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) + " "); 类名
// System.out.print(pmd.getParameterType(i) + " "); 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") + " "
+ rs.getString("name") + " " + rs.getDate("birthday")
+ " " + 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) + " "); //获取数据类型
// System.out.print(rsmd.getColumnName(i) + " "); //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);
}
}
}