XStream把xml文件转化为java对象(转)

前端之家收集整理的这篇文章主要介绍了XStream把xml文件转化为java对象(转)前端之家小编觉得挺不错的,现在分享给大家,也给大家做个参考。

原作者:http://www.blogjava.net/DLevin/archive/2012/11/30/392240.html

现在参与的项目是一个纯@H_502_14@Application Server,整个Server都是自己搭建的,使用JMS消息实现客户端和服务器的交互,交互的数据格式采用XML。说来惭愧,开始为了赶进度,所有XML消息都是使用字符串拼接的,而XML的解析则是使用DOM方式查找的。我很早就看这些代码不爽了,可惜一直没有时间去重构,最近项目加了几个人,而且美国那边也开始渐渐的把这个项目开发的控制权交给我们了,所以我开始有一些按自己的方式开发的机会了。因而最近动手开始重构这些字符串拼接的代码

XMLJava Bean的解析框架,熟悉一点的只有DigesterXStreamDigester貌似只能从XML文件解析成@H_502_14@Java Bean对象,所以只能选择XStream来做了,而且同组的其他项目也有在用XStream。一直听说XStream的使用比较简单,而且我对ThoughtWorks这家公司一直比较有好感,所以还以为引入XStream不会花太多时间,然而使用以后才发现XStream并没有想象的你那么简单。不过这个也有可能是因为我不想改变原来的XML数据格式,而之前的XML数据格式的设计自然不会考虑到如何便利的使用XStream。因而记录在使用过程中遇到的问题,供后来人参考,也为自己以后如果打算开其源码提供参考。废话就到这里了,接下来步入正题。

首先对于简单的引用,XStream使用起来确实比较简单,比如自定义标签属性、使用属性和使用子标签的定义等:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamAlias( " request " )
public class XmlRequest1 {
private static XStream xstream;
static {
xstream
= new XStream();
xstream.autodetectAnnotations(
true );
}

@XStreamAsAttribute
private String from;

@XStreamAsAttribute
@XStreamAlias(
" calculate-method " )
private String calculateMethod;

@XStreamAlias(
" request-time " )
private Date requestTime;

@XStreamAlias(
" input-files " )
private List < InputFileInfo > inputFiles;

public static String toXml(XmlRequest1 request) {
StringWriter writer
= new StringWriter();
writer.append(Constants.XML_HEADER);
xstream.toXML(request,writer);
return writer.toString();
}
public static XmlRequest1 toInstance(String xmlContent) {
return (XmlRequest1)xstream.fromXML(xmlContent);
}

@XStreamAlias(
" input-file " )
public static class InputFileInfo {
private String type;
private String fileName;

}
public static void main(String[] args) {
XmlRequest1 request
= buildXmlRequest();
System.out.println(XmlRequest1.toXml(request));
}
private static XmlRequest1 buildXmlRequest() {

}
}

对以上Request定义,我们可以得到如下结果:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> <? xml version="1.0" encoding="UTF-8" ?>
< request from ="levin@host" calculate-method ="advanced" >
< request-time > 2012-11-28 17:11:54.664 UTC </ request-time >
< input-files >
< input-file >
< type > DATA </ type >
< fileName > data.2012.11.29.dat </ fileName >
</ input-file >
< input-file >
< type > CALENDAR </ type >
< fileName > calendar.2012.11.29.dat </ fileName >
</ input-file >
</ input-files >
</ request >

可惜这个世界不会那么清净,这个格式有些时候貌似并不符合要求,比如request-time的格式、input-files的格式,我们实际需要的格式是这样的:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> <? xml version="1.0" encoding="UTF-8" ?>
< request from ="levin@host" calculate-method ="advanced" >
< request-time > 20121128T17:51:05 </ request-time >
< input-file type ="DATA" > data.2012.11.29.dat </ input-file >
< input-file type ="CALENDAR" > calendar.2012.11.29.dat </ input-file >
</ request >

