xStream完美转换XML、JSON(转）

xStream框架

xStream可以轻易的将Java对象和xml文档相互转换，而且可以修改某个特定的属性和节点名称，而且也支持json的转换；

前面有介绍过json-lib这个框架，在线博文：http://www.cnblogs.com/hoojo/archive/2011/04/21/2023805.html

以及Jackson这个框架，在线博文：http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html

它们都完美支持JSON，但是对xml的支持还不是很好。一定程度上限制了对Java对象的描述，不能让xml完全体现到对Java对象的描述。这里将会介绍xStream对JSON、XML的完美支持。xStream不仅对XML的转换非常友好，而且提供annotation注解，可以在JavaBean中完成对xml节点、属性的描述。以及对JSON也支持，只需要提供相关的JSONDriver就可以完成转换。

1. 什么作用

　　可以把JavaBean转换为（序列化为）xml

2. XStream的jar包
　　核心JAR包：xstream-1.4.7.jar；
　　必须依赖包：xpp3_min-1.1.4c（XML Pull Parser，一款速度很快的XML解析器）；

3. 使用步骤
　　XStream xstream = new XStream();
　　String xmlStr = xstream.toXML(javabean);

4. 使用细节
　　别名：把类型对应的元素名修改了
　　　　xstream.alias("china", List.class)：让List类型生成的元素名为china
　　　　xstream.alias("province", Province.class)：让Province类型生成的元素名为province
　　使用为属性：默认类的成员，生成的是元素的子元素！我们希望让类的成员生成元素的属性
　　　　xstream.useAttributeFor(Province.class, "name")：把Province类的名为name成员，生成<province>元素的name属性
　　去除Collection类型的成名：我们只需要Collection的内容，而不希望Collection本身也生成一个元素
　　　　xstream.addImplicitCollection(Province.class, "cities")：让Province类的名为cities(它是List类型的，它的内容还会生成元素)的成名不生成元素
　　去除类的指定成名，让其不生成xml元素
　　　　xstream.omitField(City.class, "description")：在生成的xml中不会出现City类的名为description的对应的元素！

一、准备工作

1、 下载jar包、及官方资源

xStream的jar下载地址：

https://nexus.codehaus.org/content/repositories/releases/com/thoughtworks/xstream/xstream-distribution/1.3.1/xstream-distribution-1.3.1-bin.zip

官方的示例很全，官方参考示例：http://xstream.codehaus.org/tutorial.html

添加xstream-1.3.1.jar文件到工程中，就可以开始下面的工作；需要的jar如下：

2、 测试用例代码

package com.hoo.test;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.StringReader;
import java.io.Writer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.codehaus.jettison.json.JSONException;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.hoo.entity.Birthday;
import com.hoo.entity.Classes;
import com.hoo.entity.ListBean;
import com.hoo.entity.Student;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
import com.thoughtworks.xstream.io.json.JettisonMappedXmlDriver;
import com.thoughtworks.xstream.io.json.JsonHierarchicalStreamDriver;
import com.thoughtworks.xstream.io.json.JsonWriter;

/**
 * <b>function:</b>Java对象和XML字符串的相互转换
 * jar-lib-version: xstream-1.3.1
 * @author hoojo
 * @createDate Nov 27, 2010 12:15:15 PM
 * @file XStreamTest.java
 * @package com.hoo.test
 * @project WebHttpUtils
 * @blog http://blog.csdn.net/IBM_hoojo
 * @email hoojo_@126.com
 * @version 1.0
 */
@SuppressWarnings("unchecked")
public class XStreamTest {

    private XStream xstream = null;
    private ObjectOutputStream  out = null;
    private ObjectInputStream in = null;

    private Student bean = null;

