java - 使用 SimpleMailMessage() 发送邮件时 Spring 中的 NullPointerException

Question

我一直在学习如何制作 Java Spring Web 服务，但在尝试发送邮件时遇到了问题。

当我尝试通过我的 Controller 发送它时，代码工作正常，但我试图在一个单独的类中获取代码，我突然得到一个 NullPointerException，即使代码是相同(据我所知)。

这是当前出现问题的函数:

package com.tenshin_arts.inventory.mail;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.UserDetails;

import com.tenshin_arts.inventory.dao.InventoryItem;
import com.tenshin_arts.inventory.dao.User;
import com.tenshin_arts.inventory.service.InventoryService;

public class InventoryMail {


       @Autowired
       private MailSender mailSender;

    public void stockBelowMinimumUpdate(InventoryItem inventoryItem) {

        String email = "xxxx@gmail.com";
        String text= "";

        text += "Het volgende product is onder het minimum gekomen:\n\n";
        text += "Productnaam: " + inventoryItem.getName();
        text += "\nProductcode: " + inventoryItem.getBarcode();
        text += "\nHuidige Voorraad: " + inventoryItem.getCurrentStock();
        text += "\nMinimum Voorraad: " + inventoryItem.getStockMinimum();
        text += "\nPrijs: " + inventoryItem.getPrice();
        text += "\nLeverancier: " + inventoryItem.getSupplier();
        text += "\n\n\nBericht voor de leverancier:";
        text += "\n\n" + inventoryItem.getBarcode();
        text += "\t" + inventoryItem.getName();
        text += "\t[aantal hier] x €" + inventoryItem.getPrice();

            System.out.println("email running");

        SimpleMailMessage mail = new SimpleMailMessage();
        mail.setFrom("xxxxx@gmail.com");
        mail.setTo(email);
        mail.setSubject("Test is gelukt!");
        mail.setText(text);



        try {
            mailSender.send(mail); //This line produces the exception
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Can't send message");
        }


    }
}

这是堆栈跟踪:

java.lang.NullPointerException
    at com.tenshin_arts.inventory.mail.InventoryMail.stockBelowMinimumUpdate(InventoryMail.java:53)
    at com.tenshin_arts.inventory.dao.InventoryDao.checkStockForMail(InventoryDao.java:152)
    at com.tenshin_arts.inventory.service.InventoryService.checkStockForMail(InventoryService.java:52)
    at com.tenshin_arts.inventory.controllers.InventoryController.databaseCallMutateItem(InventoryController.java:144)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source) 

这是我的 bean 配置:

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
        <property name="host" value="smtp.gmail.com" />
        <property name="port" value="587" />
        <property name="username" value="xxx@gmail.com" />
        <property name="password" value="xxxxx" />
        <property name="javaMailProperties">
            <props>
                <prop key="mail.smtp.auth">true</prop>
                <prop key="mail.smtp.starttls.enable">true</prop>
                <prop key="mail.smtp.ssl.trust">smtp.gmail.com</prop>
            </props>
        </property>
    </bean> 

奇怪的是，在我的映射 Controller 中，我有以下运行良好的代码(删除了与邮件无关的函数):

package com.tenshin_arts.inventory.controllers;

import java.security.Principal;
import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import com.tenshin_arts.inventory.dao.InventoryItem;
import com.tenshin_arts.inventory.dao.User;
import com.tenshin_arts.inventory.service.InventoryService;
import com.tenshin_arts.inventory.service.UsersService;

@Controller
public class InventoryController {

    private InventoryService inventoryService;
    private InventoryItem currentItem;
    private UsersService usersService;

    @Autowired
    private MailSender mailSender;

@RequestMapping(value="/sendmessage")
    @ResponseBody
    public void sendMessage(Principal principal) {
        UserDetails userDetails =
                 (UserDetails)SecurityContextHolder.getContext().getAuthentication().getPrincipal();

        List<InventoryItem> inventoryItemsList = inventoryService.getCurrent();



        User currentUser = usersService.getUserEmail(userDetails.getUsername());
        String email = currentUser.getEmail();
        String text= "";

        for(InventoryItem s : inventoryItemsList) {

            text += s.getBarcode();
            text += "\t";
            text += s.getName();
            text += "\t";
            text += s.getCurrentStock();
            text += "\t";
            text += s.getPrice();
            text += "\n";
        }




        SimpleMailMessage mail = new SimpleMailMessage();
        mail.setFrom("xxxxx@gmail.com");
        mail.setTo(email);
        mail.setSubject("Test is gelukt!");
        mail.setText(text);

        try {
            mailSender.send(mail); 
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Can't send message");
        }


    }



}

我已经通过 system.out 检查了我的 SimpleMailMessage “邮件”，所以我认为问题出在我的 MailSender bean/布线，但我不知道是什么，因为我以相同的方式布线。

你能帮我解决我的问题吗？

Answer 1

为什么会抛出 NullPointerException？

这表示 mailSender 为 null。它是 null，因为 Spring 无法将 bean 实例 Autowiring 到 mailSender。 Spring 无法做到这一点，因为它无法判断 InventoryMail 本身是一个 bean。因为 Spring 无法判断 InventoryMail 是一个 bean，所以它不会检测到 @Autowired 注释。

为什么它在 InventoryController 中起作用？

那是因为注解@Controller告诉Spring，InventoryController是一个bean，从而使Spring能够检测到@Autowired。

建议的解决方案

使用 @Component 注释您的 InventoryMail 类以告诉 Spring InventoryMail 是一个 bean。这使 Spring 能够检测到 @Autowired。