XStream - conversor personalizado

O XStream permite escrever um conversor do zero, para que o desenvolvedor possa escrever uma implementação completamente nova sobre como serializar um objeto para XML e vice-versa. Uma interface de conversor fornece três métodos -

canConvert - É uma verificação de serialização de tipo de objeto compatível.
marshal - Serializa um objeto para XML.
unmarshal - Ele desserializa um objeto de XML.

Etapa 1: implemente a interface do conversor

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;
   }
}

Etapa 2: registrar conversor

xstream.registerConverter(new StudentConverter());

Vamos agora testar o código com conversor em XStream.

Crie um arquivo de classe java chamado XStreamTester em C:\>XStream_WORKSPACE\com\tutorialspoint\xstream.

Arquivo: XStreamTester.java

package com.tutorialspoint.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);
   }
}

Verifique o resultado

Compile as classes usando javac compilador da seguinte forma -

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

Agora execute o XStreamTester para ver o resultado -

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

Verifique a saída da seguinte forma -

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

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