Store Ordered Values in Topics

Advanced List Operations

The Topic API provides the CollaborationList data structure to store ordered values and subscribe to their changes.

You can get a CollaborationList by its name in the Topic connection activation callback.

Source code

CollaborationListExample.javapackage com.vaadin.demo.collaboration;

import com.vaadin.collaborationengine.CollaborationEngine;
import com.vaadin.collaborationengine.CollaborationList;
import com.vaadin.collaborationengine.ListOperation;
import com.vaadin.collaborationengine.ListOperationResult;
import com.vaadin.collaborationengine.ListKey;
import com.vaadin.collaborationengine.UserInfo;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;

public class CollaborationListExample extends VerticalLayout {

    public CollaborationListExample() {
        // NOTE: In a real application, use the user id of the logged in user
        // instead
        String userId = System.identityHashCode(UI.getCurrent()) + "";
        UserInfo localUser = new UserInfo(userId, "User " + userId);
        CollaborationEngine.getInstance().openTopicConnection(this, "my-topic",
                localUser, connection -> {
                    CollaborationList list = connection.getNamedList("my-list");
                    ListOperationResult<Void> result = list.insertLast("foo");
                    result.getCompletableFuture().thenAccept(v -> {
                        // do something when the insertion completes
                    });
                    ListKey key = result.getKey();

                    // Replace an item using its key
                    list.set(key, "bar");

                    // Get an item value using its key
                    String bar = list.getItem(key, String.class);

                    // Insert an item at the end of the list
                    // Only succeeds if key is currently last
                    ListOperation operation1 = ListOperation.insertLast("baz")
                            .ifLast(key);
                    ListOperationResult<Boolean> result1 = list
                            .apply(operation1);
                    ListKey key1 = result1.getKey();

                    // Insert an item before key1
                    // Only succeeds if key1 is currently last
                    ListOperation operation2 = ListOperation
                            .insertBefore(key1, "qux").ifLast(key1);
                    ListOperationResult<Boolean> result2 = list
                            .apply(operation2);
                    ListKey key2 = result2.getKey();

                    // Insert an item between two keys
                    // Only succeeds if the keys are consecutive
                    ListOperation operation3 = ListOperation.insertBetween(key2,
                            key1, "xyz");
                    ListOperationResult<Boolean> result3 = list
                            .apply(operation3);

                    // Remove an item using its key
                    list.remove(key);
                    return null;
                });
    }
}

When you have gotten the list instance, you can insert values at the end of the list with the insertLast() method.

Source code

CollaborationListExample.javapackage com.vaadin.demo.collaboration;

import com.vaadin.collaborationengine.CollaborationEngine;
import com.vaadin.collaborationengine.CollaborationList;
import com.vaadin.collaborationengine.ListOperation;
import com.vaadin.collaborationengine.ListOperationResult;
import com.vaadin.collaborationengine.ListKey;
import com.vaadin.collaborationengine.UserInfo;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;

public class CollaborationListExample extends VerticalLayout {

    public CollaborationListExample() {
        // NOTE: In a real application, use the user id of the logged in user
        // instead
        String userId = System.identityHashCode(UI.getCurrent()) + "";
        UserInfo localUser = new UserInfo(userId, "User " + userId);
        CollaborationEngine.getInstance().openTopicConnection(this, "my-topic",
                localUser, connection -> {
                    CollaborationList list = connection.getNamedList("my-list");
                    ListOperationResult<Void> result = list.insertLast("foo");
                    result.getCompletableFuture().thenAccept(v -> {
                        // do something when the insertion completes
                    });
                    ListKey key = result.getKey();

                    // Replace an item using its key
                    list.set(key, "bar");

                    // Get an item value using its key
                    String bar = list.getItem(key, String.class);

                    // Insert an item at the end of the list
                    // Only succeeds if key is currently last
                    ListOperation operation1 = ListOperation.insertLast("baz")
                            .ifLast(key);
                    ListOperationResult<Boolean> result1 = list
                            .apply(operation1);
                    ListKey key1 = result1.getKey();

                    // Insert an item before key1
                    // Only succeeds if key1 is currently last
                    ListOperation operation2 = ListOperation
                            .insertBefore(key1, "qux").ifLast(key1);
                    ListOperationResult<Boolean> result2 = list
                            .apply(operation2);
                    ListKey key2 = result2.getKey();

                    // Insert an item between two keys
                    // Only succeeds if the keys are consecutive
                    ListOperation operation3 = ListOperation.insertBetween(key2,
                            key1, "xyz");
                    ListOperationResult<Boolean> result3 = list
                            .apply(operation3);

                    // Remove an item using its key
                    list.remove(key);
                    return null;
                });
    }
}

Since the insertion is asynchronous, the method returns a result object from which you can get a CompletableFuture that you can use to determine when the insertion has been done.

