java - Maven 和 "is not a known entity type"错误

Question

我使用 quickstart 原型(prototype)生成了一个 Maven 项目。于是我得到了如下的项目结构:

|-- src
| |-- main
| | |-- java      
| | |-- resources 
| |-- test
| | |-- java      
| | |-- resources 
|-- pom.xml       

我修改了“pom.xml”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>com.apress.javaee6</groupId>
  <artifactId>chapter02</artifactId>
  <version>1.0</version>
  <packaging>jar</packaging>

  <name>chapter02</name>
  <url>http://maven.apache.org</url>

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

  <build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>2.3.1</version>
        </plugin>
    </plugins>
  </build>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>javax.persistence</groupId>
        <artifactId>persistence-api</artifactId>
        <version>1.0</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>eclipselink</artifactId>
        <version>2.0.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.derby</groupId>
        <artifactId>derbyclient</artifactId>
        <version>10.6.1.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.derby</groupId>
        <artifactId>derby</artifactId>
        <version>10.6.1.0</version>
        <scope>test</scope>
    </dependency>
  </dependencies>
</project>

如您所见，我使用 derby。 “src/main/resources/META-INF/persistence.xml”是:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">

    <persistence-unit name="chapter02PU" transaction-type="RESOURCE_LOCAL">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>com.apress.javaee6.chapter02.Book</class>
        <properties>
            <property name="eclipselink.target-database" value="DERBY"/>
            <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
            <property name="eclipselink.logging.level" value="INFO"/>
            <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/chapter02DB;create=true"/>
            <property name="javax.persistence.jdbc.user" value="APP"/>
            <property name="javax.persistence.jdbc.password" value="APP"/>
        </properties>
    </persistence-unit>
</persistence>        

然后，我创建了一个“Book”类:

package com.apress.javaee6;
import javax.persistence.*;

@Entity
@NamedQuery(name = "findAllBooks", query = "SELECT b FROM Book b")
public class Book {

    // ======================================
    // =             Attributes             =
    // ======================================
    @Id
    @GeneratedValue
    private Long id;
    @Column(nullable = false)
    private String title;
    private Float price;
    @Column(length = 2000)
    private String description;
    private String isbn;
    private Integer nbOfPage;
    private Boolean illustrations;

    // ======================================
    // =            Constructors            =
    // ======================================

    public Book() {
    }

    public Book(String title, Float price, String description, String isbn, Integer nbOfPage, Boolean illustrations) {
        this.title = title;
        this.price = price;
        this.description = description;
        this.isbn = isbn;
        this.nbOfPage = nbOfPage;
        this.illustrations = illustrations;
    }

    // ======================================
    // =          Getters & Setters         =
    // ======================================
    public Long getId() {
        return id;
    }




    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Float getPrice() {
        return price;
    }

    public void setPrice(Float price) {
        this.price = price;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    public Integer getNbOfPage() {
        return nbOfPage;
    }

    public void setNbOfPage(Integer nbOfPage) {
        this.nbOfPage = nbOfPage;
    }

    public Boolean getIllustrations() {
        return illustrations;
    }

    public void setIllustrations(Boolean illustrations) {
        this.illustrations = illustrations;
    }

    // ======================================
    // =         hash, equals, toString     =
    // ======================================

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        sb.append("Book");
        sb.append("{id=").append(id);
        sb.append(", title='").append(title).append('\'');
        sb.append(", price=").append(price);
        sb.append(", description='").append(description).append('\'');
        sb.append(", isbn='").append(isbn).append('\'');
        sb.append(", nbOfPage=").append(nbOfPage);
        sb.append(", illustrations=").append(illustrations);
        sb.append('}');
        return sb.toString();
    }
}

当然还有“主类”:

package com.apress.javaee6;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;


public class Main {

    public static void main(String[] args) {

        // Creates an instance of book
        Book book = new Book();
        book.setId(1231L);
        book.setTitle("The Hitchhiker's Guide to the Galaxy");
        book.setPrice(12.5F);
        book.setDescription("Science fiction comedy series created by Douglas Adams.");
        book.setIsbn("1-84023-742-2");
        book.setNbOfPage(354);
        book.setIllustrations(false);

        // Gets an entity manager and a transaction
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("chapter02PU");
        EntityManager em = emf.createEntityManager();
        EntityTransaction tx = em.getTransaction();

        // Persists the book to the database
        tx.begin();
        em.persist(book);
        tx.commit();

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

我启动 Derby 服务器:

./derby/bin/startNetworkServer

问题是当我运行主类时:

mvn exec:java -Dexec.mainClass="com.apress.javaee6.Main"

我收到以下错误:

[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] An exception occured while executing the Java class. null

Object: Book{id=null, title='The Hitchhiker's Guide to the Galaxy', price=12.5, description='Science fiction comedy series created by Douglas Adams.', isbn='1-84023-742-2', nbOfPage=354, illustrations=false} is not a known entity type.

我认为问题出在“id=null”。但是，当我手动设置 Id 时(例如设置为 123)，我会收到相同的错误消息。我还尝试在 Book 类中使用以下注释:

@GeneratedValue(strategy=GenerationType.AUTO)

或

@GeneratedValue(strategy=GenerationType.IDENTITY)

有人解决这个错误吗？

PS:这是打开错误堆栈跟踪的 exec 命令结果:

+ Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'exec'.
[INFO] ------------------------------------------------------------------------
[INFO] Building chapter02
[INFO]    task-segment: [exec:java]
[INFO] ------------------------------------------------------------------------
[INFO] Preparing exec:java
[INFO] No goals needed for project - skipping
[INFO] [exec:java {execution: default-cli}]
[EL Finest]: 2010-08-19 13:38:37.215--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Begin predeploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Initial; factoryCount 0
[EL Finest]: 2010-08-19 13:38:37.243--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=eclipselink.orm.throw.exceptions; default value=true
[EL Finer]: 2010-08-19 13:38:37.272--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Searching for default mapping file in file:/home/zakaria/Dev/chapter02/target/classes/
[EL Finer]: 2010-08-19 13:38:37.276--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Searching for default mapping file in file:/home/zakaria/Dev/chapter02/target/classes/
[EL Finest]: 2010-08-19 13:38:37.3--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--End predeploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Predeployed; factoryCount 0
[EL Finer]: 2010-08-19 13:38:37.3--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--JavaSECMPInitializer - transformer is null.
[EL Finest]: 2010-08-19 13:38:37.3--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Begin predeploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Predeployed; factoryCount 0
[EL Finest]: 2010-08-19 13:38:37.301--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--End predeploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Predeployed; factoryCount 1
[EL Finest]: 2010-08-19 13:38:37.309--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Begin deploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Predeployed; factoryCount 1
[EL Finer]: 2010-08-19 13:38:37.315--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Could not initialize Validation Factory. Encountered following exception: java.lang.NoClassDefFoundError: javax/validation/Validation
[EL Finest]: 2010-08-19 13:38:37.323--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=eclipselink.logging.level; value=FINEST; translated value=FINEST
[EL Finest]: 2010-08-19 13:38:37.323--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=eclipselink.logging.level; value=FINEST; translated value=FINEST
[EL Finest]: 2010-08-19 13:38:37.324--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=javax.persistence.jdbc.user; value=APP
[EL Finest]: 2010-08-19 13:38:37.324--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=javax.persistence.jdbc.password; value=xxxxxx
[EL Finest]: 2010-08-19 13:38:37.429--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=eclipselink.target-database; value=DERBY; translated value=org.eclipse.persistence.platform.database.DerbyPlatform
[EL Finest]: 2010-08-19 13:38:37.437--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=javax.persistence.jdbc.driver; value=org.apache.derby.jdbc.ClientDriver
[EL Finest]: 2010-08-19 13:38:37.438--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--property=javax.persistence.jdbc.url; value=jdbc:derby://localhost:1527/chapter02DB
[EL Info]: 2010-08-19 13:38:37.439--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--EclipseLink, version: Eclipse Persistence Services - 2.0.0.v20091127-r5931
[EL Config]: 2010-08-19 13:38:37.46--ServerSession(6419763)--Connection(22664464)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--connecting(DatabaseLogin(
    platform=>DerbyPlatform
    user name=> "APP"
    datasource URL=> "jdbc:derby://localhost:1527/chapter02DB"
))
[EL Config]: 2010-08-19 13:38:37.857--ServerSession(6419763)--Connection(25782860)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Connected: jdbc:derby://localhost:1527/chapter02DB
    User: APP
    Database: Apache Derby  Version: 10.6.1.0 - (938214)
    Driver: Apache Derby Network Client JDBC Driver  Version: 10.6.1.0 - (938214)
[EL Config]: 2010-08-19 13:38:37.857--ServerSession(6419763)--Connection(10594949)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--connecting(DatabaseLogin(
    platform=>DerbyPlatform
    user name=> "APP"
    datasource URL=> "jdbc:derby://localhost:1527/chapter02DB"
))
[EL Config]: 2010-08-19 13:38:37.863--ServerSession(6419763)--Connection(29499086)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--Connected: jdbc:derby://localhost:1527/chapter02DB
    User: APP
    Database: Apache Derby  Version: 10.6.1.0 - (938214)
    Driver: Apache Derby Network Client JDBC Driver  Version: 10.6.1.0 - (938214)
[EL Info]: 2010-08-19 13:38:37.885--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU login successful
[EL Finest]: 2010-08-19 13:38:37.933--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--End deploying Persistence Unit chapter02PU; session file:/home/zakaria/Dev/chapter02/target/classes/_chapter02PU; state Deployed; factoryCount 1
[EL Finer]: 2010-08-19 13:38:38.004--ServerSession(6419763)--Thread(Thread[com.apress.javaee6.Main.main(),5,com.apress.javaee6.Main])--client acquired
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] An exception occured while executing the Java class. null

