[英]How do I, using XStream, serialize/deserialize objects in a type hierarchy?
我正在使用XStream。 目前,用其他東西替換XStream還不容易。
我有一個接口(MyInterface)和幾個實現該接口的子類(在下面的示例代碼中,有一個稱為MyImplementation)。
我想序列化和反序列化子類的實例。 我發現如果將class屬性放入XML中,我可以反序列化就好了:
<myInterfaceElement class="myPackage.MyImplementation">
<field1>value1</field1>
<field2>value2</field2>
</myInterfaceElement>
但是,我不知道如何讓XStream編寫class屬性。 序列化時如何讓XStream包含class屬性? 還是有另一種方法來對類層次結構進行序列化/反序列化,以便所有實現的元素名稱都相同,並且每個子類都可以定義自己的字段?
這是MyInterface,MyImplementation的示例,這是一個試圖使其工作的JUnit測試用例。 deserializeWithClassAttribute測試通過,而classAttributeSetInResult失敗。
package myPackage;
public interface MyInterface {
}
package myPackage;
public class MyImplementation implements MyInterface {
public String field1;
public String field2;
public MyImplementation(String field1, String field2) {
this.field1 = field1;
this.field2 = field2;
}
}
package myPackage;
import org.junit.Test;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.xml.DomDriver;
import static org.junit.Assert.*;
public class xstreamTest {
@Test
public void classAttributeSetInResult() {
MyInterface objectToSerialize = new MyImplementation("value1", "value2");
final XStream xStream = new XStream(new DomDriver());
xStream.alias("myInterfaceElement", MyInterface.class);
String xmlResult = xStream.toXML(objectToSerialize).toString();
String expectedResult =
"<myInterfaceElement class=\"myPackage.MyImplementation\">\n" +
" <field1>value1</field1>\n" +
" <field2>value2</field2>\n" +
"</myInterfaceElement>";
assertEquals(expectedResult, xmlResult);
}
@Test
public void deserializeWithClassAttribute() {
String inputXmlString =
"<myInterfaceElement class=\"myPackage.MyImplementation\">\r\n" +
" <field1>value1</field1>\r\n" +
" <field2>value2</field2>\r\n" +
"</myInterfaceElement>";
final XStream xStream = new XStream(new DomDriver());
MyInterface result = (MyInterface)xStream.fromXML(inputXmlString);
assertTrue("Instance of MyImplementation returned", result instanceof MyImplementation);
MyImplementation resultAsMyImplementation = (MyImplementation)result;
assertEquals("Field 1 deserialized", "value1", resultAsMyImplementation.field1);
assertEquals("Field 2 deserialized", "value2", resultAsMyImplementation.field2);
}
}
我通過執行以下操作解決了這個問題(感謝使用McD的提示使用Converter):
添加一個擴展ReflectionConverter的自定義轉換器:
package myPackage; import com.thoughtworks.xstream.converters.MarshallingContext; import com.thoughtworks.xstream.converters.reflection.ReflectionConverter; import com.thoughtworks.xstream.converters.reflection.ReflectionProvider; import com.thoughtworks.xstream.io.HierarchicalStreamWriter; import com.thoughtworks.xstream.mapper.Mapper; public class MyInterfaceConverter extends ReflectionConverter { public MyInterfaceConverter(Mapper mapper, ReflectionProvider reflectionProvider) { super(mapper, reflectionProvider); } @Override public void marshal(Object original, final HierarchicalStreamWriter writer, final MarshallingContext context) { writer.addAttribute("class", original.getClass().getCanonicalName()); super.marshal(original, writer, context); } @SuppressWarnings("rawtypes") @Override public boolean canConvert(Class type) { return MyInterface.class.isAssignableFrom(type); } }
設置xStream時注冊新的Converter:
@Test public void classAttributeSetInResult() { MyInterface objectToSerialize = new MyImplementation("value1", "value2"); final XStream xStream = new XStream(new DomDriver()); xStream.alias("myInterfaceElement", MyImplementation.class); xStream.registerConverter(new MyInterfaceConverter(xStream.getMapper(), xStream.getReflectionProvider())); String xmlResult = xStream.toXML(objectToSerialize).toString(); String expectedResult = "<myInterfaceElement class=\\"myPackage.MyImplementation\\">\\n" + " <field1>value1</field1>\\n" + " <field2>value2</field2>\\n" + "</myInterfaceElement>"; assertEquals(expectedResult, xmlResult); }
希望這會幫助其他人。 如果有人有更好的主意,請告訴我!
