XStream入坑指南

1.Xstream介绍

(1)Xstream介绍

Xstream是一种OXMapping 技术，是用来处理XML文件序列化的框架,在将JavaBean序列化，或将XML文件反序列化的时候，不需要其它辅助类和映射文件，使得XML序列化不再繁索。Xstream也可以将JavaBean序列化成Json或反序列化，使用非常方便。

(2)Xstream的简单例子

class Person//JavaBean实体类
{
  private String name;
  private int age;
  public Person(String name,int age)
  {
    this.name=name;
    this.age=age;
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream();
    //XML序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //XML反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);

    xstream = new XStream(new JettisonMappedXmlDriver());
    xstream.setMode(XStream.NO_REFERENCES);
    //Json序列化
    String json=xstream.toXML(bean);
    System.out.println(json);
    //Json反序列
    bean=(Person)xstream.fromXML(json);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
</test.Person>
Person [name=张三, age=19]
{"test.Person":{"name":"张三","age":19}}
Person [name=张三, age=19

注意：Xstream序列化XML时需要引用的jar包：xstream-[version].jar、xpp3-[version].jar、xmlpull-[version].jar。Xstream序列化Json需要引用的jar包：jettison-[version].jar。

使用Xstream序列化时，对JavaBean没有任何限制。JavaBean的字段可以是私有的，也可以没有getter或setter方法，还可以没有默认的构造函数。

2.Xstream的基本使用

(1)Xstream序列化XML

Xstream序列化XML时可以允许用户使用不同的XML解析器，用户可以使用一个标准的JAXP DOM解析器或自Java6集成StAX解析器。这样用户就不需要依赖xpp3-[version].jar。

Xstream序列化XML时，也可以对XML节点重命名。

public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    //XStream xstream = new XStream();//需要XPP3库
    //XStream xstream = new XStream(new DomDriver());//不需要XPP3库
    XStream xstream = new XStream(new StaxDriver());//不需要XPP3库开始使用Java6 
    xstream.alias("人",Person.class);//为类名节点重命名
    //XML序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //XML反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<?xml version="1.0" ?><人><name>张三</name><age>19</age></人>
Person [name=张三, age=19]

(2)Xstream序列化Json

Xstream序列化Json与序列化XML类似，例如：

<pre class="code-snippet__js" data-lang="cs">```

public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream(new JettisonMappedXmlDriver());//设置Json解析器
        xstream.setMode(XStream.NO_REFERENCES);//设置reference模型,不引用
    xstream.alias("人",Person.class);//为类名节点重命名
    //Json序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //Json反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

{"人":{"name":"张三","age":19}}
Person [name=张三, age=19]

3.Xstream序列化重命名

(1)为包重命名：Xstream.aliasPackage()方法

public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream();
    xstream.aliasPackage("com.lzw", "test");//为包名称重命名
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<com.lzw.Person>
  <name>张三</name>
  <age>19</age>
</com.lzw.Person>
Person [name=张三, age=19]

(2)为类重命名：Xstream.alias()方法

public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream();
    xstream.alias("人", Person.class);//为类名节点重命名
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<人>
  <name>张三</name>
  <age>19</age>
</人>
Person [name=张三, age=19]

(3)为字段重命名：Xstream.aliasField()方法

public class Test
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream();
    xstream.aliasField("姓名", Person.class,"name");//为类的字段节点重命名
    xstream.aliasField("年龄", Person.class,"age");//为类的字段节点重命名
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person>
  <姓名>张三</姓名>
  <年龄>19</年龄>
</test.Person>
Person [name=张三, age=19]

(4)省略集合根节点：Xstream.addImplicitCollection()方法

class Person
{
  private String name;
  private int age;
  private List friends;
  public Person(String name, int age, String... friends)
  {
    this.name = name;
    this.age = age;
    this.friends = Arrays.asList(friends);
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + ", friends=" + friends + "]";
  }
}
public class Test
{
  public static void main(String[] args)
  {
    Person bean =new Person("张三",19,"李四","王五","赵六");
    XStream xstream = new XStream();
    xstream.addImplicitCollection(Person.class, "friends");//省略集合根节点
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
  <string>李四</string>
  <string>王五</string>
  <string>赵六</string>
</test.Person>
Person [name=张三, age=19, friends=[李四, 王五, 赵六]]

