XStream - 注解

  • 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.
  • 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;
       }     
    }
    
  • 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);