1.使用场景

a.一次性实现一个算法的公共部分,将可变部分留给子类
b.各类中的公共方法,剥离变化后进行提取放入共同的父类中

2.DEMO

2.1

/**
 * Description:促销抽象类
 *
 * @date 2019-05-24 19:48
 */

public abstract class Promo {

    protected PromoType promoType;


    /**
     * Description:获取促销信息
     * @Date  2019-05-24 19:59
     * @Param [promoId]
     * @return java.lang.String
    **/

    public abstract String getPromoInfo(Long promoId);

    /**
     * Description:获取促销名称
     * @Date  2019-05-24 19:48
     * @Param []
     * @return java.lang.String
    **/

    protected  final String getPromoName(Long promoId){
        //调用促销mapper根据id查询促销名称
        return "促销名称X";
    }

    /**
     * Description:获取促销范围
     * @Date  2019-05-24 19:48
     * @Param []
     * @return java.lang.String
     **/

    protected  final String getPromoScope(Long promoId){
        //调用促销mapper根据id查询促销范围
        return "促销范围X";
    }


    /**
     * Description:获取促销标签
     * @Date  2019-05-24 19:48
     * @Param []
     * @return java.lang.String
     **/

    protected  final String getPromoLable(Long promoId){
        //调用促销mapper根据id查询促销范围
        return "促销标签X";
    }
    
/**
 * Description:促销类型枚举
 *
 * @date 2019-05-24 19:55
 */

public enum PromoType {
    DOWN(1,"直降"),
    ADD_MONEY_BUY(2,"加价购");

    private int  typeCode;
    private String typename;

    PromoType(int typeCode, String typename) {
        this.typeCode = typeCode;
        this.typename = typename;
    }

    public int getTypeCode() {
        return typeCode;
    }

    public String getTypename() {
        return typename;
    }
}

/**
 * Description:直降促销
 *
 * @date 2019-05-24 19:54
 */

public class PromoDown extends Promo{

    public PromoDown() {
        this.promoType=PromoType.DOWN;
    }

    @Override
    public String getPromoInfo(Long promoId) {
        String promoName = this.getPromoName(promoId);
        String promoScope = this.getPromoScope(promoId);
        String promoLable = this.getPromoLable(promoId);
        System.out.println("促销名称="+promoName);
        System.out.println("促销范围="+promoScope);
        System.out.println("促销标签="+promoLable);
        System.out.println("促销类型="+promoType.getTypename());
        return null;
    }
}

/**
 * Description:加价购促销
 *
 * @date 2019-05-24 19:54
 */

public class AddMoneyBuy extends Promo{

    public AddMoneyBuy() {
        this.promoType=PromoType.ADD_MONEY_BUY;
    }

    @Override
    public String getPromoInfo(Long promoId) {
        String promoName = this.getPromoName(promoId);
        String promoLable = this.getPromoLable(promoId);
        System.out.println("促销名称="+promoName);
        System.out.println("促销范围=全场");
        System.out.println("促销标签="+promoLable);
        System.out.println("促销类型="+promoType.getTypename());
        return null;
    }
}

/**
 * Description:测试类
 *
 * @date 2019-05-24 20:06
 */

public class Test {

    public static void main(String[] args) {
        Promo down = new PromoDown();
        Promo addBuy = new AddMoneyBuy();

        System.out.println("---->获取直降信息");
        down.getPromoInfo(1L);
        System.out.println("---->获取加价购信息");
        addBuy.getPromoInfo(2L);
    }

}

2.2

/**
 * Description:ORM映射接口
 *
 * @date 2019-05-24 20:16
 */

public interface RowMapper<T> {

    T mapRow(ResultSet rs,int rowNum) throws Exception;
}

/**
 * Description:JDBC模板抽象类
 *
 * @date 2019-05-24 20:18
 */

public abstract class JdbcTemplate {

    private DataSource dataSource;

    public JdbcTemplate(DataSource dataSource) {
        this.dataSource = dataSource;
    }


    public List<?> executeQuery(String sql, RowMapper<?> rowMapper, Object[] values) {
        try {
            //1.获取连接
            Connection conn = this.getConnection();
            //2.创建语句集
            PreparedStatement pstm = this.createPreparedStatement(conn, sql);
            //3.执行语句集
            ResultSet rs = this.executeQuery(pstm, values);
            //4.处理结果集
            List<?> result = this.paresResultSet(rs, rowMapper);
            //5.关闭结果集
            this.closeResultSet(rs);
            //6.关于语句集
            this.closePreparedStatement(pstm);
            //7.关闭连接
            this.closeConnection(conn);
            return result;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;

    }

    private Connection getConnection() throws Exception {

        return this.dataSource.getConnection();

    }

    private PreparedStatement createPreparedStatement(Connection conn, String sql) throws Exception {
        return conn.prepareStatement(sql);
    }

    private ResultSet executeQuery(PreparedStatement pstm, Object[] values) throws Exception {
        for(int i=0;i<values.length;i++){
            pstm.setObject(i,values[i]);
        }
        return pstm.executeQuery();
    }

    private List<?> paresResultSet(ResultSet rs, RowMapper<?> rowMapper) throws Exception {
        List<Object> result = new ArrayList<>();
        int rowNum = 1;
        while (rs.next()){
            result.add(rowMapper.mapRow(rs,rowNum++));
        }
        return result;
    }

    private void closeResultSet(ResultSet rs) throws Exception {
        rs.close();
    }

    private void closePreparedStatement(PreparedStatement pstm) throws Exception {
        pstm.close();
    }

    private void closeConnection(Connection conn) throws Exception{
        conn.close();
    }
}

/**
 * Description:学生类
 *
 * @date 2019-05-24 20:48
 */

public class Student {

    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

/**
 * Description:学生dao
 *
 * @date 2019-05-24 20:49
 */

public class StudentDao extends JdbcTemplate {


    public StudentDao(DataSource dataSource) {
        super(dataSource);
    }

    public List<?> selectAll(){

        String sql = "select * form student";
        return super.executeQuery(sql, new RowMapper<Student>() {
            @Override
            public Student mapRow(ResultSet rs, int rowNum) throws Exception {
                Student st = new Student();
                st.setId(rs.getLong("id"));
                st.setName(rs.getString("name"));
                return st;
            }
        },null);

    }
}