MCP 注解特殊参数
MCP 注解支持几种特殊的参数类型，为带注解的方法提供额外的上下文和功能。这些参数由框架自动注入，并排除在 JSON 模式生成之外。
特殊参数类型
McpMeta
McpMeta 类提供对 MCP 请求、通知和结果中元数据的访问。
概述
-
作为方法参数使用时自动注入
-
排除在参数计数限制和 JSON 模式生成之外
-
通过
get(String key)方法方便地访问元数据 -
如果请求中不存在元数据，则注入一个空的
McpMeta对象
在工具中的用法
@McpTool(name = "contextual-tool", description = "Tool with metadata access")
public String processWithContext(
@McpToolParam(description = "Input data", required = true) String data,
McpMeta meta) {
// Access metadata from the request
String userId = (String) meta.get("userId");
String sessionId = (String) meta.get("sessionId");
String userRole = (String) meta.get("userRole");
// Use metadata to customize behavior
if ("admin".equals(userRole)) {
return processAsAdmin(data, userId);
} else {
return processAsUser(data, userId);
}
}在资源中的用法
@McpResource(uri = "secure-data://{id}", name = "Secure Data")
public ReadResourceResult getSecureData(String id, McpMeta meta) {
String requestingUser = (String) meta.get("requestingUser");
String accessLevel = (String) meta.get("accessLevel");
// Check access permissions using metadata
if (!"admin".equals(accessLevel)) {
return new ReadResourceResult(List.of(
new TextResourceContents("secure-data://" + id,
"text/plain", "Access denied")
));
}
String data = loadSecureData(id);
return new ReadResourceResult(List.of(
new TextResourceContents("secure-data://" + id,
"text/plain", data)
));
}在提示中的用法
@McpPrompt(name = "localized-prompt", description = "Localized prompt generation")
public GetPromptResult localizedPrompt(
@McpArg(name = "topic", required = true) String topic,
McpMeta meta) {
String language = (String) meta.get("language");
String region = (String) meta.get("region");
// Generate localized content based on metadata
String message = generateLocalizedMessage(topic, language, region);
return new GetPromptResult("Localized Prompt",
List.of(new PromptMessage(Role.ASSISTANT, new TextContent(message)))
);
}@McpProgressToken
@McpProgressToken 注解标记一个参数以接收来自 MCP 请求的进度令牌。
在工具中的用法
@McpTool(name = "long-operation", description = "Long-running operation with progress")
public String performLongOperation(
@McpProgressToken String progressToken,
@McpToolParam(description = "Operation name", required = true) String operation,
@McpToolParam(description = "Duration in seconds", required = true) int duration,
McpSyncServerExchange exchange) {
if (progressToken != null) {
// Send initial progress
exchange.progressNotification(new ProgressNotification(
progressToken, 0.0, 1.0, "Starting " + operation));
// Simulate work with progress updates
for (int i = 1; i <= duration; i++) {
Thread.sleep(1000);
double progress = (double) i / duration;
exchange.progressNotification(new ProgressNotification(
progressToken, progress, 1.0,
String.format("Processing... %d%%", (int)(progress * 100))));
}
}
return "Operation " + operation + " completed";
}在资源中的用法
@McpResource(uri = "large-file://{path}", name = "Large File Resource")
public ReadResourceResult getLargeFile(
@McpProgressToken String progressToken,
String path,
McpSyncServerExchange exchange) {
File file = new File(path);
long fileSize = file.length();
if (progressToken != null) {
// Track file reading progress
exchange.progressNotification(new ProgressNotification(
progressToken, 0.0, fileSize, "Reading file"));
}
String content = readFileWithProgress(file, progressToken, exchange);
if (progressToken != null) {
exchange.progressNotification(new ProgressNotification(
progressToken, fileSize, fileSize, "File read complete"));
}
return new ReadResourceResult(List.of(
new TextResourceContents("large-file://" + path, "text/plain", content)
));
}McpSyncRequestContext / McpAsyncRequestContext
请求上下文对象提供对 MCP 请求信息和服务器端操作的统一访问。
McpSyncRequestContext 功能
public record UserInfo(String name, String email, int age) {}
@McpTool(name = "advanced-tool", description = "Tool with full server capabilities")
public String advancedTool(
McpSyncRequestContext context,
@McpToolParam(description = "Input", required = true) String input) {
// Send logging notification
context.info("Processing: " + input);
// Ping the client
context.ping();
// Send progress updates
context.progress(50); // 50% complete
// Check if elicitation is supported before using it
if (context.elicitEnabled()) {
// Request additional information from user
StructuredElicitResult<UserInfo> elicitResult = context.elicit(
e -> e.message("Need additional information"),
UserInfo.class
);
if (elicitResult.action() == ElicitResult.Action.ACCEPT) {
UserInfo userInfo = elicitResult.structuredContent();
// Use the user information
}
}
// Check if sampling is supported before using it
if (context.sampleEnabled()) {
// Request LLM sampling
CreateMessageResult samplingResult = context.sample(
s -> s.message("Process: " + input)
.modelPreferences(pref -> pref.modelHints("gpt-4"))
);
}
return "Processed with advanced features";
}McpAsyncRequestContext 功能
public record UserInfo(String name, String email, int age) {}
@McpTool(name = "async-advanced-tool", description = "Async tool with server capabilities")
public Mono<String> asyncAdvancedTool(
McpAsyncRequestContext context,
@McpToolParam(description = "Input", required = true) String input) {
return context.info("Async processing: " + input)
