JDBC 元数据信息 getMetaData()

数据库元数据信息：

import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
*
* 2008-12-7
*
* @author <a href="mailto:liyongibm@gmail.com">liyong</a>
*
*/
public class DBMD {

/**
     * @param args
     * @throws SQLException
     * @throws ClassNotFoundException
     */
    public static void main(String[] args) throws SQLException, ClassNotFoundException {

Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/jdbc";
         String user = "root";
        String password = "";
        java.sql.Connection conn = DriverManager.getConnection(url, user, password);
       
        DatabaseMetaData dbmd = conn.getMetaData();//获取数据源的信息，可以用来判断数据源是否支持某些功能，比如事务、批处理等。全在dbmd.support中
        System.out.println("db name: " + dbmd.getDatabaseProductName());
        System.out.println("tx: " + dbmd.supportsTransactions());//判断是否支持事务
        conn.close();
    }

}

参数的元数据信息

public class ParameterMetaTest {

/**
     * @param args
     * @throws SQLException
     */
    public static void main(String[] args) throws SQLException {
        Object[] params = new Object[] { "lisi", 100f };
        read("select * from user where name=? and  money > ?", params);
    }

static void read(String sql, Object[] params) throws SQLException {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            ps = conn.prepareStatement(sql);
//            ParameterMetaData pmd = ps.getParameterMetaData();
//           int count = pmd.getParameterCount();//可以获取参数个数
            for (int i = 1; i <= params.length; i++) {
                // System.out.print(pmd.getParameterClassName(i) + "\t");  类名
                // System.out.print(pmd.getParameterType(i) + "\t");  类型名
                // System.out.println(pmd.getParameterTypeName(i));  在数据库中的类型名

//以上这三条不太实用，因为有的数据库引擎是不支持的。
                ps.setObject(i, params[i - 1]);
            }

rs = ps.executeQuery();

while (rs.next()) {
                System.out.println(rs.getInt("id") + "\t"
                        + rs.getString("name") + "\t" + rs.getDate("birthday")
                        + "\t" + rs.getFloat("money"));
            }

} finally {
            JdbcUtils.free(rs, ps, conn);
        }
    }

}

结果集的元数据信息

public class ResultSetMetaDataTest {

/**
     * @param args
     * @throws SQLException
     */
    public static void main(String[] args) throws SQLException {
        List<Map<String, Object>> datas = read("select id, name as n from user where id < 5");    //n是别名 name是表中列本来的的名字
        System.out.println(datas);
    }

static List<Map<String, Object>> read(String sql) throws SQLException {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            ps = conn.prepareStatement(sql);
            rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();
            int count = rsmd.getColumnCount();//获取列数
            String[] colNames = new String[count];
            for (int i = 1; i <= count; i++) {
                // System.out.print(rsmd.getColumnClassName(i) + "\t"); //获取数据类型
                // System.out.print(rsmd.getColumnName(i) + "\t"); //获取列本来的名字
                // System.out.println(rsmd.getColumnLabel(i));
                colNames[i - 1] = rsmd.getColumnLabel(i);//获取列的别名，如果没有别名就是列的本名     
            }
            List<Map<String, Object>> datas = new ArrayList<Map<String, Object>>();

while (rs.next()) {
                Map<String, Object> data = new HashMap<String, Object>();
                for (int i = 0; i < colNames.length; i++) {
                    data.put(colNames[i], rs.getObject(colNames[i]));
                }
                datas.add(data);
            }
            return datas;
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
    }

}