class JDBCUtils {
    //声明三个成员变量
    private static String url;// 连接数据库
    private static String user;// 用户名
    private static String password;// 密码
    private static String driver;// 连接驱动
    /**
     *  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(工具类静态块)
     */
    static {
        //读取资源文件，获取值
        try {
            //1.创建Properties集合类
            Properties prop = 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");// URL:标识符统一资源
            String path = res.getPath();
            System.out.println(path);
            //2.加载文件
//            prop.load(new FileReader("src/main/resources/jdbc.properties"));
            prop.load(new FileReader(path));
            //3.获取数据,赋值(于配置文件中的属性名要一致)
            url = prop.getProperty("url");
            user = prop.getProperty("user");
            password = prop.getProperty("password");
            driver = prop.getProperty("driver");
            //注册驱动
            Class.forName(driver);
        } catch (IOException e) {
            throw new RuntimeException(e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     *  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(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();
            }
        }
    }
}

 

测试类

    public static void main(String[] args) {
        //创建方法引用方法
        List<Emp> all = new JdbcPractice7().findAll2();
        for (Emp emp : all) {
            System.out.println(emp);
        }
    }


    /**
     * 查询所有emp对象
     * @return
     */
    public List<Emp> findAll2(){
        Connection conn = null;
        Statement state = null;
        ResultSet rs =null;
        List<Emp> list = null;
        try {
//            //1.注册驱动
//            Class.forName("com.mysql.cj.jdbc.Driver");
//            //2.获取连接
//            conn = DriverManager.getConnection("jdbc:mysql:///db2", "root", "root");
            conn = JDBCUtils.getConnection();
            //3.定义sql
            String sql = "select * from emp";
            //4.获取执行sql对象
            state = conn.createStatement();
            //5.执行sql(结果集对象)
            rs = state.executeQuery(sql);
            //6.遍历结果集,封装对象,装载集合
            Emp emp= null;
            list = new ArrayList<>();
            while (rs.next()){
                //6.1获取数据
                int id = rs.getInt("id");
                String ename = rs.getString("ename");
                int job_id = rs.getInt("job_id");
                int mgr = rs.getInt("mgr");
                Date joindate = rs.getDate("joindate");
                double salary = rs.getDouble("salary");
                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 e) {
            throw new RuntimeException(e);
        }finally {
            //释放资源
            JDBCUtils.close(rs, state, conn);
        }
        return list;
    }

 运行结果：