java - 如何使用 XStream 序列化/反序列化类型层次结构中的对象？

Question

我正在使用 XStream。目前，用其他东西替代 XStream 并不容易。

我有一个接口(interface) (MyInterface) 和几个实现该接口(interface)的子类(在下面的示例代码中，有一个名为 MyImplementation)。

我想序列化和反序列化子类的实例。我发现如果将 class 属性放入 XML 中，就可以很好地反序列化:

<myInterfaceElement class="myPackage.MyImplementation">
  <field1>value1</field1>
  <field2>value2</field2>
</myInterfaceElement>

但是，我不知道如何让XStream写入类属性。如何让 XStream 在序列化时包含类属性？或者是否有另一种方法来序列化/反序列化类层次结构，以便所有实现的元素名称都相同，并且每个子类都可以定义自己的字段？

这里是 MyInterface、MyImplementation 的示例，这是一个试图使其工作的 JUnit 测试用例。 deserializeWithClassAttribute 测试通过，而 classAttributeSetInResult 失败。

<小时/>

package myPackage;

public interface MyInterface {

}

<小时/>

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;
    }
}

<小时/>

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);
    }
}

Answer 1

我通过执行以下操作解决了这个问题(感谢 McD 提示使用转换器):

1. 添加扩展 ReflectionConverter 的自定义转换器:

   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);
       }
   
   }
   

2. 在设置 xStream 时注册新转换器:

   @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);
   }
   

希望这能对其他人有所帮助。如果有人有更好的想法，请告诉我!