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05JDBC登录案例练习之查询练习(两种方式)

package cn.itcast.jdbc;

import cn.itcast.domain.Emp;

import cn.itcast.util.JDBCUtils;

import java.sql.*;

import java.util.ArrayList;

import java.util.List;

/**

- 定义一个方法，查询emp表的数据将其封装为对象，然后装载集合，返回。

public class JDBCDemo8 {

public static void main(String[] args) {
    List<Emp> list = new JDBCDemo8().findAll2();
    System.out.println(list);
    System.out.println(list.size());
}
/**
 * 查询所有emp对象
 * @return
 */
public List<Emp> findAll(){
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs = null;
    List<Emp> list = null;
    try {
        //1.注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
        //3.定义sql
        String sql = "select * from emp";
        //4.获取执行sql的对象
        stmt = conn.createStatement();
        //5.执行sql
        rs = stmt.executeQuery(sql);
        //6.遍历结果集，封装对象，装载集合
        Emp emp = null;
        list = new ArrayList<Emp>();
        while(rs.next()){
            //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) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }finally {
        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();
            }
        }
    }
    return list;
}


/**
 * 演示JDBC工具类
 * @return
 */
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.jdbc.Driver");
        //2.获取连接
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");*/
        conn = JDBCUtils.getConnection();
        //3.定义sql
        String sql = "select * from emp";
        //4.获取执行sql的对象
        stmt = conn.createStatement();
        //5.执行sql
        rs = stmt.executeQuery(sql);
        //6.遍历结果集，封装对象，装载集合
        Emp emp = null;
        list = new ArrayList<Emp>();
        while(rs.next()){
            //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) {
        e.printStackTrace();
    }finally {
        /*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();
            }
        }*/

        JDBCUtils.close(rs,stmt,conn);
    }
    return list;
}

}

原文 https://segmentfault.com/a/1190000020216694

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