我正在使用GlassFish 3 开始 Java EE 6 平台进行企业计算课程：从新手到专业
上一章是关于 EJB 的，实际上我发现它很难理解。
为了更好地理解 EJB，我一直在尝试运行本书的示例代码之一，但是每当我调用 EJB 时，我都会收到 NullPointerException。
我正在使用 NetBeans 7.3.1 以及 NetBeans 提供的 Maven 和 Glassfish 版本（Maven 似乎是 3.0.5，Glassfish 是 4.0）
这是主类的代码：
package org.beginningee6.book.chapter06;
import javax.ejb.EJB;
/**
* @author Antonio Goncalves
* APress Book - Beginning Java EE 6 with Glassfish
* --
*/
public class Main {
// ======================================
// = Attributes =
// ======================================
@EJB
private static BookEJBRemote bookEJB;
// ======================================
// = Public Methods =
// ======================================
public static void main(String[] args) {
// Creates an instance of book
Book book = new Book();
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);
book = bookEJB.createBook(book);
System.out.println("### Book created : " + book);
book.setTitle("H2G2");
book = bookEJB.updateBook(book);
System.out.println("### Book updated : " + book);
System.out.println("Execution succeeded");
}
}
这是persistence.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="chapter06PU" transaction-type="JTA">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<!--<jta-data-source>jdbc/__default</jta-data-source>-->
<jta-data-source>jdbc/chapter06DS</jta-data-source>
<class>org.beginningee6.book.chapter06.Book</class>
<properties>
<property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
<property name="eclipselink.logging.level" value="INFO"/>
</properties>
</persistence-unit>
</persistence>
这是 pom.xml：
<?xml version="1.0" encoding="UTF-8"?>
<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>org.beginningee6.book</groupId>
<artifactId>chapter06</artifactId>
<packaging>jar</packaging>
<version>2.0</version>
<name>Week5</name>
<parent>
<groupId>org.beginningee6.book</groupId>
<artifactId>chapters</artifactId>
<version>2.0</version>
</parent>
<dependencies>
<dependency>
<groupId>org.eclipse.persistence</groupId>
<artifactId>javax.persistence</artifactId>
<version>${javax.persistence-version}</version>
</dependency>
<dependency>
<groupId>org.eclipse.persistence</groupId>
<artifactId>eclipselink</artifactId>
<version>${eclipselink-version}</version>
</dependency>
<dependency>
<groupId>org.glassfish.extras</groupId>
<artifactId>glassfish-embedded-all</artifactId>
<version>${glassfish-version}</version>
</dependency>
</dependencies>
<!--To avoid multiple modules with Maven, here is what you need to manually do (it's not nice, but it works)
1) Comment the following section (maven-jar-plugin), package the jar, and deploy to GlassFish
2) Uncomment the following section, package the jar and run the Main class with app client -->
<build>
<!-- <plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>${plugin-jar-version}</version>
<configuration>
<archive>
<manifest>
<mainClass>org.beginningee6.book.chapter06.Main</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>-->
</build>
</project>
我收到此错误：
Exception in thread "main" java.lang.NullPointerException
在这一行：
book = bookEJB.updateBook(book);
显然 Maven 给出了这个错误：
Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (default-cli) on project chapter06: Command execution failed. Process exited with an error: 1 (Exit value: 1) -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (default-cli) on project chapter06: Command execution failed.
在激活 Maven 的调试选项后，错误前的最后一个命令行是：
Executing command line: C:\Program Files (x86)\Java\jdk1.7.0_21\bin\java.exe -classpath C:\Users\Manuel_Laptop\Desktop\Week5\COIT20227LabSolWeek5\Week5\target\classes;C:\Users\Manuel_Laptop\.m2\repository\org\eclipse\persistence\javax.persistence\2.0.0\javax.persistence-2.0.0.jar;C:\Users\Manuel_Laptop\.m2\repository\org\eclipse\persistence\eclipselink\2.0.1\eclipselink-2.0.1.jar;C:\Users\Manuel_Laptop\.m2\repository\org\glassfish\extras\glassfish-embedded-all\3.0.1-b19\glassfish-embedded-all-3.0.1-b19.jar org.beginningee6.book.chapter06.Main
在浏览了一些课程提示和一些论坛后，我将我的 JAVA_HOME 和 M2_HOME 设置为各自的目录，但没有任何效果。我什至找到了一个链接，指向有人在教科书的同一章（https://getsatisfaction.com/javaee6/topics/yet_another_chapter_6_ejb_problem）看到它在 StackOverflow 中引用后，但在那里找不到任何东西（没有老实说，我不明白）