我將使用自定義轉換器來解決此問題:
您的類/接口:
public static interface MyInterface {
public String getField1();
public String getField2();
}
public static class MyImplementation implements MyInterface {
public String field1;
public String field2;
public MyImplementation(String field1, String field2) {
this.field1 = field1;
this.field2 = field2;
}
public String getField1() { return field1; }
public String getField2() { return field2; }
}
相當快速和骯臟的轉換器:
public static class MyInterfaceConverter implements Converter {
private static final String ATTR_NAME_CLASS = "concrete-class";
private static final String NODE_NAME_FIELD1 = "field1";
private static final String NODE_NAME_FIELD2 = "field2";
public boolean canConvert(Class type)
{
return type.equals(MyImplementation.class);
}
public void marshal(Object obj, HierarchicalStreamWriter writer, MarshallingContext context)
{
if (obj == null)
// no need to save null-objects
return;
final String type = obj.getClass().getSimpleName();
final MyInterface myInterface;
if (obj instanceof MyImplementation)
myInterface = (MyInterface) obj;
// else if (...)
// ...
else
throw new IllegalArgumentException("Cannot convert objects of type " + obj.getClass());
writer.addAttribute(ATTR_NAME_CLASS, type);
marshalAttribute(writer, context, NODE_NAME_FIELD1, myInterface.getField1());
marshalAttribute(writer, context, NODE_NAME_FIELD2, myInterface.getField2());
}
private static void marshalAttribute(HierarchicalStreamWriter writer, MarshallingContext context, String attrName, Object val)
{
if (val != null) {
writer.startNode(attrName);
context.convertAnother(val);
writer.endNode();
}
}
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context)
{
final String type = reader.getAttribute(ATTR_NAME_CLASS);
String field1Value = null, field2Value = null;
while (reader.hasMoreChildren()) {
reader.moveDown();
if (NODE_NAME_FIELD1.equals(reader.getNodeName()))
field1Value = (String)context.convertAnother(null, String.class);
else if (NODE_NAME_FIELD2.equals(reader.getNodeName()))
field2Value = (String)context.convertAnother(null, String.class);
reader.moveUp();
}
if (MyImplementation.class.getSimpleName().equals(type)) {
return new MyImplementation(field1Value, field2Value);
}
throw new IllegalArgumentException("Cannot unmarshal objects of type " + type);
}
}
測試/使用/ XStream初始化:
@Test
public void classAttributeSetInResult() {
MyInterface objectToSerialize = new MyImplementation("value1", "value2");
final XStream xStream = new XStream(new DomDriver());
xStream.alias("myInterfaceElement", MyImplementation.class);
// xStream.alias("myInterfaceElement", OtherImplementation.class);
xStream.registerConverter(new MyInterfaceConverter());
String xmlResult = xStream.toXML(objectToSerialize).toString();
String expectedResult =
"<myInterfaceElement concrete-class=\"MyImplementation\">\r\n" +
" <field1>value1</field1>\r\n" +
" <field2>value2</field2>\r\n" +
"</myInterfaceElement>";
assertEquals(expectedResult, xmlResult);
}
@Test
public void deserializeWithClassAttribute() {
String inputXmlString =
"<myInterfaceElement concrete-class=\"MyImplementation\">\r\n" +
" <field1>value1</field1>\r\n" +
" <field2>value2</field2>\r\n" +
"</myInterfaceElement>";
final XStream xStream = new XStream(new DomDriver());
xStream.alias("myInterfaceElement", MyImplementation.class);
// xStream.alias("myInterfaceElement", OtherImplementation.class);
xStream.registerConverter(new MyInterfaceConverter());
MyInterface result = (MyInterface)xStream.fromXML(inputXmlString);
assertTrue("Instance of MyImplementation returned", result instanceof MyImplementation);
MyImplementation resultAsMyImplementation = (MyImplementation)result;
assertEquals("Field 1 deserialized", "value1", resultAsMyImplementation.field1);
assertEquals("Field 2 deserialized", "value2", resultAsMyImplementation.field2);
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.