为什么我会收到此错误？线程＆＃34; main＆＃34;中的例外情况java.lang.NoClassDefFoundError：javax / persistence / Persistence

Question

我已经在Stackoverflow上搜索了这个问题的答案，但我能找到的唯一答案（here）不起作用（我添加了hibernate-jpa并没有区别）。

以下是GitHub上此project源代码的链接。同样，这里有相关的主要文件。

POM文件：

<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>ca.thirdgear</groupId>
  <artifactId>healthmonitor</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>healthmonitor</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.39</version>
    </dependency>

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>5.2.7.Final</version>
    </dependency>

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>5.3.4.Final</version>
    </dependency>

  </dependencies>

  <build>

        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <archive>
                        <manifest>
                            <mainClass>ca.thirdgear.healthmonitor.SystemMonitor</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
            <plugin>
            <!-- Build an executable JAR -->
            <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.0.2</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <classpathPrefix>lib/</classpathPrefix>
                            <mainClass>ca.thirdgear.healthmonitor.SystemMonitor</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
        <resources>
        <resource>
            <directory>src/main/resources/META-INF</directory>
        </resource>
    </resources>
  </build>

</project>

persistence.xml @src / main / resources / META-INF：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

  <persistence-unit name="healthmonitor" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>ca.thirdgear.healthcheck.entities.User</class>
    <class>ca.thirdgear.healthcheck.entities.TwilioAccount</class>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://192.168.1.172:3306/HomeAutomation" />
      <property name="javax.persistence.jdbc.user" value="root" />
      <property name="javax.persistence.jdbc.password" value="xxxxxxxxxxxxxxxx" />
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
    </properties>
  </persistence-unit>
</persistence> 

主要课程：

package ca.thirdgear.healthmonitor;

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import entities.User;

public class SystemMonitor 
{

    public static void main(String[] args) 
    {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("healthmonitor");
        EntityManager em = emf.createEntityManager();

        em.getTransaction().begin();

        List<User> users = em.createNamedQuery("User.findAll", User.class).getResultList();

        for(User u : users)
        {
            System.out.println(u.getFirstName());
        }


        em.getTransaction().commit();
        em.close();
        emf.close();        
    }

}

用户实体类：

package entities;

import java.security.Principal;
import java.util.Objects;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.validation.constraints.NotNull;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;


@Entity
@Table(name = "AuthenticatedUsers")
@NamedQueries(
        {
            @NamedQuery(name = "User.findByEmail",
                    query = "SELECT u FROM User u WHERE u.email = :email"),

            @NamedQuery(name = "User.findByEmailAndPassword",
                query = "SELECT u FROM User u WHERE u.email = :email AND u.password = :password"),

            @NamedQuery(name = "User.findByPassword",
                query = "SELECT u FROM User u WHERE u.password = :password"),

            @NamedQuery(name = "User.findAll",
                query = "SELECT a FROM User a")
        }
)


/**
 * Defines an Authenticated application User.
 */
public class User implements Principal
{
    //PK for entity
    @Id
    @Basic(optional = false)
    @NotNull
    @Column(name = "email", nullable = false)
    private String email;

    @Basic(optional = false)
    @NotNull
    @Column(name = "firstName", nullable = false)
    private String firstName;

    @Basic(optional = false)
    @NotNull
    @Column(name = "lastName", nullable = false)
    private String lastName;

    @Basic(optional = false)
    @NotNull
    @Column(name = "phoneNumber", nullable = false)
    private String phoneNumber;

    @Basic(optional = false)
    @NotNull
    @Column(name = "role", nullable = false)
    private String role;

    @Basic(optional = false)
    @NotNull
    @Column(name = "password", nullable = false)
    private String password;

    @Basic(optional = false)
    @NotNull
    @Column(name = "activeStatus", nullable = false, length = 1)
    private String activeStatus;

    //default constructor
    public User() 
    {
        //not used
    }

    //constructor
    public User(String firstName, String password, String role) 
    {
        this.firstName = firstName;
        this.password = password;
        this.role = role;
    }

    public String getEmail()
    {
        return email;
    }

    public void setEmail(String email)
    {
        this.email = email;
    }

    public String getFirstName()
    {
        return firstName;
    }

    public void setFirstName(String firstName)
    {
        this.firstName = firstName;
    }

    public String getLastName()
    {
        return lastName;
    }

    public void setLastName(String lastName)
    {
        this.lastName = lastName;
    }

    public String getPhoneNumber()
    {
        return phoneNumber;
    }

    public void setPhoneNumber(String phoneNumber)
    {
        this.phoneNumber = phoneNumber;
    }

    public String getRole()
    {
        return role;
    }

    public void setRole(String role)
    {
        this.role = role;
    }

    public String getPassword()
    {
        return password;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public String getActiveStatus()
    {
        return activeStatus;
    }

    public void setActiveStatus(String activeStatus)
    {
        this.activeStatus = activeStatus;
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(this.firstName, this.lastName, this.phoneNumber,
                this.email, this.role, this.password, this.activeStatus);
    }

