1、簡單的轉(zhuǎn)換器：
首先創(chuàng)建示例的環(huán)境，
下面介紹的是最基礎(chǔ)的轉(zhuǎn)換器，首先創(chuàng)建一個Person類：
package com.thoughtworks.xstream.examples;
public class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
接著，我們創(chuàng)建一個實例，并轉(zhuǎn)化他：
package com.thoughtworks.xstream.examples;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.xml.DomDriver;
public class PersonTest {
public static void main(String[] args) {
Person person = new Person();
person.setName("Guilherme");
XStream xStream = new XStream(new DomDriver());
System.out.println(xStream.toXML(person));
}
}
如你所料，得到下面的結(jié)果：
<com.thoughtworks.xstream.examples.Person>
<name>Guilherme</name>
</com.thoughtworks.xstream.examples.Person>
下面我們?yōu)閜erson類創(chuàng)建一個別名：
XStream xStream = new XStream(new DomDriver());
xStream.alias("person", Person.class);
System.out.println(xStream.toXML(person));
現(xiàn)在的結(jié)果就很易讀了：
<person>
<name>Guilherme</name>
</person>
到此，我們已經(jīng)建立好一個可以供我們實驗的基礎(chǔ)例子了，下面我們來看看XStream的轉(zhuǎn)換器能為我們做些什么：
2，創(chuàng)建一個Person轉(zhuǎn)換器：
下面我們來創(chuàng)建一個簡單的轉(zhuǎn)換器，它能：
1，用來轉(zhuǎn)換Person類
2，將Person實例轉(zhuǎn)換成XML
3，將xml轉(zhuǎn)換為Person實例
首先創(chuàng)建一個PersonConverter類，并讓這個類實現(xiàn)Converter接口：
package com.thoughtworks.xstream.examples;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class PersonConverter implements Converter {
public boolean canConvert(Class clazz) {
return false;
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
return null;
}
}
下面，我們首先告訴轉(zhuǎn)換器，我們只能轉(zhuǎn)換Person類，而不是別的類，包括其子類：
public boolean canConvert(Class clazz) {
return clazz.equals(Person.class);
}
這一步很簡單，除非你是用來處理泛型的轉(zhuǎn)換器是會困難一點。
Marshal方法是用來將對象轉(zhuǎn)換為XML的，他有三個參數(shù)：
1，我們準備轉(zhuǎn)換的對象
2，我們準備輸出對象的writer
3，當前的marshaling context
首先我們將object轉(zhuǎn)換成Person
Person person = (Person) value;
接著，我們就可以開始輸出數(shù)據(jù)了，首先我們創(chuàng)建一個叫做fullname的節(jié)點，并將person的名字傳給他：
writer.startNode("fullname");
writer.setValue(person.getName());
writer.endNode();
呵呵～很簡單吧，
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Person person = (Person) value;
writer.startNode("fullname");
writer.setValue(person.getName());
writer.endNode();
}
我們可以任意次數(shù)的調(diào)用start/end node方法，但需要記住，你必須在打開一個節(jié)點之后記住關(guān)閉它。一般來說，執(zhí)行轉(zhuǎn)換的操作在setValue方法調(diào)用時發(fā)生。
下面，我們進入unmarshal方法，我們使用moveDown和moveUp方法在節(jié)點樹層次中移動，所以，這里我們只需要簡單的moveDown，得到值，再moveUp：
Person person = new Person();
reader.moveDown();
person.setName(reader.getValue());
reader.moveUp();
最后，我們得到了一個這樣的轉(zhuǎn)換器：
package com.thoughtworks.xstream.examples;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class PersonConverter implements Converter {
public boolean canConvert(Class clazz) {
return clazz.equals(Person.class);
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Person person = (Person) value;
writer.startNode("fullname");
writer.setValue(person.getName());
writer.endNode();
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
Person person = new Person();
reader.moveDown();
person.setName(reader.getValue());
reader.moveUp();
return person;
}
}
接著，我們在我們的main方法中注冊這個轉(zhuǎn)化器：
package com.thoughtworks.xstream.examples;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.xml.DomDriver;
public class PersonTest {
public static void main(String[] args) {
Person person = new Person();
person.setName("Guilherme");
XStream xStream = new XStream(new DomDriver());
xStream.registerConverter(new PersonConverter());
xStream.alias("person", Person.class);
System.out.println(xStream.toXML(person));
}
}
注意到我們怎么注冊我們的轉(zhuǎn)換器了么？只需要下面簡單的一句：
xStream.registerConverter(new PersonConverter());
最終得到的結(jié)果是：
<person>
<fullname>Guilherme</fullname>
</person>
也許你會說：這只改變了我輸出的樹，我需要用它來轉(zhuǎn)換數(shù)據(jù)。
下面我們來嘗試在person標簽中創(chuàng)建一個叫做fullname的屬性，而不是新創(chuàng)建一個節(jié)點：
3，一種可選的方式：
首先，為Person創(chuàng)建一個toString方法，里面包含了所有能用來重新創(chuàng)建一個Person實例的數(shù)據(jù)：
