# Roster Item Exchange

# Roster Item Exchange Support

This extension is used to send rosters, roster groups and roster entries from one XMPP Entity to another. It also provides an easy way to hook up custom logic when entries are received from other XMPP clients.

Follow these links to learn how to send and receive roster items:

- Send a complete roster
- Send a roster's group
- Send a roster's entry
- Receive roster entries

JEP related: JEP-93

## Send a complete roster

### Description

Sometimes it is useful to send a whole roster to another user. Smack provides a very easy way to send a complete roster to another XMPP client.

### Usage

Create an instance of RosterExchangeManager and use the #send(Roster, String) message to send a roster to a given user. The first parameter is the roster to send and the second parameter is the id of the user that will receive the roster entries.

### Example

In this example we can see how user1 sends his roster to user2.

>           // Connect to the server and log in
>           conn1 = new XMPPConnection(host);
>           conn1.login(server_user1, pass1);

>           // Create a new roster exchange manager on conn1
>           RosterExchangeManager rosterExchangeManager = new RosterExchangeManager(conn1);
>           // Send user1's roster to user2
>           rosterExchangeManager.send(conn1.getRoster(), user2);

## Send a roster's group

### Description

It is also possible to send a roster group to another XMPP client. A roster group groups a set of roster entries under a name.

### Usage

Create an instance of RosterExchangeManager and use the #send(RosterGroup, String) message to send a roster group to a given user. The first parameter is the roster group to send and the second parameter is the id of the user that will receive the roster entries.

### Example

In this example we can see how user1 sends his roster groups to user2.

>           // Connect to the server and log in
>           conn1 = new XMPPConnection(host);
>           conn1.login(server_user1, pass1);

>           // Create a new roster exchange manager on conn1
>           RosterExchangeManager rosterExchangeManager = new RosterExchangeManager(conn1);
>           // Send user1's RosterGroups to user2
>           for (Iterator it = conn1.getRoster().getGroups(); it.hasNext(); )
>               rosterExchangeManager.send((RosterGroup)it.next(), user2);

## Send a roster's entry

### Description

Sometimes you may need to send a single roster entry to another XMPP client. Smack also lets you send items at this granularity level.

### Usage

Create an instance of RosterExchangeManager and use the #send(RosterEntry, String) message to send a roster entry to a given user. The first parameter is the roster entry to send and the second parameter is the id of the user that will receive the roster entries.

### Example

In this example we can see how user1 sends a roster entry to user2.

>           // Connect to the server and log in
>           conn1 = new XMPPConnection(host);
>           conn1.login(server_user1, pass1);

>           // Create a new roster exchange manager on conn1
>           RosterExchangeManager rosterExchangeManager = new RosterExchangeManager(conn1);
>           // Send a roster entry (any) to user2
>           rosterExchangeManager1.send((RosterEntry)conn1.getRoster().getEntries().next(), user2);

## Receive roster entries

### Description

Since roster items are sent between XMPP clients, it is necessary to listen to possible roster entries receptions. Smack provides a mechanism that you can use to execute custom logic when roster entries are received.

### Usage

1. Create a class that implements the RosterExchangeListener interface.
2. Implement the method entriesReceived(String, Iterator) that will be called when new entries are received with custom logic.
3. Add the listener to the RosterExchangeManager that works on the desired XMPPConnection.

### Example

In this example we can see how user1 sends a roster entry to user2 and user2 adds the received entries to his roster.

>           // Connect to the server and log in the users
>           conn1 = new XMPPConnection(host);
>           conn1.login(server_user1, pass1);
>           conn2 = new XMPPConnection(host);
>           conn2.login(server_user2, pass2);
>           final Roster user2_roster = conn2.getRoster();

>           // Create a RosterExchangeManager that will help user2 to listen and accept
>           the entries received
>           RosterExchangeManager rosterExchangeManager2 = new RosterExchangeManager(conn2);
>           // Create a RosterExchangeListener that will iterate over the received roster entries
>           RosterExchangeListener rosterExchangeListener = new RosterExchangeListener() {
>               public void entriesReceived(String from, Iterator rosterEntries) {
>                   for (Iterator it = rosterEntries; it.hasNext();) {
>                       try {
>                           // Get the received entry
>                           RosterEntry entry = (RosterEntry) it.next();
>                           // Display the entry on the console
>                           System.out.println(entry);
>                           // Add the entry to the user2's roster
>                           user2_roster.createEntry(entry);
>                       }
>                       catch (XMPPException e) {
>                           e.printStackTrace();
>                       }
>                   }
>               }
>           };
>           // Add the RosterExchangeListener to the RosterExchangeManager that user2 is using
>           rosterExchangeManager2.addRosterListener(rosterExchangeListener);

>           // Create a RosterExchangeManager that will help user1 to send his roster
>           RosterExchangeManager rosterExchangeManager1 = new RosterExchangeManager(conn1);
>           // Send user1's roster to user2
>           rosterExchangeManager1.send(conn1.getRoster(), user2);