feat: add container block example

block-kit/README.md

@@ -9,6 +9,7 @@ Read the [docs](https://docs.slack.dev/block-kit/) to learn concepts behind thes
 ### Blocks
 
 - **[Actions](https://docs.slack.dev/reference/block-kit/blocks/actions-block)**: Holds multiple interactive elements. [Implementation](./src/main/java/blocks/Actions.java).
+- **[Container](https://docs.slack.dev/reference/block-kit/blocks/container-block)**: A general-purpose wrapper for grouping child blocks together, with a configurable size. [Implementation](./src/main/java/blocks/Container.java).
 - **[Context](https://docs.slack.dev/reference/block-kit/blocks/context-block)**: Provides contextual info, which can include both images and text. [Implementation](./src/main/java/blocks/Context.java).
 - **[Divider](https://docs.slack.dev/reference/block-kit/blocks/divider-block)**: Visually separates pieces of info inside of a message. [Implementation](./src/main/java/blocks/Divider.java).
 - **[File](https://docs.slack.dev/reference/block-kit/blocks/file-block)**: Displays info about remote files. [Implementation](./src/main/java/blocks/File.java).

block-kit/src/main/java/blocks/Container.java

@@ -0,0 +1,45 @@
+package blocks;
+
+import com.slack.api.model.block.Blocks;
+import com.slack.api.model.block.ContainerBlock;
+import com.slack.api.model.block.composition.BlockCompositions;
+import com.slack.api.model.block.element.BlockElements;
+import java.util.List;
+
+/**
+ * A general-purpose wrapper for grouping child blocks together, with a configurable size.
+ * {@link https://docs.slack.dev/reference/block-kit/blocks/container-block/}
+ */
+public class Container {
+    /**
+     * A collapsible container with sections, a divider, context, and actions.
+     */
+    public static ContainerBlock example01() {
+        ContainerBlock block = Blocks.container(c -> c.blockId("bkb_container_bulk_update")
+                .title(BlockCompositions.plainText("Bulk update: 2 records selected"))
+                .subtitle(BlockCompositions.plainText("Review changes before confirming"))
+                .isCollapsible(true)
+                .childBlocks(Blocks.asBlocks(
+                        Blocks.section(s -> s.blockId("record-row-1")
+                                .text(BlockCompositions.markdownText(
+                                        "*DCW-1024*\nStatus: Open → Closed\nAssignee: @princessdonut → @carl"))),
+                        Blocks.divider(d -> d.blockId("bulk-div-1")),
+                        Blocks.section(s -> s.blockId("record-row-2")
+                                .text(BlockCompositions.markdownText(
+                                        "*DCW-1025*\nStatus: In Progress → Closed\nAssignee: @mordecai → @carl"))),
+                        Blocks.divider(d -> d.blockId("bulk-div-2")),
+                        Blocks.context(ctx -> ctx.blockId("bulk-status-bar")
+                                .elements(List.of(BlockCompositions.markdownText(
+                                        ":white_check_mark: 2 records will be updated • Status → Closed • Assignee → @carl")))),
+                        Blocks.actions(a -> a.blockId("bulk-actions")
+                                .elements(List.of(
+                                        BlockElements.button(b -> b.text(
+                                                        BlockCompositions.plainText(pt -> pt.text("Confirm All").emoji(true)))
+                                                .style("primary")
+                                                .actionId("bulk_confirm")),
+                                        BlockElements.button(b -> b.text(
+                                                        BlockCompositions.plainText(pt -> pt.text("Cancel").emoji(true)))
+                                                .actionId("bulk_cancel"))))))));
+        return block;
+    }
+}

block-kit/src/test/java/blocks/ContainerTest.java

@@ -0,0 +1,93 @@
+package blocks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.google.gson.JsonParser;
+import com.slack.api.model.block.ContainerBlock;
+import com.slack.api.util.json.GsonFactory;
+import org.junit.jupiter.api.Test;
+
+public class ContainerTest {
+    @Test
+    public void testExample01() {
+        ContainerBlock block = Container.example01();
+        String actual = GsonFactory.createSnakeCase().toJson(block);
+        String expected = """
+            {
+              "type": "container",
+              "block_id": "bkb_container_bulk_update",
+              "title": {
+                "type": "plain_text",
+                "text": "Bulk update: 2 records selected"
+              },
+              "subtitle": {
+                "type": "plain_text",
+                "text": "Review changes before confirming"
+              },
+              "is_collapsible": true,
+              "child_blocks": [
+                {
+                  "type": "section",
+                  "block_id": "record-row-1",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "*DCW-1024*\\nStatus: Open → Closed\\nAssignee: @princessdonut → @carl"
+                  }
+                },
+                {
+                  "type": "divider",
+                  "block_id": "bulk-div-1"
+                },
+                {
+                  "type": "section",
+                  "block_id": "record-row-2",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "*DCW-1025*\\nStatus: In Progress → Closed\\nAssignee: @mordecai → @carl"
+                  }
+                },
+                {
+                  "type": "divider",
+                  "block_id": "bulk-div-2"
+                },
+                {
+                  "type": "context",
+                  "block_id": "bulk-status-bar",
+                  "elements": [
+                    {
+                      "type": "mrkdwn",
+                      "text": ":white_check_mark: 2 records will be updated • Status → Closed • Assignee → @carl"
+                    }
+                  ]
+                },
+                {
+                  "type": "actions",
+                  "block_id": "bulk-actions",
+                  "elements": [
+                    {
+                      "type": "button",
+                      "text": {
+                        "type": "plain_text",
+                        "text": "Confirm All",
+                        "emoji": true
+                      },
+                      "style": "primary",
+                      "action_id": "bulk_confirm"
+                    },
+                    {
+                      "type": "button",
+                      "text": {
+                        "type": "plain_text",
+                        "text": "Cancel",
+                        "emoji": true
+                      },
+                      "action_id": "bulk_cancel"
+                    }
+                  ]
+                }
+              ]
+            }
+            """;
+        assertEquals(JsonParser.parseString(expected), JsonParser.parseString(actual));
+    }
+}