最近也遇到了这种问题。在参考了上面列出的axtavt的答案（以及一堆其他问题线程）之后，我对这类问题做了一个总结：
- 包含
JAXBElement 列表（或数组）的容器类
对象，其中此列表（或数组）被注释
@XmlAnyElement，因此可以生成动态元素名称。
- 一个
XmlAdapter 类，用于处理之间的编组/解组
映射到/从这个容器类。
- 用
@XmlJavaTypeAdapter注释你的java bean的任何Map字段，
将此XmlAdapter 类作为其值（或者您可以简单地使用
直接使用容器类，如下所示）。
这里我以Map<String, String>为例，这里
{"key1": "value1", "key2": "value2"}
将被编组到
<root>
<key1>value1</key1>
<key2>value2</key2>
</root>
下面是完整的sn-p & cmets代码，以及例子：
1、容器（用于@XmlAnyElement）
/**
* <dl>
* <dt>References:
* </dt>
* <dd>
* <ul>
* <li><a href="http://stackoverflow.com/questions/21382202/use-jaxb-xmlanyelement-type-of-style-to-return-dynamic-element-names">Dynamic element names in JAXB</a></li>
* <li><a href="http://stackoverflow.com/questions/3941479/jaxb-how-to-marshall-map-into-keyvalue-key">Marshal Map into key-value pairs</a></li>
* <li><a href="http://stackoverflow.com/questions/3293493/dynamic-tag-names-with-jaxb">Dynamic tag names with JAXB</a></li>
* </ul>
* </dd>
* </dl>
* @author MEC
*
*/
@XmlType
public static class MapWrapper{
private List<JAXBElement<String>> properties = new ArrayList<>();
public MapWrapper(){
}
/**
* <p>
* Funny fact: due to type erasure, this method may return
* List<Element> instead of List<JAXBElement<String>> in the end;
* </p>
* <h4>WARNING: do not use this method in your programme</h4>
* <p>
* Thus to retrieve map entries you've stored in this MapWrapper, it's
* recommended to use {@link #toMap()} instead.
* </p>
* @return
*/
@XmlAnyElement
public List<JAXBElement<String>> getProperties() {
return properties;
}
public void setProperties(List<JAXBElement<String>> properties) {
this.properties = properties;
}
/**
* <p>
* Only use {@link #addEntry(JAXBElement)} and {{@link #addEntry(String, String)}
* when this <code>MapWrapper</code> instance is created by yourself
* (instead of through unmarshalling).
* </p>
* @param key map key
* @param value map value
*/
public void addEntry(String key, String value){
JAXBElement<String> prop = new JAXBElement<String>(new QName(key), String.class, value);
addEntry(prop);
}
public void addEntry(JAXBElement<String> prop){
properties.add(prop);
}
@Override
public String toString() {
return "MapWrapper [properties=" + toMap() + "]";
}
/**
* <p>
* To Read-Only Map
* </p>
*
* @return
*/
public Map<String, String> toMap(){
//Note: Due to type erasure, you cannot use properties.stream() directly when unmashalling is used..
List<?> props = properties;
return props.stream().collect(Collectors.toMap(MapWrapper::extractLocalName, MapWrapper::extractTextContent));
}
/**
* <p>
* Extract local name from <code>obj</code>, whether it's javax.xml.bind.JAXBElement or org.w3c.dom.Element;
* </p>
* @param obj
* @return
*/
@SuppressWarnings("unchecked")
private static String extractLocalName(Object obj){
Map<Class<?>, Function<? super Object, String>> strFuncs = new HashMap<>();
strFuncs.put(JAXBElement.class, (jaxb) -> ((JAXBElement<String>)jaxb).getName().getLocalPart());
strFuncs.put(Element.class, ele -> ((Element) ele).getLocalName());
return extractPart(obj, strFuncs).orElse("");
}
/**
* <p>
* Extract text content from <code>obj</code>, whether it's javax.xml.bind.JAXBElement or org.w3c.dom.Element;
* </p>
* @param obj
* @return
*/
@SuppressWarnings("unchecked")
private static String extractTextContent(Object obj){
Map<Class<?>, Function<? super Object, String>> strFuncs = new HashMap<>();
strFuncs.put(JAXBElement.class, (jaxb) -> ((JAXBElement<String>)jaxb).getValue());
strFuncs.put(Element.class, ele -> ((Element) ele).getTextContent());
return extractPart(obj, strFuncs).orElse("");
}
/**
* Check class type of <code>obj</code> according to types listed in <code>strFuncs</code> keys,
* then extract some string part from it according to the extract function specified in <code>strFuncs</code>
* values.
