XStream - 注解

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  简述

  XStream 支持注解类似于自动配置而不是编码。在上一章中，我们已经在代码中看到了以下配置。

  
  xstream.alias("student", Student.class);
  xstream.alias("note", Note.class);
  xstream.useAttributeFor(Student.class, "studentName");
  xstream.aliasField("name", Student.class, "studentName");
  xstream.addImplicitCollection(Student.class, "notes");
  

  以下代码片段说明了如何使用注解以更简单的方式完成相同的工作。

  
  @XStreamMooas("student")   //define class level alias
  class Student {
     @XStreamMooas("name")   //define field level alias
     @XStreamAsAttribute     //define field as attribute
     private String studentName;
     
     @XStreamImplicit        //define list as an implicit collection
     private List<Note> notes = new ArrayList<Note>();
     
     @XStreamOmitField       //omit a field to not to be a part of XML
     private int type;
  }
  

  让我们使用 XStream 测试上述注解。

  在其中创建一个名为 XStreamTester 的 java 类文件 C:\>XStream_WORKSPACE\com\jc2182\xstream.
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  文件：XStreamTester.java

  
  package com.jc2182.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.annotations.XStreamMooas;
  import com.thoughtworks.xstream.annotations.XStreamAsAttribute;
  import com.thoughtworks.xstream.annotations.XStreamImplicit;
  import com.thoughtworks.xstream.annotations.XStreamOmitField;
  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.processAnnotations(Student.class);      
        //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."));
        student.setType(1);
        
        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;
        }
     }
  }
  @XStreamMooas("student")
  class Student {
     @XStreamMooas("name")
     @XStreamAsAttribute   
     private String studentName;
     @XStreamImplicit
     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;
     }
     
     @XStreamOmitField    
     private int type;
     public int getType() {
        return type;
     }
     public void setType(int type) {
        this.type = type;
     }
  }
  @XStreamMooas("note")
  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;
     }     
  }
  

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  验证结果

  使用编译类 javac 编译器如下 -

  
  C:\XStream_WORKSPACE\com\jc2182\xstream>javac XStreamTester.java
  

  现在运行 XStreamTester 以查看结果 -

  
  C:\XStream_WORKSPACE\com\jc2182\xstream>java XStreamTester
  

  验证输出如下 -

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

  为了指示 XStream 框架处理注解，需要在序列化 xml 之前添加以下命令。

  
  xstream.processAnnotations(Student.class);      
  

  或者

  
  xstream.autodetectAnnotations(true);