package com.thoughtworks.xstream.examples;
public class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return getName();
}
}
現(xiàn)在，我們就能把我們的轉(zhuǎn)化器簡寫為：
package com.thoughtworks.xstream.examples;
import com.thoughtworks.xstream.converters.basic.AbstractSingleValueConverter;
public class PersonConverter extends AbstractSingleValueConverter {
public boolean canConvert(Class clazz) {
return clazz.equals(Person.class);
}
public Object fromString(String str) {
Person person = new Person();
person.setName(string);
return person;
}
}
現(xiàn)在，輸出的XML也會變得更易讀（為person創(chuàng)建別名person之后）：
<person>Guilherme</person>
名字變成了一個內(nèi)置的值，而不是一個單獨的節(jié)點。
4，轉(zhuǎn)換Date：
我們已經(jīng)知道Converter接口是怎樣工作的了，現(xiàn)在我們來創(chuàng)建一個使用Locale對象轉(zhuǎn)換時間的轉(zhuǎn)換器：
在我們的轉(zhuǎn)換器構(gòu)造方法中，我們將傳入一個Locale對象，該Locale對象會作為一個成員屬性被轉(zhuǎn)換器持有：
package com.thoughtworks.xstream.examples;
import java.util.Locale;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class DateConverter implements Converter {
private Locale locale;
public DateConverter(Locale locale) {
super();
this.locale = locale;
}
public boolean canConvert(Class clazz) {
return false;
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
return null;
}
}
現(xiàn)在，讓我們能轉(zhuǎn)換任何繼承了Calendar對象的類：
public boolean canConvert(Class clazz) {
return Calendar.class.isAssignableFrom(clazz);
}
首先，我們來將Calendar轉(zhuǎn)換成本地化的字符串：首先我們把object轉(zhuǎn)化成Calendar,得到Date對象，并使用DataFormatter來得到一個本地化的時間：
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Calendar calendar = (Calendar) value;
// grabs the date
Date date = calendar.getTime();
// grabs the formatter
DateFormat formatter = DateFormat.getDateInstance(DateFormat.FULL,
this.locale);
// formats and sets the value
writer.setValue(formatter.format(date));
}
另一方面，在unmarshall方法中，我們創(chuàng)建了一個GregorianCalendar，得到本地化的DataFormat實例，將字符串轉(zhuǎn)換成Date對象，并賦值給GregorianCalendar。
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
// creates the calendar
GregorianCalendar calendar = new GregorianCalendar();
// grabs the converter
DateFormat formatter = DateFormat.getDateInstance(DateFormat.FULL,
this.locale);
// parses the string and sets the time
try {
calendar.setTime(formatter.parse(reader.getValue()));
} catch (ParseException e) {
throw new ConversionException(e.getMessage(), e);
}
// returns the new object
return calendar;
}
注意：
1，記住一些DataFormat實現(xiàn)不是線程安全的，所以，不要讓你的轉(zhuǎn)換器持有DataFormat的引用
2，在經(jīng)過了保存和加載的過程后，該轉(zhuǎn)換器可以將其他Calendar實現(xiàn)轉(zhuǎn)換為GregorianCalendar。如果這不是你希望的，只需要修改canConvert方法，并在類型只有為GregorianCalendar的時候再返回true。
現(xiàn)在，我們得到了下面這個轉(zhuǎn)換器：
package com.thoughtworks.xstream.examples;
import java.text.DateFormat;
import java.text.ParseException;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Locale;
import com.thoughtworks.xstream.converters.ConversionException;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class DateConverter implements Converter {
private Locale locale;
public DateConverter(Locale locale) {
super();
this.locale = locale;
}
public boolean canConvert(Class clazz) {
return Calendar.class.isAssignableFrom(clazz);
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Calendar calendar = (Calendar) value;
Date date = calendar.getTime();
DateFormat formatter = DateFormat.getDateInstance(DateFormat.FULL,
this.locale);
writer.setValue(formatter.format(date));
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
GregorianCalendar calendar = new GregorianCalendar();
DateFormat formatter = DateFormat.getDateInstance(DateFormat.FULL,
this.locale);
try {
calendar.setTime(formatter.parse(reader.getValue()));
} catch (ParseException e) {
throw new ConversionException(e.getMessage(), e);
}
return calendar;
}
}
現(xiàn)在，我們來測試一下，創(chuàng)建一個main方法：
1，創(chuàng)建一個calendar，
2，創(chuàng)建XStream對象