    /**
     * <b>function:</b>初始化资源准备
     * @author hoojo
     * @createDate Nov 27, 2010 12:16:28 PM
     */
    @Before
    public void init() {
        try {
            xstream = new XStream();
            //xstream = new XStream(new DomDriver()); // 需要xpp3 jar
        } catch (Exception e) {
            e.printStackTrace();
        }
        bean = new Student();
        bean.setAddress("china");
        bean.setEmail("jack@email.com");
        bean.setId(1);
        bean.setName("jack");
        Birthday day = new Birthday();
        day.setBirthday("2010-11-22");
        bean.setBirthday(day);
    }

    /**
     * <b>function:</b>释放对象资源
     * @author hoojo
     * @createDate Nov 27, 2010 12:16:38 PM
     */
    @After
    public void destory() {
        xstream = null;
        bean = null;
        try {
            if (out != null) {
                out.flush();
                out.close();
            }
            if (in != null) {
                in.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.gc();
    }

    public final void fail(String string) {
        System.out.println(string);
    }

    public final void failRed(String string) {
        System.err.println(string);
    }
}

通过XStream对象的toXML方法就可以完成Java对象到XML的转换，toXML方法还有2个相同签名的方法，需要传递一个流。然后通过流来完成xml信息的输出。

3、 需要的JavaBean

package com.hoo.entity;

public class Student {
    private int id;
    private String name;
    private String email;
    private String address;
    private Birthday birthday;
    //getter、setter
    public String toString() {
        return this.name + "#" + this.id + "#" + this.address + "#" + this.birthday + "#" + this.email;
    }
}

二、Java转换成XML

1、 JavaBean转换XM

/**
 * <b>function:</b>Java对象转换成XML字符串
 * @author hoojo
 * @createDate Nov 27, 2010 12:19:01 PM
 */
@Test
public void writeBean2XML() {
    try {
        fail("------------Bean->XML------------");
        fail(xstream.toXML(bean));
        fail("重命名后的XML");
        //类重命名
        //xstream.alias("account", Student.class);
        //xstream.alias("生日", Birthday.class);
        //xstream.aliasField("生日", Student.class, "birthday");
        //xstream.aliasField("生日", Birthday.class, "birthday");
        //fail(xstream.toXML(bean));
        //属性重命名
        xstream.aliasField("邮件", Student.class, "email");
        //包重命名
        xstream.aliasPackage("hoo", "com.hoo.entity");
        fail(xstream.toXML(bean));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

看结果中的第一份xml内容，是没有经过然后修改或重命名的文档，按照原样输出。文档中的第二份文档的package经过重命名，email属性也经过重命名以及类名也可以进行重命名的。

运行后结果如下：

------------Bean->XML------------

<com.hoo.entity.Student>
  <id>1</id>
  <name>jack</name>
  <email>jack@email.com</email>
  <address>china</address>
  <birthday>
    <birthday>2010-11-22</birthday>
  </birthday>
</com.hoo.entity.Student>

重命名后的XML

<hoo.Student>
  <id>1</id>
  <name>jack</name>
  <邮件>jack@email.com</邮件>
  <address>china</address>
  <birthday>
    <birthday>2010-11-22</birthday>
  </birthday>
</hoo.Student>

2、 将List集合转换成xml文档

/**
 * <b>function:</b>将Java的List集合转换成XML对象
 * @author hoojo
 * @createDate Nov 27, 2010 12:20:07 PM
 */
@Test
public void writeList2XML() {
    try {
        //修改元素名称
        xstream.alias("beans", ListBean.class);
        xstream.alias("student", Student.class);
        fail("----------List-->XML----------");
        ListBean listBean = new ListBean();
        listBean.setName("this is a List Collection");

        List<Object> list = new ArrayList<Object>();
        list.add(bean);
        list.add(bean);//引用bean
        //list.add(listBean);//引用listBean，父元素

        bean = new Student();
        bean.setAddress("china");
        bean.setEmail("tom@125.com");
        bean.setId(2);
        bean.setName("tom");
        Birthday day = new Birthday("2010-11-22");
        bean.setBirthday(day);

        list.add(bean);
        listBean.setList(list);

