If you run a select query where the number of columns and their data types are unknown, you may extract the number of attributes, their data types, etc from the populated result-set.
This technique is very important to understand when you are writing code to generate a dynamic view for an application.
package com.t4b.jdbc.mysql.test;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
public class ResultSetExtraction {
public static void main(String args[]) {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e1) {
e1.printStackTrace();
}
try {
Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test");
PreparedStatement pStatement = connection.prepareStatement("select * from users");
ResultSet rs = pStatement.executeQuery();
ResultSetMetaData rSetMetaData = rs.getMetaData();
int colCount = rSetMetaData.getColumnCount();
System.out.println("Columns are: ");
for (int c = 1; c <= colCount; c++) {
System.out.print(" " + rSetMetaData.getColumnName(c));
System.out.print(" " + rSetMetaData.getColumnDisplaySize(c));
System.out.print(" " + rSetMetaData.getColumnTypeName(c));
System.out.println();
}
while (rs.next()) {
for (int c = 1; c <= colCount; c++) {
if (rSetMetaData.getColumnTypeName(c).equalsIgnoreCase("VARCHAR")) {
System.out.print(" " + rs.getString(c));
} else if (rSetMetaData.getColumnTypeName(c).equalsIgnoreCase("NUMBER")) {
System.out.print(" " + rs.getInt(c));
} else {
// write code for other data types
}
}
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
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