MOXy XPath解组元素为null

分类：编程问答

如何解决MOXy XPath解组元素为null

我试图使用XPath跳过camunda：property元素到List中，以跳过不必要的包装器元素。不幸的是，我的propertyList始终为null。这位于任务类中。任何帮助将不胜感激。

编辑＃1： 我遵循了以下链接，该链接本来可以帮助解决我的问题，但没有成功。 http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html是官方指南。显然，maven pom.xml文件存在一些挑战。我怀疑问题出在pom文件中。 我遵循了本指南https://www.javacodegeeks.com/2012/07/eclipselink-moxy-as-jaxb-provider.html，但仍然没有使它起作用。

pom.xml文件

<?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.example</groupId>
    <artifactId>BPMN-Marshaller</artifactId>
    <version>1.0-SNAPSHOT</version>
    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <repositories><repository>
        <id>EclipseLink Repo</id>
        <url>http://download.eclipse.org/rt/eclipselink/maven.repo</url>
        <name>EclipseLink Repo</name>
    </repository></repositories>
    <dependencies>
        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>org.eclipse.persistence.moxy</artifactId>
            <version>3.0.0-M1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.3</version>
        </dependency>
        <!-- Runtime,com.sun.xml.bind module -->
        <dependency>
            <groupId>org.glassfish.jaxb</groupId>
            <artifactId>jaxb-runtime</artifactId>
            <version>2.3.2</version>
        </dependency>
        <dependency>
            <groupId>jakarta.xml.bind</groupId>
            <artifactId>jakarta.xml.bind-api</artifactId>
            <version>2.3.2</version>
        </dependency>
    </dependencies>

</project>

jaxb.properties文件与我的Java类位于相同的包和文件夹中（请参见带有名称“项目结构”的附件图像）

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

package-info.java文件

@XmlSchema(namespace="http://www.omg.org/spec/BPMN/20100524/MODEL",elementFormDefault=XmlNsForm.QUALIFIED,xmlns = {@XmlNs(prefix="bpmn",namespaceURI="http://www.omg.org/spec/BPMN/20100524/MODEL"),@XmlNs(prefix = "camunda",namespaceURI = "http://camunda.org/schema/1.0/bpmn")})

package bpmn;

import javax.xml.bind.annotation.*;

xml文件片段

<?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:camunda="http://camunda.org/schema/1.0/bpmn" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" id="Definitions_13d3a6z" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="4.1.1">
  <bpmn:process id="Process_1tovjba" isExecutable="true">
    <bpmn:startEvent id="StartEvent_1">
      <bpmn:outgoing>Flow_06i118e</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:task id="Activity_1d3friu" name="Task 1">
      <bpmn:extensionElements>
        <camunda:properties>
          <camunda:property name="start_date" value="01-04-2018" />
          <camunda:property name="duration" value="5" />
        </camunda:properties>
      </bpmn:extensionElements>
      <bpmn:incoming>Flow_06i118e</bpmn:incoming>
      <bpmn:outgoing>Flow_0linmbs</bpmn:outgoing>
    </bpmn:task>

定义类

@XmlRootElement
public class Definitions {

 private String id;
 private Process process;



    public Definitions(){};
    public Definitions(String id,Process process){
        super();
        this.id = id;
        this.process = process;
    }

    @XmlAttribute
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @XmlElement
    public Process getProcess() {
        return process;
    }

    public void setProcess(Process process) {
        this.process = process;
    }

    @Override
    public String toString(){
        return "Definitions [id23=" + id + ",process=23499999999999999" + process + "]";
    }

}

进程类

public class Process {

    private String id;
    private List<Task> taskList;
    private List<SequenceFlow> sequenceFlowList;

    public Process(){};
    public Process(String id,List<Task> taskList,List<SequenceFlow> sequenceFlowList){
        super();
        this.id = id;
        this.taskList = taskList;
        this.sequenceFlowList = sequenceFlowList;
    }

    @XmlAttribute
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @XmlElement(name = "task")
    public List<Task> getTaskList() {
        return taskList;
    }

    public void setTaskList(List<Task> taskList) {
        this.taskList = taskList;
    }