        //将ListBean中的集合设置空元素，即不显示集合元素标签
        //xstream.addImplicitCollection(ListBean.class, "list");

        //设置reference模型
        //xstream.setMode(XStream.NO_REFERENCES);//不引用
        xstream.setMode(XStream.ID_REFERENCES);//id引用
        //xstream.setMode(XStream.XPATH_ABSOLUTE_REFERENCES);//绝对路径引用

        //将name设置为父类（Student）的元素的属性
        xstream.useAttributeFor(Student.class, "name");
        xstream.useAttributeFor(Birthday.class, "birthday");
        //修改属性的name
        xstream.aliasAttribute("姓名", "name");
        xstream.aliasField("生日", Birthday.class, "birthday");

        fail(xstream.toXML(listBean));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

上面的代码运行后，结果如下：

----------List-->XML----------

<beans id="1">
  <name>this is a List Collection</name>
  <list id="2">
    <student id="3" 姓名="jack">
      <id>1</id>
      <email>jack@email.com</email>
      <address>china</address>
      <birthday id="4" 生日="2010-11-22"/>
    </student>
    <student reference="3"/>
    <student id="5" 姓名="tom">
      <id>2</id>
      <email>tom@125.com</email>
      <address>china</address>
      <birthday id="6" 生日="2010-11-22"/>
    </student>
  </list>
</beans>

如果不加xstream.addImplicitCollection(ListBean.class, "list");

这个设置的话，会出现一个List节点包裹着Student节点元素。添加addImplicitCollection可以忽略这个list节点元素。那么上面的list节点就不存在，只会在beans元素中出现name、student这2个xml元素标签；

setMode是设置相同的对象的引用方式，如果设置XStream.NO_REFERENCES就是不引用，会输出2分相同的Student元素。如果是XStream.ID_REFERENCES会引用相同的那个对象的id属性，如果是XStream.XPATH_ABSOLUTE_REFERENCES引用，那么它将显示xpath路径。上面采用的id引用，<student reference="3"/>这个引用了id=3的那个student标签元素；

useAttributeFor是设置某个节点显示到父节点的属性中，也就是将指定class中的指定属性，在这个class元素节点的属性中显示。

如：<student><name>hoojo</name></student>

设置好后就是这样的结果：<student name=”hoojo”></student>

aliasAttribute是修改属性名称。

3、 在JavaBean中添加Annotation注解进行重命名设置

先看看JavaBean的代码

package com.hoo.entity;

import java.util.Arrays;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.List;
import com.thoughtworks.xstream.annotations.XStreamAlias;
import com.thoughtworks.xstream.annotations.XStreamAsAttribute;
import com.thoughtworks.xstream.annotations.XStreamConverter;
import com.thoughtworks.xstream.annotations.XStreamImplicit;
import com.thoughtworks.xstream.annotations.XStreamOmitField;

@XStreamAlias("class")
public class Classes {

    /*
     * 设置属性显示
     */
    @XStreamAsAttribute
    @XStreamAlias("名称")
    private String name;

    /*
     * 忽略
     */
    @XStreamOmitField
    private int number;

    @XStreamImplicit(itemFieldName = "Students")
    private List<Student> students;

    @SuppressWarnings("unused")
    @XStreamConverter(SingleValueCalendarConverter.class)
    private Calendar created = new GregorianCalendar();

    public Classes(){}
    public Classes(String name, Student... stu) {
        this.name = name;
        this.students = Arrays.asList(stu);
    }
    //getter、setter
}
SingleValueCalendarConverter.java这个是一个类型转换器

package com.hoo.entity;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
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;

public class SingleValueCalendarConverter implements Converter {
     public void marshal(Object source, HierarchicalStreamWriter writer,
                MarshallingContext context) {
            Calendar calendar = (Calendar) source;
            writer.setValue(String.valueOf(calendar.getTime().getTime()));
        }

        public Object unmarshal(HierarchicalStreamReader reader,
                UnmarshallingContext context) {
            GregorianCalendar calendar = new GregorianCalendar();
            calendar.setTime(new Date(Long.parseLong(reader.getValue())));
            return calendar;
        }