3，注冊該轉(zhuǎn)換器，并使用Brazilian Portuguese本地化對象
4，將對象轉(zhuǎn)化成XML
代碼如下：
package com.thoughtworks.xstream.examples;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Locale;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.xml.DomDriver;
public class DateTest {
public static void main(String[] args) {
// grabs the current date from the virtual machine
Calendar calendar = new GregorianCalendar();
// creates the xstream
XStream xStream = new XStream(new DomDriver());
// brazilian portuguese locale
xStream.registerConverter(new DateConverter(new Locale("pt", "br")));
// prints the result
System.out.println(xStream.toXML(calendar));
}
}
可以得到類似如下的結(jié)果：
<gregorian-calendar>Sexta-feira, 10 de Fevereiro de 2006</gregorian-calendar>
注意，我們沒有為GregorianCalendar創(chuàng)建任何別名，而gregorian-calendar就是默認的名字。
下面我們來試試unmarshal 方法：
// loads the calendar from the string
Calendar loaded = (Calendar) xStream
.fromXML("<gregorian-calendar>Sexta-feira, 10 de Fevereiro de 2006</gregorian-calendar>");
然后打印出該日期：
// prints using the system defined locale
System.out.println(DateFormat.getDateInstance(DateFormat.SHORT).format(
loaded.getTime()));
得到的結(jié)果為：
2/10/06
5，復(fù)雜的轉(zhuǎn)換器：
創(chuàng)建另一個例子：
我們已經(jīng)創(chuàng)建了兩個對象了，現(xiàn)在把它們組合起來：
package com.thoughtworks.xstream.examples;
public class Birthday {
private Person person;
private Calendar date;
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
public Calendar getDate() {
return date;
}
public void setDate(Calendar date) {
this.date = date;
}
}
要轉(zhuǎn)換該類，XStream一點問題都沒有。這里，我們實現(xiàn)自己的轉(zhuǎn)換器主要是為了驗證，在這里，我們想重用我們剛才的PersonConverter和CalendarConverter。canConvert仍然很簡單，不過這里，我們不需要再為每一個屬性重新寫轉(zhuǎn)換方法了，我們只需要使用已經(jīng)注冊了的轉(zhuǎn)換器來完成轉(zhuǎn)換：
package com.thoughtworks.xstream.examples;
import java.util.Calendar;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class BirthdayConverter implements Converter {
public boolean canConvert(Class clazz) {
return Birthday.class == clazz;
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Birthday birthday = (Birthday)value;
if (value.getPerson() != null) {
writer.startNode("person");
context.convertAnother(value.getPerson());
writer.endNode();
}
if (value.getDate() != null) {
writer.startNode("birth");
context.convertAnother(value.getDate());
writer.endNode();
}
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
Birthday birthday = new Birthday();
while (reader.hasMoreChildren()) {
reader.moveDown();
if ("person".equals(reader.getNodeName())) {
Person person = (Person)context.convertAnother(birthday, Person.class);
birthday.setPerson(person);
} else if ("birth".equals(reader.getNodeName())) {
Calendar date = (Calendar)context.convertAnother(birthday, Calendar.class);
birthday.setDate(date);
}
reader.moveUp();
}
return birthday;
}
}
如果birthday實例能夠確保不會出現(xiàn)null值，那么我們就可以去掉marshal和unmarshal方法中對null情況的判斷，也不需要循環(huán)，而直接根據(jù)tag的名字進行解析：
package com.thoughtworks.xstream.examples;
import java.util.Calendar;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
public class BirthdayConverter implements Converter {
public boolean canConvert(Class clazz) {
return Birthday.class == clazz;
}
public void marshal(Object value, HierarchicalStreamWriter writer,
MarshallingContext context) {
Birthday birthday = (Birthday)value;
writer.startNode("person");
context.convertAnother(value.getPerson());
writer.endNode();
writer.startNode("birth");
context.convertAnother(value.getDate());
writer.endNode();
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
Birthday birthday = new Birthday();
reader.moveDown();
Person person = (Person)context.convertAnother(birthday, Person.class);
birthday.setPerson(person);
reader.moveUp();
reader.moveDown();
Calendar date = (Calendar)context.convertAnother(birthday, Calendar.class);
birthday.setDate(date);
reader.moveUp();
return birthday;
}
}