对不同Date格式的支持可以是用Converter实现,在XStream中默认使用自己实现的DateConverter,它支持的格式是:yyyy-MM-dd HH:mm:ss.S 'UTC',然而我们现在需要的格式是yyyy-MM-dd’T’HH:mm:ss,如果使用XStream直接注册DateConverter,可以使用配置自己的DateConverter,但是由于DateConverter的构造函数的定义以及@XStreamConverter的构造函数参数的支持方式的限制,貌似DateConverter不能很好的支持注解方式的注册,因而我时间了一个自己的DateConverter支持注解:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> public class LevinDateConverter extends DateConverter {
public LevinDateConverter(String dateFormat) {
super (dateFormat, new String[] { dateFormat });
}
}

requestTime字段中需要加入以下注解定义:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamConverter(value = LevinDateConverter. class ,strings = { " yyyyMMdd'T'HH:mm:ss " })
@XStreamAlias(
" request-time " )
private Date requestTime;

对集合类,XStream提供了@XStreamImplicit注解,以将集合中的内容摊平到上一层XML元素中,其中itemFieldName的值为其使用的标签名,此时InputFileInfo类中不需要@XStreamAlias标签的定义:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamImplicit(itemFieldName = " input-file " )
private List < InputFileInfo > inputFiles;

InputFileInfo中的字段,type作为属性很容易,只要为它加上@XStreamAsAttribute注解即可,而将fileName作为input-file标签的一个内容字符串,则需要使用ToAttributedValueConverter,其中Converter的参数为需要作为字符串内容的字段名:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamConverter(value = ToAttributedValueConverter. class ,strings = { " fileName " })
public static class InputFileInfo {
@XStreamAsAttribute
private String type;
private String fileName;

}

XStream对枚举类型的支持貌似不怎么好,默认注册EnumSingleValueConverter只是使用了Enum提供的name()和静态的valueOf()方法enum转换成String或将String转换回enum。然而有些时候XML的字符串和类定义的enum值并不完全匹配,最常见的就是大小写的不匹配,此时需要写自己的Converter。在这种情况下,我一般会在enum中定义一个name属性,这样就可以自定义enum的字符串表示。比如有TimePeriodenum

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> public enum TimePeriod {
MONTHLY(
" monthly " ),WEEKLY( " weekly " ),DAILY( " daily " );

private String name;

public String getName() {
return name;
}

private TimePeriod(String name) {
this .name = name;
}

public static TimePeriod toEnum(String timePeriod) {
try {
return Enum.valueOf(TimePeriod. class ,timePeriod);
}
catch (Exception ex) {
for (TimePeriod period : TimePeriod.values()) {
if (period.getName().equalsIgnoreCase(timePeriod)) {
return period;
}
}
throw new IllegalArgumentException( " Cannot convert < " + timePeriod + " > to TimePeriod enum " );
}
}
}

我们可以编写以下Converter以实现对枚举类型的更宽的容错性:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> public class LevinEnumSingleNameConverter extends EnumSingleValueConverter {
private static final String CUSTOM_ENUM_NAME_METHOD = " getName " ;
private static final String CUSTOM_ENUM_VALUE_OF_METHOD = " toEnum " ;

private Class <? extends Enum <?>> enumType;

public LevinEnumSingleNameConverter(Class <? extends Enum <?>> type) {
super (type);
this .enumType = type;
}

@Override
public String toString(Object obj) {
Method method
= getCustomEnumNameMethod();
if (method == null ) {
return super .toString(obj);
}
else {
try {
return (String)method.invoke(obj,(Object[]) null );
}
catch (Exception ex) {
return super .toString(obj);
}
}
}