        @SuppressWarnings("unchecked")
        public boolean canConvert(Class type) {
            return type.equals(GregorianCalendar.class);
        }
}

再看看测试用例代码

@Test
public void writeList2XML4Annotation() {
    try {
        failRed("---------annotation Bean --> XML---------");
        Student stu = new Student();
        stu.setName("jack");
        Classes c = new Classes("一班", bean, stu);
        c.setNumber(2);
        //对指定的类使用Annotation
        //xstream.processAnnotations(Classes.class);
        //启用Annotation
        //xstream.autodetectAnnotations(true);
        xstream.alias("student", Student.class);
        fail(xstream.toXML(c));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

当启用annotation或是对某个特定的类启用annotation时，上面的classes这个类才有效果。如果不启用annotation，运行后结果如下：

---------annotation Bean --> XML---------

<com.hoo.entity.Classes>
  <name>一班</name>
  <number>2</number>
  <students class="java.util.Arrays$ArrayList">
    <a class="student-array">
      <student>
        <id>1</id>
        <name>jack</name>
        <email>jack@email.com</email>
        <address>china</address>
        <birthday>
          <birthday>2010-11-22</birthday>
        </birthday>
      </student>
      <student>
        <id>0</id>
        <name>jack</name>
      </student>
    </a>
  </students>
  <created>
    <time>1303292056718</time>
    <timezone>Asia/Shanghai</timezone>
  </created>
</com.hoo.entity.Classes>

当启用annotation后xstream.processAnnotations(Classes.class)，结果如下：

---------annotation Bean --> XML---------

<class 名称="一班">
  <Students>
    <id>1</id>
    <name>jack</name>
    <email>jack@email.com</email>
    <address>china</address>
    <birthday>
      <birthday>2010-11-22</birthday>
    </birthday>
  </Students>
  <Students>
    <id>0</id>
    <name>jack</name>
  </Students>
  <created>1303292242937</created>
</class>

4、 Map集合转换xml文档

/**
 * <b>function:</b>Java Map集合转XML
 * @author hoojo
 * @createDate Nov 27, 2010 1:13:26 PM
 */
@Test
public void writeMap2XML() {
    try {
        failRed("---------Map --> XML---------");
        Map<String, Student> map = new HashMap<String, Student>();
        map.put("No.1", bean);//put

        bean = new Student();
        bean.setAddress("china");
        bean.setEmail("tom@125.com");
        bean.setId(2);
        bean.setName("tom");
        Birthday day = new Birthday("2010-11-22");
        bean.setBirthday(day);
        map.put("No.2", bean);//put

        bean = new Student();
        bean.setName("jack");
        map.put("No.3", bean);//put

        xstream.alias("student", Student.class);
        xstream.alias("key", String.class);
        xstream.useAttributeFor(Student.class, "id");
        xstream.useAttributeFor("birthday", String.class);
        fail(xstream.toXML(map));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

运行后结果如下：

---------Map --> XML---------

<map>
  <entry>
    <key>No.3</key>
    <student id="0">
      <name>jack</name>
    </student>
  </entry>
  <entry>
    <key>No.1</key>
    <student id="1">
      <name>jack</name>
      <email>jack@email.com</email>
      <address>china</address>
      <birthday birthday="2010-11-22"/>
    </student>
  </entry>
  <entry>
    <key>No.2</key>
    <student id="2">
      <name>tom</name>
      <email>tom@125.com</email>
      <address>china</address>
      <birthday birthday="2010-11-22"/>
    </student>
  </entry>
</map>

