Как да получите мета данни от базата данни

java.sql.DatabaseMetaData интерфейс предоставя методи за получаване на метаданни на вашия свързан сървър на база данни. Примерите по-долу ще ви покажат как да направите това един по един.

java.sql.DatabaseMetaData Инстанция

Обектът DatabaseMetaData се извлича от обекта Connection на базата данни.

DatabaseMetaData dbmd = dbConn.getMetaData();

Име и версия на DB

String dbProductName = dbmd.getDatabaseProductName();
String dbProductVersion = dbmd.getDatabaseProductVersion();

int dbMajorVersion = dbmd.getDatabaseMajorVersion();
int dbMinorVersion = dbmd.getDatabaseMinorVersion();

Версия на JDBC драйвер

int jdbcDriverMajorVersion = dbmd.getDriverMajorVersion();
int jdbcDriverMinorVersion = dbmd.getDriverMinorVersion();

Списък с бази данни

ResultSet rs = dbmd.getCatalogs();
if(rs!=null)
{
      while(rs.next())
      {
          String catalogName = rs.getString(1);
	  System.out.println("Database catalog : " + catalogName);
      }
}

Списък с таблици

// Get all tables of this database.
ResultSet tblRs = dbmd.getTables(catalogName, "", "", null);				
if(tblRs!=null)
{
	while(tblRs.next())
	{
		// Get table
		String tmpDBName = tblRs.getString(1);
		String tmpTblName = tblRs.getString(3);
		System.out.println("DB : " + tmpDBName + " , table : " + tmpTblName);
         }
}

Списък с колони на таблицата

// Get columns
ResultSet columnRs = dbmd.getColumns(catalogName, "", tmpTblName, "");
						
if(columnRs!=null)
{
	while(columnRs.next())
	{
		// Get column type and name.
		String cType = columnRs.getString(6);
						
	        String cName = columnRs.getString(4);
		
		System.out.println("Column Name : " + cName + " , Column Type : " + cType);
	}
}

Пълен примерен код

Примерът по-долу ще използва MySQL сървър на база данни.

public class DatabaseMetaDataExample {

	public static void main(String[] args) {
		
		try
		{
			/* Below are db connection required data. */
			String ip = "localhost";
			int port = 3306;
			String dbName = "test";
			String userName = "root";
			String password = "";
	
			DatabaseMetaDataExample dbmdExample = new DatabaseMetaDataExample();
			
			// Get database connection.
			Connection dbConn = dbmdExample.getMySqlConnection(ip, port, dbName, userName, password);
			
			// Get database metadata. 
			DatabaseMetaData dbmd = dbConn.getMetaData();
			
			// Get db name.
			String dbProductName = dbmd.getDatabaseProductName();
			System.out.println("DB product name : " + dbProductName);
			
			// Get db product version.
			String dbProductVersion = dbmd.getDatabaseProductVersion();
			System.out.println("DB product version : " + dbProductVersion);
			
			// Get db major & minor version.
			int dbMajorVersion = dbmd.getDatabaseMajorVersion();
			System.out.println("DB major version : " + dbMajorVersion);
			int dbMinorVersion = dbmd.getDatabaseMinorVersion();
			System.out.println("DB minor version : " + dbMinorVersion);
			
			// Get jdbc driver major & minor version.
			int jdbcDriverMajorVersion = dbmd.getDriverMajorVersion();
			System.out.println("JDBC driver major version : " + jdbcDriverMajorVersion);
			int jdbcDriverMinorVersion = dbmd.getDriverMinorVersion();
			System.out.println("JDBC driver minor version : " + jdbcDriverMinorVersion);
			
			// Get all database catalogs.
			ResultSet rs = dbmd.getCatalogs();
			if(rs!=null)
			{
				while(rs.next())
				{
					String catalogName = rs.getString(1);
					System.out.println("Database catalog : " + catalogName);
					
					// Get all tables of this database.
					ResultSet tblRs = dbmd.getTables(catalogName, "", "", null);
					
					if(tblRs!=null)
					{
						while(tblRs.next())
						{
							// Get table
							String tmpDBName = tblRs.getString(1);
							String tmpTblName = tblRs.getString(3);
							System.out.println("DB : " + tmpDBName + " , table : " + tmpTblName);
							
							// Get columns
							ResultSet columnRs = dbmd.getColumns(catalogName, "", tmpTblName, "");
							
							if(columnRs!=null)
							{
								while(columnRs.next())
								{
									// Get column type and name.
									String cType = columnRs.getString(6);
									
									String cName = columnRs.getString(4);
									
									System.out.println("Column Name : " + cName + " , Column Type : " + cType);
								}
							}
							
						}
					}
					
				}
			}
			
			
			dbmdExample.closeDBResource(null, dbConn);
		} catch (SQLException ex) {
			ex.printStackTrace();
		}
	}
	
	/* This method return java.sql.Connection object from MySQL server. */
	public Connection getMySqlConnection(String ip, int port, String dbName, String userName, String password)
	{
		/* Declare and initialize a sql Connection variable. */
		Connection ret = null;
		
		try
		{
		
			/* Register for mysql jdbc driver class. */
			Class.forName("com.mysql.jdbc.Driver");
			
			/* Create mysql connection url. */
			String mysqlConnUrl = "jdbc:mysql://" + ip + ":" + port + "/" + dbName;
			
			/* Get the mysql Connection object. */
			ret = DriverManager.getConnection(mysqlConnUrl, userName , password);
		}catch(Exception ex)
		{
			ex.printStackTrace();
		}finally
		{
			return ret;
		}
	}
	
	/* Close statement and connection after use, this can avoid resource waste. */
	public void closeDBResource(Statement stmt, Connection conn)
	{
		try
		{
			if(stmt!=null)
			{
				stmt.close();
				stmt = null;
			}
			
			if(conn!=null)
			{
				conn.close();
				conn = null;
			}
		}catch(Exception ex)
		{
			ex.printStackTrace();
		}
	}

}

Изходен код:

1. [id за изтегляне=”2567″]

Справка:

1. Интерфейс DatabaseMetaData