Java 如何在Maven多模块Spring web应用程序中自动连接类？

我正在开发包含Maven多模块项目的应用程序。当尝试从另一个模块@Autowire一个服务类时，我得到了

java.lang.NoClassDefFoundError:

使这个项目唯一的是两个web模块之间的依赖关系

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>

<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>

<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>

模块Y

---

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>

<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>

<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>

两个模块都是SpringMVCweb项目（pom.xml打包都是war）

运行应用程序会抛出

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)

---

有什么想法吗？

您必须在与模块Y关联的pom.xml文件中定义对模块X的输出war文件的依赖关系。 然而，有两个war文件并在它们之间放置依赖项是很奇怪的。据我所知，您将拥有2个web应用程序。如果我猜对了，模块X不知何故是整个系统的业务层（包括服务），因此足以从中生成jar文件，并将模块Y定义为web模块。

---

但是，您需要在模块Y的pom.xml文件中明确地对模块X具有maven依赖关系。

依赖于另一个WAR模块的WAR模块无法访问依赖模块生成的类。因此，您必须将

module-x

中的类提供给

module-y

中的类。有两种方法可以做到这一点

备选方案1：更清洁的设计

---

将公共类抽象到一个单独的JAR模块中，并声明从

module-x

和

module-y

到该模块的依赖关系

选项2：从

module-y

---

首先，在

module-x

中配置

maven-war插件

，将这些类打包为一个单独的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>

---

很难说，除非你包含更多的信息——最好是一些pom.xml——war插件的更多信息都包含在选项2中，但是我得到了同样的错误。你认为这与组件扫描有关吗？如果是相同的堆栈跟踪，那么组件扫描与此无关。如果这是一个组件扫描错误，就会出现类似于

没有匹配类型的bean的情况。。。找到

。这是一个工作样本。将其与代码进行比较，找出导致错误的差异。如果这不起作用，请发布一个完整的示例项目来演示您的问题。感谢您花时间创建示例项目。我正在检查它，会让你知道结果的。刚刚开始在这个项目上再次工作。您提供的示例项目工作正常，但我更改了pom.xml以支持在eclipse中定义的服务器上运行应用程序，并且我得到了

org.springframework.beans.factory.BeanCreationException:创建名为“fooController”的bean，该名称在文件…\…\fooController.class]中定义：bean类型的后期处理失败[class org.example.web.FooController]失败；嵌套异常为java.lang.IllegalStateException:未能为资源元数据内省bean类[org.example.web.FooController]：找不到它所依赖的类

<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>