Source code

CollaborationListExample.javapackage com.vaadin.demo.collaboration;

import com.vaadin.collaborationengine.CollaborationEngine;
import com.vaadin.collaborationengine.CollaborationList;
import com.vaadin.collaborationengine.ListOperation;
import com.vaadin.collaborationengine.ListOperationResult;
import com.vaadin.collaborationengine.ListKey;
import com.vaadin.collaborationengine.UserInfo;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;

public class CollaborationListExample extends VerticalLayout {

    public CollaborationListExample() {
        // NOTE: In a real application, use the user id of the logged in user
        // instead
        String userId = System.identityHashCode(UI.getCurrent()) + "";
        UserInfo localUser = new UserInfo(userId, "User " + userId);
        CollaborationEngine.getInstance().openTopicConnection(this, "my-topic",
                localUser, connection -> {
                    CollaborationList list = connection.getNamedList("my-list");
                    ListOperationResult<Void> result = list.insertLast("foo");
                    result.getCompletableFuture().thenAccept(v -> {
                        // do something when the insertion completes
                    });
                    ListKey key = result.getKey();

                    // Replace an item using its key
                    list.set(key, "bar");

                    // Get an item value using its key
                    String bar = list.getItem(key, String.class);

                    // Insert an item at the end of the list
                    // Only succeeds if key is currently last
                    ListOperation operation1 = ListOperation.insertLast("baz")
                            .ifLast(key);
                    ListOperationResult<Boolean> result1 = list
                            .apply(operation1);
                    ListKey key1 = result1.getKey();

                    // Insert an item before key1
                    // Only succeeds if key1 is currently last
                    ListOperation operation2 = ListOperation
                            .insertBefore(key1, "qux").ifLast(key1);
                    ListOperationResult<Boolean> result2 = list
                            .apply(operation2);
                    ListKey key2 = result2.getKey();

                    // Insert an item between two keys
                    // Only succeeds if the keys are consecutive
                    ListOperation operation3 = ListOperation.insertBetween(key2,
                            key1, "xyz");
                    ListOperationResult<Boolean> result3 = list
                            .apply(operation3);

                    // Remove an item using its key
                    list.remove(key);
                    return null;
                });
    }
}

The result object also provides the ListKey of the inserted item, which you can use to replace the item itself, get its current value or remove it from the list.

Source code

CollaborationListExample.javapackage com.vaadin.demo.collaboration;

import com.vaadin.collaborationengine.CollaborationEngine;
import com.vaadin.collaborationengine.CollaborationList;
import com.vaadin.collaborationengine.ListOperation;
import com.vaadin.collaborationengine.ListOperationResult;
import com.vaadin.collaborationengine.ListKey;
import com.vaadin.collaborationengine.UserInfo;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;

public class CollaborationListExample extends VerticalLayout {

    public CollaborationListExample() {
        // NOTE: In a real application, use the user id of the logged in user
        // instead
        String userId = System.identityHashCode(UI.getCurrent()) + "";
        UserInfo localUser = new UserInfo(userId, "User " + userId);
        CollaborationEngine.getInstance().openTopicConnection(this, "my-topic",
                localUser, connection -> {
                    CollaborationList list = connection.getNamedList("my-list");
                    ListOperationResult<Void> result = list.insertLast("foo");
                    result.getCompletableFuture().thenAccept(v -> {
                        // do something when the insertion completes
                    });
                    ListKey key = result.getKey();

                    // Replace an item using its key
                    list.set(key, "bar");

                    // Get an item value using its key
                    String bar = list.getItem(key, String.class);

