尝试使用 JPA 连接到 Java 中的 Dockerised DB2 时，实体管理器为空，也使用 maven 和 Open Liberty

Question

所以我正在开发一个 API，我正在尝试使用 JPA 实体管理器从 java 连接到 DB2 的本地 docker 实例。 在运行 Apache Maven 并获得构建成功后，我尝试从 Postman 发出 GET 请求来测试端点并从 DB2 获取所有用户的列表。 我收到以下错误，指出实体管理器为空。 我尝试过在线研究，但似乎无法找到解决方案。 Dao 类与之前使用 Derby 而不是 DB2 的迭代相比几乎没有变化，并且运行良好。 我想知道我哪里出错了，需要改变什么，是否不需要什么。 下面提供的是 xml 文件和包含实体管理器的 DAO java 类。 DB2 的所有属性都是正确的，因为它们与我能够从 Eclipse 的数据库开发中完成的成功连接相比没有改变。 当时使用的驱动程序是 db2jcc4，我认为它与据说用于 maven 依赖项的驱动程序不同，所以不确定这是否是一个问题。

邮差：

错误 500：java.lang.NullPointerException：无法调用“javax.persistence.EntityManager.createNamedQuery(String, java.lang.Class)”，因为“this.em”为空

马文：

[INFO] [ERROR ] CWWJP0015E: org.eclipse.persistence.jpa.PersistenceProvider 持久性提供程序尝试为 jpa-unit 持久性单元创建容器实体管理器工厂时发生错误。 发生以下错误：异常 [EclipseLink-28018] (Eclipse Persistence Services - 2.7.9.v20210604-2c549e2208): org.eclipse.persistence.exceptions.EntityManagerSetupException

[INFO] 异常描述：PersistenceUnit [jpa-unit] 的预部署失败。

[信息] 内部异常：javax.persistence.PersistenceException：CWWJP0013E：服务器找不到 jpa-unit 持久性单元的 java:comp/DefaultDataSource 数据源，因为它遇到以下异常：javax.naming.NameNotFoundException：javax.naming .NameNotFoundException: java:comp/DefaultDataSource。

pom.xml

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  
  <groupId>com.obdoblock</groupId>
  <artifactId>hyperledger-api</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>
  
  <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <!-- Liberty configuration -->
        <liberty.var.default.http.port>3500</liberty.var.default.http.port>
        <liberty.var.default.https.port>9443</liberty.var.default.https.port>
        <liberty.var.app.context.root>api</liberty.var.app.context.root>
        <!-- TestDB Configuration -->
        <version.ibm.db2>11.5.6.0</version.ibm.db2>
    </properties>

    <dependencies>
        <!-- Provided dependencies -->
        <dependency>
            <groupId>jakarta.platform</groupId>
            <artifactId>jakarta.jakartaee-api</artifactId>
            <version>8.0.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.eclipse.microprofile</groupId>
            <artifactId>microprofile</artifactId>
            <version>3.3</version>
            <type>pom</type>
            <scope>provided</scope>
        </dependency>
        <!-- For tests -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>5.6.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-rs-client</artifactId>
            <version>3.3.6</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-rs-extension-providers</artifactId>
            <version>3.3.6</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.eclipse</groupId>
            <artifactId>yasson</artifactId>
            <version>1.0.7</version>
            <scope>test</scope>
        </dependency>
        <!-- DB2 connector -->
        <dependency>
            <groupId>com.ibm.db2</groupId>
            <artifactId>jcc</artifactId>
            <version>11.5.6.0</version>
        </dependency>
        <!-- Hyperledger Fabric Gateway for Blockchain -->
        <dependency>
            <groupId>org.hyperledger.fabric</groupId>
            <artifactId>fabric-gateway-java</artifactId>
            <version>2.2.0</version>
        </dependency>

    </dependencies>

    <build>
        <finalName>${project.artifactId}</finalName>
        <plugins>
            <!-- Enable liberty-maven plugin -->
            <plugin>
                <groupId>io.openliberty.tools</groupId>
                <artifactId>liberty-maven-plugin</artifactId>
                <version>3.3.4</version>
                <configuration>
                    <copyDependencies>
                        <location>${project.build.directory}/liberty/wlp/usr/shared/resources</location>
                        <dependency>
                            <groupId>com.ibm.db2</groupId>
                            <artifactId>jcc</artifactId>
                            <version>11.5.6.0</version>
                        </dependency>
                    </copyDependencies>
                </configuration>
            </plugin>
            <!-- Plugin to run functional tests -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-failsafe-plugin</artifactId>
                <version>2.22.2</version>
                <configuration>
                    <systemPropertyVariables>
                        <http.port>${liberty.var.default.http.port}</http.port>
                        <context.root>${liberty.var.app.context.root}</context.root>
                    </systemPropertyVariables>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.2.3</version>
            </plugin>
            <!-- Plugin to run unit tests -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.2</version>
            </plugin>
        </plugins>
    </build>
</project>

