“线程中的异常”；“主要”；使用Jaxb解组/封送时的java.lang.NullPointerException

我使用JAXB将给定的输入Xml文件解组到Java对象中 然后将其还原为Xml字符串。 我的Xml文件如下所示：

<bpmn2:definitions xmlns:bpmn2="http://www.omg.org/spec/BPMN/20100524/MODEL" id="_Definitions_1">
    <bpmn2:process id="_500441" name="process">
    </bpmn2:process>
</bpmn2:definitions>

进程。类：

@XmlRootElement(namespace = "http://www.omg.org/spec/BPMN/20100524/MODEL")
public class Definitions {
    @XmlAttribute
    private String id;

    @XmlElement(name = "bpmn2:process")
    private Process process;

    @XmlElement(name = "bpmndi:BPMNDiagram")
    private Diagram diagram;

    public Definitions() {
    }
    public Definitions(String id, Process process, Diagram diagram) {
        this.id = id;
        this.process = process;
        this.diagram = diagram;
    }
    public Process getProcess() {
        return process;
    }
    public Diagram getDiagram() {
        return diagram;
    }
    public String getId() {
        return id;
    }
}

@XmlAccessorType(XmlAccessType.FIELD)
public class Process {
    @XmlAttribute
    private String id;
    public Process() {
    }
    public Process(String id) {
        this.id = id;
    }
    public String getId() {
        return id;
    }
}

public class Model {
    @XmlElement
    private Process process;
    public Model() {
    }
    public Model(String processId, Process p) {
        this.id = processId;
        this.process = p;
    }
}

public static void main(String[] args) throws IOException, JSONException, JAXBException {
        BpmnToJsonImport bj = new BpmnToJsonImport();
        InputStream is = BpmnToJsonImport.class.getResourceAsStream("myXml.txt");
        String Str = IOUtils.toString(is);
        StringReader sr = new StringReader(Str);
        JAXBContext context = JAXBContext.newInstance(Definitions.class, Model.class);
        Unmarshaller unmarshaller = context.createUnmarshaller();

        Definitions d = (Definitions) unmarshaller.unmarshal(sr);
        Model model = new Model(d.getProcess().getId(), d.getProcess());

        StringWriter sw = new StringWriter();

        Marshaller marshaller = context.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
        marshaller.marshal(model, sw);
        String str = sw.toString();
        System.out.println(str);

    }

型号。类别：

@XmlRootElement(namespace = "http://www.omg.org/spec/BPMN/20100524/MODEL")
public class Definitions {
    @XmlAttribute
    private String id;

    @XmlElement(name = "bpmn2:process")
    private Process process;

    @XmlElement(name = "bpmndi:BPMNDiagram")
    private Diagram diagram;

    public Definitions() {
    }
    public Definitions(String id, Process process, Diagram diagram) {
        this.id = id;
        this.process = process;
        this.diagram = diagram;
    }
    public Process getProcess() {
        return process;
    }
    public Diagram getDiagram() {
        return diagram;
    }
    public String getId() {
        return id;
    }
}

@XmlAccessorType(XmlAccessType.FIELD)
public class Process {
    @XmlAttribute
    private String id;
    public Process() {
    }
    public Process(String id) {
        this.id = id;
    }
    public String getId() {
        return id;
    }
}

public class Model {
    @XmlElement
    private Process process;
    public Model() {
    }
    public Model(String processId, Process p) {
        this.id = processId;
        this.process = p;
    }
}

public static void main(String[] args) throws IOException, JSONException, JAXBException {
        BpmnToJsonImport bj = new BpmnToJsonImport();
        InputStream is = BpmnToJsonImport.class.getResourceAsStream("myXml.txt");
        String Str = IOUtils.toString(is);
        StringReader sr = new StringReader(Str);
        JAXBContext context = JAXBContext.newInstance(Definitions.class, Model.class);
        Unmarshaller unmarshaller = context.createUnmarshaller();