* @param obj
* @param strFuncs
* @return
*/
private static <ObjType, T> Optional<T> extractPart(ObjType obj, Map<Class<?>, Function<? super ObjType, T>> strFuncs){
for(Class<?> clazz : strFuncs.keySet()){
if(clazz.isInstance(obj)){
return Optional.of(strFuncs.get(clazz).apply(obj));
}
}
return Optional.empty();
}
}
注意事项：
- 对于 JAXB Binding，你需要注意的是这个
getProperties 方法，由 @XmlAnyElement 注释。
- 为了方便使用，这里介绍两个
addEntry方法。他们
应该小心使用，因为事情可能会变得可怕
当它们用于刚刚解组的 MapWrapper 到 JAXBContext（而不是您自己通过 new 运算符创建的）时是错误的。
-
这里介绍
toMap用于信息探测，即帮助检查
映射存储在此 MapWrapper 实例中的条目。
2、适配器（XmlAdapter）
XmlAdapter 与 @XmlJavaTypeAdapter 成对使用，在这种情况下，仅当 Map<String, String> 用作 bean 属性时才需要。
/**
* <p>
* ref: http://stackoverflow.com/questions/21382202/use-jaxb-xmlanyelement-type-of-style-to-return-dynamic-element-names
* </p>
* @author MEC
*
*/
public static class MapAdapter extends XmlAdapter<MapWrapper, Map<String, String>>{
@Override
public Map<String, String> unmarshal(MapWrapper v) throws Exception {
Map<String, String> map = v.toMap();
return map;
}
@Override
public MapWrapper marshal(Map<String, String> m) throws Exception {
MapWrapper wrapper = new MapWrapper();
for(Map.Entry<String, String> entry : m.entrySet()){
wrapper.addEntry(new JAXBElement<String>(new QName(entry.getKey()), String.class, entry.getValue()));
}
return wrapper;
}
}
3、例子
这里有两个例子展示了容器和适配器的用法。
3.1 示例1
要映射这个 xml：
<root>
<key1>value1</key1>
<key2>value2</key2>
<root>
您可以使用以下类：
@XmlRootElement(name="root")
public class CustomMap extends MapWrapper{
public CustomMap(){
}
}
测试代码：
CustomMap map = new CustomMap();
map.addEntry("key1", "value1");
map.addEntry("key1", "value2");
StringWriter sb = new StringWriter();
JAXBContext.newInstance(CustomMap.class).createMarshaller().marshal(map, sb);
out.println(sb.toString());
注意这里没有使用@XmlJavaTypeAdapter。
3.2 示例2
要映射这个 xml：
<root>
<map>
<key1>value1</key1>
<key2>value2</key2>
</map>
<other>other content</other>
</root>
您可以使用以下类：
@XmlRootElement(name="root")
@XmlType(propOrder={"map", "other"})
public class YetAnotherBean{
private Map<String, String> map = new HashMap<>();
private String other;
public YetAnotherBean(){
}
public void putEntry(String key, String value){
map.put(key, value);
}
@XmlElement(name="map")
@XmlJavaTypeAdapter(MapAdapter.class)
public Map<String, String> getMap(){
return map;
}
public void setMap(Map<String, String> map){
this.map = map;
}
@XmlElement(name="other")
public String getOther(){
return other;
}
public void setOther(String other){
this.other = other;
}
}
测试代码：
YetAnotherBean yab = new YetAnotherBean();
yab.putEntry("key1", "value1");
yab.putEntry("key2", "value2");
yab.setOther("other content");
StringWriter sb = new StringWriter();
JAXBContext.newInstance(YetAnotherBean.class).createMarshaller().marshal(yab, sb);
out.println(sb.toString());
请注意，@XmlJavaTypeAdapter 应用于 Map<String, String> 字段，并以 MapAdapter 作为其值。
3.3 示例3
现在让我们为这些元素添加一些属性。由于一些神秘的原因，我要映射这种 XML 结构：
<sys-config>
<sys-params>
<ACCESSLOG_FILE_BY attr="C" desc="AccessLog file desc">SYSTEM</ACCESSLOG_FILE_BY>
<ACCESSLOG_WRITE_MODE attr="D" desc="">DB</ACCESSLOG_WRITE_MODE>
<CHANEG_BUTTON_IMAGES attr="E" desc="Button Image URL, eh, boolean value. ...Wait, what?">FALSE</CHANEG_BUTTON_IMAGES>
</sys-params>
</sys-config>
如您所见，系统参数名称都设置为元素的名称，而不是其属性。为了解决这个问题，我们可以再次使用JAXBElement 的帮助：
@XmlRootElement(name="sys-config")
public class SysParamConfigXDO{
private SysParamEntries sysParams = new SysParamEntries();
public SysParamConfigXDO(){
}
public void addSysParam(String name, String value, String attr, String desc){
sysParams.addEntry(name, value, attr, desc);;
}
@XmlElement(name="sys-params")
@XmlJavaTypeAdapter(SysParamEntriesAdapter.class)
