无法在Spring中实例化类

Question

我是Java Spring的新手。我写了一个代码来发送电子邮件。但我无法使它工作，因为它总是抛出NullPointerException。这是我的代码段

邮件类

package com.example.MailService;

import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;

 public class Mail {

    private MailSender mailSender;

    public void setMailSender(MailSender mailSender) {
        this.mailSender = mailSender;
    }


    public void sendMail(String from, String to, String subject, String msg) {
        SimpleMailMessage message = new SimpleMailMessage();

        message.setFrom(from);
        message.setTo(to);
        message.setSubject(subject);
        message.setText(msg);
        mailSender.send(message);   
    }

}

XML配置文件

<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="username" />
    <property name="password" value="password" />

    <property name="javaMailProperties">
       <props>
              <prop key="mail.smtp.auth">true</prop>
              <prop key="mail.smtp.starttls.enable">true</prop>
           </props>
    </property>
</bean>

    <bean id="mail" class="com.example.MailService.Mail">
        <property name="mailSender" ref="mailSender" />
    </bean>

控制器

@Autowired
private Mail mail;

  @RequestMapping(value = "/sendmail", method = RequestMethod.GET)
    public String sendEMail(HttpServletRequest request, ModelMap model)
    {
        mail.sendMail("exfrom@gmail.com", "exTo@gmail.com", "Testing123",  "Testing only \n\n Hello Spring Email Sender");
        return "sendmail";
    }

控制器中的sendEmail方法存在问题。它无法实例化邮件变量。我无法弄清楚这里有什么问题，因为我对Spring来说是全新的。请帮我完成这项工作。

提前致谢

这是错误日志

java.lang.NullPointerException
    com.example.controller.FrontController.sendEMail(FrontController.java:144)
    sun.reflect.GeneratedMethodAccessor44.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)
    org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259)

应用上下文配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:mongo="http://www.springframework.org/schema/data/mongo"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/data/mongo http://www.springframework.org/schema/data/mongo/spring-mongo.xsd">

    <mvc:annotation-driven />
    <context:component-scan base-package="com.example" />

    <mvc:resources mapping="/resources/**" location="/resources/" />

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/views/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles3.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/tiles-definitions.xml</value>
            </list>
        </property>
    </bean>

    <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="username" />
    <property name="password" value="password" />

    <property name="javaMailProperties">
       <props>
              <prop key="mail.smtp.auth">true</prop>
              <prop key="mail.smtp.starttls.enable">true</prop>
           </props>
    </property>
</bean>

    <bean id="mail" class="com.example.MailService.Mail">
        <property name="mailSender" ref="mailSender" />
    </bean>

    <mongo:mongo host="localhost" port="27017"/>

    <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
        <constructor-arg name="mongo" ref="mongo" />
        <constructor-arg name="databaseName" value="test" />
    </bean>

    <context:annotation-config />

    <bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />

</beans>

Servlet上下文配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

    <display-name>test App</display-name>

    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/dispatcher-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring-security.xml</param-value>
    </context-param>

    <filter>
        <filter-name>springSecurityFilterChain</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>springSecurityFilterChain</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

</web-app>

Answer 1

尝试使用应用程序上下文获取邮件bean：

ApplicationContext ctx = new ClassPathXmlApplicationContext("name of xml file where you configured mail properties");

然后：

Mail mailSender = ctx.getBean("mail");

如果这样可行，则问题可能是您的xml文件未加载。

Answer 2

您也可以使用：

<context:component-scan base-package="com" /> // here com is base package name

示例：

xml：

<!--Mail Configuration-->
    <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="user@gmail.com" />
        <property name="password" value="gmail" />
        <property name="javaMailProperties">
            <props>
                <prop key="mail.smtp.auth">true</prop>
                <prop key="mail.smtp.starttls.enable">true</prop>
            </props>
        </property>
    </bean>

在课堂上你可以使用这段代码：

@Service
public class MailEventLogin{

    @Autowired
    private MailSender mailSender;    

    public void sendEmail(String from, String to, String subject, String message) {
        try{
            SimpleMailMessage msg = new SimpleMailMessage();
            msg.setFrom(from);
            msg.setTo(to);
            msg.setSubject(subject);
            msg.setText(message);
            mailSender.send(msg);

        }catch (Exception e) {
            e.printStackTrace();
        }
    }
}

现在，您想要发送邮件，只需调用此类对象并调用方法并传递参数。邮件将被发送。

如果有任何问题发布给我。