(5)把字段节点设置成属性：Xstream.useAttributeFor()方法

public class Test
{
  public static void main(String[] args)
  {
    Person bean =new Person("张三",19,"李四","王五","赵六");
    XStream xstream = new XStream();
    xstream.useAttributeFor(Person.class, "name");//把字段节点设置成属性
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person name="张三">
  <age>19</age>
  <friends class="java.util.Arrays$ArrayList">
    <a class="string-array">
      <string>李四</string>
      <string>王五</string>
      <string>赵六</string>
    </a>
  </friends>
</test.Person>
Person [name=张三, age=19, friends=[李四, 王五, 赵六]]

(6)隐藏字段：xstream.omitField()方法

public class Test
{
  public static void main(String[] args)
  {
    Person bean =new Person("张三",19,"李四","王五","赵六");
    XStream xstream = new XStream();
    xstream.omitField(Person.class, "friends");//把字段节点隐藏
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
</test.Person>
Person [name=张三, age=19, friends=null]

4.Xstream注解的使用

(1)设置Xstream应用注解

使用Xstream注解前需要对Xstream进行配置，可以使用两种方式：应用某个JavaBean类的注解或自动使用JavaBean类的注解。代码如下：

XStream xstream = new XStream();
xstream.processAnnotations(Person.class);//应用Person类的注解
xstream.autodetectAnnotations(true);//自动检测注解

(2)重命名注解：@XStreamAlias()

@XStreamAlias("人")
class Person
{
  @XStreamAlias("姓名")
  private String name;
  @XStreamAlias("年龄")
  private int age;
  @XStreamAlias("朋友")
  private List friends;
  public Person(String name, int age, String... friends)
  {
    this.name = name;
    this.age = age;
    this.friends = Arrays.asList(friends);
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + ", friends=" + friends + "]";
  }
}

程序运行结果：

<人>
  <姓名>张三</姓名>
  <年龄>19</年龄>
  <朋友 class="java.util.Arrays$ArrayList">
    <a class="string-array">
      <string>李四</string>
      <string>王五</string>
      <string>赵六</string>
    </a>
  </朋友>
</人>
Person [name=张三, age=19, friends=[李四, 王五, 赵六]]

(3)省略集合根节点：@XStreamImplicit

class Person
{
  private String name;
  private int age;
  //@XStreamImplicit//只隐藏集合根节点
  @XStreamImplicit(itemFieldName="朋友")//设置重复的节点名，可能会导致无法反序列化
  private List<String> friends;
  public Person(String name, int age, String... friends)
  {
    this.name = name;
    this.age = age;
    this.friends = Arrays.asList(friends);
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + ", friends=" + friends + "]";
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
  <朋友>李四</朋友>
  <朋友>王五</朋友>
  <朋友>赵六</朋友>
</test.Person>
Person [name=张三, age=19, friends=[李四, 王五, 赵六]]

(4)把字段节点设置成属性：@XStreamAsAttribute

class Person
{
  @XStreamAsAttribute
  private String name;
  @XStreamAsAttribute
  private int age;
  private List<String> friends;
  public Person(String name, int age, String... friends)
  {
    this.name = name;
    this.age = age;
    this.friends = Arrays.asList(friends);
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + ", friends=" + friends + "]";
  }
}

程序运行结果：

<test.Person name="张三" age="19">
  <friends class="java.util.Arrays$ArrayList">
    <a class="string-array">
      <string>李四</string>
      <string>王五</string>
      <string>赵六</string>
    </a>
  </friends>
</test.Person>
Person [name=张三, age=19, friends=[李四, 王五, 赵六]]