5、 用OutStream输出流写XML

/**
 * <b>function:</b>用OutStream输出流写XML
 * @author hoojo
 * @createDate Nov 27, 2010 1:13:48 PM
 */
@Test
public void writeXML4OutStream() {
    try {
        out = xstream.createObjectOutputStream(System.out);
        Student stu = new Student();
        stu.setName("jack");
        Classes c = new Classes("一班", bean, stu);
        c.setNumber(2);
        failRed("---------ObjectOutputStream # JavaObject--> XML---------");
        out.writeObject(stu);
        out.writeObject(new Birthday("2010-05-33"));
        out.write(22);//byte
        out.writeBoolean(true);
        out.writeFloat(22.f);
        out.writeUTF("hello");

    } catch (Exception e) {
        e.printStackTrace();
    }
}

使用输出流后，可以通过流对象完成xml的构建，即使没有JavaBean对象，你可以用流来构建一个复杂的xml文档，运行后结果如下：

---------ObjectOutputStream # JavaObject--> XML---------

<object-stream>
  <com.hoo.entity.Student>
    <id>0</id>
    <name>jack</name>
  </com.hoo.entity.Student>
  <com.hoo.entity.Birthday>
    <birthday>2010-05-33</birthday>
  </com.hoo.entity.Birthday>
  <byte>22</byte>
  <boolean>true</boolean>
  <float>22.0</float>
  <string>hello</string>
</object-stream>

三、XML内容转换Java对象

1、 用InputStream将XML文档转换成java对象

/**
 * <b>function:</b>用InputStream将XML文档转换成java对象
 * 需要额外的jar xpp3-main.jar
 * @author hoojo
 * @createDate Nov 27, 2010 1:14:52 PM
 */
@Test
public void readXML4InputStream() {
    try {
        String s = "<object-stream><com.hoo.entity.Student><id>0</id><name>jack</name>" +
          "</com.hoo.entity.Student><com.hoo.entity.Birthday><birthday>2010-05-33</birthday>" +
          "</com.hoo.entity.Birthday><byte>22</byte><boolean>true</boolean><float>22.0</float>" +
          "<string>hello</string></object-stream>";
        failRed("---------ObjectInputStream## XML --> javaObject---------");
        StringReader reader = new StringReader(s);
        in = xstream.createObjectInputStream(reader);
        Student stu = (Student) in.readObject();
        Birthday b = (Birthday) in.readObject();
        byte i = in.readByte();
        boolean bo = in.readBoolean();
        float f = in.readFloat();
        String str = in.readUTF();
        System.out.println(stu);
        System.out.println(b);
        System.out.println(i);
        System.out.println(bo);
        System.out.println(f);
        System.out.println(str);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

读取后，转换的Java对象，结果如下：

---------ObjectInputStream## XML --> javaObject---------

jack#0#null#null#null
2010-05-33
22
true
22.0
hello

2、 将xml文档转换成Java对象

/**
 * <b>function:</b>将XML字符串转换成Java对象
 * @author hoojo
 * @createDate Nov 27, 2010 2:39:06 PM
 */
@Test
public void readXml2Object() {
    try {
        failRed("-----------Xml >>> Bean--------------");
        Student stu = (Student) xstream.fromXML(xstream.toXML(bean));
        fail(stu.toString());

        List<Student> list = new ArrayList<Student>();
        list.add(bean);//add

        Map<String, Student> map = new HashMap<String, Student>();
        map.put("No.1", bean);//put

        bean = new Student();
        bean.setAddress("china");
        bean.setEmail("tom@125.com");
        bean.setId(2);
        bean.setName("tom");
        Birthday day = new Birthday("2010-11-22");
        bean.setBirthday(day);
        list.add(bean);//add
        map.put("No.2", bean);//put

        bean = new Student();
        bean.setName("jack");
        list.add(bean);//add
        map.put("No.3", bean);//put

        failRed("==========XML >>> List===========");
        List<Student> studetns = (List<Student>) xstream.fromXML(xstream.toXML(list));
        fail("size:" + studetns.size());//3
        for (Student s : studetns) {
            fail(s.toString());
        }

        failRed("==========XML >>> Map===========");
        Map<String, Student> maps = (Map<String, Student>) xstream.fromXML(xstream.toXML(map));
        fail("size:" + maps.size());//3
        Set<String> key = maps.keySet();
        Iterator<String> iter = key.iterator();
        while (iter.hasNext()) {
            String k = iter.next();
            fail(k + ":" + map.get(k));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

