设计模式02-策略设计模式

职责分明，功能单一的原则

RowHandler接口只负责对从数据库中查询出来的结果集进行操作，至于最终返回成什么样的数据结构，需要自己去实现；

import java.sql.ResultSet;

public interface RowHandler<T> {
    T handle(ResultSet rs);
}

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

public class RecordQuery {
    private final java.sql.Connection connection;
    public RecordQuery(Connection connection) {
        this.connection = connection;
    }
    public <T> T query(RowHandler<T> handler, String sql, Object... params) {
        try {
            PreparedStatement stmt = connection.prepareStatement(sql);
            int index = 1;
            for (Object param : params) {
                stmt.setObject(index++, param);
            }
            ResultSet resultSet = stmt.executeQuery();
            return handler.handle(resultSet);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

}