MCP发送消息至会话失败问题排查咨询

Hey there, let's break down how to troubleshoot the issue where your MCP service fails to send messages to a session. First, let's start by reviewing your provided service code, then walk through common checkpoints step by step:

@Service
public class McpWeatherService {    
    @Tool(description = "根据城市名称获取天气预报")
    public String getWeatherByCity(String city) {
        Map<String, String> mockData = Map.of(
                "西安", "晴天",
                "北京", "小雨",
                "上海", "大雨"
        );
        return mockData.getOrDefault(city, "抱歉：未查询到对应城市！");
    }
}

• Verify session connection status
  First off, make sure your MCP service can actually reach the session management component. Double-check that you've configured the correct session address and port, and confirm there's no firewall or network policy blocking the connection. You can run quick tests like telnet <session-host> <session-port> to rule out basic connectivity issues.

• Validate @Tool annotation configuration
  The @Tool annotation is what hooks your method into the MCP framework, so it's worth verifying it's set up correctly. Does your framework require any extra attributes beyond description—like a unique method ID or permission settings? A misconfigured annotation could prevent your service from being registered to the session router entirely.

• Check parameter passing and serialization
  When sending messages to the session, keep an eye on how the city parameter is being handled. Are you passing null values accidentally? Is there character encoding mismatch leading to garbled text? If the session expects JSON-formatted data but your service returns a raw string without proper serialization, the message might fail to be parsed on the other end.

• Confirm session routing and service mapping
  Some MCP frameworks need explicit configuration (either via config classes or XML) to map your service methods to specific session topics. Make sure this mapping is set up correctly—if the session can't find the route tied to getWeatherByCity, it won't know how to handle your message.

• Dig into error logs
  This is usually the most helpful step. Check your MCP service's error logs for specific exceptions related to message sending—things like connection timeouts, missing route entries, or permission denials. Logs will almost always point you directly to the root cause.

备注：内容来源于stack exchange，提问作者Lnstark