Using ajax.apex
Force.com Cookbook Sample Code
Chapter 13: Getting Started with Visualforce - Using AJAX in a Visualforce Page
To download all the code samples, access the Cookbook. - 
public class contactController {
// Return a list of the ten most recently modified contacts
public List<Contact> getContacts() {
return [SELECT Id, Name, Account.Name, Phone, Email FROM Contact ORDER BY LastModifiedDate DESC LIMIT 10];
}
// Get the 'id' query parameter from the URL of the page.
// If it's not specified, return an empty contact.
// Otherwise, issue a SOQL query to return the contact from the
// database.
public Contact getContact() {
Id id = System.currentPageReference().getParameters().get('id');
return id == null ? new Contact() : [SELECT Id, Name FROM Contact WHERE Id = :id];
}
}
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