设计模式 – 模板设计模式

ゞ浴缸里的玫瑰 2022-12-17 08:41 188阅读 0赞

# 模板设计模式 #

模板方法模式（Template Method Pattern），又叫模板模式(Template Pattern)，在一个抽象类公开定义了执行它的方法的模板。它的子类可以按需要重写方法实现，但调用将以抽象类中定义的方式进行。

该模式的主要优点如下。  
1） 它封装了不变部分，扩展可变部分。它把认为是不变部分的算法封装到父类中实现，而把可变部分算法由子类继承实现，便于子类继续扩展。  
2） 它在父类中提取了公共的部分代码，便于代码复用。  
3） 部分方法是由子类实现的，因此子类可以通过扩展方式增加相应的功能，符合开闭原则。

# 案例 #

JdbcTemplate uml 图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center]

## 1 pom ##

<dependencies>
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
            </dependency>
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.47</version>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid</artifactId>
                <version>1.1.16</version>
            </dependency>
    
        </dependencies>

## 2 JdbcFactory ##

import com.alibaba.druid.pool.DruidDataSourceFactory;
    
    import javax.sql.DataSource;
    import java.util.HashMap;
    import java.util.Map;
    
    public class JdbcFactory { 
    
        /** * ###########################DB配置######################## */
        private static final String URL = "jdbc:mysql://localhost:3306/test?charset=utf8mb4&serverTimezone=UTC&useUnicode=true&useSSL=false";
        private static final String USERNAME = "root";
        private static final String PASSWORD = "123456";
        private static final String DRIVER = "com.mysql.jdbc.Driver";
    
    
        private static DataSource db;
    
        static { 
    
            Map<String, String> map = new HashMap<>();
            map.put(DruidDataSourceFactory.PROP_DRIVERCLASSNAME, DRIVER);
            map.put(DruidDataSourceFactory.PROP_URL, URL);
            map.put(DruidDataSourceFactory.PROP_USERNAME, USERNAME);
            map.put(DruidDataSourceFactory.PROP_PASSWORD, PASSWORD);
            try { 
                db = DruidDataSourceFactory.createDataSource(map);
            } catch (Exception e) { 
                db = null;
                e.printStackTrace();
            }
    
        }
    
        private JdbcFactory() { 
    
        }
    
    
        public static DataSource getInstance() { 
            return db;
        }
    
    
    }

## 3 RowMapper ##

/** * ORM 定制化接口 */
    public interface RowMapper<T> { 
    
        T mapRow(ResultSet rs, int rowNum) throws SQLException;
    
    }

## 4 JdbcTemplate ##

import javax.sql.DataSource;
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.List;
    
    public abstract class JdbcTemplate { 
    
    
        private DataSource dataSource;
    
        public JdbcTemplate(DataSource dateSource) { 
    
            this.dataSource = dateSource;
        }
    
    
        public <T> List<T> executeQuery(String sql, RowMapper<T> rowMapper, Object[] values) { 
    
            try { 
                //1 获取连接
                Connection connection = this.getConnection();
                //2 创建语句集
                PreparedStatement pstm = this.createPrepareStatement(connection, sql);
                //3 执行语句集
                ResultSet rs = execute(pstm, values);
                //4 处理结果集
                List<T> list = paresResultSet(rs, rowMapper);
                //5 关闭结果集
                this.closeResultSet(rs);
                //6 关闭语句集
                this.closeStatement(pstm);
                //7 关闭连接
                this.closeConnection(connection);
                //8 返回
                return list;
            } catch (Exception e) { 
                e.printStackTrace();
            }
    
    
            return new ArrayList<>();
        }
    
        protected void closeConnection(Connection connection) throws SQLException { 
    
            if (connection != null) { 
                connection.close();
            }
    
        }
    
        protected void closeStatement(PreparedStatement pstm) throws SQLException { 
            pstm.close();
        }
    
    
        protected void closeResultSet(ResultSet rs) throws SQLException { 
            rs.close();
        }
    
        protected <T> List<T> paresResultSet(ResultSet rs, RowMapper<T> rowMapper) throws SQLException { 
            List<T> result = new ArrayList<>();
            int rowNum = 1;
            while (rs.next()) { 
                result.add(rowMapper.mapRow(rs, rowNum++));
            }
            return result;
    
        }
    
        private ResultSet execute(PreparedStatement pstm, Object[] values) throws SQLException { 
    
            if (values != null) { 
                for (int i = 0; i < values.length; i++) { 
                    pstm.setObject(i, values[i]);
                }
            }
            return pstm.executeQuery();
        }
    
        protected PreparedStatement createPrepareStatement(Connection connection, String sql) throws SQLException { 
    
    
            return connection.prepareStatement(sql);
    
        }
    
        private Connection getConnection() throws SQLException { 
    
            return this.dataSource.getConnection();
        }
    
    
    }

## 5 业务类 ##

@Data
    @AllArgsConstructor
    @NoArgsConstructor
    @ToString
    public class Student { 
    
        private Integer id;
    
        private String name;
    
        private Integer age;
    
    
    }
    
    
    
    public class StudentDao extends JdbcTemplate { 
    
        public StudentDao(DataSource dateSource) { 
            super(dateSource);
        }
    
    
        public List<Student> selectAll() { 
            String sql = "select * from t_student";
            return super.executeQuery(sql, (rs, rowNum) -> { 
                Student student = new Student();
                student.setId(rs.getInt("id"));
                student.setAge(rs.getInt("age"));
                student.setName(rs.getString("name"));
                return student;
            }, null);
    
        }
    
    
    }

## 6 测试 ##

public class JdbcTest { 
    
    
        public static void main(String[] args) throws Exception { 
    
            DataSource instance = JdbcFactory.getInstance();
            StudentDao studentDao=new StudentDao(instance);
            List<Student> students = studentDao.selectAll();
            System.out.println(students.toString());
    
    
        }
    
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center 1]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center 1]: /images/20221122/6a94bcefe415476888179385f12f4586.png