feat: add structured logging support with severity levels

- Add client and server-side logging capabilities with configurable severity levels
- Implement logging message notifications with DEBUG to EMERGENCY levels
- Add logging consumers for client-side log handling
- Update documentation with logging examples and configuration
- Add comprehensive tests for logging functionality
- Fix typo in README.md (notificaiotn -> notification)

- Centralize MCP method names as constants
  - Move all JSON-RPC method names to McpSchema class as static constants
  - Replace hardcoded method strings with constant references in McpAsyncClient
    and McpAsyncServer
  - Update test cases to use new method name constants

Resolves #35

Author: tzolov

README.md

@@ -16,7 +16,7 @@ The project consists of two main modules:
 
 Java implementation of the Model Context Protocol specification. It includes:
 - Synchronous and asynchronous [MCP Client](https://github.com/spring-projects-experimental/spring-ai-mcp/blob/main/mcp/README.md#client-usage-examples) and [MCP Server](https://github.com/spring-projects-experimental/spring-ai-mcp/blob/main/mcp/README.md#server-usage-examples) implementations
-- Standard MCP operations support (tool discovery, resource management, prompt handling). Support for request and notificaiotn handling.
+- Standard MCP operations support (tool discovery, resource management, prompt handling, structured logging). Support for request and notification handling.
 - [Stdio](https://spec.modelcontextprotocol.io/specification/basic/transports/#stdio) and [SSE](https://spec.modelcontextprotocol.io/specification/basic/transports/#http-with-sse) transport implementations. 
 - [Find more](./mcp/README.md).
 

docs/ref-server.md

@@ -136,10 +136,6 @@ McpServer.using(transport)
     .sync();
 ```
 
-### Implementation Notes
-
-- The server factory uses a builder pattern for configuration
-- Default server info is "mcp-server" version "1.0.0" if not specified
 - Tool handlers must be thread-safe as they may be called concurrently
 - The synchronous server is implemented as a wrapper around the asynchronous server
 - Resource and prompt providers use cursor-based pagination
@@ -160,3 +156,59 @@ Tool handlers implement this interface to define:
 - Tool name and description
 - Input schema for validation
 - Execution logic in the call method
+
+### Logging Capabilities
+
+The MCP Server supports logging functionality that allows sending log messages with different severity levels to the Client. This feature can be enabled through server capabilities configuration.
+
+#### Enabling Logging
+
+```java
+McpServer.using(transport)
+    .serverInfo("my-server", "1.0.0")
+    .capabilities(ServerCapabilities.builder().logging().build())
+    .sync(); // or .async()
+```
+
+#### Logging Levels
+
+The server supports the following logging levels:
+- TRACE
+- DEBUG
+- INFO
+- WARN
+- ERROR
+- FATAL
+
+#### Sending Log Messages
+
+For synchronous servers:
+```java
+LoggingMessageNotification notification = McpSchema.LoggingMessageNotification.builder()
+    .level(McpSchema.LoggingLevel.INFO)
+    .logger("my-logger")
+    .data("Log message")
+    .build();
+
+mcpSyncServer.loggingNotification(notification);
+```
+
+For asynchronous servers:
+```java
+LoggingMessageNotification notification = McpSchema.LoggingMessageNotification.builder()
+    .level(McpSchema.LoggingLevel.INFO)
+    .logger("my-logger")
+    .data("Log message")
+    .build();
+
+mcpAsyncServer.loggingNotification(notification)
+    .subscribe();
+```
+
+- Logging works even if the logging capability is not enabled
+- Null notifications are rejected with a McpError
+- Log messages include:
+  - Level: The severity level of the message
+  - Logger: The name of the logger (typically identifies the source)
+  - Data: The actual log message content
+- The server implementation is transport-agnostic, allowing different transport mechanisms to handle the log messages

mcp/README.md

@@ -186,6 +186,63 @@ McpTransport transport = new SseClientTransport(webClientBuilder);
 ```
 
 
+### Client Capabilities
+
+The client can be configured with various capabilities:
+
+```java
+var capabilities = ClientCapabilities.builder()
+    .roots(true)      // Enable filesystem roots support with list changes notifications
+    .sampling()       // Enable LLM sampling support
+    .build();
+```
+
+#### Roots Support
+
+Roots define the boundaries of where servers can operate within the filesystem:
+
+```java
+// Add a root dynamically
+client.addRoot(new Root("file:///path", "description"));
+
+// Remove a root
+client.removeRoot("file:///path");
+
+// Notify server of roots changes
+client.rootsListChangedNotification();
+```
+
+The roots capability allows servers to:
+- Request the list of accessible filesystem roots
+- Receive notifications when the root list changes
+- Understand which directories and files they have access to
+
+#### Sampling Support
+
+Sampling enables servers to request LLM interactions ("completions" or "generations") through the client:
+
+```java
+// Configure sampling handler
+Function<CreateMessageRequest, CreateMessageResult> samplingHandler = request -> {
+    // Sampling implementation that interfaces with LLM
+    return new CreateMessageResult(response);
+};
+
+// Create client with sampling support
+var client = McpClient.using(transport)
+    .capabilities(ClientCapabilities.builder()
+        .sampling()
+        .build())
+    .samplingHandler(samplingHandler)
+    .build();
+```
+
+This capability allows:
+- Servers to leverage AI capabilities without requiring API keys
+- Clients to maintain control over model access and permissions
+- Support for both text and image-based interactions
+- Optional inclusion of MCP server context in prompts
+
 ## Server Usage Examples
 
 ### MCP Server (Sync API)
@@ -307,10 +364,36 @@ var capabilities = ServerCapabilities.builder()
     .resources(false, true)  // Resource support with list changes notifications
     .tools(true)            // Tool support with list changes notifications
     .prompts(true)          // Prompt support with list changes notifications
+    .logging()              // Enable logging support (enabled by default with loging level INFO)
     .build();
 ```
 
-### Tool Registration
+#### Logging Support
+
+The server provides structured logging capabilities that allow sending log messages to clients with different severity levels:
+
+```java
+// Send a log message to clients
+server.loggingNotification(LoggingMessageNotification.builder()
+    .level(LoggingLevel.INFO)
+    .logger("custom-logger")
+    .data("Custom log message")
+    .build());
+```
+
+Supported logging levels (in order of increasing severity):
+- DEBUG (0)
+- INFO (1)
+- NOTICE (2)
+- WARNING (3)
+- ERROR (4)
+- CRITICAL (5)
+- ALERT (6)
+- EMERGENCY (7)
+
+Clients can control the minimum logging level they receive through the `mcpClient.setLoggingLevel(level)` request. Messages below the set level will be filtered out.
+
+#### Tool Registration
 
 ```java
 var toolRegistration = new ToolRegistration(
@@ -326,7 +409,7 @@ var toolRegistration = new ToolRegistration(
 );
 ```
 
-### Resource Registration
+#### Resource Registration
 
 ```java
 var resourceRegistration = new ResourceRegistration(
@@ -338,7 +421,7 @@ var resourceRegistration = new ResourceRegistration(
 );
 ```
 
-### Prompt Registration
+#### Prompt Registration
 
 ```java
 var promptRegistration = new PromptRegistration(