服务器.xml

<server description="Obdoblock REST Server">
    <featureManager>
        <feature>jaxrs-2.1</feature>
        <feature>openapi-3.1</feature>
        <feature>jpa-2.2</feature>
        <feature>cdi-2.0</feature>
    </featureManager>
  
    <httpEndpoint 
        httpPort="${default.http.port}" 
        httpsPort="${default.https.port}"
        id="defaultHttpEndpoint" 
        host="*" 
    />

    <webApplication 
        location="hyperledger-api.war" 
        contextRoot="${app.context.root}"
    />
    
    <!-- DB2 Library Configuration -->
    <library id="DB2JCCLib">
        <fileset dir="${shared.resource.dir}" includes="*.jar" />
    </library>
    
    
    <dataSource jndiName="jdbc/db2">
        <jdbcDriver libraryRef="jdbcLib"/>
        <properties
            databaseName="testdb"
            serverName="localhost" 
            portNumber="50000"
            user="****" password="****"
        />
    </dataSource>
</server>

持久化文件

<?xml version="1.0" encoding="UTF-8"?>
<!-- TODO: This will have to be configured by ENV as well -->
<!-- https://www.eclipse.org/eclipselink/documentation/2.5/jpa/extensions/p_ddl_generation.htm -->
<persistence version="2.2"
    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_2.xsd">
    <persistence-unit name="jpa-unit" transaction-type="JTA">
        <properties>
            <!-- Connection Specific -->
            <property name="hibernate.dialect" value="org.hibernate.dialect.DB2Dialect"/>

            <property name="javax.persistence.jdbc.driver" value="com.ibm.db2.jcc.DB2Driver" />
            <property name="javax.persistence.jdbc.url"    value="jdbc:db2://localhost:50000/testdb" />
            <property name="javax.persistence.jdbc.user" value="****" />
            <property name="javax.persistence.jdbc.password" value="****" />

            <property name="show_sql" value="true"/>
            <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
        </properties>
    </persistence-unit>
</persistence>

用户道

package dao;

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.enterprise.context.RequestScoped;
import models.*;

@RequestScoped
public class UserDao {
    
    @PersistenceContext(name = "jpa-unit")
    private EntityManager em;

    public void createUser(Users user){
        em.persist(user);
    }

    public Users readUser(int userId){
        return em.find(Users.class, userId);
    }

    public List<Users> readAllUsers(){
        return em.createNamedQuery("Users.findAll", Users.class).getResultList();
    }


    public void updateUser(Users user){
        em.merge(user);
    }

    public void deleteUser(Users userId){
        em.remove(userId);
    }

    public List<Users> findUser(String email){
        return em.createNamedQuery("Users.findUser", Users.class)
            .setParameter("email", email)
            .getResultList(); 
    }

    public void createHistory(History hist){
        em.persist(hist);
    }
    //wait this doesnt do anything? 
    public Users readHistory(int id){
        return em.find(Users.class, id);
    }

    public List<History> readAllHistory(){
        return em.createNamedQuery("History.findAll", History.class).getResultList();
    }

}

版本：

• Docker：20.10.8，构建 3967b7d
• DB2：ibm/db2 docker 映像版本 11.5.6
• Maven：3.8.3
• Java：JDK 14.0.2

如果需要更多详细信息，我很乐意提供。 谢谢，迪伦

Answer 1

您的persistence.xml不正确。 它应该指向server.xml配置的数据源，而不是指定驱动程序属性。

像这样：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2"
    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_2.xsd">
    <persistence-unit name="jpa-unit" transaction-type="JTA">
        <jta-data-source>jdbc/guestbookDS</jta-data-source>
        <properties>
            <property name="javax.persistence.schema-generation.database.action" value="create" />
            <property name="javax.persistence.schema-generation.create-database-schemas" value="true" />
            <property name="javax.persistence.schema-generation.scripts.action" value="create" />
            <property name="javax.persistence.schema-generation.scripts.create-target" value="create.ddl"/>  
<!--
            <property name="eclipselink.ddl-generation" value="create-or-extend-tables"/>
            <property name="eclipselink.ddl-generation.output-mode" value="both" />
            -->
        </properties>
    </persistence-unit>
</persistence>

您可以在此处查看这个使用 JPA 和数据库的非常简单的 Liberty 项目https://github.com/stocktrader-ops/db-sat-demo （它使用 PostgreSQL 而不是 DB2，但您应该只使用您的数据源设置）