使用Spring Boot“bootrun”启动的应用程序在包含Gradle Vaadin插件时导致NoClassDefFoundError

Question

我的目标是建立一个简单的多模块项目，它使用Spring Boot2、Gradle4.x和Vaadin8.x作为UI。Vaadin目前只用于其中的一个子项目，其他的子项目提供服务或只是库。

我从这个非常好的Spring教程开始，它（尽管使用了旧的Gradle语法）产生了一个可以工作的测试项目。它包含一个“Libaray”子项目和一个依赖于前者的“Application”子项目。“bootrun”和“bootjar”Gradle任务都像一个魅力一样工作，并且在我将一些配置集中在父构建中后仍然工作。grade。

然后我将Vaadin Gradle插件添加到“Application”项目中，并更改endpoint以显示一个简单的Vaadin标签。

问题是，现在使用“bootrun”时，启动的应用程序不再能够访问它所依赖的“库”中的类。如果我删除代码中的任何依赖项，应用程序就可以工作，但一旦我从“Library”（例如“MyService”）中引用了一个类，它就会以“java.lang.ClassNotFoundException”崩溃。

但是，当使用“bootjar”部署相同的应用程序并运行jar时，一切都可以工作，因此模块间依赖关系可以得到解决。

以下是相关的示例代码（不包括导入）：

Hello.app.DemoApplication

@SpringBootApplication(scanBasePackages = "hello")
@RestController
public class DemoApplication {
    //Service defined in dependent sub-project
    private final MyService myService;

    public DemoApplication(MyService myService) {
        this.myService = myService;
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

hello.app.startup

/** Entry point for the Vaadin 8 UI */
@SpringUI
@SpringView
public class StartUI extends UI implements View {

    @Override
    protected void init(final VaadinRequest request) {
        setContent(new Label("Hello vaadin"));
    }
}

plugins { id "io.spring.dependency-management" version "1.0.5.RELEASE" }
ext { springBootVersion = '2.0.3.RELEASE' }
jar {
    baseName = 'library'
    version = '0.0.1-SNAPSHOT'
}
dependencies {
    implementation('org.springframework.boot:spring-boot-starter')
    testImplementation('org.springframework.boot:spring-boot-starter-test')
}
dependencyManagement {
    imports { mavenBom("org.springframework.boot:spring-boot-dependencies:${springBootVersion}") }
}

plugins {
    id "io.spring.dependency-management" version "1.0.5.RELEASE"
    id "org.springframework.boot" version "2.0.3.RELEASE"
    id 'com.devsoap.plugin.vaadin'version '1.3.1' //Add vaadin support
}
bootJar {
    baseName = 'application'
    version = '0.0.1-SNAPSHOT'
}
dependencies {
    implementation project(':library') // Contains "MyService"
    implementation('org.springframework.boot:spring-boot-starter-actuator')
    implementation('org.springframework.boot:spring-boot-starter-web')
    testImplementation('org.springframework.boot:spring-boot-starter-test')
}

subprojects {
    //Only plugins configured here applied to sub-projects.
    apply plugin: "java-library"
    apply plugin: "eclipse"
    repositories { mavenCentral() } 
    sourceCompatibility = 1.8
}

java.lang.IllegalStateException: Cannot load configuration class: hello.app.DemoApplication
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:414) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanFactory(ConfigurationClassPostProcessor.java:254) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:284) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:128) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:694) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:532) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    ...
Caused by: java.lang.IllegalStateException: Unable to load cache item
    at org.springframework.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:79) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.cglib.core.internal.LoadingCache.get(LoadingCache.java:34) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:116) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:291) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:480) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.cglib.proxy.Enhancer.createClass(Enhancer.java:337) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer.createClass(ConfigurationClassEnhancer.java:138) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer.enhance(ConfigurationClassEnhancer.java:110) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:403) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 12 common frames omitted
Caused by: java.lang.NoClassDefFoundError: hello/service/MyService
    at java.lang.Class.getDeclaredConstructors0(Native Method) ~[na:1.8.0_151]
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2671) ~[na:1.8.0_151]
    at java.lang.Class.getDeclaredConstructors(Class.java:2020) ~[na:1.8.0_151]
    at org.springframework.cglib.proxy.Enhancer.generateClass(Enhancer.java:566) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ...
Caused by: java.lang.ClassNotFoundException: hello.service.MyService
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_151]
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_151]
    ... 34 common frames omitted

Answer 1

Spring依赖项管理插件真的很麻烦，并不是所有的插件都支持它（比如Gradle Vaadin插件）。我会跳过它，而是使用Gradle的BOM支持。https://docs.gradle.org/4.6/userguide/managing_transitive_dependencies.html#sec:bom_import