模板模式

• Z时代
• 2024-01-10
• 分类：综合

模板模式

模板模式又叫做模板方法模式，是指定义一个算法的骨架，并允许子类为一个或者多个步骤提供实现。模板方法使得子类在不改变算法结构的情况下，重新定义算法的某些结构。属于行为性设计模式。

适用场景

1. 一次性实现一个算法的不变的部分，并将可变的行为留给子类来实现。
2. 各子类中公共的行为被提取并集中到一个公共的父类种中，从而避免大量的重复代码。

缺点

1. 类数目的增加
2. 间接的增加了系统的复杂度
3. 继承关系自身缺点，如果父类增加新的抽象方法，所有子类都要改一遍

JdbcTemplate.class

public abstract class JdbcTemplate {
    private DataSource dataSource;
    public JdbcTemplate(DataSource dataSource) {
        this.dataSource = dataSource;
    }
    public List<?> executeQuery(String sql, RowMapper<?> mapper, Object[] values) {
        try {
            Connection conn = this.getConnection();
            PreparedStatement pStatement = this.getPrepareStatement(conn, sql);
            ResultSet resultSet = this.executeQuery(pStatement, values);
            List<?> list = this.parseResultSet(resultSet, mapper);
            this.closeResultSet(resultSet);
            this.closeStatement(pStatement);
            this.closeConnection(conn);
            return list;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
    public Connection getConnection() throws Exception {
        return this.dataSource.getConnection();
    }
    protected PreparedStatement getPrepareStatement(Connection conn, String sql) throws Exception {
        return conn.prepareStatement(sql);
    }
    protected ResultSet executeQuery(PreparedStatement pStatement, Object[] values) throws Exception {
        if (values == null) {
            return pStatement.executeQuery();
        }
        for (int i = 0; i < values.length; i++) {
            pStatement.setObject(i, values[i]);
        }
        return pStatement.executeQuery();
    }
    protected List<?> parseResultSet(ResultSet resultSet, RowMapper<?> mapper) throws Exception {
        List<Object> result = new ArrayList<Object>();
        int rownum = 1;
        while (resultSet.next()) {
            result.add(mapper.mapRow(resultSet, rownum++));
        }
        return result;
    }
    protected void closeConnection(Connection conn) throws Exception {
        conn.close();
    }
    protected void closeStatement(PreparedStatement pStatement) throws Exception {
        pStatement.close();
    }
    protected void closeResultSet(ResultSet resultSet) throws Exception {
        resultSet.close();
    }
}

MemberDAO.class

public class MemberDAO extends JdbcTemplate {
    public MemberDAO(DataSource dataSource) {
        super(dataSource);
    }
    public List<?> selectAll() {
        String sql = "select * from t_user";
        return super.executeQuery(sql, new RowMapper<Object>() {
            public Object mapRow(ResultSet rs, int rowNum) throws Exception {
                Member member = new Member();
                member.setUsername(rs.getString("username"));
                member.setPassword(rs.getString("password"));
                member.setAge(rs.getInt("age"));
                member.setAddress(rs.getString("address"));
                return member;
            }
        }, null);
    }
}

Member.class

public class Member {
    private String username;
    private String password;
    private String nickname;
    private int age;
    private String address;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getNickname() {
        return nickname;
    }
    public void setNickname(String nickname) {
        this.nickname = nickname;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

RowMapper.class

public interface RowMapper<T> {
    T mapRow(ResultSet rs, int rowNum) throws Exception;
}

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