定制转换器（Custom Converter）

XStream允许从头开始编写转换器，以便开发人员可以编写一个全新的实现，介绍如何将对象序列化为XML，反之亦然。 转换器接口提供三种方法 -

• canConvert - 检查支持的对象类型序列化。

• marshal - 它将对象序列化为XML。

• unmarshal - 它从XML unmarshal序列化对象。

第1步:实现转换器接口

class StudentConverter implements Converter {
   public boolean canConvert(Class object) {
      return object.equals(Student.class);
   }
   public void marshal(Object value, HierarchicalStreamWriter writer, MarshallingContext context) {
      Student student = (Student) value;
      writer.startNode("name");
      writer.setValue(student.getName().getFirstName() + "," + student.getName().getLastName());
      writer.endNode();
   }
   public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
      reader.moveDown();
      String[] nameparts = reader.getValue().split(",");
      Student student = new Student(nameparts[0],nameparts[1]);
      reader.moveUp();
      return student;
   }
}	

第2步:注册转换器

xstream.registerConverter(new StudentConverter());

现在让我们在XStream中使用转换器测试代码。

在C:\》XStream_WORKSPACE\com\xnip\xstream创建名为XStreamTester的java类文件。

File: XStreamTester.java

package cn.xnip.xstream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.sax.SAXSource;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.stream.StreamResult;
import org.xml.sax.InputSource;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.annotations.XStreamAlias;
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;
import com.thoughtworks.xstream.io.xml.StaxDriver;
public class XStreamTester {
   public static void main(String args[]) {
      XStreamTester tester = new XStreamTester();
      XStream xstream = new XStream(new StaxDriver());
      Student student = tester.getStudentDetails();		
      xstream.autodetectAnnotations(true);
      xstream.registerConverter(new StudentConverter());
      //Object to XML Conversion
      String xml = xstream.toXML(student);
      System.out.println(formatXml(xml));		
   }	
   private Student getStudentDetails() {
      Student student = new Student("Mahesh","Parashar");		
      return student;
   }
   public static String formatXml(String xml) {
      try {
         Transformer serializer = SAXTransformerFactory.newInstance().newTransformer();
         serializer.setOutputProperty(OutputKeys.INDENT, "yes");
         serializer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
         Source xmlSource = new SAXSource(new InputSource(
            new ByteArrayInputStream(xml.getBytes())));
         StreamResult res =  new StreamResult(new ByteArrayOutputStream());            
         serializer.transform(xmlSource, res);
         return new String(((ByteArrayOutputStream)res.getOutputStream()).toByteArray());
      } catch(Exception e) {
         return xml;
      }
   }   
}
@XStreamAlias("student")
class Student {
   @XStreamAlias("name")
   private Name studentName;
   public Student(String firstName, String lastName) {
      this.studentName = new Name(firstName, lastName);
   }
   public Name getName() {
      return studentName;
   }	
}
class Name {
   private String firstName;
   private String lastName;
   public Name(String firstName, String lastName) {
      this.firstName = firstName;
      this.lastName = lastName;
   }
   public String getFirstName() {
      return firstName;
   }
   public String getLastName() {
      return lastName;
   }     
}
class StudentConverter implements Converter {
   public void marshal(Object value, HierarchicalStreamWriter writer,
      MarshallingContext context) {
      Student student = (Student) value;
      writer.startNode("name");
      writer.setValue(student.getName().getFirstName() + "," + student.getName().getLastName());
      writer.endNode();
   }
   public Object unmarshal(HierarchicalStreamReader reader,
      UnmarshallingContext context) {
      reader.moveDown();
      String[] nameparts = reader.getValue().split(",");
      Student student = new Student(nameparts[0],nameparts[1]);
      reader.moveUp();
      return student;
   }
   public boolean canConvert(Class object) {
      return object.equals(Student.class);
   }
}	

验证结果 (Verify the Result)

使用javac编译器编译类如下 -

C:\XStream_WORKSPACE\com\xnip\xstream>javac XStreamTester.java

现在运行XStreamTester来查看结果 -

C:\XStream_WORKSPACE\com\xnip\xstream>java XStreamTester

验证输出如下 -

<?xml version = "1.0" encoding = "UTF-8"?>
<student>
   <name>Mahesh,Parashar</name>
</student>