目录

XStream - 转换器( Converters)

XStream转换器是XStream库的关键组件,它负责将对象转换为XML,反之亦然。 XStream为常见类型提供了大量转换器,例如基元,字符串,文件,集合,数组和日期。

使用转换器

让我们使用SingleValueConvertor,其目的是将对象转换为单个字符串。 我们将使用SingleValueConvertor将对象写为属性字符串。

创建转换器

class NameConverter implements SingleValueConverter {
   public Object fromString(String name) {
      String[] nameparts = name.split(",");
      return new Name(nameparts[0], nameparts[1]);
   }
   public String toString(Object name) {
      return ((Name)name).getFirstName() + "," + ((Name)name).getLastName();
   }
   public boolean canConvert(Class type) {
      return type.equals(Name.class);
   }	
}

注册转换器

xstream.registerConverter(new NameConverter());

示例没有转换器

让我们首先在XStream中测试没有转换器的代码。

在C:\> XStream_WORKSPACE\com\iowiki\xstream中创建名为XStreamTester的java类文件。

File: XStreamTester.java

package com.iowiki.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.annotations.XStreamAsAttribute;
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);
      //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")
   @XStreamAsAttribute
   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;
   }     
}

Verify the Result

使用javac编译器编译类如下 -

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

现在运行XStreamTester来查看结果 -

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

验证输出如下 -

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

转换器示例

现在让我们在XStream中使用转换器测试代码。

在C:\> XStream_WORKSPACE\com\iowiki\xstream中创建名为XStreamTester的java类文件。

File: XStreamTester.java

package com.iowiki.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.annotations.XStreamAsAttribute;
import com.thoughtworks.xstream.converters.SingleValueConverter;
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 NameConverter());
      //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")
   @XStreamAsAttribute	
   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 NameConverter implements SingleValueConverter  {
   public Object fromString(String name) {
      String[] nameparts = name.split(",");
      return new Name(nameparts[0], nameparts[1]);
   }
   public String toString(Object name) {
      return ((Name)name).getFirstName() + "," + ((Name)name).getLastName();
   }
   public boolean canConvert(Class type) {
      return type.equals(Name.class);
   }
}

Verify the Result

使用javac编译器编译类如下 -

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

现在运行XStreamTester来查看结果 -

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

验证输出如下 -

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

定制转换器

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