coding of java mysql to retrieve data using hashmap and while loop

Question

I don't know how to retrieve data using hashmap and while loop from my database. plz help me.
My code is

    package com.glomindz.mercuri.dao;

    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.util.HashMap;

    import com.glomindz.mercuri.util.MySingleTon;

          public class UserServicesDAO {

private Connection connection;

public UserServicesDAO() {
    //connection = new MySingleTon().getConnection();
    connection = MySingleTon.getInstance().getConnection();

}

public void get_all_data() {
    HashMap<Integer, String> result = new HashMap<Integer, String>();
    String query = "SELECT * FROM spl_user_master";
    try {
        PreparedStatement stmt = connection.prepareStatement(query);
        boolean execute = stmt.execute();
        System.out.println(execute);
        ResultSet resultSet = stmt.getResultSet();
        System.out.println(resultSet.getMetaData());

    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public static void main(String[] args) {
    new UserServicesDAO().get_all_data();
}
 }

What's wrong with the code?

Mapping all data into HashMaps is a very very bad idea for any code that is part of a released product. I just switched to a company where that was the standard, and it is one hell of unstable unreadable code. I wish the programmer who designed that years ago will die a painful death some day. — ssindelar
– ssindelar, Commented Jul 8, 2013 at 12:34

juergen d · Accepted Answer · 2013-07-08 12:30:00Z

6

You can get values from your records in a loop like this

ResultSet resultSet = stmt.getResultSet();
while (resultSet.next()) {
    String someStringValue = resultSet.getString("some_column_name");
    int someIntegerValue = resultSet.getInt("some_other_column_name");
    //...
}

edited Jul 8, 2013 at 12:30

answered Jul 8, 2013 at 12:24

juergen d

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Comments

Guillaume · Accepted Answer · 2013-07-08 12:33:32Z

1

You're creating a map but you're not returning it, also you're not putting the SQL result it the map result:

public Map<Integer, String> get_all_data() {
    HashMap<Integer, String> result = new HashMap<Integer, String>();
    String query = "SELECT * FROM spl_user_master";
    try {
        PreparedStatement stmt = connection.prepareStatement(query);
        boolean execute = stmt.execute();
        System.out.println(execute);
        ResultSet resultSet = stmt.getResultSet();
        System.out.println(resultSet.getMetaData());
        while (resultSet.next()) {
              result.put(resultSet.getInt(...), resultSet.getString(...));
        }
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return result;
}

In the code above ... should be the column name

answered Jul 8, 2013 at 12:33

Guillaume

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3 Comments

atikul hussain Over a year ago

i have modifed my code but then it gives a message java.sql.SQLException: Column 'SELECT * FROM spl_user_master' not found.

Guillaume Over a year ago

Not sure what you're doing but in the code above '...' should be replaced by the column name, not by the SQL query

Guillaume Over a year ago

A Map<Integer, String> is probably not the right structure to store data from a table with 8 columns. Create a user class and instantiate it for each row in your resultset

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