(5)隐藏字段：@XStreamOmitField

class Person
{
  private String name;
  private int age;
  @XStreamOmitField
  private List<String> friends;
  public Person(String name, int age, String... friends)
  {
    this.name = name;
    this.age = age;
    this.friends = Arrays.asList(friends);
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + ", friends=" + friends + "]";
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
</test.Person>
Person [name=张三, age=19, friends=null]

(6)设置转换器：@XStreamConverter()

class Person
{
  private String name;
  private int age;
        @XStreamConverter(value=BooleanConverter.class,booleans={false},strings={"男","女"})
  private boolean sex;
  public Person(String name, int age, boolean sex)
{
    this.name = name;
    this.age = age;
    this.sex=sex;
  }
  @Override
  public String toString()
{
    return "Person [name=" + name + ", age=" + age + ", sex=" + sex + "]";
  }
}

程序运行结果：

<test.Person>
  <name>张三</name>
  <age>19</age>
  <sex>男</sex>
</test.Person>
Person [name=张三, age=19, sex=true]

5.Xstream自定义的转换器

(1)Xstream自带的转换器

Xstream内部有许多转换器，用于JavaBean对象到XML或Json之间的转换。这些转换器的详细信息网址：http://xstream.codehaus.org/converters.html

(2)使用自定义的转换器

class Person
{
  private String name;
  private int age;
  public Person(String name, int age)
{
    this.name = name;
    this.age = age;
  }
  public String getName()
{
    return name;
  }
  public void setName(String name)
{
    this.name = name;
  }
  public int getAge()
{
    return age;
  }
  public void setAge(int age)
{
    this.age = age;
  }
  @Override
  public String toString()
{
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class PersonConverter implements Converter 
{
  @Override//定义转换器能转换的JavaBean类型
  public boolean canConvert(Class type)
{
    return type.equals(Person.class);
  }
  @Override//把对象序列化成XML或Json
  public void marshal(Object value, HierarchicalStreamWriter writer, 
MarshallingContext context)
{
    Person person = (Person) value;
        writer.startNode("姓名");
        writer.setValue(person.getName());
        writer.endNode();
        writer.startNode("年龄");
        writer.setValue(person.getAge()+"");
        writer.endNode();
        writer.startNode("转换器");
        writer.setValue("自定义的转换器");
        writer.endNode();
  }
  @Override//把XML或Json反序列化成对象
  public Object unmarshal(HierarchicalStreamReader reader, 
UnmarshallingContext context)
{
       Person person = new Person("",-1);
           reader.moveDown();
           person.setName(reader.getValue());
           reader.moveUp();
           reader.moveDown();
           person.setAge(Integer.parseInt(reader.getValue()));
           reader.moveUp();
           return person;
  }
}
public class Test
{
  public static void main(String[] args)
{
    Person bean =new Person("张三",19);
    XStream xstream = new XStream();
    xstream.registerConverter(new PersonConverter());//注册转换器
    //序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

<test.Person>
  <姓名>张三</姓名>
  <年龄>19</年龄>
  <转换器>自定义的转换器</转换器>
</test.Person>
Person [name=张三, age=19]

(3)常用的转换器接口与抽象类

SingleValueConverter：单值转换接口

AbstractSingleValueConverter：单值转换抽象类

Converter：常规转换器接口

6.Xstream对象流的使用

(1)Xstream对象输出流

class Person
{
  private String name;
  private int age;
  public Person(String name, int age)
  {
    this.name = name;
    this.age = age;
  }
}
public class Test
{
  public static void main(String[] args) throws IOException
  {    
    XStream xstream = new XStream();
    ObjectOutputStream out = xstream.createObjectOutputStream(System.out);
    out.writeObject(new Person("张三",12));
    out.writeObject(new Person("李四",19));
    out.writeObject("Hello");
    out.writeInt(12345);
    out.close();
  }
}

程序运行结果：

<object-stream>
  <test.Person>
    <name>张三</name>
    <age>12</age>
  </test.Person>
  <test.Person>
    <name>李四</name>
    <age>19</age>
  </test.Person>
  <string>Hello</string>
  <int>12345</int>
</object-stream>

