In this example I will discuss about ResultSetMetaData interface and its usage. It represents an object that can be used to get information about the types and properties of the columns in a ResultSet object.
The ResultSetMetaData extends the Wrapper interface, which is an interface for JDBC classes that provide the ability to retrieve the delegate instance when the instance in question is in fact a proxy class.
The ResultSetMetaData exists since JDK1.2.
The ResultSetMetaData in Java
To see how ResultSetMetaData is used, firstly create a database, a table and put some data in it by executing this SQL:
1 2 3 4 5 6 7 8 9 | create database db_test;create table db_test.tbl_one ( id int not null auto_increment key, name varchar(20) not null, surname varchar(20) not null);insert into db_test.tbl_one values (1,'John','Doe');insert into db_test.tbl_one values (2,'Jane','Doe'); |
After that, create a class called RSMDExample with this source code:
RSMDExample.java
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 | package com.javacodegeeks.examples;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.ResultSetMetaData;import java.sql.SQLException;public class RSMDExample { public static void main(String[] args) { String host = "jdbc:mysql://localhost/"; String db = "db_test"; String user = "root"; String password = "bitnami"; String sqlQuery = "Select * from tbl_one"; try { Class.forName("com.mysql.jdbc.Driver"); Connection conn = DriverManager.getConnection(host+db,user,password); ResultSet rs = conn.createStatement().executeQuery(sqlQuery); ResultSetMetaData rsmd = rs.getMetaData(); int cols = rsmd.getColumnCount(); System.out.printf("The query fetched %d columns\n",cols); System.out.println("These columns are: "); for (int i=1;i<=cols;i++) { String colName = rsmd.getColumnName(i); String colType = rsmd.getColumnTypeName(i); System.out.println(colName+" of type "+colType); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } }} |
Firstly, I am adding the necessary database drivers for MySQL database. Then, I establish a connection with the database on line 20 (make sure to change the host, username and password).
After that, I get a ResultSet instance after executing the query on line 16, which selects all the data from the table. Next, I get the ResultSetMetaData instance from the ResultSet. This instance, allows me to access some data from the table I was querying, like the number of the columns (line 25), column name (line 29), column type (line 30), and so on.
When this program is run, it gives this output:
1 2 3 4 5 | The query fetched 3 columnsThese columns are: id of type INTname of type VARCHARsurname of type VARCHAR |
Download Code
You can download the full source code of this example here : ResultSetMetaDataExample
