SessionTrees (Diffusion)

All Superinterfaces:

Feature

All Known Subinterfaces:

Topics
```
public interface SessionTrees
extends Feature
```
This feature allows a client session to configure session trees.
A session tree is a virtual view of the topic tree presented to a session by fetch and subscription operations. Custom session trees for different sessions can be configured using declarative rules maintained by the server to meet data security, data optimisation, or personalisation and localisation requirements. Each session can be presented with a unique session tree based on its session properties.
A session tree is produced by applying branch mappings to the topic tree. Branch mappings are organised into branch mapping tables. Each branch mapping table is assigned to a unique path – the session tree branch.
A session tree is composed of session paths. Each session path is mapped via the branch mapping tables to a unique topic path.
A branch mapping table is an ordered list of (session filter, topic tree branch) pairs. For example, the branch mapping table for the session tree branch market/prices might be:
```
 Session filter                           Topic tree branch
 ==============                           =================
 USER_TIER is '1' or $Country is 'DE'     backend/discounted_prices
 USER_TIER is '2'                         backend/standard_prices
 $Principal is ''                         backend/delayed_prices
 
```
With this configuration, if an unauthenticated session (one that matches the $Principal is '' session filter) subscribes to the session path market/prices/X, and there is a topic bound to the topic path backend/delayed_prices/X, the subscription will complete. The session will receive a subscription notification under the session path market/prices/X, together with the topic properties and the value of the topic. The session is unaware that the data originates from a topic bound to a different topic path. If no topic is bound to backend/delayed_prices/X, the subscription will not resolve and the session will receive no data, even if there is a topic bound to market/prices/X.
Session trees complement the data transformation capabilities of topic views. In our example, the time delayed time feed at backend/delayed_prices could be maintained by a topic view using the delay by clause.
Branch mappings are persisted by the server and shared across a cluster, in a similar manner to topic views, security stores, and metric collectors. Branch mappings are editable using this feature, and via the management console.
For a given session and session path, at most one branch mapping applies. The applicable branch mapping is chosen as follows:
- Each branch mapping table with session tree branch that is a prefix of the session path is considered. For a given table, the first branch mapping with a session filter that matches the session's properties is the one that applies. A branch mapping table may have no applicable branch mappings for a session.
- If there are several such branch mapping tables with a branch mapping that for the session, the one with the longest prefix of the session path applies.
- If no branch mapping table has a branch mapping for the session, the session path is translated to the identical topic path.
Access control

To subscribe to or fetch from a session path, a session must be granted the appropriate path permission to the session path for the operation (SELECT_TOPIC, or READ_TOPIC). The session doesn't require any permissions to the topic path of the topic providing the data.
To create or replace branch mappings, a session needs the MODIFY_TOPIC path permission for the session tree branch of the branch mapping table, EXPOSE_BRANCH path permission for the topic tree branch of each branch mapping, and (if an existing table with the same session tree branch is being replaced) EXPOSE_BRANCH permission for each branch mapping of existing table.
To retrieve a branch mapping table, a session needs the READ_TOPIC path permission for its session tree branch.
Accessing the feature

This feature may be obtained from a session as follows:
```
 SessionTrees sessionTrees = session.feature(SessionTrees.class);
 
```
This feature is also extended by the Topics feature. This means is it possible to use the methods described here through the Topics feature.
Since:

6.7

Nested Class Summary

Nested Classes
Modifier and Type	Interface and Description
`static interface`	`SessionTrees.BranchMapping` A session tree branch mapping.
`static interface`	`SessionTrees.BranchMappingTable` A session tree branch mapping table.
`static class`	`SessionTrees.InvalidBranchMappingException` Exception indicating an invalid `SessionTrees.BranchMapping` or `SessionTrees.BranchMappingTable`.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`CompletableFuture<SessionTrees.BranchMappingTable>`	`getBranchMappingTable(String sessionTreeBranch)` Retrieve a branch mapping table from the server.
`CompletableFuture<List<String>>`	`listSessionTreeBranchesWithMappings()` Retrieve the session tree branches of the server's branch mapping tables.
`CompletableFuture<?>`	`putBranchMappingTable(SessionTrees.BranchMappingTable branchMappingTable)` Create or replace a branch mapping table.

Methods inherited from interface com.pushtechnology.diffusion.client.session.Feature
getSession

- Method Detail
  - putBranchMappingTable
```
CompletableFuture<?> putBranchMappingTable(SessionTrees.BranchMappingTable branchMappingTable)
```
    Create or replace a branch mapping table.
    The server ensures that there is at most one branch mapping table for a session tree branch. Putting a new branch mapping table will replace any previous branch mapping table with the same session tree branch. To remove all branch mappings for a session tree branch, put an empty branch mapping table.
    Parameters:
    
    branchMappingTable - the new table
    
    Returns:
    a CompletableFuture that completes when a response is received from the server.
    If the task completes successfully, the CompletableFuture result will be null. The result type is any rather than Void to provide forward compatibility with future iterations of this API that may provide a non-null result with a more specific result type.
    Otherwise, the CompletableFuture will complete exceptionally with a CompletionException. Common reasons for failure, listed by the exception reported as the cause, include:
    
    SessionTrees.InvalidBranchMappingException – if branchMappingTable or one of its branch mappings is invalid;
    PermissionsException – if the calling session does not have the MODIFY_TOPIC permission for the session tree branch of the branch mapping table, EXPOSE_BRANCH permission for each branch mapping of branchMappingTable, and (if there is an existing table for the session tree branch) EXPOSE_BRANCH permission for each branch mapping of existing table;
    ClusterRoutingException – if the operation failed due to a transient cluster error;
    SessionClosedException – if the session is closed.
  - listSessionTreeBranchesWithMappings
```
CompletableFuture<List<String>> listSessionTreeBranchesWithMappings()
```
    Retrieve the session tree branches of the server's branch mapping tables. The results will only include the session tree branches of branch mapping tables that have at least one branch mapping and for which the calling session has READ_TOPIC path permission for the session tree branch.
    Individual branch mapping tables can be retrieved using getBranchMappingTable(String).
    Returns:
    a CompletableFuture that completes when a response is received from the server, returning a list of session tree branches in path order.
    If the task fails, the CompletableFuture will complete exceptionally with a CompletionException. Common reasons for failure, listed by the exception reported as the cause, include:
    
    SessionClosedException – if the session is closed.
  - getBranchMappingTable
```
CompletableFuture<SessionTrees.BranchMappingTable> getBranchMappingTable(String sessionTreeBranch)
```
    Retrieve a branch mapping table from the server.
    If there is no branch mapping table at the given session tree branch, this method will return an empty branch mapping table.
    Parameters:
    
    sessionTreeBranch - the session tree branch that identifies the branch mapping table
    
    Returns:
    a CompletableFuture that completes when a response is received from the server, returning the branch mapping table for sessionTreeBranch.
    If the task fails, the CompletableFuture will complete exceptionally with a CompletionException. Common reasons for failure, listed by the exception reported as the cause, include:
    
    PermissionsException – if the calling session does not have the READ_TOPIC permission for sessionTreeBranch;
    SessionClosedException – if the session is closed.

Interface SessionTrees

Access control

Accessing the feature

Nested Class Summary

Method Summary

Methods inherited from interface com.pushtechnology.diffusion.client.session.Feature

Method Detail

putBranchMappingTable

listSessionTreeBranchesWithMappings

getBranchMappingTable