JAXB编组，忽略nillable
JAXB编组，忽略nillable
提问于 2016-08-29 18:34:25
我有一个带有带注释nillable=true的变量的类，我不希望它们出现在xml中。这个类是从一个不能修改的xsd生成的。
例如:一个类看起来像这样：
public class Hi {
...
@XmlElement(name = "hello", nillable = true)
protected Long hello;
...
}该对象使用JAXBContext创建的编组程序进行编组。生成的xml变成：
...
<hello xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
...类Hi是从不能更改的xsd生成的。我的问题是，如果"hello“为null，有没有办法让编组程序忽略nillable参数，并且不向xml输出任何内容？
Stack Overflow用户
回答已采纳
发布于 2016-09-01 19:07:31
多亏了Nicolas Filotto，我成功地让它根据我的需要工作，下面是xmlstreamwriter的最终代码(DelegateXMLStreamWriter只是将调用传递给输入委托)：
注意:这仍将打印非空的nillable元素，但不会向这些元素写入任何属性或名称空间。我还没有测试如果父级是nillable但子级是设置的，它是否有效。
public class XMLExportStreamWriter extends DelegateXMLStreamWriter {
private Set<String> nillableElements;
private final Stack<String> path = new Stack<>();
private boolean nillable;
private boolean notNull;
private String localName;
private String namespaceURI;
private String prefix;
public XMLExportStreamWriter(XMLStreamWriter delegate) throws XMLStreamException {
super.setDelegate(delegate);
}
public void setNillableElements(Set<String> nillableElements) {
this.nillableElements = nillableElements;
}
@Override
public void writeStartElement(String localName) throws XMLStreamException {
if (!isNillable(localName)) {
super.writeStartElement(localName);
} else {
setElementArgs(null, localName, null);
}
}
@Override
public void writeStartElement(String namespaceURI, String localName) throws XMLStreamException {
if (!isNillable(localName)) {
super.writeStartElement(namespaceURI, localName);
} else {
setElementArgs(null, localName, namespaceURI);
}
}
@Override
public void writeStartElement(String prefix, String localName, String namespaceURI)
throws XMLStreamException {
if (!isNillable(localName)) {
super.writeStartElement(prefix, localName, namespaceURI);
} else {
setElementArgs(prefix, localName, namespaceURI);
}
}
@Override
public void writeEndElement() throws XMLStreamException {
if (!this.nillable || this.notNull) {
super.writeEndElement();
}
this.path.pop();
if (this.nillable) {
this.nillable = this.nillableElements.contains(toPath());
}
}
@Override
public void writeCharacters(String text) throws XMLStreamException {
if (this.nillable) {
if (text != null) {
this.notNull = true;
forceStartElement();
super.writeCharacters(text);
}
} else {
super.writeCharacters(text);
}
}
@Override
public void writeCharacters(char[] text, int start, int len) throws XMLStreamException {
if (this.nillable) {
if (text != null) {
this.notNull = true;
forceStartElement();
super.writeCharacters(text, start, len);
}
} else {
super.writeCharacters(text, start, len);
}
}
@Override
public void writeAttribute(String localName, String value) throws XMLStreamException {
if (!this.nillable) {
super.writeAttribute(localName, value);
}
}
@Override
public void writeAttribute(String namespaceURI, String localName, String value)
throws XMLStreamException {
if (!this.nillable) {
super.writeAttribute(namespaceURI, localName, value);
}
}
@Override
public void writeAttribute(String prefix, String namespaceURI, String localName, String value)
throws XMLStreamException {
if (!this.nillable) {
super.writeAttribute(prefix, namespaceURI, localName, value);
}
}
@Override
public void writeNamespace(String prefix, String namespaceURI) throws XMLStreamException {
if (!this.nillable) {
super.writeNamespace(prefix, namespaceURI);
}
}
private void forceStartElement() throws XMLStreamException {
if (this.prefix != null) {
super.writeStartElement(this.prefix, this.localName, this.namespaceURI);
} else if (this.namespaceURI != null) {
super.writeStartElement(this.namespaceURI, this.localName);
} else {
super.writeStartElement(this.localName);
}
}
private boolean isNillable(String localName) {
this.notNull = false;
this.path.push(localName);
this.nillable = this.nillableElements.contains(toPath());
return this.nillable;
}
private void setElementArgs(String prefix, String localName, String namespaceURI) {
this.prefix = prefix;
this.localName = localName;
this.namespaceURI = namespaceURI;
}
private String toPath() {
StringBuilder sb = new StringBuilder();
boolean first = true;
for (String element : this.path) {
if (first) {
first = false;
} else {
sb.append('/');
}
sb.append(element);
}
return sb.toString();
}
}我还修改了路径以跳过将集合考虑在内的方法：
private static Set<String> pathsToSkip(Class<?> clazz) {
// Make sure that the class is annotated with XmlRootElement
XmlRootElement rootElement = clazz.getAnnotation(XmlRootElement.class);
if (rootElement == null) {
throw new IllegalArgumentException("XmlRootElement is missing");
}
// Create the root name from the annotation or from the class name
String rootName = ("##default".equals(rootElement.name()) ?
clazz.getSimpleName().substring(0, 1).toLowerCase() + clazz.getSimpleName().substring(1) :
rootElement.name());
// Set that will contain all the paths
Set<String> pathsToSkip = new HashSet<>();
addPathsToSkip(rootName, clazz, pathsToSkip);
return pathsToSkip;
}
private static void addPathsToSkip(String parentPath, Class<?> clazz,
Set<String> pathsToSkip) {
// Iterate over all the fields
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
XmlElement xmlElement = field.getAnnotation(XmlElement.class);
if (xmlElement != null) {
// Create the name of the element from the annotation or the field name
String elementName = ("##default".equals(xmlElement.name()) ?
field.getName() :
xmlElement.name());
String path = parentPath + "/" + elementName;
if (xmlElement.nillable()) {
// It is nillable so we add it to the paths to skip
pathsToSkip.add(path);
} else {
// It is not nillable so we check the fields corresponding
// to the field type
// If it's a collection we need to get the generic type
if (Collection.class.isAssignableFrom(field.getType())) {
ParameterizedType fieldGenericType = (ParameterizedType) field
.getGenericType();
Class<?> fieldGenericTypeClass = (Class<?>) fieldGenericType
.getActualTypeArguments()[0];
addPathsToSkip(path, fieldGenericTypeClass, pathsToSkip);
} else {
addPathsToSkip(path, field.getType(), pathsToSkip);
}
}
}
}
}它的名字是这样的：
BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(new File(filePath)));
XMLExportStreamWriter exportStreamWriter = new XMLExportStreamWriter(XMLOutputFactory.newInstance().createXMLStreamWriter(
bufferedWriter);
exportStreamWriter.setNillableElements(getNillablePaths(MyClass.class));页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/39204125
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