@Override
public Object fromString(String str) {
Method method
= getCustomEnumStaticValueOfMethod();
if (method == null ) {
return enhancedFromString(str);
}
try {
return method.invoke( null ,str);
}
catch (Exception ex) {
return enhancedFromString(str);
}
}

private Method getCustomEnumNameMethod() {
try {
return enumType.getMethod(CUSTOM_ENUM_NAME_METHOD,(Class <?> []) null );
}
catch (Exception ex) {
return null ;
}
}

private Method getCustomEnumStaticValueOfMethod() {
try {
Method method
= enumType.getMethod(CUSTOM_ENUM_VALUE_OF_METHOD,(Class <?> []) null );
if (method.getModifiers() == Modifier.STATIC) {
return method;
}
return null ;
}
catch (Exception ex) {
return null ;
}
}

private Object enhancedFromString(String str) {
try {
return super .fromString(str);
}
catch (Exception ex) {
for (Enum <?> item : enumType.getEnumConstants()) {
if (item.name().equalsIgnoreCase(str)) {
return item;
}
}
throw new IllegalStateException( " Cannot converter < " + str + " > to enum < " + enumType + " > " );
}
}
}

如下方式使用即可:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamAsAttribute
@XStreamAlias(
" time-period " )
@XStreamConverter(value
= LevinEnumSingleNameConverter. class )
private TimePeriod timePeriod;

double类型,貌似默认的DoubleConverter实现依然不给力,它不支持自定义的格式,比如我们想在序列化的时候用一下格式: ###,##0.0########,此时又需要编写自己的Converter

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> public class FormatableDoubleConverter extends DoubleConverter {
private String pattern;
private DecimalFormat formatter;

public FormatableDoubleConverter(String pattern) {
this .pattern = pattern;
this .formatter = new DecimalFormat(pattern);
}

@Override
public String toString(Object obj) {
if (formatter == null ) {
return super .toString(obj);
}
else {
return formatter.format(obj);
}
}

@Override
public Object fromString(String str) {
try {
return super .fromString(str);
}
catch (Exception ex) {
if (formatter != null ) {
try {
return formatter.parse(str);
}
catch (Exception e) {
throw new IllegalArgumentException( " Cannot parse < " + str + " > to double value " ,e);
}
}
throw new IllegalArgumentException( " Cannot parse < " + str + " > to double value " ,ex);
}
}

public String getPattern() {
return pattern;
}
}

使用方式和之前的Converter类似:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @XStreamAsAttribute
@XStreamConverter(value
= FormatableDoubleConverter. class ,strings = { " ###,##0.0######## " })
private double value;

最后,还有两个XStream没法实现的,或者说我没有找到一个更好的实现方式的场景。第一种场景是XStream不能很好的处理对象组合问题:

在面向对象编程中,一般尽量的倾向于抽取相同的数据成一个类,而通过组合的方式构建整个数据结构。比如Student类中有nameaddressAddress是一个类,它包含citycodestreet等信息,此时如果要对Student对象做如下格式序列化:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < student name =”Levin”>
<city > shanghai </ city >
< street > zhangjiang </ street >
< code > 201203 </ code >
</ student >

貌似我没有找到可以实现的方式,XStream能做是在中间加一层address标签。对这种场景的解决方案,一种是将Address中的属性平摊到Student类中,另一种是让Student继承自Address类。不过貌似这两种都不是比较理想的办法。

第二种场景是XStream不能很好的处理多态问题:

比如我们有一个Trade类,它可能表示不同的产品:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> public class Trade {
private String tradeId;
private Product product;

}
abstract class Product {
private String name;
public Product(String name) {
this .name = name;
}

}
class FX extends Product {
private double ratio;
public FX() {
super ( " fx " );
}

}
class Future extends Product {
private double maturity;
public Future() {
super ( " future " );
}

}

通过一些简单的设置,我们能得到如下XML格式:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < trades >
< trade trade-id ="001" >
< product class ="levin.xstream.blog.FX" name ="fx" ratio ="0.59" />
</ trade >
< trade trade-id ="002" >
< product class ="levin.xstream.blog.Future" name ="future" maturity ="2.123" />
</ trade >
</ trades >

