如何在Maven多模块Spring Web应用程序中自动装配类？
问题内容：
我正在开发包含Maven多模块项目的应用程序。当尝试@Autowire来自另一个模块的服务类时，我得到了java.lang.NoClassDefFoundError:让该项目与众不同的是，依赖关系在2个Web模块之间。
父项目
Pom.xml
<project>
<groupId>com.test.simple-project</groupId>
<artifactId>simple-parent</artifactId>
<packaging>pom</packaging>
<modules>
<module>module-x</module>
<module>module-y</module>
</modules>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
模块X
Pom.xml
<project>
<artifactId>module-x</artifactId>
<parent>
<groupId>${project.groupId}</groupId>
<artifactId>simple-parent</artifactId>
</parent>
<packaging>war</packaging>
<dependencies>
...
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-eclipse-plugin</artifactId>
<version>2.9</version>
<configuration>
<additionalProjectnatures>
<projectnature>org.springframework.ide.eclipse.core.springnature</projectnature>
</additionalProjectnatures>
<additionalBuildcommands>
<buildcommand>org.springframework.ide.eclipse.core.springbuilder</buildcommand>
</additionalBuildcommands>
<downloadSources>true</downloadSources>
<downloadJavadocs>true</downloadJavadocs>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.5.1</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
<compilerArgument>-Xlint:all</compilerArgument>
<showWarnings>true</showWarnings>
<showDeprecation>true</showDeprecation>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<configuration>
<mainClass>org.test.int1.Main</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
package com.test.module-x.service;
@Service("userService")
public class UserServiceImpl implements UserService {
}
模块Y
Pom.xml
<project>
<artifactId>module-y</artifactId>
<parent>
<groupId>${project.groupId}</groupId>
<artifactId>simple-parent</artifactId>
<version>${project.version}</version>
</parent>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>com.test.simpleproject</groupId>
<artifactId>module-x</artifactId>
</dependency>
...
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-eclipse-plugin</artifactId>
<version>2.9</version>
<configuration>
<additionalProjectnatures>
<projectnature>org.springframework.ide.eclipse.core.springnature</projectnature>
</additionalProjectnatures>
<additionalBuildcommands>
<buildcommand>org.springframework.ide.eclipse.core.springbuilder</buildcommand>
</additionalBuildcommands>
<downloadSources>true</downloadSources>
<downloadJavadocs>true</downloadJavadocs>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.5.1</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
<compilerArgument>-Xlint:all</compilerArgument>
<showWarnings>true</showWarnings>
<showDeprecation>true</showDeprecation>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<configuration>
<mainClass>org.test.int1.Main</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
Y分量扫描
<context:component-scan base-package="com.test.module-x.service" />
@Controller
public class SimpleController {
@Autowired
private UserService userService;
}
这两个模块都是Spring mvc Web 项目（两个pom.xml打包都是战争）
运行应用抛出 java.lang.NoClassDefFoundError: com/test/module-x/service/UserService
java.lang.NoClassDefFoundError: Lcom/test/module-x/service/UserService;
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2570)
at java.lang.Class.getDeclaredFields(Class.java:1903)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.findResourceMetadata(CommonAnnotationBeanPostProcessor.java:324)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:285)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:846)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:498)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:626)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:651)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:599)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:665)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:518)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:459)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
有任何想法吗？
问题答案：
与另一个WAR模块具有依赖关系的WAR模块无法访问由依赖关系模块生成的类。因此，你必须提供在类module-x中的那些module-y。有两种方法可以做到这一点。
选项1：更清洁的设计
将公共类抽象到一个单独的JAR模块中，并声明二者之间的依赖关系module-x以及module-y对此模块的依赖。
选项2：可访问从中的类声明的module-x类module-y
首先，将maven-war-pluginin 配置为module-x将类打包为单独的JAR文件。
<project>
<artifactId>module-x</artifactId>
<packaging>war</packaging>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<attachClasses>true</attachClasses>
<classesClassifier>classes</classesClassifier>
</configuration>
</plugin>
</plugins>
</build>
现在，声明对module-x中的依赖module-y：
<project>
<artifactId>module-y</artifactId>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>module-x</artifactId>
<version>${project.version}</version>
<classifier>classes</classifier>
</dependency>
</dependencies>
</project>