.then(context.progress(25))
.then(context.ping())
.flatMap(v -> {
// Perform elicitation if supported
if (context.elicitEnabled()) {
return context.elicitation(UserInfo.class)
.map(userInfo -> "Processing for user: " + userInfo.name());
}
return Mono.just("Processing...");
})
.flatMap(msg -> {
// Perform sampling if supported
if (context.sampleEnabled()) {
return context.sampling("Process: " + input)
.map(result -> "Completed: " + result);
}
return Mono.just("Completed: " + msg);
});
}McpTransportContext
用于无状态操作的轻量级上下文。
使用示例
@McpTool(name = "stateless-tool", description = "Stateless tool with context")
public String statelessTool(
McpTransportContext context,
@McpToolParam(description = "Input", required = true) String input) {
// Limited context access
// Useful for transport-level operations
return "Processed in stateless mode: " + input;
}
@McpResource(uri = "stateless://{id}", name = "Stateless Resource")
public ReadResourceResult statelessResource(
McpTransportContext context,
String id) {
// Access transport context if needed
String data = loadData(id);
return new ReadResourceResult(List.of(
new TextResourceContents("stateless://" + id, "text/plain", data)
));
}CallToolRequest
需要访问带有动态模式的完整请求的工具的特殊参数。
使用示例
@McpTool(name = "dynamic-tool", description = "Tool with dynamic schema support")
public CallToolResult processDynamicSchema(CallToolRequest request) {
Map<String, Object> args = request.arguments();
// Process based on whatever schema was provided at runtime
StringBuilder result = new StringBuilder("Processed:\n");
for (Map.Entry<String, Object> entry : args.entrySet()) {
result.append(" ").append(entry.getKey())
.append(": ").append(entry.getValue()).append("\n");
}
return CallToolResult.builder()
.addTextContent(result.toString())
.build();
}混合参数
@McpTool(name = "hybrid-tool", description = "Tool with typed and dynamic parameters")
public String processHybrid(
@McpToolParam(description = "Operation", required = true) String operation,
@McpToolParam(description = "Priority", required = false) Integer priority,
CallToolRequest request) {
// Use typed parameters for known fields
String result = "Operation: " + operation;
if (priority != null) {
result += " (Priority: " + priority + ")";
}
// Access additional dynamic arguments
Map<String, Object> allArgs = request.arguments();
// Remove known parameters to get only additional ones
Map<String, Object> additionalArgs = new HashMap<>(allArgs);
additionalArgs.remove("operation");
additionalArgs.remove("priority");
if (!additionalArgs.isEmpty()) {
result += " with " + additionalArgs.size() + " additional parameters";
}
return result;
}带进度令牌
@McpTool(name = "flexible-with-progress", description = "Flexible tool with progress")
public CallToolResult flexibleWithProgress(
@McpProgressToken String progressToken,
CallToolRequest request,
McpSyncServerExchange exchange) {
Map<String, Object> args = request.arguments();
if (progressToken != null) {
exchange.progressNotification(new ProgressNotification(
progressToken, 0.0, 1.0, "Processing dynamic request"));
}
// Process dynamic arguments
String result = processDynamicArgs(args);
if (progressToken != null) {
exchange.progressNotification(new ProgressNotification(
progressToken, 1.0, 1.0, "Complete"));
}
return CallToolResult.builder()
.addTextContent(result)
.build();
}参数注入规则
最佳实践
使用 McpMeta 获取上下文
@McpTool(name = "context-aware", description = "Context-aware tool")
public String contextAware(
@McpToolParam(description = "Data", required = true) String data,
McpMeta meta) {
// Always check for null values in metadata
String userId = (String) meta.get("userId");
if (userId == null) {
userId = "anonymous";
}
return processForUser(data, userId);
}进度令牌空值检查
@McpTool(name = "safe-progress", description = "Safe progress handling")
public String safeProgress(
@McpProgressToken String progressToken,
@McpToolParam(description = "Task", required = true) String task,
McpSyncServerExchange exchange) {
// Always check if progress token is available
if (progressToken != null) {
exchange.progressNotification(new ProgressNotification(
progressToken, 0.0, 1.0, "Starting"));
}
// Perform work...
if (progressToken != null) {
exchange.progressNotification(new ProgressNotification(
progressToken, 1.0, 1.0, "Complete"));
}
return "Task completed";
}选择正确的上下文
-
使用
McpSyncRequestContext/McpAsyncRequestContext统一访问请求上下文，支持有状态和无状态操作，并提供便捷的辅助方法 -
当只需要传输级别上下文时，使用
McpTransportContext进行简单的无状态操作 -
对于最简单的情况，完全省略上下文参数
能力检查
在使用客户端功能之前，务必检查功能支持
@McpTool(name = "capability-aware", description = "Tool that checks capabilities")
public String capabilityAware(
McpSyncRequestContext context,
@McpToolParam(description = "Data", required = true) String data) {
// Check if elicitation is supported before using it
if (context.elicitEnabled()) {
// Safe to use elicitation
var result = context.elicit(UserInfo.class);
// Process result...
}
// Check if sampling is supported before using it
if (context.sampleEnabled()) {
// Safe to use sampling
var samplingResult = context.sample("Process: " + data);
// Process result...
}
// Note: Stateless servers do not support bidirectional operations
// (roots, elicitation, sampling) and will return false for these checks
return "Processed with capability awareness";
}
