XStream - Aliasing de coleções implícitas

O aliasing de coleções implícitas é usado quando uma coleção deve ser representada em XML sem exibir as raízes. Por exemplo, em nosso caso, precisamos exibir cada nota uma por uma, mas não no nó raiz 'notas'. Vamos modificar nosso exemplo novamente e adicionar o seguinte código a ele.

xstream.addImplicitCollection(Student.class, "notes");

Vamos testar a serialização dos objetos acima usando o 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 java.util.ArrayList;
import java.util.List;

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.io.xml.StaxDriver;

public class XStreamTester {

   public static void main(String args[]) {
   
      XStreamTester tester = new XStreamTester();
      XStream xstream = new XStream(new StaxDriver());
      
      xstream.alias("student", Student.class);
      xstream.alias("note", Note.class);
      xstream.aliasField("name", Student.class, "studentName");
      xstream.addImplicitCollection(Student.class, "notes");
      
      Student student = tester.getStudentDetails();
      
      //Object to XML Conversion
      String xml = xstream.toXML(student);
      System.out.println(formatXml(xml));		
   }	

   private Student getStudentDetails() {
      Student student = new Student("Mahesh");
      
      student.addNote(new Note("first","My first assignment."));
      student.addNote(new Note("second","My Second assignment."));
      
      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;
      }
   }
}

class Student {
   private String studentName;
   private List<Note> notes = new ArrayList<Note>();
   
   public Student(String name) {
      this.studentName = name;
   }
   
   public void addNote(Note note) {
      notes.add(note);
   }
   
   public String getName() {
      return studentName;
   }
   
   public List<Note> getNotes() {
      return notes;
   }
}

class Note {
   private String title;
   private String description;
   
   public Note(String title, String description) {
      this.title = title;
      this.description = description;
   }
   
   public String getTitle() {
      return title;
   }
   
   public String getDescription() {
      return description;
   }     
}

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 como segue -

<?xml version = "1.0" encoding = "UTF-8"?>
<student>
   <name>Mahesh</name>
   <note>
      <title>first</title>
      <description>My first assignment.</description>
   </note>
   
   <note>
      <title>second</title>
      <description>My Second assignment.</description>
   </note>
</student>

No resultado acima, podemos ver que o nome está vindo como um nó filho e precisamos dele como um atributo do nó raiz. Para substituí-lo, siga a próxima seção.

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