        Definitions d = (Definitions) unmarshaller.unmarshal(sr);
        Model model = new Model(d.getProcess().getId(), d.getProcess());

        StringWriter sw = new StringWriter();

        Marshaller marshaller = context.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
        marshaller.marshal(model, sw);
        String str = sw.toString();
        System.out.println(str);

    }

主要方法：

@XmlRootElement(namespace = "http://www.omg.org/spec/BPMN/20100524/MODEL")
public class Definitions {
    @XmlAttribute
    private String id;

    @XmlElement(name = "bpmn2:process")
    private Process process;

    @XmlElement(name = "bpmndi:BPMNDiagram")
    private Diagram diagram;

    public Definitions() {
    }
    public Definitions(String id, Process process, Diagram diagram) {
        this.id = id;
        this.process = process;
        this.diagram = diagram;
    }
    public Process getProcess() {
        return process;
    }
    public Diagram getDiagram() {
        return diagram;
    }
    public String getId() {
        return id;
    }
}

@XmlAccessorType(XmlAccessType.FIELD)
public class Process {
    @XmlAttribute
    private String id;
    public Process() {
    }
    public Process(String id) {
        this.id = id;
    }
    public String getId() {
        return id;
    }
}

public class Model {
    @XmlElement
    private Process process;
    public Model() {
    }
    public Model(String processId, Process p) {
        this.id = processId;
        this.process = p;
    }
}

public static void main(String[] args) throws IOException, JSONException, JAXBException {
        BpmnToJsonImport bj = new BpmnToJsonImport();
        InputStream is = BpmnToJsonImport.class.getResourceAsStream("myXml.txt");
        String Str = IOUtils.toString(is);
        StringReader sr = new StringReader(Str);
        JAXBContext context = JAXBContext.newInstance(Definitions.class, Model.class);
        Unmarshaller unmarshaller = context.createUnmarshaller();

        Definitions d = (Definitions) unmarshaller.unmarshal(sr);
        Model model = new Model(d.getProcess().getId(), d.getProcess());

        StringWriter sw = new StringWriter();

        Marshaller marshaller = context.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
        marshaller.marshal(model, sw);
        String str = sw.toString();
        System.out.println(str);

    }

当它尝试使用d.getProcess.getId检索进程id时，我得到

---

java.lang.NullPointerException您映射的名称空间限定不正确。不能在元素名称中包含前缀

@XmlElement(name = "BPMNDiagram")
private Diagram diagram;

要映射名称空间限定，可以使用包级别的

@XmlSchema

注释

package info.java

@XmlSchema( 
    namespace =  "http://www.omg.org/spec/BPMN/20100524/MODEL",
    elementFormDefault = XmlNsForm.QUALIFIED) 
package example;

import javax.xml.bind.annotation.XmlNsForm;
import javax.xml.bind.annotation.XmlSchema;

了解更多信息

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尝试为XML文件使用完全限定路径。例如：C:\MyFolder\myXml.txt可能是找不到myXml.txt。如果找到，可能是您的“Process.class”没有“name”字段？问题不在于文件，因为当我这样做时：System.out.println（d.getId（））它给了我bpmn2:definitions的id。我不需要这个名字，你有很多问题。java不编译，而且您还没有提供Diagram类。通过从definitions.class中删除“bpmn2”命名空间限定符，我能够克服您的错误，因此我可以说您在某个地方有注释错误。我按照您的建议解决了流程指定命名空间的问题，但对于BPMNDiagram，我得到了相同的错误，我必须使用另一个命名空间“”。我尝试了这种方法@XmlSchema（namespace=“”，elementFormDefault=XmlNsForm.QUALIFIED，xmlns={@javax.xml.bind.annotation.xmlns（prefix=“bpmn2”，namespaceURI=“”），@javax.xml.bind.annotation.xmlns（prefix=“bpmndi”，namespaceURI=“）}，但它不起作用