模板模式（Template）_java实现

//20210127
写在前面：刚期末考试完，考了面向对象，里边儿有23个设计模式，我寻思着考完挨个儿实现一下，本文实现模板模式

模板模式核心思想：

• 如果完成某件事的步骤就那么几个，那么我们就可以定义一个模板专门用于完成某件事情，就好像实现一个框架，子类往里边填充步骤的具体内容就行
• 举例：做成一道菜的步骤有择菜、洗菜、炒菜，那么我们就可以定义一个模板，分为择菜、洗菜、炒菜，然后如果想要做出西红柿炒蛋，那就先挑选并处理西红柿和鸡蛋（择菜），再洗西红柿、打鸡蛋（洗菜），最后下锅炒（炒菜），这样西红柿鸡蛋的具体步骤就填充进框架了，外界只用调用填充好的子类就可以做出西红柿炒鸡蛋了

程序源代码

• 此处实现一个JDBC模板，更接近我们的使用和学习
• 注：需要导入mysql官方jar包，否则会报错ClassNotFound

/**
 * 抽象dao层——模板
 */

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public abstract class AbstractDao {
    protected Object find(String sql,Object[] params){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        Object obj = null;
        try{
            conn = JDBCUtils.getConnection();
            ps = conn.prepareStatement(sql);
            for (int i = 0;i<params.length;++i){
                ps.setObject(i+1,params[i]);
            }
            rs = ps.executeQuery();
            while(rs.next()){
                obj = rowMapper(rs);
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            JDBCUtils.free(rs,ps,conn);
        }
        return obj;
    }

    protected abstract Object rowMapper(ResultSet rs) throws SQLException;
    //同时可以添加insert，update等方法
}

//具体dao层

import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * UserDAO
 */
public class UserDAO extends AbstractDao{
    public User findUser(int userId){
        String sql = "select * from user where id = ?";//预语句
        Object[] params = new Object[]{userId};
        Object user = super.find(sql,params);
//        System.out.println((User)user);
        return (User)user;

    }

    @Override
    protected Object rowMapper(ResultSet rs) throws SQLException {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setAge(rs.getInt("age"));
        user.setSex(rs.getString("sex"));
        user.setAddress(rs.getString("address"));

        return user;
    }
}

/**
 * 用户类
 */
public class User {
    private Integer id;
    private String name;
    private Integer age;
    private String sex;
    private String address;

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

/**
 * jdbc工具类
 */

import java.sql.*;

public class JDBCUtils {
    private static String url = "jdbc:mysql://localhost:3306/jdbcstudy";
    private static String user = "root";
    private static String password = "******";

    private JDBCUtils(){}

    static {
        try{
            Class.forName("com.mysql.jdbc.Driver");
        } catch(ClassNotFoundException e){
            throw new ExceptionInInitializerError(e);
        }
    }

    public static Connection getConnection() throws SQLException{
        return DriverManager.getConnection(url,user,password);
    }

    public static void free(ResultSet rs, PreparedStatement ps , Connection conn){
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(ps!=null){
            try {
                ps.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }

}

//测试主类
public class Main {
    public static void main(String[] args) {
        UserDAO dao = new UserDAO();
        System.out.println(dao.findUser(1));
        System.out.println(dao.findUser(2));
        System.out.println(dao.findUser(3));
        System.out.println(dao.findUser(4));
    }
}

• 数据库创建&添加table语句如下：

create table user(
id int primary key auto_increment,
name varchar(20) not null,
age int,
sex varchar(2) not null,
address varchar(50)
);

insert into user(name,age,sex,address) values ("张三","18","男","河北唐山");


insert into user(name,age,sex,address) values ("李四","16","男","河南驻马店");


insert into user(name,age,sex,address) values ("王五","22","女","北京朝阳区");


insert into user(name,age,sex,address) values ("赵六",null,"男",null);

• 数据库cmd终端输出如下：
  

• 输出如下:
  

以上
希望对大家有所帮助