XStream - 自定义转换器

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  简述

  XStream 允许从头开始编写转换器，以便开发人员可以编写关于如何将对象序列化为 XML 的全新实现，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 − 将对象序列化为 XML。
  • unmarshal - 它从 XML 反序列化一个对象。
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  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;
     }
  }  
  

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  第 2 步：注册转换器

  
  xstream.registerConverter(new StudentConverter());
  

  现在让我们用 XStream 中的转换器测试代码。

  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 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.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;
        }
     }   
  }
  @XStreamMooas("student")
  class Student {
     @XStreamMooas("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

  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,Parashar</name>
  </student>