运行后结果如下：

-----------Xml >>> Bean--------------

jack#1#china#2010-11-22#jack@email.com
==========XML >>> List===========
size:3
jack#1#china#2010-11-22#jack@email.com
tom#2#china#2010-11-22#tom@125.com
jack#0#null#null#null
==========XML >>> Map===========
size:3
No.3:jack#0#null#null#null
No.1:jack#1#china#2010-11-22#jack@email.com
No.2:tom#2#china#2010-11-22#tom@125.com

怎么样，成功的完成XML到JavaBean、List、Map的转换，更多对象转换还需要大家一一尝试。用法类似~这里就不一样赘述。

四、XStream对JSON的支持

xStream对JSON也有非常好的支持，它提供了2个模型驱动。用这2个驱动可以完成Java对象到JSON的相互转换。使用JettisonMappedXmlDriver驱动，将Java对象转换成json，需要添加jettison.jar

1、 用JettisonMappedXmlDriver完成Java对象到JSON的转换

/**
 * <b>function:</b>XStream结合JettisonMappedXmlDriver驱动，转换Java对象到JSON
 * 需要添加jettison jar
 * @author hoojo
 * @createDate Nov 27, 2010 1:23:18 PM
 */
@Test
public void writeEntity2JETTSON() {
    failRed("=======JettisonMappedXmlDriver===JavaObject >>>> JaonString=========");
    xstream = new XStream(new JettisonMappedXmlDriver());
    xstream.setMode(XStream.NO_REFERENCES);
    xstream.alias("student", Student.class);
    fail(xstream.toXML(bean));
}

运行后结果如下：

=======JettisonMappedXmlDriver===JavaObject >>>> JaonString=========

{"student":{"id":1,"name":"jack","email":"jack@email.com","address":"china","birthday":[{},"2010-11-22"]}}

JSON的转换和XML的转换用法一样，只是创建XStream需要传递一个参数，这个参数就是xml到JSON映射转换的驱动。这里会降到两个驱动，分别是JettisonMappedXmlDriver、JsonHierarchicalStreamDriver。

2、 JsonHierarchicalStreamDriver完成Java对象到JSON的转换

/**
 * <b>function:</b>用XStream结合JsonHierarchicalStreamDriver驱动
 * 转换java对象为JSON字符串
 * @author hoojo
 * @createDate Nov 27, 2010 1:16:46 PM
 */
@Test
public void writeEntiry2JSON() {
    failRed("======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========");
    xstream = new XStream(new JsonHierarchicalStreamDriver());
    //xstream.setMode(XStream.NO_REFERENCES);
    xstream.alias("student", Student.class);
    failRed("-------Object >>>> JSON---------");
    fail(xstream.toXML(bean));

    //failRed("========JsonHierarchicalStreamDriver==删除根节点=========");
    //删除根节点
    xstream = new XStream(new JsonHierarchicalStreamDriver() {
        public HierarchicalStreamWriter createWriter(Writer out) {
            return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);
        }
    });
    //xstream.setMode(XStream.NO_REFERENCES);
    xstream.alias("student", Student.class);
    fail(xstream.toXML(bean));
}

运行后结果如下：

======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========

-------Object >>>> JSON---------

{"student": {
  "id": 1,
  "name": "jack",
  "email": "jack@email.com",
  "address": "china",
  "birthday": {
    "birthday": "2010-11-22"
  }
}}
{
  "id": 1,
  "name": "jack",
  "email": "jack@email.com",
  "address": "china",
  "birthday": {
    "birthday": "2010-11-22"
  }
}

