java - Spring Boot fat jar 中出现NoClassDefFoundError，但相关性在已编译的存档中，并且应用程序在IDE中运行良好

更新：已解决

由于某种原因，我用来加载自定义类的类加载器（扩展了GenModel）没有已经加载的类的上下文，这是我所没有想到的。因此，即使从调试角度加载了GenModel，也没有从modelLoader角度加载它。

解决方案：URLClassLoader实例可以交给父上下文。我不知道确切要处理哪个上下文，只是检索了我知道已经加载的GenModel类的上下文，弄清楚该上下文显然将包含GenModel。因此，最后我只更改了一行代码：

URLClassLoader modelLoader = new URLClassLoader(new URL[]{modelURL});

成为

URLClassLoader modelLoader = new URLClassLoader(new URL[]{modelURL},GenModel.class.getClassLoader());

这样就解决了！

向@EvilToad大喊大叫，他通过他的评论使我走上了正轨！

原始问题：

我正在构建一个原型，该原型将已编译的h2o神经网络模型实现为Web服务，并在运行时注入模型。该应用程序在Spring Boot嵌入式Tomcat服务器中运行，并且是Maven项目。我在Maven POM中具有以下依赖项：

<dependency>
  <groupId>ai.h2o</groupId>
  <artifactId>h2o-genmodel</artifactId>
  <version>3.8.2.3</version>
</dependency>

此依赖项包括类hex.genmodel.GenModel。
当应用程序启动时，它将使用URLClassLoader加载自定义模型类，并将其强制转换为GenModel。相关代码如下：

import hex.genmodel.GenModel;

...

@Bean
public NeuralNetPredictor neuralNetPredictor() throws InstantiationException, IllegalAccessException, ClassNotFoundException, IOException {
    URL modelURL = (new File(this.modelJarPath)).toURI().toURL();
    URLClassLoader modelLoader = new URLClassLoader(new URL[]{modelURL});
    GenModel rawModel = (GenModel) modelLoader.loadClass(this.modelClassName).newInstance();
    modelLoader.close();

    return new NeuralNetPredictor(rawModel, this.modelClassName);
}

这是我的POM：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>TVGML</groupId>
    <artifactId>neuralnetpredictor</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>1.3.5.RELEASE</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>ai.h2o</groupId>
            <artifactId>h2o-genmodel</artifactId>
            <version>3.8.2.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>1.3.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>2.2.2</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>2.2.2</version>
        </dependency>
    </dependencies>
    <properties>
        <java.version>1.8</java.version>
    </properties>
</project>

当我使用以下IntelliJ配置制作和运行应用程序时，一切运行良好：

IntelliJ run config

一切加载完毕，服务器按预期启动，所有功能正常运行，等等。

另一方面，如果我执行的mvn clean install或package也可以正常运行，但是当我运行java -jar <myjarartifact>时，应用程序将引发异常：

... Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.----.research.machinelearning.neuralnets.NeuralNetPredictor]: Factory method 'neuralNetPredictor' threw exception; nested exception is java.lang.NoClassDefFoundError: hex/genmodel/GenModel

... Caused by: java.lang.NoClassDefFoundError: hex/genmodel/GenModel

... Caused by: java.lang.ClassNotFoundException: hex.genmodel.GenModel

这是让我不满意的部分：当我查看由弹簧靴产生的胖罐子时，hex.genmodel.GenModel在那里，与其他依赖项没有什么不同：

GenModel class in fat jar dependencies

更新：
这是堆栈跟踪

Exception in thread "main" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:62)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:54)
    ... 1 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name '/model': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.------.research.machinelearning.neuralnets.NeuralNetPredictor com.------.research.machinelearning.neuralnets.NeuralNetPredictorController.pred; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'neuralNetPredictor' defined in com.------.research.machinelearning.neuralnets.NeuralNetService: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.------.research.machinelearning.neuralnets.NeuralNetPredictor]: Factory method 'neuralNetPredictor' threw exception; nested exception is java.lang.NoClassDefFoundError: hex/genmodel/GenModel
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1214)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:839)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:538)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:766)
    at org.springframework.boot.SpringApplication.createAndRefreshContext(SpringApplication.java:361)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1191)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1180)
    at com.------.research.machinelearning.neuralnets.NeuralNetService.main(NeuralNetService.java:34)
    ... 6 more
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.------.research.machinelearning.neuralnets.NeuralNetPredictor com.------.research.machinelearning.neuralnets.NeuralNetPredictorController.pred; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'neuralNetPredictor' defined in com.------.research.machinelearning.neuralnets.NeuralNetService: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.------.research.machinelearning.neuralnets.NeuralNetPredictor]: Factory method 'neuralNetPredictor' threw exception; nested exception is java.lang.NoClassDefFoundError: hex/genmodel/GenModel
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:573)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 23 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'neuralNetPredictor' defined in com.------.research.machinelearning.neuralnets.NeuralNetService: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.------.research.machinelearning.neuralnets.NeuralNetPredictor]: Factory method 'neuralNetPredictor' threw exception; nested exception is java.lang.NoClassDefFoundError: hex/genmodel/GenModel
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:599)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1123)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1018)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1192)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1116)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1014)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:545)
    ... 25 more
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.------.research.machinelearning.neuralnets.NeuralNetPredictor]: Factory method 'neuralNetPredictor' threw exception; nested exception is java.lang.NoClassDefFoundError: hex/genmodel/GenModel
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588)
    ... 37 more
Caused by: java.lang.NoClassDefFoundError: hex/genmodel/GenModel
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at com.------.research.machinelearning.neuralnets.NeuralNetService.neuralNetPredictor(NeuralNetService.java:46)
    at com.------.research.machinelearning.neuralnets.NeuralNetService$$EnhancerBySpringCGLIB$$352d44ca.CGLIB$neuralNetPredictor$0(<generated>)
    at com.------.research.machinelearning.neuralnets.NeuralNetService$$EnhancerBySpringCGLIB$$352d44ca$$FastClassBySpringCGLIB$$21caa282.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:356)
    at com.------.research.machinelearning.neuralnets.NeuralNetService$$EnhancerBySpringCGLIB$$352d44ca.neuralNetPredictor(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162)
    ... 38 more
Caused by: java.lang.ClassNotFoundException: hex.genmodel.GenModel
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 60 more

任何见解都将不胜感激！

最佳答案

可以将URLClassLoader实例传递给父上下文。我不知道确切要传递哪个上下文，而是检索了我知道已经加载的GenModel类的上下文，弄清楚该上下文显然包含GenModel。因此，最后我只更改了一行代码：

URLClassLoader modelLoader = new URLClassLoader(new URL[]{modelURL});

成为

URLClassLoader modelLoader = new URLClassLoader(new URL[]{modelURL},GenModel.class.getClassLoader());

这样就解决了！

向@EvilToad大喊大叫，他通过他的评论使我走上了正轨！