                    // Insert an item at the end of the list
                    // Only succeeds if key is currently last
                    ListOperation operation1 = ListOperation.insertLast("baz")
                            .ifLast(key);
                    ListOperationResult<Boolean> result1 = list
                            .apply(operation1);
                    ListKey key1 = result1.getKey();

                    // Insert an item before key1
                    // Only succeeds if key1 is currently last
                    ListOperation operation2 = ListOperation
                            .insertBefore(key1, "qux").ifLast(key1);
                    ListOperationResult<Boolean> result2 = list
                            .apply(operation2);
                    ListKey key2 = result2.getKey();

                    // Insert an item between two keys
                    // Only succeeds if the keys are consecutive
                    ListOperation operation3 = ListOperation.insertBetween(key2,
                            key1, "xyz");
                    ListOperationResult<Boolean> result3 = list
                            .apply(operation3);

                    // Remove an item using its key
                    list.remove(key);
                    return null;
                });
    }
}

Advanced List Operations

The ListOperation class allows you to prepare a list operation that can then be applied to the list using the CollaborationList::apply method.

The reason you may want to use this class is to define certain conditions that must be met when the operation is attempted. If a condition isn’t met, the operation isn’t be completed. This is useful to protect against duplicate operations.

Static methods of ListOperation

insertFirst() Value is inserted at the beginning of the list.
insertLast() Value is inserted at the end of the list.
insertBefore() Value is inserted immediately before a specified key.
insertAfter() Value is inserted immediately after a specified key.
insertBetween() Shorthand for insertAfter(value, keyBefore).ifNext(keyBefore, keyAfter).

Conditional methods of ListOperation

ifFirst(key) The specified key must be the first in the list.
ifLast(key) The specified key must be the last in the list.
ifPrev(key, keyPrev) The specified keyPrev must be immediately before key.
ifNext(key, keyNext) The specified keyNext must be immediately after key.
ifEmpty() The list must have no entries.
ifNotEmpty() The list must have at least one entry.

Source code

CollaborationListExample.javapackage com.vaadin.demo.collaboration;

import com.vaadin.collaborationengine.CollaborationEngine;
import com.vaadin.collaborationengine.CollaborationList;
import com.vaadin.collaborationengine.ListOperation;
import com.vaadin.collaborationengine.ListOperationResult;
import com.vaadin.collaborationengine.ListKey;
import com.vaadin.collaborationengine.UserInfo;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;

public class CollaborationListExample extends VerticalLayout {

    public CollaborationListExample() {
        // NOTE: In a real application, use the user id of the logged in user
        // instead
        String userId = System.identityHashCode(UI.getCurrent()) + "";
        UserInfo localUser = new UserInfo(userId, "User " + userId);
        CollaborationEngine.getInstance().openTopicConnection(this, "my-topic",
                localUser, connection -> {
                    CollaborationList list = connection.getNamedList("my-list");
                    ListOperationResult<Void> result = list.insertLast("foo");
                    result.getCompletableFuture().thenAccept(v -> {
                        // do something when the insertion completes
                    });
                    ListKey key = result.getKey();

                    // Replace an item using its key
                    list.set(key, "bar");

                    // Get an item value using its key
                    String bar = list.getItem(key, String.class);

                    // Insert an item at the end of the list
                    // Only succeeds if key is currently last
                    ListOperation operation1 = ListOperation.insertLast("baz")
                            .ifLast(key);
                    ListOperationResult<Boolean> result1 = list
                            .apply(operation1);
                    ListKey key1 = result1.getKey();

                    // Insert an item before key1
                    // Only succeeds if key1 is currently last
                    ListOperation operation2 = ListOperation
                            .insertBefore(key1, "qux").ifLast(key1);
                    ListOperationResult<Boolean> result2 = list
                            .apply(operation2);
                    ListKey key2 = result2.getKey();

                    // Insert an item between two keys
                    // Only succeeds if the keys are consecutive
                    ListOperation operation3 = ListOperation.insertBetween(key2,
                            key1, "xyz");
                    ListOperationResult<Boolean> result3 = list
                            .apply(operation3);

                    // Remove an item using its key
                    list.remove(key);
                    return null;
                });
    }
}

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Documentation

Documentation

Store Ordered Values in Topics

Advanced List Operations