依赖注入 - Maven 多模块项目上的 java.lang.NoClassDefFoundError

Question

我从事一个 Maven 多模块项目。这些模块是：名为entities 的持久性模块被打包为jar，名为services 的服务模块被打包为jar 和名为web 的Web 模块被打包为war。 pom如下：

<groupId>com.af</groupId>
<artifactId>eMuse</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>

<modules>
    <module>entities</module>
    <module>services</module>
    <module>web</module>
</modules>

每个模块都有自己的应用程序上下文文件，我在其中声明 bean。

entities-context.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="actionDAO" class="com.af.dao.impl.ActionDAOImpl" />
    <bean id="milestoneDAO" class="com.af.dao.impl.MilestoneDAOImpl" />
    <bean id="milestoneMarksDAO" class="com.af.dao.impl.MilestoneMarksDAOImpl" />
    <bean id="milestoneTypeDAO" class="com.af.dao.impl.MilestoneTypeDAOImpl" />
    <bean id="studentDAO" class="com.af.dao.impl.StudentDAOImpl" />
    <bean id="studentsActionsDAO" class="com.af.dao.impl.StudentsActionsDAOImpl"></bean>
    <bean id="teamDAO" class="com.af.dao.impl.TeamDAOImpl" />
    <bean id="toolDAO" class="com.af.dao.impl.ToolDAOImpl" />
</beans>

服务上下文.xml

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

    <bean id="studentService" class="com.af.service.impl.StudentServiceImpl"/>
       <property name="studentDAO" ref="studentDAO"/>
       <property name="teamDAO" ref="teamDAO"/>
    </bean>
    <import resource="/entities-context.xml"/>
</beans>

还在服务pom.xml 中添加了对实体模块的依赖。

<parent>
    <groupId>com.af</groupId>
    <artifactId>eMuse</artifactId>
    <version>1.0-SNAPSHOT</version>
</parent>
<artifactId>services</artifactId>

<dependency>
        <groupId>com.af</groupId>
        <artifactId>entities</artifactId>
        <version>1.0-SNAPSHOT</version>
</dependency>

以及web模块配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.1.xsd">


    <mvc:annotation-driven />

    <context:component-scan base-package="com.af" />
    <import resource="classpath*:services-context.xml"/>
    <!-- Tiles configuration -->

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass">
            <value>org.springframework.web.servlet.view.tiles2.TilesView</value>
        </property>
    </bean>
    <bean id="tilesConfigurer"
        class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/tiles.xml</value>
            </list>
        </property>
    </bean>
    <mvc:default-servlet-handler />
</beans>

web/pom.xml

<parent>
    <groupId>com.af</groupId>
    <artifactId>eMuse</artifactId>
    <version>1.0-SNAPSHOT</version>
</parent>
<artifactId>web</artifactId>
<packaging>war</packaging>
<dependencies>
    <dependency>
        <groupId>com.af</groupId>
        <artifactId>services</artifactId>
        <version>1.0-SNAPSHOT</version>
        <exclusions>
            <exclusion>
                <groupId>com.af</groupId>
                <artifactId>entities</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
 <!-- other dependencies-->
 </dependencies>

当我跑步时：

 @Controller
 public class TestController {

    @Autowired
    private StudentService studentService;

    @RequestMapping(value="/index", method = RequestMethod.GET)
    public String test(Model model){

        StudentModel stud = StudentModelMapper.mapStudentDTO(studentService.getStudentById(1));
        model.addAttribute("name", stud.getFirstName());
        return "index";
    }


 }

我得到了例外：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.af.service.StudentService com.af.controller.TestController.studentService; nested exception is java.lang.NoClassDefFoundError: Lcom/af/service/StudentService;

谁能告诉我我做错了什么？

编辑：我访问服务模块中实体 jar 的应用程序上下文文件然后访问 web 模块中的服务应用程序上下文文件的方式是否正确？

Answer 1

您专门从网络 POM 中排除了 jar：

<exclusions>
            <exclusion>
                <groupId>com.af</groupId>
                <artifactId>entities</artifactId>
            </exclusion>
        </exclusions>

这是您在运行时需要的传递依赖。

你得到一个 NoClassDefFoundError 因为你可以编译代码，但在运行时你需要它。

只需删除排除项，实体 jar 将在运行时添加。