使用JsonHierarchicalStreamDriver转换默认会给转换后的对象添加一个根节点，但是在构建JsonHierarchicalStreamDriver驱动的时候，你可以重写createWriter方法，删掉根节点。

看上面的结果，一个是默认带根节点的JSON对象，它只是将类名作为一个属性，将对象作为该属性的一个值。而另一个没有带根属性的JSON就是通过重写createWriter方法完成的。

3、 将List集合转换成JSON字符串

@Test
public void writeList2JSON() {
    failRed("======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========");
    JsonHierarchicalStreamDriver driver = new JsonHierarchicalStreamDriver();
    xstream = new XStream(driver);
    //xstream = new XStream(new JettisonMappedXmlDriver());//转换错误
    //xstream.setMode(XStream.NO_REFERENCES);
    xstream.alias("student", Student.class);

    List<Student> list = new ArrayList<Student>();
    list.add(bean);//add

    bean = new Student();
    bean.setAddress("china");
    bean.setEmail("tom@125.com");
    bean.setId(2);
    bean.setName("tom");
    Birthday day = new Birthday("2010-11-22");
    bean.setBirthday(day);
    list.add(bean);//add

    bean = new Student();
    bean.setName("jack");
    list.add(bean);//add

    fail(xstream.toXML(list));

    //failRed("========JsonHierarchicalStreamDriver==删除根节点=========");
    //删除根节点
    xstream = new XStream(new JsonHierarchicalStreamDriver() {
        public HierarchicalStreamWriter createWriter(Writer out) {
            return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);
        }
    });
    xstream.alias("student", Student.class);
    fail(xstream.toXML(list));
}

运行后结果如下

======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========

##{"list": [
  {
    "id": 1,
    "name": "jack",
    "email": "jack@email.com",
    "address": "china",
    "birthday": {
      "birthday": "2010-11-22"
    }
  },
  {
    "id": 2,
    "name": "tom",
    "email": "tom@125.com",
    "address": "china",
    "birthday": {
      "birthday": "2010-11-22"
    }
  },
  {
    "id": 0,
    "name": "jack"
  }
]}
#[
  {
    "id": 1,
    "name": "jack",
    "email": "jack@email.com",
    "address": "china",
    "birthday": {
      "birthday": "2010-11-22"
    }
  },
  {
    "id": 2,
    "name": "tom",
    "email": "tom@125.com",
    "address": "china",
    "birthday": {
      "birthday": "2010-11-22"
    }
  },
  {
    "id": 0,
    "name": "jack"
  }
]

上面的list1是使用JsonHierarchicalStreamDriver 转换的，当然你也可以使用JettisonMappedXmlDriver驱动进行转换；用JettisonMappedXmlDriver转换后，你会发现格式不同而且没有根属性。

4、 Map转换json

@Test
public void writeMap2JSON() {
    failRed("======JsonHierarchicalStreamDriver==== Map >>>> JaonString=========");
    xstream = new XStream(new JsonHierarchicalStreamDriver());
    //xstream = new XStream(new JettisonMappedXmlDriver());
    xstream.alias("student", Student.class);

    Map<String, Student> map = new HashMap<String, Student>();
    map.put("No.1", bean);//put

    bean = new Student();
    bean.setAddress("china");
    bean.setEmail("tom@125.com");
    bean.setId(2);
    bean.setName("tom");
    bean.setBirthday(new Birthday("2010-11-21"));
    map.put("No.2", bean);//put

    bean = new Student();
    bean.setName("jack");
    map.put("No.3", bean);//put

    fail(xstream.toXML(map));

