Spring @Autowired 不工作并返回 null

Question

我在 Spring @Autowired 上遇到问题：

MailSender.java

package com.example.package.util;

@Component
public class MailSender {
    @Autowired
    public MailSender(VelocityEngine velocityEngine, JavaMailSender mailSender) {
        this.velocityEngine = velocityEngine;
        this.mailSender = mailSender;
    }

    public void send() {
        // Dosomething
    }

    private final VelocityEngine velocityEngine;

    private final JavaMailSender mailSender;
}

MailService.java

package com.example.package.service;

@Service
public class MailService {
    public void sendEmail(String email) {
        // mailSender is always null
        String mailBody = mailSender.send();
    }

    // Autowired here is not working
    @Autowired
    @Qualifier("myMailSender")
    private MailSender mailSender;

    // Autowired here is working
    @Autowired
    private UserDao userDao;
}

配置

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

<!-- Mail Service -->
<bean id="velocityEngine" class="org.springframework.ui.velocity.VelocityEngineFactoryBean">
    <property name="resourceLoaderPath" value="classpath:/mails" />
    <property name="preferFileSystemAccess" value="false" />
</bean>
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="host" value="smtp.mailgun.org" />
    <property name="username" value="postmaster@testzilla.org" />
    <property name="password" value="" />
    <property name="javaMailProperties">
        <props>
            <prop key="mail.smtp.auth">true</prop>
            <prop key="mail.smtp.starttls.enable">true</prop>
        </props>
    </property>
</bean>
<bean id="myMailSender" 
        class="com.example.package.service.MailService">
    <property name="mailSender" ref="mailSender" />
</bean>

正如我上面提到的，mailSender 对象总是 null in MailService class。

可能 MailSender class 和 MailService class 中的 mailSender 对象存在冲突。变量名相同，但不同

所以我尝试重命名变量，但仍然没有用。

单元测试类：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({"classpath:test-spring-context.xml"})
public class MailSenderTest {
    @Autowired
    @Qualifier("myMailSender")
    private MailSender mailSender;

    @Test
    public void test() {
        String templatePath = "/verifyEmail.vm";
        Map<String, Object> model = new HashMap<String, Object>();

        System.out.println(mailSender);

        String mailBody = mailSender.getMailContent(templatePath, model);
        System.out.println(mailBody);
    }
}

当我运行测试用例时，出现以下异常：

Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.example.package.util.MailSender com.example.package.service.UserService.mailSender; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.example.package.util.MailSender] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true), @org.springframework.beans.factory.annotation.Qualifier(value=testzillaMailSender)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 54 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.example.package.util.MailSender] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true), @org.springframework.beans.factory.annotation.Qualifier(value=testzillaMailSender)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1308)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1054)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:949)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 56 more

你能帮我吗？谢谢

Answer 1

您的 MailService class 不受 spring 管理。一种方法是添加注释（如@Service）让 spring 为您处理。例如

@Service
public class MailService {
    public void sendEmail(String email) {
        String templatePath = "/verifyEmail.vm";
        Map<String, Object> model = new HashMap<String, Object>();
        model.put("email", email);

        // mailSender is always null
        String mailBody = mailSender.getMailContent(templatePath, model);
    }

    // Autowired here is not working
    @Autowired
    private MailSender mailSender;
}

Answer 2

其中有几处错误。

您似乎使用了 XML 和 Java 配置的不幸混合体。您的 MailSender 已被注释为 @Component，因此您不需要任何 XML 来定义它（假设您的组件扫描已正确定义）。

此外，它没有无参数构造函数，因此您尝试在 XML 中使用的机制无效。

此外，在希望自动装配的类中，他们将 @Qualifier("myMailSender") 注释放在字段上。 MailSender 尚未命名，因此不存在具有该名称的 MailSender。您可以只删除 @Qualifier 注释。但是，如果您确实需要确保它是来自多个选项的特定 bean，那么您应该在 @Controller 注释中为它命名，如下所示：

@Component("myMailSender")

Answer 3

您需要添加配置 xml <context:component-scan base-package="package.of.your.service"/>

为了spring拿起这个。

根据我在您的配置中看到的情况，您只有 <context:component-scan base-package="com.example.package" /> 。我的猜测是这是在不同的包中。

Spring @Autowired 不工作并返回 null

Spring @Autowired not working and returning null

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