注意：XStream对象流是通过标准java.io.ObjectOutputStream和java.io.ObjectInputStream对象。因为XML文档只能有一个根节点,必须包装在一个序列化的所有元素 额外的根节点。 这个根节点默认 < object-stream > 上面的例子所示。

(2)Xstream对象输出流

class Person
{
  private String name;
  private int age;
  public Person(String name, int age)
  {
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class Test
{
  public static void main(String[] args) throws IOException, ClassNotFoundException
  {
    String s="<object-stream><test.Person><name>张三</name><age>12</age></test.Person><int>12345</int></object-stream>";
    StringReader reader = new StringReader(s);
    XStream xstream = new XStream();
    ObjectInputStream in = xstream.createObjectInputStream(reader);
    System.out.println((Person) in.readObject());
    System.out.println(in.readInt());
  }
}

程序运行结果：

Person [name=张三, age=12]
12345

7.Xstream持久化API

(1)保存JavaBean对象

class Person
{
  private String name;
  private int age;
  public Person(String name, int age)
  {
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class Test
{
  public static void main(String[] args) throws IOException, ClassNotFoundException
  {
    PersistenceStrategy strategy = new FilePersistenceStrategy(new File("D:\\tmp"));
    List list = new XmlArrayList(strategy);
    list.add(new Person("张三",13));//保存数据
    list.add(new Person("李四",21));
    list.add(new Person("王五",17));
  }
}

程序运行结果：如果我们检查D:\tmp目录,有三个文件:int@0.xml、int@1.xml、int@2.xml；每个对象都被序列化到XML文件里。

(2)读取并删除JavaBean对象

public class Test
{
  public static void main(String[] args) throws IOException, ClassNotFoundException
  {
    PersistenceStrategy strategy = new FilePersistenceStrategy(new File("D:\\tmp"));
    List list = new XmlArrayList(strategy);
    for (Iterator it = list.iterator(); it.hasNext();)
    {
      System.out.println((Person) it.next());
      it.remove();//删除对象序列化文件
    }
  }
}

程序运行结果：

Person [name=张三, age=13]
Person [name=李四, age=21]
Person [name=王五, age=17]

8.Xstream操作Json

(1)Xstream序列化Json的重命名

@XStreamAlias("人")
class Person
{
  @XStreamAlias("姓名")
  private String name;
  @XStreamAlias("年龄")
  private int age;
  public Person(String name, int age)
{
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString()
{
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class Test
{
  public static void main(String[] args)
{
    Person bean=new Person("张三",19);
    XStream xstream = new XStream(new JettisonMappedXmlDriver());//设置Json解析器
    xstream.autodetectAnnotations(true);
    //Json序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
    //Json反序列化
    bean=(Person)xstream.fromXML(xml);
    System.out.println(bean);
  }
}

程序运行结果：

{"人":{"姓名":"张三","年龄":19}}
Person [name=张三, age=19]

注意：Xstream序列化Json的重命名的方式与其序列化成XML的方式一样！

(2)去掉序列化Json的根节点

class Person
{
  private String name;
  private int age;
  public Person(String name, int age)
  {
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString()
  {
    return "Person [name=" + name + ", age=" + age + "]";
  }
}
public class Test00
{
  public static void main(String[] args)
  {
    Person bean=new Person("张三",19);
    XStream xstream = new XStream(new JsonHierarchicalStreamDriver()
    {
      public HierarchicalStreamWriter createWriter(Writer writer)
      {
        return new JsonWriter(writer, JsonWriter.DROP_ROOT_MODE);
      }
    });
    //Json序列化
    String xml = xstream.toXML(bean);
    System.out.println(xml);
  }
}

程序运行结果：

1. { "name": "张三", "age": 19 }

注意：去掉根节点后的Json串是不能反序列化的，因为XStream 不知道它的类型。

(3)Json的解析器区别

前面两个例子使用了不同的Json解析器，这里说明他们的不同之处：

1. JettisonMappedXmlDriver：是支持序列化和反序列化Json的。
2. JsonHierarchicalStreamDriver：只支持序列化，不支持反序列化。