Object: Book{id=1231, title='The Hitchhiker's Guide to the Galaxy', price=12.5, description='Science fiction comedy series created by Douglas Adams.', isbn='1-84023-742-2', nbOfPage=354, illustrations=false} is not a known entity type.
[INFO] ------------------------------------------------------------------------
[INFO] Trace
org.apache.maven.lifecycle.LifecycleExecutionException: An exception occured while executing the Java class. null
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:719)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:569)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:539)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:387)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:348)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:180)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:328)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
    at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:60)
    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:616)
    at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
    at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
    at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
    at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
Caused by: org.apache.maven.plugin.MojoExecutionException: An exception occured while executing the Java class. null
    at org.codehaus.mojo.exec.ExecJavaMojo.execute(ExecJavaMojo.java:346)
    at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:490)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:694)
    ... 17 more
Caused by: 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:616)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:291)
    at java.lang.Thread.run(Thread.java:636)
Caused by: java.lang.IllegalArgumentException: Object: Book{id=1231, title='The Hitchhiker's Guide to the Galaxy', price=12.5, description='Science fiction comedy series created by Douglas Adams.', isbn='1-84023-742-2', nbOfPage=354, illustrations=false} is not a known entity type.
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.registerNewObjectForPersist(UnitOfWorkImpl.java:4147)
    at org.eclipse.persistence.internal.jpa.EntityManagerImpl.persist(EntityManagerImpl.java:368)
    at com.apress.javaee6.Main.main(Main.java:30)
    ... 6 more
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4 seconds
[INFO] Finished at: Thu Aug 19 13:38:38 CEST 2010
[INFO] Final Memory: 8M/68M
[INFO] ------------------------------------------------------------------------
[EL Finer]: 2010-08-19 13:38:38.213--UnitOfWork(24128584)--Thread(Thread[Finalizer,8,system])--release unit of work
[EL Finer]: 2010-08-19 13:38:38.214--ClientSession(23817301)--Thread(Thread[Finalizer,8,system])--client released

非常感谢，问候。

Answer 1

I thought that the problem was the "id=null". But, when I set the Id manually (to 123 for example), I get the same error message.

