Creating an SQL text-area and sending the query to the database

I want to create an SQL interface where the user can execute only "SELECT" queries and by clicking on a submit button, the query will be sent to the database

and i want to know how to make an SQL statement that receives the user query and execute it

something like that :

private static final String var = "SELECT query sent by the user"; 

public String executeUserQuery() {
    return executeQuery(var);
}

and it only has to be a SELECT query, he don't have the right to do anything else, except reading data.