作为数据文件,对Java类的定义显然是不合理的,因而简单一些,我们可以编写自己的Converterclass属性product去除

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> xstream.registerConverter( new ProductConverter(
xstream.getMapper(),xstream.getReflectionProvider()));

public ProductConverter(Mapper mapper,ReflectionProvider reflectionProvider) {
super (mapper,reflectionProvider);
}

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

@Override
protected Object instantiateNewInstance(HierarchicalStreamReader reader,UnmarshallingContext context) {
Object currentObject
= context.currentObject();
if (currentObject != null ) {
return currentObject;
}

String name
= reader.getAttribute( " name " );
if ( " fx " .equals(name)) {
return reflectionProvider.newInstance(FX. class );
}
else if ( " future " .equals(name)) {
return reflectionProvider.newInstance(Future. class );
}
throw new IllegalStateException( " Cannot convert < " + name + " > product " );
}
}

在所有Production上定义@XStreamAlias(“product”)注解。这时的XML输出结果为:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < trades >
< trade trade-id ="001" >
< product name ="fx" ratio ="0.59" />
</ trade >
< trade trade-id ="002" >
< product name ="future" maturity ="2.123" />
</ trade >
</ trades >

然而如果有人希望XML输出结果如下呢?

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < trades >
< trade trade-id ="001" >
< fx ratio ="0.59" />
</ trade >
< trade trade-id ="002" >
< future maturity ="2.123" />
</ trade >
</ trades >

大概找了一下,可能可以定义自己的Mapper解决,不过XStream的源码貌似比较复杂,没有时间深究这个问题,留着以后慢慢解决吧。

补充:

Map类型数据,XStream默认使用以下格式显示

< map class ="linked-hash-map" >
< entry >
< string > key1 </ string >
< string > value1 </ string >
</ entry >
< entry >
< string > key2 </ string >
< string > value2 </ string >
</ entry >
</ map >

但是对一些简单的Map,我们希望如下显示

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < map >
< entry key ="key1" value ="value1" />
< entry key ="key2" value ="value2" />
</ map >

对这种需求需要通过编写Converter解决,继承自MapConverter,覆盖以下函数,这里的Map默认keyvalue都是String类型,如果他们不是String类型,需要另外添加逻辑:

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> @SuppressWarnings( " rawtypes " )
@Override
public void marshal(Object source,HierarchicalStreamWriter writer,
MarshallingContext context) {
Map map
= (Map) source;
for (Iterator iterator = map.entrySet().iterator(); iterator.hasNext();) {
Entry entry
= (Entry) iterator.next();
ExtendedHierarchicalStreamWriterHelper.startNode(writer,mapper()
.serializedClass(Map.Entry.
class ),entry.getClass());

writer.addAttribute(
" key " ,entry.getKey().toString());
writer.addAttribute(
" value " ,entry.getValue().toString());
writer.endNode();
}
}

@Override
@SuppressWarnings({
" unchecked " , " rawtypes " })
protected void putCurrentEntryIntoMap(HierarchicalStreamReader reader,
UnmarshallingContext context,Map map,Map target) {
Object key
= reader.getAttribute( " key " );
Object value
= reader.getAttribute( " value " );

target.put(key,value);
}

但是只是使用Converter,得到的结果多了一个class属性

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> < map class ="linked-hash-map" >
< entry key ="key1" value ="value1" />
< entry key ="key2" value ="value2" />
</ map >

XStream中,如果定义的字段是一个父类或接口,在序列化是会默认加入class属性以确定反序列化时用的类,为了去掉这个class属性,可以定义默认的实现类来解决(虽然感觉这种解决方案不太好,但是目前还没有找到更好的解决方案)。

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--> xstream.addDefaultImplementation(LinkedHashMap. class ,Map. class );

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