@Autowired注入PushDataTraceLogService时出现NullPointerException问题

问题描述 #

我定义了一个继承RuntimeException的异常类PushDataException，添加了@Component注解并通过@Autowired注入PushDataTraceLogService，但使用该服务时出现空指针异常。已知pushDataTraceLog实例不为空，但pushDataTraceLogService始终为null。

相关代码 #

异常类代码 #

@Component  
public class PushDataException extends RuntimeException {

    @Autowired
    private PushDataTraceLogService pushDataTraceLogService;
}

PushDataTraceLogService接口 #

public interface PushDataTraceLogService { 
    void save(PushDataTraceLog pushDataTraceLog);
}

实现类代码 #

@Service
public class PushDataTraceLogServiceImpl implements PushDataTraceLogService {

    @Autowired
    private PushDataTraceLogRepository pushDataTraceLogRepository;

    @Override
    public void save(PushDataTraceLog pushDataTraceLog) {
        pushDataTraceLogRepository.save(pushDataTraceLog);
        PushDataTraceLog.destroy();
    }
}

堆栈跟踪信息 #

java.lang.NullPointerException: null
at com.publicissapient.kpidashboard.apis.pushdata.util.PushDataException.setTraceLog(PushDataException.java:60)
at com.publicissapient.kpidashboard.apis.pushdata.util.PushDataException.<init>(PushDataException.java:52)
at com.publicissapient.kpidashboard.apis.pushdata.service.impl.AuthExposeAPIServiceImpl.validateToken(AuthExposeAPIServiceImpl.java:127)
at com.publicissapient.kpidashboard.apis.pushdata.controller.PushDataController.savePushDataBuilds(PushDataController.java:67)
at com.publicissapient.kpidashboard.apis.pushdata.controller.PushDataController$$FastClassBySpringCGLIB$$61a69129.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:793)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763)
at org.springframework.validation.beanvalidation.MethodValidationInterceptor.invoke(MethodValidationInterceptor.java:123)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708)
at com.publicissapient.kpidashboard.apis.pushdata.controller.PushDataController$$EnhancerBySpringCGLIB$$a6ea830e.savePushDataBuilds(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1070)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:681)

原因分析 #

1. 异常类未被Spring容器管理：虽然加了@Component，但异常通常是通过new PushDataException()手动实例化的，这种方式创建的对象不在Spring管控范围内，Spring不会自动注入@Autowired字段。
2. RuntimeException实例化机制限制：继承自RuntimeException的类，实例化时不经过Spring的Bean创建流程，导致依赖注入失效。

解决方案 #

方案一：构造函数传入服务 #

不在异常类中依赖注入，而是在抛出异常时将服务作为参数传入：

public class PushDataException extends RuntimeException {
    private final PushDataTraceLogService pushDataTraceLogService;

    // 构造函数接收服务实例
    public PushDataException(String message, PushDataTraceLogService service) {
        super(message);
        this.pushDataTraceLogService = service;
        setTraceLog();
    }

    private void setTraceLog() {
        PushDataTraceLog log = new PushDataTraceLog();
        // 设置日志属性
        pushDataTraceLogService.save(log);
    }
}

抛出异常时，从Spring管理的Bean中获取服务传入：

// 在Spring管理的Service类中
@Autowired
private PushDataTraceLogService pushDataTraceLogService;

// 抛出异常的逻辑
throw new PushDataException("Token验证失败", pushDataTraceLogService);

方案二：重构代码，日志逻辑移出异常类 #

将保存日志的逻辑从异常类中剥离，在抛出异常前完成日志操作：

// 在Service类中
@Autowired
private PushDataTraceLogService pushDataTraceLogService;

public void validateToken() {
    if (token无效) {
        // 先保存日志
        PushDataTraceLog log = new PushDataTraceLog();
        // 设置日志信息
        pushDataTraceLogService.save(log);
        // 再抛出异常
        throw new PushDataException("Token验证失败");
    }
}

这种方式让异常类只负责传递异常信息，符合单一职责原则，是最推荐的做法。

方案三：通过ApplicationContext手动获取Bean（不推荐） #

如果必须在异常类中使用服务，可以通过ApplicationContext手动获取：

@Component  
public class PushDataException extends RuntimeException {
    private static ApplicationContext applicationContext;

    @Autowired
    public void setApplicationContext(ApplicationContext context) {
        applicationContext = context;
    }

    private void setTraceLog() {
        PushDataTraceLogService service = applicationContext.getBean(PushDataTraceLogService.class);
        PushDataTraceLog log = new PushDataTraceLog();
        service.save(log);
    }
}

注意：这种方式会增加代码耦合度，且需要确保ApplicationContext已完成初始化。

内容的提问来源于stack exchange，提问作者shivani chittauri