public SysParamEntries getSysParams() {
return sysParams;
}
public void setSysParams(SysParamEntries sysParams) {
this.sysParams = sysParams;
}
@Override
public String toString() {
return "SysParamConfigXDO [sysParams=" + sysParams + "]";
}
}
@XmlRootElement(name="root")
public class SysParamXDO extends SysParamEntriesWrapper{
public SysParamXDO(){
}
}
@SuppressWarnings("unchecked")
@XmlType
public class SysParamEntriesWrapper{
/**
* <p>
* Here is the tricky part:
* <ul>
* <li>When this <code>SysParamEntriesWrapper</code> is created by yourself, objects
* stored in this <code>entries</code> list is of type SystemParamEntry</li>
* <li>Yet during the unmarshalling process, this <code>SysParamEntriesWrapper</code> is
* created by the JAXBContext, thus objects stored in the <code>entries</code> is
* of type Element actually.</li>
* </ul>
* </p>
*/
List<JAXBElement<SysParamEntry>> entries = new ArrayList<>();
public SysParamEntriesWrapper(){
}
public void addEntry(String name, String value, String attr, String desc){
addEntry(new SysParamEntry(name, value, attr, desc));
}
public void addEntry(String name, String value){
addEntry(new SysParamEntry(name, value));
}
public void addEntry(SysParamEntry entry){
JAXBElement<SysParamEntry> bean = new JAXBElement<SysParamEntry>(new QName("", entry.getName()), SysParamEntry.class, entry);
entries.add(bean);
}
@XmlAnyElement
public List<JAXBElement<SysParamEntry>> getEntries() {
return entries;
}
public void setEntries(List<JAXBElement<SysParamEntry>> entries) {
this.entries = entries;
}
@Override
public String toString() {
return "SysParammEntriesWrapper [entries=" + toMap() + "]";
}
public Map<String, SysParamEntry> toMap(){
Map<String, SysParamEntry> retval = new HashMap<>();
List<?> entries = this.entries;
entries.stream().map(SysParamEntriesWrapper::convertToParamEntry).
forEach(entry -> retval.put(entry.getName(), entry));;
return retval;
}
private static SysParamEntry convertToParamEntry(Object entry){
String name = extractName(entry);
String attr = extractAttr(entry);
String desc = extractDesc(entry);
String value = extractValue(entry);
return new SysParamEntry(name, value, attr, desc);
}
@SuppressWarnings("unchecked")
private static String extractName(Object entry){
return extractPart(entry, nameExtractors).orElse("");
}
@SuppressWarnings("unchecked")
private static String extractAttr(Object entry){
return extractPart(entry, attrExtractors).orElse("");
}
@SuppressWarnings("unchecked")
private static String extractDesc(Object entry){
return extractPart(entry, descExtractors).orElse("");
}
@SuppressWarnings("unchecked")
private static String extractValue(Object entry){
return extractPart(entry, valueExtractors).orElse("");
}
private static <ObjType, RetType> Optional<RetType> extractPart(ObjType obj, Map<Class<?>,
Function<? super ObjType, RetType>> extractFuncs ){
for(Class<?> clazz : extractFuncs.keySet()){
if(clazz.isInstance(obj)){
return Optional.ofNullable(extractFuncs.get(clazz).apply(obj));
}
}
return Optional.empty();
}
private static Map<Class<?>, Function<? super Object, String>> nameExtractors = new HashMap<>();
private static Map<Class<?>, Function<? super Object, String>> attrExtractors = new HashMap<>();
private static Map<Class<?>, Function<? super Object, String>> descExtractors = new HashMap<>();
private static Map<Class<?>, Function<? super Object, String>> valueExtractors = new HashMap<>();
static{
nameExtractors.put(JAXBElement.class, jaxb -> ((JAXBElement<SysParamEntry>)jaxb).getName().getLocalPart());
nameExtractors.put(Element.class, ele -> ((Element) ele).getLocalName());
