如果在我自己的方法中发生异常，则使用stax解析器编写XML，然后如何存储或访问以前的数据

Question

在下面的示例中，当我们进入writeOneMoreElement（）方法并发生Exception时，如何访问我们在XML上编写的先前数据。如果writeOneMoreElement（）方法发生异常，我们在这里松开每个条目。

public class xmlSample {
  public static void main(String[] args) {
    XMLOutputFactory factory = XMLOutputFactory.newInstance();
    try {

        XMLStreamWriter writer1 = factory.createXMLStreamWriter(new FileWriter("E:\\sampleXML.xml"));
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        XMLOutputFactory xmlOutputFactory = new WstxOutputFactory();
        XMLStreamWriter2 xtw = (XMLStreamWriter2) new WstxOutputFactory()
                .createXMLStreamWriter(byteArrayOutputStream, "UTF-8");

        xtw.writeStartDocument("UTF-8", "1.1");
        xtw.setPrefix("itm", "http://adt.cmn.xmlns.commons.platform.actiance.com/core/1.0");

        xtw.writeStartElement("document");
        xtw.writeStartElement("data1");
        xtw.writeCharacters("Sagar");
        xtw.writeEndElement();

        XMLStreamWriter2 writer2 = writeOneMoreElement(xtw);

        writer2.writeStartElement("data2");
        writer2.writeCharacters("Shubham");
        writer2.writeEndElement();

        writeOneMoreElement(writer2);

        writer2.writeEndDocument();
        writer2.close();
        xtw.flush();
        xtw.close();

        System.out.println("XML :" + new String(byteArrayOutputStream.toByteArray()));

    } catch (XMLStreamException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

private static XMLStreamWriter2 writeOneMoreElement(XMLStreamWriter2 writer2)
        throws XMLStreamException, IOException {

    try {
        writer2.writeStartElement("ABC");
        writer2.writeStartElement("data2");
        writer2.writeAttribute("name2", "value2");
        writer2.writeAttribute("otherAttribute", "true");
        writer2.writeEndElement();

        writer2.writeStartElement("data3");
        writer2.writeAttribute("name3", "value3");
        writer2.writeAttribute("otherAttribute", "true");
        writer2.writeEndElement();

        writer2.writeEndElement();

        writer2.flush();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return writer2;
 }
}

Answer 1

Exceptions的一个规则是，无论哪一行抛出异常，之后的所有行都将在您到达catch和finally块之前执行。因此，此行System.out.println("XML :" + new String(byteArrayOutputStream.toByteArray()));永远不会执行，但在程序结束之前，byteArrayOutputStream中的值仍然可用。

一种可能的解决方案是再次在println()块中运行相同的catch方法。像这样：

public static void main(String[] args) {
    XMLOutputFactory factory = XMLOutputFactory.newInstance();
    //Initializing the ByteArrayOutputStream outside the try block, so that it is still available after that scope.
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    try {

        XMLStreamWriter writer1 = factory.createXMLStreamWriter(new FileWriter("E:\\sampleXML.xml"));
        //ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        XMLOutputFactory xmlOutputFactory = new WstxOutputFactory();
        XMLStreamWriter2 xtw = (XMLStreamWriter2) new WstxOutputFactory()
                .createXMLStreamWriter(byteArrayOutputStream, "UTF-8");

        xtw.writeStartDocument("UTF-8", "1.1");
        xtw.setPrefix("itm", "http://adt.cmn.xmlns.commons.platform.actiance.com/core/1.0");

        xtw.writeStartElement("document");
        xtw.writeStartElement("data1");
        xtw.writeCharacters("Sagar");
        xtw.writeEndElement();

        XMLStreamWriter2 writer2 = writeOneMoreElement(xtw);

        writer2.writeStartElement("data2");
        writer2.writeCharacters("Shubham");
        writer2.writeEndElement();

        //Exception thrown here
        writeOneMoreElement(writer2);

        //Unexecuted code from here onwards
        writer2.writeEndDocument();
        writer2.close();
        xtw.flush();
        xtw.close();

        System.out.println("XML :" + new String(byteArrayOutputStream.toByteArray()));

    } catch (XMLStreamException e) {
        e.printStackTrace();
        /*Proof of concept. This line will print out all the values inserted into the ByteArrayOutputStream up to
        the point where the Exception was thrown.*/
        System.out.println("XML :" + new String(byteArrayOutputStream.toByteArray()));
    } catch (IOException e) {
        e.printStackTrace();
    }

}

private static XMLStreamWriter2 writeOneMoreElement(XMLStreamWriter2 writer2)
        throws XMLStreamException/*, IOException*/ {
    //By the way, why does this method throw IOException? It's unnecessary, and you can remove it.
    try {
        writer2.writeStartElement("ABC");
        writer2.writeStartElement("data2");
        writer2.writeAttribute("name2", "value2");
        writer2.writeAttribute("otherAttribute", "true");
        writer2.writeEndElement();

        writer2.writeStartElement("data3");
        writer2.writeAttribute("name3", "value3");
        writer2.writeAttribute("otherAttribute", "true");
        writer2.writeEndElement();

        writer2.writeEndElement();

        writer2.flush();
        //I'm throwing an Exception here on purpose to trigger the catch block.
        throw new XMLStreamException();
    }       
    catch (Exception e) {
        e.printStackTrace();
        // I'm rethrowing the Exception on purpose.
        throw e;
    } 
    //This line won't work for now, but you can change it back.
    //return writer2;
 }

运行该程序，您将获得预期的XMLStreamException以及不完整的数据。

XML :<?xml version='1.1' encoding='UTF-8'?><document><data1>Sagar</data1><ABC><data2 name2="value2" otherAttribute="true" /><data3 name3="value3" otherAttribute="true" /></ABC>