如何在HierarchicalStreamReader转换器中使用xml标记获取xml元素的值

时间：2019-06-20 11:46:25

标签： java spring-boot spring-batch xstream

我正在尝试使用spring batch将XML解析为Java对象，并且我将HierarchicalStreamReader用作转换器来解析并将XML标记中的对象值转换为POJO字段。但是，在进行转换时，我必须使用moveup（）和moveDown（）方法来解析数据，我认为这不是遵循的好习惯，因为如果XML标记中的字段位置发生更改，则会导致代码重写。我已经尝试过getAttribute（String name）方法，以使用其标记名来实现对我要获取的参数的更多控制，但是这给了我我无法修复的错误。

此外，该接口没有足够的文档。请帮助我解决这个问题，或建议我采用一种受控转换器的方法。预先感谢...

Student.xml 

<students>
    <student>
        <name>Tony Tester</name>
        <rollNo>1</rollNo>
        <enrollmentDate>2016-10-31</enrollmentDate>
        <sampleTimeStamp>2016-11-07T05:50:45</sampleTimeStamp>
        <salary>16.57</salary>
    </student>
    <student>
        <name>Nick Newbie</name>
        <rollNo>2</rollNo>
        <enrollmentDate>2017-10-31</enrollmentDate>
        <sampleTimeStamp>2016-11-07T05:50:45</sampleTimeStamp>
        <salary>29.68</salary>
    </student>
    <student>
        <name>Ian Intermediate</name>
        <rollNo>3</rollNo>
        <enrollmentDate>2018-10-31</enrollmentDate>
        <sampleTimeStamp>2016-11-07T05:50:45</sampleTimeStamp>
        <salary>789.62</salary>
    </student>
</students>

StudentDTO.java 

@XmlRootElement(name="student")
public class StudentDTO 
{
    private String name;
    private Integer rollNo;    
    private Date enrollmentDate;
    private Date sampleTimeStamp;
    private BigDecimal salary;
    ... getter, setter and constructor
}

StudentConverter.java 

public class StudentConverter implements Converter
{

    @Override
    public boolean canConvert(@SuppressWarnings("rawtypes") Class type) 
    {
        return type.equals(StudentDTO.class);
    }

    @Override
    public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) 
    {
        // Nothing to marshal
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) 
    {
        //reader.getAttribute(0) -- line causing error
                //reader.getAttribute("name") -- return null
                //reader.getAttributeCount() -- always return 0
        reader.moveDown();      
        StudentDTO student = new StudentDTO();
        student.setName(reader.getValue());

        reader.moveUp();
        reader.moveDown();
        student.setRollNo(Integer.parseInt(reader.getValue()));

        reader.moveUp();
        reader.moveDown();
        try 
        {
            student.setEnrollmentDate(new SimpleDateFormat("yyyy-MM-dd").parse(reader.getValue()));
        } 
        catch (ParseException e) 
        {
            e.printStackTrace();
        }

        reader.moveUp();
        reader.moveDown();
        try 
        {
            student.setSampleTimeStamp(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss").parse(reader.getValue()));
        }
        catch (ParseException e) 
        {
            e.printStackTrace();
        }

        reader.moveUp();
        reader.moveDown();
        student.setSalary(new BigDecimal(reader.getValue()));

        return student;
    }

}

用于reader.getAttribute（0）的StackTrace 

java.lang.IllegalArgumentException
    at org.springframework.util.xml.XMLEventStreamReader.getAttribute(XMLEventStreamReader.java:211)
    at org.springframework.util.xml.XMLEventStreamReader.getAttributeValue(XMLEventStreamReader.java:192)
    at com.thoughtworks.xstream.io.xml.StaxReader.getAttribute(StaxReader.java:92)
    at com.thoughtworks.xstream.io.ReaderWrapper.getAttribute(ReaderWrapper.java:56)
    at com.example.demo.utility.StudentConverter.unmarshal(StudentConverter.java:33)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:70)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
    at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1230)
    at org.springframework.oxm.xstream.XStreamMarshaller.doUnmarshal(XStreamMarshaller.java:826)
    at org.springframework.oxm.xstream.XStreamMarshaller.unmarshalXmlStreamReader(XStreamMarshaller.java:786)
    at org.springframework.oxm.xstream.XStreamMarshaller.unmarshalXmlEventReader(XStreamMarshaller.java:777)
    at org.springframework.oxm.support.AbstractMarshaller.unmarshalStaxSource(AbstractMarshaller.java:411)
    at org.springframework.oxm.support.AbstractMarshaller.unmarshal(AbstractMarshaller.java:354)
    at org.springframework.batch.item.xml.StaxEventItemReader.doRead(StaxEventItemReader.java:255)
    at org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader.read(AbstractItemCountingItemStreamItemReader.java:92)
    at org.springframework.batch.item.support.SynchronizedItemStreamReader.read(SynchronizedItemStreamReader.java:55)
    at org.springframework.batch.item.support.SynchronizedItemStreamReader$$FastClassBySpringCGLIB$$987ea09.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:136)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:124)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
    at org.springframework.batch.item.support.SynchronizedItemStreamReader$$EnhancerBySpringCGLIB$$66d53b5e.read(<generated>)
    at org.springframework.batch.core.step.item.SimpleChunkProvider.doRead(SimpleChunkProvider.java:94)
    at org.springframework.batch.core.step.item.SimpleChunkProvider.read(SimpleChunkProvider.java:161)
    at org.springframework.batch.core.step.item.SimpleChunkProvider$1.doInIteration(SimpleChunkProvider.java:119)
    at org.springframework.batch.repeat.support.RepeatTemplate.getNextResult(RepeatTemplate.java:375)
    at org.springframework.batch.repeat.support.RepeatTemplate.executeInternal(RepeatTemplate.java:215)
    at org.springframework.batch.repeat.support.RepeatTemplate.iterate(RepeatTemplate.java:145)
    at org.springframework.batch.core.step.item.SimpleChunkProvider.provide(SimpleChunkProvider.java:113)
    at org.springframework.batch.core.step.item.ChunkOrientedTasklet.execute(ChunkOrientedTasklet.java:69)
    at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:407)
    at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:331)
    at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140)
    at org.springframework.batch.core.step.tasklet.TaskletStep$2.doInChunkContext(TaskletStep.java:273)
    at org.springframework.batch.core.scope.context.StepContextRepeatCallback.doInIteration(StepContextRepeatCallback.java:82)
    at org.springframework.batch.repeat.support.TaskExecutorRepeatTemplate$ExecutingRunnable.run(TaskExecutorRepeatTemplate.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

[注意]：：我尝试使用以下属性进行调试：

reader.getAttribute(0)-引发错误

reader.getAttribute("name")-返回null

reader.getAttributeCount()-始终返回0

我不确定为什么reader.getAttributeCount（）返回零，因为每个学生条目有5个字段。

我想要做的是对StudentConverter.unmarshal部分进行更多控制，我想通过属性名称或标识符来获取属性值，而不是通过xml中的位置来获取属性值，因为位置是动态的，以后可能会更改。

1 个答案:

答案 0 :(得分：0)

从XML的角度来看，当您拥有 > uncenter.distance(matrix(1:6,nrow=2)) [,1] [,2] [1,] -0.3163105 -0.3591645 [2,] -0.3591645 -0.4142136 之类的内容时，<a b="...">...</a>是一个元素，而a是一个属性。

您的XML没有任何属性。这就是为什么b的值为零，而.getAttributeCount()的例外。

实现所需目标的一种常用方法是使用杰克逊（Jackson）这样的工具，并根据需要的输入和输出使用相关的配置/注释来匹配每个字段。有关如何处理的基本说明，请参见here。

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