Working with Resources

The resource system enables LLM-powered applications to access structured content through a unified interface. Resources are identified by URIs and can represent any type of content that might be useful for an LLM to process. The AJ MCP client provides methods for discovering and accessing resources exposed by the server.

Listing Resources

To list available resources:

List<ResourceItem> resourceList = mcpClient.listResources();
assertEquals(2, resourceList.size(), "Expected exactly two resources");

ResourceItem blob = getResourceRef("blob", resourceList);
assertNotNull(blob, "Resource 'blob' should not be null");
assertEquals("blob", blob.getName(), "Name mismatch for 'blob'");
assertEquals("file:///blob", blob.getUri(), "URI mismatch for 'blob'");
assertEquals("image/jpg", blob.getMimeType(), "MIME type mismatch for 'blob'");
assertEquals("A nice pic", blob.getDescription(), "Description mismatch for 'blob'");

listResources() requests and caches the first/default page. Use listResources(int pageNo) for another page. Each page is cached independently, so requesting page 2 does not overwrite page 0.

List<ResourceItem> resourceList = mcpClient.listResources(1);
assertEquals(2, resourceList.size(), "Expected exactly two resources");

Reading Resource Contents

To read the contents of a resource:

GetResourceResult.ResourceResultDetail response = mcpClient.readResource("file:///text");
assertEquals(1, response.getContents().size(), "Expected exactly one content");

ResourceContent contents = response.getContents().get(0);

ResourceContentText textContents = (ResourceContentText) contents;
assertEquals("file:///text", textContents.getUri(), "URI should be 'file:///text'");
assertEquals("text888", textContents.getText(), "Text content should be 'text'");

The readResource() method returns a ResourceResultDetail containing an array of resource contents. Each resource content can be either text content or binary content, depending on the resource's MIME type.

GetResourceResult.ResourceResultDetail response = mcpClient.readResource("file:///blob");
assertEquals(1, response.getContents().size(), "Expected exactly one content");

ResourceContent contents = response.getContents().get(0);

ResourceContentBinary blobContents = (ResourceContentBinary) contents;
assertEquals("file:///blob", blobContents.getUri(), "URI should be 'file:///blob'");
assertEquals("blob", blobContents.getBlob(), "Blob content should be 'blob'");

Resource templates registered by the server can be listed and read through their expanded URI. For interoperable pagination, prefer listResourceTemplatePage(cursor) and pass the returned opaque nextCursor unchanged.

GetResourceResult.ResourceResultDetail response = mcpClient.readResource("file:///text-template/hello");
assertEquals(1, response.getContents().size(), "Expected exactly one content");

ResourceContent contents = response.getContents().get(0);

ResourceContentText textContents = (ResourceContentText) contents;
assertEquals("file:///text-template/hello", textContents.getUri(), "URI should be 'file:///text-template/hello'");
assertEquals("text hello", textContents.getText(), "Text content should be 'text hello'");

Resource Subscriptions

The client can subscribe to resource changes to receive notifications when resources are updated:

mcpClient.subscribeResource("test://resource/path");

To stop receiving notifications for a resource:

mcpClient.unsubscribeResource("test://resource/path");