    @Override
    public String toString()
    {
        return "User{" + ", firstName=" + firstName
                + ", lastName=" + lastName
                + ", phoneNumber=" + phoneNumber
                + ", email=" + email
                + ", role=" + role
                + ", password=" + password
                + ", activeStatus=" + activeStatus;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) 
        {
            return true;
        }

        if (obj == null) 
        {
            return false;
        }

        if (getClass() != obj.getClass()) 
        {
            return false;
        }

        final User other = (User) obj;
        return Objects.equals(this.firstName, other.firstName)
                && Objects.equals(this.lastName, other.lastName)
                && Objects.equals(this.phoneNumber, other.phoneNumber)
                && Objects.equals(this.email, other.email)
                && Objects.equals(this.role, other.role)
                && Objects.equals(this.password, other.password)
                && Objects.equals(this.activeStatus, other.activeStatus);
    }

    /**
     * Method implementation from Principal interface.
     *
     * @return The name of the Principal.
     */
    public String getName() {
        return firstName;
    }
}

此时，我所关心的只是从一个实体读取一些属性并将其打印到命令行。当我执行我的jar文件时，我得到以下stacktrace。

MikesMBP:target Mike$ java -jar healthmonitor-0.0.1-SNAPSHOT.jar 
Exception in thread "main" java.lang.NoClassDefFoundError: javax/persistence/Persistence
    at ca.thirdgear.healthmonitor.SystemMonitor.main(SystemMonitor.java:41)
Caused by: java.lang.ClassNotFoundException: javax.persistence.Persistence
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 1 more

我的persistence.xml文件不正确吗？这是我的POM文件吗？我缺少一些配置吗？我真的很难过，因为我认为这将是一项微不足道的任务。

如果重要的话我正在使用Eclipse Neon，而且我确实将Java设置为使用SE-1.8。

谢谢。

Answer 1

尝试将此添加到您的pom.xml：

<!-- https://mvnrepository.com/artifact/javax.persistence/persistence-api -->
<dependency>
    <groupId>javax.persistence</groupId>
    <artifactId>persistence-api</artifactId>
    <version>1.0.2</version>
</dependency>

Answer 2

这个问题的答案在于Maven POM文件。

需要Maven shade插件，然后将所有必需的jar文件捆绑/打包到最终的目标jar文件中。这消除了NoClassDefFoundError。这个post就是这个答案的参考。

接下来，persistence.xml文件被明确列为POM文件中的资源。这个post提供了参考。

这是更新的POM文件。请参阅下半部分了解更改。

<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>ca.thirdgear</groupId>
  <artifactId>healthmonitor</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>healthmonitor</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.39</version>
    </dependency>

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>5.2.7.Final</version>
    </dependency>

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>5.4.0.Final</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.hibernate.javax.persistence/hibernate-jpa-2.1-api -->
    <dependency>
        <groupId>org.hibernate.javax.persistence</groupId>
        <artifactId>hibernate-jpa-2.1-api</artifactId>
        <version>1.0.0.Final</version>
    </dependency>

    <dependency>
        <groupId>javax.persistence</groupId>
        <artifactId>persistence-api</artifactId>
        <version>1.0.2</version>
    </dependency>

  </dependencies>

  <build>

        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <archive>
                        <manifest>
                            <mainClass>ca.thirdgear.healthmonitor.SystemMonitor</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
            <plugin>
            <!-- Build an executable JAR -->
            <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.0.2</version>
                <configuration>
                    <archive>
                        <manifest>

                            <mainClass>ca.thirdgear.healthmonitor.SystemMonitor</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.3</version>
                    <executions>
                        <execution>
                            <phase>package</phase>
                            <goals>
                                <goal>shade</goal>
                            </goals>
                        </execution>
                    </executions>
            </plugin>   
        </plugins>

        <resources>
            <resource>
                <directory>src/main/resources/META-INF</directory>
                <targetPath>META-INF</targetPath>
                <includes>
                    <include>persistence.xml</include>
                </includes>
            </resource>
        </resources>
  </build>

</project>