不，您不应该在使用 GeneratedValue 时设置 Id。

Anybody has the solution to this error?

问题的根本原因是 BOOK 表未生成(因此 EclipseLink 无法正确映射 Book 实体，然后无法识别它作为一个实体)。

发生这种情况是因为您的 persistence.xml 中列出的类的完全限定名称与实际的 FQN 不匹配(com.apress.javaee6.chapter02.Book与 com.apress.javaee6.Book).

因此，要么更改类的包，要么修复 persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">

    <persistence-unit name="chapter02PU" transaction-type="RESOURCE_LOCAL">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>com.apress.javaee6.Book</class>
        <properties>
            <property name="eclipselink.target-database" value="DERBY"/>
            <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
            <property name="eclipselink.logging.level" value="INFO"/>
            <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/chapter02DB;create=true"/>
            <property name="javax.persistence.jdbc.user" value="APP"/>
            <property name="javax.persistence.jdbc.password" value="APP"/>
        </properties>
    </persistence-unit>
</persistence>  

然后运行你的 mvn exec:java -Dexec.mainClass="com.apress.javaee6.Main" 将会成功:

 mvn exec:java -Dexec.mainClass="com.apress.javaee6.Main" -e+ Error stacktraces are turned on.[INFO] Scanning for projects...[INFO] Searching repository for plugin with prefix: 'exec'.[INFO] ------------------------------------------------------------------------[INFO] Building Q3521044 - Maven and the “is not a known entity type” error[INFO]    task-segment: [exec:java][INFO] ------------------------------------------------------------------------[INFO] Preparing exec:java[INFO] No goals needed for project - skipping[INFO] [exec:java {execution: default-cli}][EL Info]: 2010-08-19 16:39:54.442--ServerSession(2698418)--EclipseLink, version: Eclipse Persistence Services - 2.0.0.v20091127-r5931[EL Info]: 2010-08-19 16:39:55.875--ServerSession(2698418)--file:/home/pascal/Projects/stackoverflow/Q3521044/target/classes/_chapter02PU login successful[EL Warning]: 2010-08-19 16:39:56.219--ServerSession(2698418)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.0.0.v20091127-r5931): org.eclipse.persistence.exceptions.DatabaseExceptionInternal Exception: java.sql.SQLException: Table/View 'SEQUENCE' already exists in Schema 'APP'.Error Code: -1Call: CREATE TABLE SEQUENCE (SEQ_NAME VARCHAR(50) NOT NULL, SEQ_COUNT DECIMAL(15), PRIMARY KEY (SEQ_NAME))Query: DataModifyQuery(sql="CREATE TABLE SEQUENCE (SEQ_NAME VARCHAR(50) NOT NULL, SEQ_COUNT DECIMAL(15), PRIMARY KEY (SEQ_NAME))")[EL Info]: 2010-08-19 16:39:56.574--ServerSession(2698418)--file:/home/pascal/Projects/stackoverflow/Q3521044/target/classes/_chapter02PU logout successful[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESSFUL[INFO] ------------------------------------------------------------------------[INFO] ------------------------------------------------------------------------[INFO] Total time: 11 seconds[INFO] Finished at: Thu Aug 19 16:39:56 CEST 2010[INFO] Final Memory: 17M/88M[INFO] ------------------------------------------------------------------------

但在我看来，错误报告的很差，EclipseLink 应该报告表丢失。

引用资料

• JPA 1.0 规范
  • 6.2.1.6 映射文件、jar 文件、类、排除未列出的类