attrExtractors.put(JAXBElement.class, jaxb -> ((JAXBElement<SysParamEntry>)jaxb).getValue().getAttr());
attrExtractors.put(Element.class, ele -> ((Element) ele).getAttribute("attr"));
descExtractors.put(JAXBElement.class, jaxb -> ((JAXBElement<SysParamEntry>)jaxb).getValue().getDesc());
descExtractors.put(Element.class, ele -> ((Element) ele).getAttribute("desc"));
valueExtractors.put(JAXBElement.class, jaxb -> ((JAXBElement<SysParamEntry>)jaxb).getValue().getValue());
valueExtractors.put(Element.class, ele -> ((Element) ele).getTextContent());
}
}
public class SysParamEntriesAdapter extends XmlAdapter<SysParamEntriesWrapper, SysParamEntries>{
@Override
public SysParamEntries unmarshal(SysParamEntriesWrapper v) throws Exception {
SysParamEntries retval = new SysParamEntries();
v.toMap().values().stream().forEach(retval::addEntry);
return retval;
}
@Override
public SysParamEntriesWrapper marshal(SysParamEntries v) throws Exception {
SysParamEntriesWrapper entriesWrapper = new SysParamEntriesWrapper();
v.getEntries().forEach(entriesWrapper::addEntry);
return entriesWrapper;
}
}
public class SysParamEntries{
List<SysParamEntry> entries = new ArrayList<>();;
public SysParamEntries(){
}
public SysParamEntries(List<SysParamEntry> entries) {
super();
this.entries = entries;
}
public void addEntry(SysParamEntry entry){
entries.add(entry);
}
public void addEntry(String name, String value){
addEntry(name, value, "C");
}
public void addEntry(String name, String value, String attr){
addEntry(name, value, attr, "");
}
public void addEntry(String name, String value, String attr, String desc){
entries.add(new SysParamEntry(name, value, attr, desc));
}
public List<SysParamEntry> getEntries() {
return entries;
}
public void setEntries(List<SysParamEntry> entries) {
this.entries = entries;
}
@Override
public String toString() {
return "SystemParamEntries [entries=" + entries + "]";
}
}
@XmlType
public class SysParamEntry{
String name;
String value = "";
String attr = "";
String desc = "";
public SysParamEntry(){
}
public SysParamEntry(String name, String value) {
super();
this.name = name;
this.value = value;
}
public SysParamEntry(String name, String value, String attr) {
super();
this.name = name;
this.value = value;
this.attr = attr;
}
public SysParamEntry(String name, String value, String attr, String desc) {
super();
this.name = name;
this.value = value;
this.attr = attr;
this.desc = desc;
}
@XmlTransient
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@XmlValue
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
@XmlAttribute(name="attr")
public String getAttr() {
return attr;
}
public void setAttr(String attr) {
this.attr = attr;
}
@XmlAttribute(name="desc")
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
@Override
public String toString() {
return "SystemParamEntry [name=" + name + ", value=" + value + ", attr=" + attr + ", desc=" + desc + "]";
}
}
测试时间到了：
//Marshal
SysParamConfigXDO xdo = new SysParamConfigXDO();
xdo.addSysParam("ACCESSLOG_FILE_BY", "SYSTEM", "C", "AccessLog file desc");
xdo.addSysParam("ACCESSLOG_WRITE_MODE", "DB", "D", "");
xdo.addSysParam("CHANEG_BUTTON_IMAGES", "FALSE", "E", "Button Image URL, eh, boolean value. ...Wait, what?");
JAXBContext jaxbCtx = JAXBContext.newInstance(SysParamConfigXDO.class, SysParamEntries.class);
jaxbCtx.createMarshaller().marshal(xdo, System.out);
//Unmarshal
Path xmlFile = Paths.get("path_to_the_saved_xml_file.xml");
JAXBContext jaxbCtx = JAXBContext.newInstance(SysParamConfigXDO.class, SysParamEntries.class);
SysParamConfigXDO xdo = (SysParamConfigXDO) jaxbCtx.createUnmarshaller().unmarshal(xmlFile.toFile());
out.println(xdo.toString());