Question

我目前正在尝试使用JAXB将一些XML解组为java对象，并且我得到一个奇怪的Null指针异常。解组时这只是一个问题。我可以和这些课程一起训练。以下是相关的代码片段（不相关的部分用“......”表示）：

JAXB Root元素：

...
@XmlRootElement(name="assets")
public class Assets {
    String product;
    Images images = new Images();

    ...

    Public Assets() {}

    ...

    public String getProduct() { return this.product; }

    @XmlAttribute(name="product")
    public void setProduct(String newProduct) { this.product = newProduct; }

    public Images getImages() { return this.images; }

    @XmlElement(name="images")
    public void setImages(Images newImages) { this.images = newImages; }

    ...
}

根元素的Images子元素：

...
@XmlRootElement(name="images")
@XmlSeeAlso(Image.class)
@XmlType(propOrder = {"mainAsset", "image"})
public class Images {
    List<Image> images;
    Image mainAsset;

    private static char counter = 'a';
    private static final String prefix = "product-image-";

    // Here's the part that causes the NPE
    @XmlAnyElement(lax=true)
    public List<JAXBElement<Image>> getImage() {
        final List<JAXBElement<Image>> imageList = new ArrayList<JAXBElement<Image>>();
        for (final Image g : this.images) {
            imageList.add(new JAXBElement(new QName(prefix + counter++), Image.class, g));
        }
        counter = 'a';
        return imageList;
    }

    @XmlElement(name="renditions")
    public void setImage(List<Image> newImages) { this.images = newImages; }

    public Image getMainAsset() { return this.mainAsset; }

    @XmlElement(name="main-asset-name")
    public void setMainAsset(Image newMainAsset) { this.mainAsset = newMainAsset; }
}

解组XML的逻辑：

...
public void modifyXML() {
try {
    JAXBContext context = JAXBContext.newInstance(Assets.class, Images.class, Image.class);
    Unmarshaller um = context.createUnmarshaller();
    File f = new File("/path/to/my.xml");
    Assets assets = (Assets) um.unmarshal(f);
    ...
} catch (JAXBException e) {
    e.printStackTrace();
}
}
...

最后，我试图解组的XML（可能有助于知道这个xml文件实际上是使用JAXB marshaller生成的，它运行没有任何问题）：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assets product="TEST PRODUCT">
    <images>
        <main-asset-name>
            <path>stuff.jpg</path>
            <title>theTitle</path>
            <alt>theAlt</path>
            <description>theDescription</description>
        </main-asset-name>
        <product-image-a>
            <path>48x48.jpg</path>
            <title>theTitle</path>
            <alt>theAlt</path>
            <description>theDescription</description>
        </product-image-a>
        <product-image-b>
            <path>140x140.jpg</path>
            <title>theTitle</path>
            <alt>theAlt</path>
            <description>theDescription</description>
        </product-image-b>
        <product-image-c>
            <path>1280x1280.jpg</path>
            <title>theTitle</path>
            <alt>theAlt</path>
            <description>theDescription</description>
        </product-image-c>
        <product-image-d>
            <path>319x319.jpg</path>
            <title>theTitle</path>
            <alt>theAlt</path>
            <description>theDescription</description>
        </product-image-d>
    </images>
</assets>

好的，这就是所有相关代码（我认为）。当我运行我的程序时，我在调用unmarshaller之后立即收到以下错误：

java.lang.NullPointerException
    at com.my.companys.name.Images.getImage(Images.java:25)

引用的行号是for循环在我的Images.java类文件中开始的行。

有没有人知道为什么this.images可能在这里为空？任何帮助是极大的赞赏。提前谢谢。

Answer 1

这是我一直在使用的解决方案。这是一个黑客攻击，但地狱......它完成了这项工作。

首先，我将原始xml作为字符串而不是将其作为文件读取：

public void modifyXML() {
    try {
        JAXBContext context = JAXBContext.newInstance(Assets.class, Image.class);
        Unmarshaller um = context.createUnmarshaller();
        // This xml should be formatted in a way that JAXB can work with
        String rawXML = getRawXML("/path/to/my.xml");
        // Hand the modified xml to the unmarshaller
        Assets umAssets = (Assets) um.unmarshal(new StreamSource(new StringReader(rawXML)));
        // Do stuff with umAssets
        ...
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private String getRawXML(String path) throws IOException {
    String xml = readFile(path, StandardCharsets.UTF_8);
    // This should make it so JAXB can handle the xml properly
    xml = xml.replaceAll("<main-asset-name>", "<image>");
    xml = xml.replaceAll("</main-asset-name>", "</image>");
    xml = xml.replaceAll("<product-image.*>", "<image>");
    return xml.replaceAll("</product-image.*>", "</image>");
}

private String readFile(String path, Charset encoding) throws IOException {
    // A simple file reader
    byte[] encoded = Files.readAllBytes(Paths.get(path));
    return new String(encoded, encoding);
}

这似乎可以解决问题，所以我现在要使用它。当然，如果有人有解决方案，我仍然愿意接受更好的解决方案。

使用@XmlAnyElement批注解组XML时出现空指针异常

1 个答案: