[大数据]使用反射动态的实现对不同表的通用单条查询

/**
 * 使用反射动态的实现对不同表的通用查询
 * @author baihang
 * @create 2022-03-04 17:43
 */
public class CommonQuery {
    @Test
    public void test() {
        String sql = "select id stuId, name stuName from student where id = ?;";
        Student queryInstance = getQueryInstance(Student.class, sql, 1002);
        System.out.println(queryInstance);

        String sql1 = "select teamID, teamName, location, arena from teams where teamID = ?;";
        Teams queryInstance1 = getQueryInstance(Teams.class, sql1, 1);
        System.out.println(queryInstance1);
    }

    public <T> T getQueryInstance(Class<T> clazz, String sql, Object...args) {
        Connection connection = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        try {
            connection = JDBCUtils.getConnection();
            ps = connection.prepareStatement(sql);
            for(int i = 0; i < args.length; i++) {
                //对sql语句设置占位符
                ps.setObject(i + 1, args[i]);
            }
            //获取结果集
            resultSet = ps.executeQuery();
            //获取结果集的元数据（数据的描述）
            ResultSetMetaData rsmd = resultSet.getMetaData();
            //获取结果集列数
            int columnCount = rsmd.getColumnCount();
            if(resultSet.next()) {
                T t = clazz.newInstance();//使用反射动态获取类（表）的对象
                for(int i = 0; i < columnCount; i++) {
                    //获取每个列的值
                    Object objectValue = resultSet.getObject(i + 1);
                    //获取结果集每个列的别名 ---> 对应Java类属性名
                    //String columnLabel = rsmd.getColumnName(i + 1);   //不靠谱，不推荐使用！！！
                    String columnLabel = rsmd.getColumnLabel(i + 1);    //推荐使用！！！
                    //利用反射获取列名columnName对应的属性
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    //将t对象对应的属性赋值为objectValue
                    field.set(t, objectValue);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            JDBCUtils.closeResource(connection, ps, resultSet);
        }
        return null;
    }
}

?二、teams表（类）

public class Teams {
    private int teamID;
    private String teamName;
    private String location;
    private String arena;

    public Teams() {
    }

    public Teams(int teamID, String teamName, String location, String arena) {
        this.teamID = teamID;
        this.teamName = teamName;
        this.location = location;
        this.arena = arena;
    }

    @Override
    public String toString() {
        return "Teams{" +
                "teamID=" + teamID +
                ", teamName='" + teamName + '\'' +
                ", location='" + location + '\'' +
                ", arena='" + arena + '\'' +
                '}';
    }

    public int getTeamID() {
        return teamID;
    }

    public void setTeamID(int teamID) {
        this.teamID = teamID;
    }

    public String getTeamName() {
        return teamName;
    }

    public void setTeamName(String teamName) {
        this.teamName = teamName;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String getArena() {
        return arena;
    }

    public void setArena(String arena) {
        this.arena = arena;
    }
}