编辑文章

描述:

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### springboot配置
#### maven配置
```
<dependencies>
		<dependency>
			<groupId>org.springframework.ai</groupId>
			<artifactId>spring-ai-starter-mcp-server-webmvc</artifactId>
            <version>1.0.1</version>
        </dependency>
	</dependencies>
```
#### yaml配置
```
spring:
  ai:
    mcp:
      server:
        stdio: false # 禁用stdio协议
        name: wbw-mcp-server # mcp-server名称
        sse-endpoint: /mcp # 启动sse协议，并指定端点路径为/sse
        enabled: true # 组件启用
```
### 访问 /mcp服务器时，报错如下：
```
jakarta.servlet.ServletException: java.lang.NullPointerException: Cannot invoke "io.modelcontextprotocol.spec.McpServerSession$Factory.create(io.modelcontextprotocol.spec.McpServerTransport)" because "this.sessionFactory" is null
	at org.springframework.web.servlet.function.ErrorHandlingServerResponse.handleError(ErrorHandlingServerResponse.java:70) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.function.AbstractServerResponse.writeTo(AbstractServerResponse.java:105) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.function.support.HandlerFunctionAdapter.handle(HandlerFunctionAdapter.java:112) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.44.jar:6.0]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.44.jar:6.0]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.2.10.jar:6.2.10]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.2.10.jar:6.2.10]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.2.10.jar:6.2.10]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.2.10.jar:6.2.10]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1769) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63) ~[tomcat-embed-core-10.1.44.jar:10.1.44]
	at java.base/java.lang.Thread.run(Thread.java:833) ~[na:na]
Caused by: java.lang.NullPointerException: Cannot invoke "io.modelcontextprotocol.spec.McpServerSession$Factory.create(io.modelcontextprotocol.spec.McpServerTransport)" because "this.sessionFactory" is null
	at io.modelcontextprotocol.server.transport.WebMvcSseServerTransportProvider.lambda$handleSseConnection$6(WebMvcSseServerTransportProvider.java:266) ~[mcp-spring-webmvc-0.10.0.jar:0.10.0]
	at org.springframework.web.servlet.function.SseServerResponse.writeToInternal(SseServerResponse.java:95) ~[spring-webmvc-6.2.10.jar:6.2.10]
	at org.springframework.web.servlet.function.AbstractServerResponse.writeTo(AbstractServerResponse.java:101) ~[spring-webmvc-6.2.10.jar:6.2.10]
	... 41 common frames omitted
```
### 原因
经过分析发现，主要是由于mcp自动装配的类：org.springframework.ai.mcp.server.autoconfigure.McpServerAutoConfiguration#mcpSyncServer没有初始化,在启动类打印mcpSyncServer是否懒加载，分析发现该bean时满足加载条件，但是不知道为啥就是类型时懒加载，导致没法加载
![图片alt](https://i.likeu.site/api/file/download?fileId=ac641c56-2e21-49cc-b006-d40d51c0dcdd ''图片title'')
```
public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BoboServiceApplication.class, args);

ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        String[] beanNames = context.getBeanDefinitionNames();
        for (String beanName : beanNames) {
            BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
            if (beanName.contains("mcpSyncServer")) {
                System.out.println("Bean: " + beanName + " is lazy: " + beanDefinition.isLazyInit());
            }
        }
    }
```
发现提示时懒加载，导致初始化时没有加载
![图片alt](https://i.likeu.site/api/file/download?fileId=4acb0973-e815-45b2-ac3a-bbef4a8e7569 ''图片title'')
### 解决办法
通过 BeanDefinitionRegistryPostProcessor 在运行时修改 Bean 定义，禁用懒加载：
```
package com.bowen.service.config;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.Configuration;

/**
 * 解决mcpSyncServer类首次启动时懒加载，导致报错了
 */
@Configuration
public class McpServerBeanDefinitionConfig implements BeanDefinitionRegistryPostProcessor {

@Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        // 检查是否存在 mcpSyncServer Bean 定义
        if (registry.containsBeanDefinition("mcpSyncServer")) {
            BeanDefinition beanDefinition = registry.getBeanDefinition("mcpSyncServer");
            // 禁用懒加载
            beanDefinition.setLazyInit(false);
            System.out.println("Disabled lazy initialization for mcpSyncServer");
        }
    }

@Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        // 不需要额外处理
    }
}
```