添加java-melody依赖后Spring Boot出现空指针异常，需补充哪些配置？

在Spring Boot应用中添加java-melody starter依赖后，每次访问都会抛出空指针异常。

添加的POM依赖：

<dependency>
    <groupId>net.bull.javamelody</groupId>
    <artifactId>javamelody-spring-boot-starter</artifactId>
    <version>1.92.0</version>
</dependency>

异常触发点与ValidationService相关，相关代码如下：

AuthenticationService核心代码 #

@Slf4j
@Service
public class AuthenticationService implements IAuthenticationService {
    @Autowired
    private ValidationService validationService;
    @Autowired
    private UserLoginDao userLoginDao;

    public TempLoginModel doSoftLogin(@Valid UserLoginRequest request) {
        UserLogin userLogin = userLoginDao.findByUsernameAndCorporateCode(request.getUsername())
                .orElseThrow(() -> new UsernameNotFoundException(
                        env.getProperty("message.authentication.service.wrong.credential")));

        validationService.exceptionIfUserLoginNotActivated
                .andThen(validationService.exceptionIfUserLoginLocked)
                .accept(userLogin);

        String jwtToken = JWTUtil.createJwt(request.getUsername(),
                userLogin.getUserInformation().getMobileNumber());

        return new TempLoginModel(jwtToken);
    }
}

ValidationService核心代码 #

@Slf4j
@Service
public class ValidationService {
    public Consumer<UserLogin> exceptionIfUserLoginNotActivated = (user) -> {
        if (!user.isActivated()) {
            throw new NoAccessException(env.getProperty("message.user.login.not.activate"));
        }
    };

    public Consumer<UserLogin> exceptionIfUserLoginLocked = (user) -> {
        if (user.getWrongLoginAttempt() >= getWrongPasswordAttemptCount()) {
            throw new NoAccessException(env.getProperty("message.user.login.locked"));
        }
    };
}

异常栈信息：

java.lang.NullPointerException: null
    at com.java.corporate.service.impl.AuthenticationService.exceptionIfInvalidLogin(AuthenticationService.java:355)
    at com.java.corporate.service.impl.AuthenticationService.doSoftLogin(AuthenticationService.java:190)
    at com.java.corporate.service.impl.AuthenticationService$$FastClassBySpringCGLIB$$1d9d9fd9.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:771)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
    at net.bull.javamelody.MonitoringSpringInterceptor.invoke(MonitoringSpringInterceptor.java:76)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)

核心原因 #

1. Spring AOP代理与成员变量冲突：JavaMelody通过Spring AOP生成CGLIB代理对象增强服务类时，不会自动代理类的public成员变量（如ValidationService中的两个Consumer实例）。当AuthenticationService调用代理后的ValidationService的成员变量时，会拿到空引用，触发空指针。
2. ValidationService依赖缺失：代码中env（Environment）未注入，即使代理问题解决，env.getProperty()也会抛出空指针。

解决步骤 #

1. 重构ValidationService，替换成员变量式Consumer
   将Consumer改为普通方法，同时注入必要依赖：

   @Slf4j
   @Service
   public class ValidationService {
       @Autowired
       private Environment env;
       // 假设错误登录尝试次数配置在application.properties中
       @Value("${security.wrong-login-attempt-count:5}")
       private int wrongLoginAttemptCount;
   
       public void validateUserLogin(UserLogin userLogin) {
           checkUserActivated(userLogin);
           checkUserLoginLocked(userLogin);
       }
   
       private void checkUserActivated(UserLogin user) {
           if (!user.isActivated()) {
               throw new NoAccessException(env.getProperty("message.user.login.not.activate"));
           }
       }
   
       private void checkUserLoginLocked(UserLogin user) {
           if (user.getWrongLoginAttempt() >= wrongLoginAttemptCount) {
               throw new NoAccessException(env.getProperty("message.user.login.locked"));
           }
       }
   }
   

2. 修改AuthenticationService的调用逻辑
   替换原有的Consumer链式调用为普通方法调用：

   // 替换原来的Consumer调用代码
   validationService.validateUserLogin(userLogin);
   

3. JavaMelody的可选配置
   基础场景下starter默认配置即可运行，若需要自定义监控规则，可在application.properties中添加：

   # 排除静态资源或无需监控的接口
   javamelody.excluded-urls=/css/**,/js/**,/health/**
   # 排除特定包下的类不被监控
   javamelody.excluded-packages=com.java.corporate.util
   # 开启监控页面的登录验证（可选）
   javamelody.authorized-users=admin:admin123
   

   若遇到AOP代理冲突，可强制使用CGLIB代理：

   spring.aop.proxy-target-class=true
   

内容的提问来源于stack exchange，提问作者Sudan Shrestha