    @XmlElement(name = "sequenceFlow")
    public List<SequenceFlow> getSequenceFlowList() {
        return sequenceFlowList;
    }

    public void setSequenceFlowList(List<SequenceFlow> sequenceFlowList) {
        this.sequenceFlowList = sequenceFlowList;
    }
}

任务类

public class Task {

    private String id;
    private String name;
    private List<Property> propertyList;

    public Task(){}
    public Task(String id,String name,List<Property> propertyList){
        super();
        this.id = id;
        this.name = name;
        this.propertyList = propertyList;
    }

    @XmlAttribute
    @JsonProperty("text")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlAttribute
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @XmlElement(name = "property")
    @XmlPath("bpmn:extensionElements/camunda:properties/camunda:property")
    public List<Property> getPropertyList() {
        return propertyList;
    }

    public void setPropertyList(List<Property> propertyList) {
        this.propertyList = propertyList;
    }
}

属性类

public class Property {

    private String name;
    private String value;

    public Property(){}
    public Property(String name,String value) {
        super();
        this.name = name;
        this.value = value;
    }

    @XmlAttribute
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlAttribute
    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

主类

public class XMLToObject {
    public static void main(String[] args) {

        try {

            File file = new File("process.bpmn");
            JAXBContext jaxbContext = JAXBContext.newInstance(Definitions.class);
            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
            Definitions definitions = (Definitions) jaxbUnmarshaller.unmarshal(file);
            System.out.println(definitions.getProcess().getTaskList().get(0).getPropertyList());

        } catch (JAXBException e) {
            e.printStackTrace();
        }


    }
}

Project Structure

解决方法

我对您的方法进行了以下更改，并且能够从您的XML文件访问duration和start_date属性数据。

顺便说一下，我正在使用OpenJDK 14。但是这种方法也可以在版本8中运行。

我正在使用的POM具有以下依赖性：

        <dependency>
            <groupId>com.sun.activation</groupId>
            <artifactId>javax.activation</artifactId>
            <version>1.2.0</version>
        </dependency>

        <!-- 
             Use 2.3.1 below to prevent "illegal 
             reflective access operation" warnings.
        -->
        <dependency>
            <groupId>javax.xml.bind</groupId>
            <artifactId>jaxb-api</artifactId>
            <version>2.3.1</version>
        </dependency>

        <dependency>
            <groupId>com.sun.xml.bind</groupId>
            <artifactId>jaxb-core</artifactId>
            <version>2.3.0.1</version>
        </dependency>

        <dependency>
            <groupId>com.sun.xml.bind</groupId>
            <artifactId>jaxb-impl</artifactId>
            <version>2.3.1</version>
        </dependency>

        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>eclipselink</artifactId>
            <version>2.7.6</version>
        </dependency>

（为此测试，我跳过了Jackson的依赖关系。）

我还在POM的末尾添加了以下部分，以处理属性文件：

    <!-- to copy the jaxb.properties file to its class package: -->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <excludes>
                    <exclude>**/*.java</exclude>
                </excludes>
            </resource>
        </resources>
    </build>

这可确保将属性文件及其相关的类文件部署到正确的位置。

我添加了代码以检查正在使用哪个JAXB提供程序-只是肯定的确认：

    private void checkProvider() throws JAXBException {
        JAXBContext jc = JAXBContext.newInstance(Definitions.class);

        String jaxbContextImpl = jc.getClass().getName();
        if(MOXY_JAXB_CONTEXT.equals(jaxbContextImpl)) {
            System.out.println("EclipseLink MOXy");
        } else if(METRO_JAXB_CONTEXT.equals(jaxbContextImpl)) {
            System.out.println("Metro");
        } else {
            System.out.println("Other");
        }
    }

我修改了代码以遍历属性数据，以显式打印最终的属性值：

List<Property> props = definitions.getProcess().getTaskList().get(0).getPropertyList();
props.forEach(prop -> {
    System.out.println(prop.getName() + " - " + prop.getValue());
});
//System.out.println(definitions.getProcess().getTaskList().get(0).getPropertyList());

结果输出为：

EclipseLink MOXy
start_date - 01-04-2018
duration - 5

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