In this example we shall show you how to set the fetch size of an SQL query. When changing the fetch size of a database, every time data is fetched from the database, the number of rows fetched will be equal to the size specified. To set the fetch size of an SQL query one should perform the following steps:
- Load the JDBC driver, using the
forName(String className)API method of the Class. In this example we use the MySQL JDBC driver. - Create a Connection to the database. Invoke the
getConnection(String url, String user, String password)API method of the DriverManager to create the connection. - Create a Statement, with the
createStatement()API method of the Connection. - Get the statement fetch size, with the
getFetchSize()API method of the Statement. In order to set the fetch size of the statement invoke thesetFetchSize(int rows)API method of the Statement. Now all ResultSets created from that statement will use that fetch size. - Change the fetch size of the ResultSet, with the
setFetchSize(int rows)API method of the ResultSet. It will override the Statement threshold and the rows fetched from the database will be specified by the resultSet fetch size,
as described in the code snippet below.
package com.javacodegeeks.snippets.core;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class SQLPrefetchSize {
public static void main(String[] args) {
Connection connection = null;
try {
// Load the MySQL JDBC driver
String driverName = "com.mysql.jdbc.Driver";
Class.forName(driverName);
// Create a connection to the database
String serverName = "localhost";
String schema = "test";
String url = "jdbc:mysql://" + serverName + "/" + schema;
String username = "username";
String password = "password";
connection = DriverManager.getConnection(url, username, password);
System.out.println("Successfully Connected to the database!");
} catch (ClassNotFoundException e) {
System.out.println("Could not find the database driver " + e.getMessage());
} catch (SQLException e) {
System.out.println("Could not connect to the database " + e.getMessage());
}
try {
// Get the fetch size of a statement
Statement statement = connection.createStatement();
int fetchSize = statement.getFetchSize();
System.out.println("Statement fetch size : " + fetchSize);
// Set the fetch size on the statement; all result sets created from that statement will use that fetch size
statement.setFetchSize(100);
// Create a result set
ResultSet resultSet = statement.executeQuery("SELECT * FROM test_table");
// Change the fetch size on the result set; the next time data needs to be fetched from the database, the driver will copy over as many rows as is specified by the current fetch size (overrides the statement threshold)
resultSet.setFetchSize(50);
} catch (SQLException e) {
}
}
}
Example Output:
Successfully Connected to the database!
Statement fetch size : 0
This was an example of how to set the fetch size of an SQL query in Java.
