Accessing Metadata in Java Servlet

To make operations on the database we should know the data formats of the database. When using a ResultSet it is possible to access metadata for the data returned from the query. To obtain an object which encapsulates this metadata, use the method getMetaData () from the ResultSet class. This method returns an object of the ResultSetMetaData class and allows us to determine the number and type of columns.

The following is an example of how to use ResultSetMetaData:

String sql= "select * from Emp_info";
ResultSet rs = stmt.executeQuery (sql);
ResultSetMetaData metaData = rs.getMetaData ();
int column Count = metaData.getColumnCount ();
for (int count=1; count <= columnCount; count++)
{
     String columnType = metaData.getColumnTypeName (count);
     String column Name = metaData.getColumnName (count);
     System.out.println ("Column name:" + columnName + "Type:" + columnType);
}
The output of this appears as follows:
Column name: emp no Type: varchar
Column name: emp name Type: varchar
Column name: designation Type: varchar
Column name: date_of_joining Type: date
Column name: salary_in_rupees Type: float

 

Methods in the class ResultSetMetadata

Table lists the methods in the class ResultSetMetadata, with a short description.

                               Table Methods in the class ResultSetMetadata.

The class DatabaseMetadata

Like ResultSetMetaData we can get metadata for databases. The DatabaseMetaData class is used for obtaining database metadata. Like ResultsetMetaData, DataBaseMetaData also contains several methods which describe the database. Here is an example which uses DatabaseMetaData to retrieve a list of tables from the database:

DatabaseMetaData dbmd = dbCon.getMetaData ();
ResultSet rs = dbmd.getTables (null, null, "*", null);
while (rs.next ())
System.out.println (rs.getString (1) +" "+ rs.getString (3));
 

The above code displays the catalogue name and table name. The output is the following:

Catalogue                                                 Table-Name

/home/matt/classes/Exercises           PSYCHICVAMPIRES

/home/matt/classes/Exercises           BUSINESS CONTACTS                                               

/home/matt/classes/Exercises           SOCIAL CONTACTS

The getTables () method of the class DataBaseMetaData returns the object of ResultSet with ten columns (which describe the table).

There are many database metadata methods used in the programming Some of the commonly used database metadata methods are listed in Table.

                 Table List of some methods in the class DataBaseMetaData.