Spring数据JPA:类路径资源[]无法解析为URL，因为它不存在

我对Spring有点陌生，但我决定将SpringDataJPA用于个人项目。 我开始学习教程，但有自己的修改。（如下所示）

运行代码时，我会遇到异常：

...
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:53)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class dal.access.DBAccess: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: Unable to resolve persistence unit root URL
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1548)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:300)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:296)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:973)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:750)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
    at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:84)
    at dal.test.Application.main(Application.java:20)
    ... 6 more
Caused by: javax.persistence.PersistenceException: Unable to resolve persistence unit root URL
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.determineDefaultPersistenceUnitRootUrl(DefaultPersistenceUnitManager.java:529)
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.preparePersistenceUnitInfos(DefaultPersistenceUnitManager.java:402)
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.afterPropertiesSet(DefaultPersistenceUnitManager.java:384)
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:285)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:317)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1607)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1544)
    ... 17 more
Caused by: java.io.FileNotFoundException: class path resource [] cannot be resolved to URL because it does not exist
    at org.springframework.core.io.ClassPathResource.getURL(ClassPathResource.java:178)
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.determineDefaultPersistenceUnitRootUrl(DefaultPersistenceUnitManager.java:526)
    ... 23 more

我的代码如下：

buildscript {
    repositories {
        maven { url "http://repo.spring.io/libs-milestone" }
        mavenLocal()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:0.5.0.M6")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'spring-boot'

sourceSets {
    main {
        java {
            srcDirs = ["src"]
        }
    }
}

jar {
    baseName = 'dal-jar-test'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
    maven { url "http://repo.spring.io/libs-milestone" }
    maven { url "https://repository.jboss.org/nexus/content/repositories/releases" }
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:0.5.0.M6")
    compile("org.springframework:spring-orm:4.0.0.RC1")
    compile("org.springframework.data:spring-data-jpa:1.4.1.RELEASE")
    compile("org.hibernate:hibernate-entitymanager:4.2.1.Final")
    compile("com.h2database:h2:1.3.172")
    testCompile("junit:junit:4.11")
}

task wrapper(type: Wrapper) {
    gradleVersion = '1.8'
}

POJO课程：

package dal.entities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class EntityA {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long    id;
    private String  firstName;
    private String  lastName;

    protected EntityA() {}

    public EntityA(String firstName, String lastName) {
        this.firstName  =   firstName;
        this.lastName   =   lastName;
    }

    @Override
    public String toString() {
        return String.format("EntityA[id=%d, firstName='%s', lastName='%s']",
                             id,firstName,lastName);
    }
}

存储库界面：

package dal.repositories;

import java.util.List;

import org.springframework.data.repository.CrudRepository;

import dal.entities.EntityA;

public interface EntityARepository extends CrudRepository<EntityA, Long> {
    List<EntityA> findByLastName(String lastName);
}

最后是主要课程：

package dal.test;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

import dal.access.DBAccess;
import dal.entities.EntityA;
import dal.repositories.EntityARepository;

@Configuration
@EnableJpaRepositories
public class Application {

    public static void main(String[] args) {
        AbstractApplicationContext ctx = new AnnotationConfigApplicationContext(DBAccess.class);
        EntityARepository repositoryA = ctx.getBean(EntityARepository.class);

        // save a couple entities
        repositoryA.save(new EntityA("boy", "boy"));
        repositoryA.save(new EntityA("girl", "girl"));

        // fetch all entities
        Iterable<EntityA> As = repositoryA.findAll();
        for (EntityA entityA : As) {
            System.out.println(entityA);
        }

        ctx.close();
    }
}

package.dal.test；
导入org.springframework.context.annotation.AnnotationConfigApplicationContext；
导入org.springframework.context.annotation.Configuration；
导入org.springframework.context.support.AbstractApplicationContext；
导入org.springframework.data.jpa.repository.config.EnableJpaRepositories；
导入dal.access.DBAccess；
导入dal.entities.EntityA；
导入dal.repositories.EntityARepository；
@配置
@授权代理
公共类应用程序{
公共静态void main（字符串[]args）{
AbstractApplicationContext ctx=新注释ConfigApplicationContext（DBAccess.class）；
EntityARepository repositoryA=ctx.getBean（EntityARepository.class）；
//保存两个实体
保存（新实体（“男孩”）；
保存（新实体（“女孩”）；
//获取所有实体
Iterable As=repositoria.findAll（）；
for（EntityA EntityA:As）{
系统输出打印项次（entityA）；
}
ctx.close（）；
}
}

正如代码所示，每个类都位于不同的包中。（可能这就是问题所在，因为当我在同一个包中创建所有类时，所有的工作都很完美）当使用java命令行运行gradle生成的jar时，会出现异常

有人能帮我吗

---

谢谢大家!

根据您提供的示例和Spring数据示例项目：

如果您将实体放在不同的包中，您应该明确指定spring应该在其中查找这些实体的包，它不能真正扫描所有项目，因为从性能和内存消耗的角度来看这都不合理

因此，在您的示例中，实体存在于“dal.entities”包中。 您应该如下配置LocalContainerEntityManagerFactoryBean：

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) {
    LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean();
    lef.setDataSource(dataSource);
    lef.setJpaVendorAdapter(jpaVendorAdapter);
    lef.setPackagesToScan("dal.entities"); // !!! you might want to place here more than one package, its vararg
    return lef;
}

我已经下载了示例项目（我没有gradle，所以我使用了maven build），将实体放在不同的包中，它就工作了）

如果你不想配置你的东西，你可能想考虑创建一个持久性XML，它将指定这些实体的列表，但这是完全不同的故事。

---

希望这有帮助

谢谢你的回答！但当我将包更改为像您建议的那样扫描时，出现了另一个异常：NoSuchBeanDefinitionException，在此之后，我了解到应用程序类上的注释需要移动到DBAccess类，此外，我还需要将basePackages属性添加到@EnableJpaRepositories注释中，这将让spring找到我的repositories类并实现它们。

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) {
    LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean();
    lef.setDataSource(dataSource);
    lef.setJpaVendorAdapter(jpaVendorAdapter);
    lef.setPackagesToScan("dal.entities"); // !!! you might want to place here more than one package, its vararg
    return lef;
}