描述

java.sql.ResultSetMetaData是JDBC规范中定义的结果集元数据接口，元数据即描述数据的数据，它不存储查询的具体行数据，而是描述ResultSet的结构特征，核心作用是：

• 获取结果集中列的总数、列名、列标签。
• 查询每列的SQL类型、Java类型、精度、刻度等属性。
• 判断列是否可为空、是否为自动递增列等特性。
• 适用于动态查询场景（不知道查询结果的列结构时，动态解析列信息）。

详细接口说明请参考JDBC官方网站 (opens new window)。

方法

YashanDB JDBC驱动对ResultSetMetaData接口有如下方法：

方法	返回类型
getColumnCount()	int
isAutoIncrement(int column)	boolean
isCaseSensitive(int column)	boolean
isSearchable(int column)	boolean
isCurrency(int column)	boolean
isNullable(int column)	int
isSigned(int column)	boolean
getColumnLabel(int column)	String
getColumnName(int column)	String
getPrecision(int column)	int
getScale(int column)	int
getColumnDisplaySize(int column)	int
getColumnType(int column)	int
getColumnTypeName(int column)	String
isReadOnly(int column)	boolean
isWritable(int column)	boolean
isDefinitelyWritable(int column)	boolean
getColumnClassName(int column)	String

示例

package quickstart;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

public class ResultSetMetaDataExample {

    public static Connection getConnection() throws SQLException, ClassNotFoundException {
        String url = "jdbc:yasdb://192.168.1.2:1688/yasdb";
        Properties info = new Properties();
        info.setProperty("user", "username");
        info.setProperty("password", "passwd");
        Class.forName("com.yashandb.jdbc.Driver");
        return DriverManager.getConnection(url, info);
    }

    // 打印 ResultSet 结构
    public void printResultSetStructure(ResultSet rs) throws SQLException {
        ResultSetMetaData meta = rs.getMetaData();
        int cols = meta.getColumnCount();

        for (int i = 1; i <= cols; i++) {
            String name = meta.getColumnName(i);
            String type = meta.getColumnTypeName(i);
            System.out.println(name + " (" + type + ")");
        }
    }

    // 自动映射到 Map
    public Map<String, Object> toMap(ResultSet rs) throws SQLException {
        Map<String, Object> map = new HashMap<>();
        ResultSetMetaData meta = rs.getMetaData();

        for (int i = 1; i <= meta.getColumnCount(); i++) {
            String colName = meta.getColumnName(i);
            map.put(colName, rs.getObject(i));
        }
        return map;
    }

    // 验证查询结果
    public void validateResultSet(ResultSet rs) throws SQLException {
        ResultSetMetaData meta = rs.getMetaData();

        for (int i = 1; i <= meta.getColumnCount(); i++) {
            if (meta.isNullable(i) == ResultSetMetaData.columnNoNulls) {
                Object value = rs.getObject(i);
                if (rs.wasNull()) {
                    throw new SQLException("Column " + meta.getColumnName(i) + " cannot be NULL");
                }
            }
        }
    }

    // 生成 CSV 表头
    public String generateCSVHeader(ResultSet rs) throws SQLException {
        ResultSetMetaData meta = rs.getMetaData();
        StringBuilder header = new StringBuilder();

        for (int i = 1; i <= meta.getColumnCount(); i++) {
            if (i > 1) header.append(",");
            header.append(meta.getColumnLabel(i));
        }
        return header.toString();
    }

    // 类型安全读取
    public Object getValueSafely(ResultSet rs, int columnIndex) throws SQLException {
        ResultSetMetaData meta = rs.getMetaData();
        String className = meta.getColumnClassName(columnIndex);

        if ("java.lang.String".equals(className)) {
            return rs.getString(columnIndex);
        } else if ("java.lang.Integer".equals(className)) {
            return rs.getInt(columnIndex);
        } else if ("java.math.BigDecimal".equals(className)) {
            return rs.getBigDecimal(columnIndex);
        }
        return rs.getObject(columnIndex);
    }

    public static void main(String[] args) {
        try (Connection conn = getConnection();
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT 1 AS ID, 'Alice' AS NAME, 12.34 AS AMOUNT FROM DUAL")) {
            ResultSetMetaDataExample example = new ResultSetMetaDataExample();
            example.printResultSetStructure(rs);
            System.out.println(example.generateCSVHeader(rs));
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }
    }
}

正常情况下，程序输出如下：

ID (INTEGER)
NAME (CHAR)
AMOUNT (NUMBER)
ID,NAME,AMOUNT