    //failRed("========JsonHierarchicalStreamDriver==删除根节点=========");
    //删除根节点
    xstream = new XStream(new JsonHierarchicalStreamDriver() {
        public HierarchicalStreamWriter createWriter(Writer out) {
            return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);
        }
    });
    xstream.alias("student", Student.class);
    fail(xstream.toXML(map));
}

运行后结果如下：

======JsonHierarchicalStreamDriver==== Map >>>> JaonString=========

{"map": [
  [
    "No.3",
    {
      "id": 0,
      "name": "jack"
    }
  ],
  [
    "No.1",
    {
      "id": 1,
      "name": "jack",
      "email": "jack@email.com",
      "address": "china",
      "birthday": {
        "birthday": "2010-11-22"
      }
    }
  ],
  [
    "No.2",
    {
      "id": 2,
      "name": "tom",
      "email": "tom@125.com",
      "address": "china",
      "birthday": {
        "birthday": "2010-11-21"
      }
    }
  ]
]}
[
  [
    "No.3",
    {
      "id": 0,
      "name": "jack"
    }
  ],
  [
    "No.1",
    {
      "id": 1,
      "name": "jack",
      "email": "jack@email.com",
      "address": "china",
      "birthday": {
        "birthday": "2010-11-22"
      }
    }
  ],
  [
    "No.2",
    {
      "id": 2,
      "name": "tom",
      "email": "tom@125.com",
      "address": "china",
      "birthday": {
        "birthday": "2010-11-21"
      }
    }
  ]
]

5、 将JSON转换java对象

/**
 * <b>function:</b>JsonHierarchicalStreamDriver可以将简单的json字符串转换成java对象，list、map转换不成功；
 * JsonHierarchicalStreamDriver读取JSON字符串到java对象出错
 * @author hoojo
 * @createDate Nov 27, 2010 1:22:26 PM
 * @throws JSONException
 */
@Test
public void readJSON2Object() throws JSONException {
    String json = "{\"student\": {" +
        "\"id\": 1," +
        "\"name\": \"haha\"," +
        "\"email\": \"email\"," +
        "\"address\": \"address\"," +
        "\"birthday\": {" +
            "\"birthday\": \"2010-11-22\"" +
        "}" +
    "}}";
    //JsonHierarchicalStreamDriver读取JSON字符串到java对象出错，但JettisonMappedXmlDriver可以
    xstream = new XStream(new JettisonMappedXmlDriver());
    xstream.alias("student", Student.class);
    fail(xstream.fromXML(json).toString());

    //JettisonMappedXmlDriver转换List集合出错，但JsonHierarchicalStreamDriver可以转换正确
    //JettisonMappedXmlDriver 转换的字符串 {"list":{"student":[{"id":1,"name":"haha","email":"email","address":"address","birthday":[{},"2010-11-22"]}]},"student":{"id":2,"name":"tom","email":"tom@125.com","address":"china","birthday":[{},"2010-11-22"]}}
    json = "{\"list\": [{" +
            "\"id\": 1," +
            "\"name\": \"haha\"," +
            "\"email\": \"email\"," +
            "\"address\": \"address\"," +
            "\"birthday\": {" +
              "\"birthday\": \"2010-11-22\"" +
            "}" +
           "},{" +
            "\"id\": 2," +
            "\"name\": \"tom\"," +
            "\"email\": \"tom@125.com\"," +
            "\"address\": \"china\"," +
            "\"birthday\": {" +
              "\"birthday\": \"2010-11-22\"" +
            "}" +
          "}]}";
    System.out.println(json);//用js转换成功
    List list = (List) xstream.fromXML(json);
    System.out.println(list.size());//0好像转换失败
}

运行后结果如下：

haha#1#address#2010-11-22#email

{"list": [{"id": 1,"name": "haha","email": "email","address": "address","birthday": {"birthday": "2010-11-22"}},
{"id": 2,"name": "tom","email": "tom@125.com","address": "china","birthday": {"birthday": "2010-11-22"}}]}
0

JSON到Java的转换是fromXML方法。