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Merge pull request #314345 from lilyjma/java-mcp-resource-ref
Add Java MCP resource trigger reference doc
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‎articles/azure-functions/functions-bindings-mcp-resource-trigger.md‎

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> For C#, the Azure Functions MCP extension supports only the [isolated worker model](dotnet-isolated-process-guide.md).
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This first example shows how to use resource to implement the UI element of MCP Apps.
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> [!IMPORTANT]
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> The MCP extension in Java supports resource today. Documentation coming soon.
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Example code for JavaScript isn't currently available. See the TypeScript example for general guidance.
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The following code registers a resource named `Weather Widget` that serves an interactive weather display as bundled HTML content. The resource uses the `ui://` scheme to indicate it's an MCP App UI resource.
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```java
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private static final String RESOURCE_METADATA = """
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{
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"ui": {
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"prefersBorder": true
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}
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}
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""";
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@FunctionName("GetWeatherWidget")
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public String getWeatherWidget(
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@McpResourceTrigger(
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name = "context",
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uri = "ui://weather/index.html",
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resourceName = "Weather Widget",
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title = "Weather Widget",
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description = "Interactive weather display for MCP Apps",
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mimeType = "text/html;profile=mcp-app")
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@McpMetadata(
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name = "context",
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json = RESOURCE_METADATA)
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String context,
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final ExecutionContext executionContext) {
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executionContext.getLogger().info("GetWeatherWidget: serving weather widget UI");
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return java.nio.file.Files.readString(file.toPath(), StandardCharsets.UTF_8);
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}
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```
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A tool can reference this resource by declaring a `resourceUri` in its metadata, pointing to `ui://weather/index.html`. When the tool is invoked, the MCP host fetches the resource and renders it:
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```java
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private static final String TOOL_METADATA = """
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{
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"ui": {
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"resourceUri": "ui://weather/index.html"
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}
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}
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""";
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@FunctionName("GetWeather")
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public String getWeather(
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@McpToolTrigger(
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name = "GetWeather",
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description = "Returns current weather for a location via Open-Meteo.")
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@McpMetadata(
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name = "GetWeather",
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json = TOOL_METADATA)
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String context,
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@McpToolProperty(
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name = "location",
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propertyType = "string",
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description = "City name to check weather for (e.g., Seattle, New York, Miami)")
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String location,
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final ExecutionContext executionContext) {
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executionContext.getLogger().info("GetWeather: looking up weather for '" + location + "'");
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Object result = weatherService.getCurrentWeather(location);
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return MAPPER.writeValueAsString(result);
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}
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```
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For the complete code example, see [WeatherFunction.java](https://github.com/Azure-Samples/remote-mcp-functions-java/blob/main/samples/McpWeatherApp/src/main/java/com/function/weather/WeatherFunction.java).
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[!INCLUDE [functions-mcp-extension-powershell-note](../../includes/functions-mcp-extension-powershell-note.md)]
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## Attributes
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Apply the `@McpResourceTrigger` annotation to a function parameter to define an MCP resource trigger.
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The `@McpResourceTrigger` annotation supports the following properties:
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| Property | Description |
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|---|---|
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| **`name`** | Required. The binding name for the resource invocation context parameter. |
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| **`uri`** | Required. The URI of the MCP resource (for example, `"file://readme.md"` or `"ui://weather/index.html"`). |
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| **`resourceName`** | Required. The display name of the MCP resource. |
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| **`title`** | Optional. A human-readable title for display purposes. Unlike `resourceName`, which is a programmatic identifier, this is a friendly label for UI presentation. |
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| **`description`** | Optional. A human-readable description of this resource. |
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| **`mimeType`** | Optional. The MIME type of the resource content (for example, `"text/plain"`, `"text/html"`, `"image/png"`, `"text/html;profile=mcp-app"`). |
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| **`size`** | Optional. The size of the resource in bytes. Defaults to `-1` (not specified). |
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| **`dataType`** | Optional. Defines how the Functions runtime should treat the parameter value. Possible values: `""` (default, deserialize to parameter type), `"string"`, `"binary"`. |
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## Metadata annotation
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You can optionally apply `@McpMetadata` on the same parameter as `@McpResourceTrigger` to attach arbitrary JSON metadata to the resource. This metadata is surfaced in the MCP protocol's `_meta` field when clients call `resources/list`.
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The `@McpMetadata` annotation supports the following properties:
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| Property | Description |
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|---|---|
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| **`name`** | Required. The binding parameter name. Should match the `name` value of the trigger annotation on the same parameter. |
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| **`json`** | Required. The metadata as a valid JSON string. Can include any arbitrary key-value pairs such as author information, version numbers, UI hints, or tags. |
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**Example:**
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```java
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@McpResourceTrigger(
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name = "context",
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uri = "file://readme.md",
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resourceName = "readme",
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description = "Application readme file",
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mimeType = "text/plain")
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@McpMetadata(
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name = "context",
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json = "{\"author\": \"John Doe\", \"version\": 1.0}")
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```
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See the [Example section](#example) for complete examples.
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The MCP resource trigger binds the resource invocation context to a function parameter. The trigger can bind to the following types: `String`, or `byte[]` for binary content.
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### Resource URIs
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Use the `@McpMetadata` annotation to provide extra metadata for resources. This metadata is a JSON-serialized string included in the `meta` field of each resource when clients call `resources/list`. It can affect how the resource content is displayed or processed.
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### Return types
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The MCP resource trigger supports the following return types:
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| Type | Description |
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| --- | --- |
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| `String` | Returned as text content in the MCP `ReadResourceResult`. |
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| `byte[]` | Returned as base64-encoded binary content in the MCP `ReadResourceResult`. Set `dataType = "binary"` on the annotation when returning binary content. |
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### Resource discovery
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