使用XStream是实现XML与Java对象的转换(2)--别名

五、使用别名(Alias)

首先，有这样一段Java代码：

import java.util.ArrayList;
import java.util.List;

import com.thoughtworks.xstream.XStream;

public class XStreamTest2 {
   public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        System.out.println(xstream.toXML(teamBlog));
   }

}
class Blog {
    private Author writer;
    private List entries = new ArrayList();

    public Blog(Author writer) {
            this.writer = writer;
    }

    public void add(Entry entry) {
            entries.add(entry);
    }

    public List getContent() {
            return entries;
    }
}

class Author {
    private String name;
    public Author(String name) {
            this.name = name;
    }
    public String getName() {
            return name;
    }
}

class Entry {
    private String title, description;
    public Entry(String title, String description) {
            this.title = title;
            this.description = description;
    }
}

对于上面这段代码，现在我要将一个Blog对象转换成为XML字符串，产生的结果是：

<cn.tjpu.zhw.xml.Blog>
  <writer>
    <name>Guilherme Silveira</name>
  </writer>
  <entries>
    <cn.tjpu.zhw.xml.Entry>
      <title>first</title>
      <description>My first blog entry.</description>
    </cn.tjpu.zhw.xml.Entry>
    <cn.tjpu.zhw.xml.Entry>
      <title>tutorial</title>
      <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
    </cn.tjpu.zhw.xml.Entry>
  </entries>
</cn.tjpu.zhw.xml.Blog>

但是，我要将一个Blog对象转换成为下面的XML字符串的形式：

<blog author="Guilherme Silveira">
  <entry>
    <title>first</title>
    <description>My first blog entry.</description>
  </entry>
  <entry>
    <title>tutorial</title>
    <description>
        Today we have developed a nice alias tutorial. Tell your friends! NOW!
    </description>
  </entry>
</blog>

该怎么办呢？

这就需要用到别名转换方法了！

下面我们就一步步的调整代码：

1，给类起别名

需求：将节点cn.tjpu.zhw.xml.Blog、cn.tjpu.zhw.xml.Entry重命名为blog和entry

添加代码：

xstream.alias("blog", Blog.class);
xstream.alias("entry", Entry.class);

即main方法如下：

public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        xstream.alias("blog", Blog.class);
        xstream.alias("entry", Entry.class);
        System.out.println(xstream.toXML(teamBlog));
   }

运行结果如下：

<blog>
  <writer>
    <name>Guilherme Silveira</name>
  </writer>
  <entries>
    <entry>
      <title>first</title>
      <description>My first blog entry.</description>
    </entry>
    <entry>
      <title>tutorial</title>
      <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
    </entry>
  </entries>
</blog>

2，给字段其别名

需求：将writer节点重命名为author节点

添加代码：

xstream.aliasField("author", Blog.class, "writer");

即main方法为：

public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        xstream.alias("blog", Blog.class);
        xstream.alias("entry", Entry.class);
        xstream.aliasField("author", Blog.class, "writer");
        System.out.println(xstream.toXML(teamBlog));
   }

运行结果如下：

<blog>
  <author>
    <name>Guilherme Silveira</name>
  </author>
  <entries>
    <entry>
      <title>first</title>
      <description>My first blog entry.</description>
    </entry>
    <entry>
      <title>tutorial</title>
      <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
    </entry>
  </entries>
</blog>

3，使用隐式集合(Implicit Collection)

隐式集合：当你不想将一个集合的根节点呈现出来的时候，它就是一个隐式集合。

数组、Collection、Map都可以成为隐式集合。

需求：隐藏entries节点

添加代码：

xstream.addImplicitCollection(Blog.class, "entries");

则main方法如下：

public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        xstream.alias("blog", Blog.class);
        xstream.alias("entry", Entry.class);
        xstream.aliasField("author", Blog.class, "writer");
        xstream.addImplicitCollection(Blog.class, "entries");
        System.out.println(xstream.toXML(teamBlog));
   }

运行结果：

<blog>
  <author>
    <name>Guilherme Silveira</name>
  </author>
  <entry>
    <title>first</title>
    <description>My first blog entry.</description>
  </entry>
  <entry>
    <title>tutorial</title>
    <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
  </entry>
</blog>

4，给XML属性起别名

需求：将writer节点，改成blog节点的authot属性

添加代码：

xstream.useAttributeFor(Blog.class, "writer");

即main方法如下：

   

public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        xstream.alias("blog", Blog.class);
        xstream.alias("entry", Entry.class);
        xstream.useAttributeFor(Blog.class, "writer");
        xstream.aliasField("author", Blog.class, "writer");
        xstream.addImplicitCollection(Blog.class, "entries");
        System.out.println(xstream.toXML(teamBlog));
   }

但是运行的结果却是不是预想的那样：

<blog>
  <author>
    <name>Guilherme Silveira</name>
  </author>
  <entry>
    <title>first</title>
    <description>My first blog entry.</description>
  </entry>
  <entry>
    <title>tutorial</title>
    <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
  </entry>
</blog>

可以看到，运行的结果根本就没有变化，为什么？

因为，还缺少一个转换器，XML节点的属性是一个String字符串，但是Author类不是字符串，这就需要一个转换器将Author对象转换成一个String对象、同时能够将String对象反转换为Author对象：

//定义一个转换器，如果使用，则需要在使用时注册到对应的XStream对象中
class AuthorConverter implements SingleValueConverter {
   /*该方法用于从Author对象中提取一个String字符串*/
    public String toString(Object obj) {
            return ((Author) obj).getName();
    }
    /*该方法用于从一个String字符串生成Author对象*/
    public Object fromString(String name) {
            return new Author(name);
    }
    /*该方法告诉XStream对象，该转换器可以转换哪种类型的对象*/
    public boolean canConvert(Class type) {
            return type.equals(Author.class);
    }
}

新的main方法如下：

public class XStreamTest2 {
   public static void main(String[] args) {
      Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
        teamBlog.add(new Entry("first","My first blog entry."));
        teamBlog.add(new Entry("tutorial",
                "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

        XStream xstream = new XStream();
        xstream.alias("blog", Blog.class);
        xstream.alias("entry", Entry.class);
        //设置XML节点的属性
        xstream.useAttributeFor(Blog.class, "writer");
        //注册转换器
        xstream.registerConverter(new AuthorConverter());
        xstream.aliasField("author", Blog.class, "writer");
        xstream.addImplicitCollection(Blog.class, "entries");
        System.out.println(xstream.toXML(teamBlog));
   }
}

到此为止，运行的结果就会真正的向预期的那样：

<blog author="Guilherme Silveira">
  <entry>
    <title>first</title>
    <description>My first blog entry.</description>
  </entry>
  <entry>
    <title>tutorial</title>
    <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
  </entry>
</blog>

5，使用包名别名

需求：有时候需要事项不同包里面的相同类名的节点之间的相互映射，这时就需要改变一下包名了

添加代码：

xstream.aliasPackage("org.thoughtworks", "cn.tjpu.zhw.xml");

即更改main方法：

public static void main(String[] args) {
   Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
     teamBlog.add(new Entry("first","My first blog entry."));
     teamBlog.add(new Entry("tutorial",
             "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));

     XStream xstream = new XStream();
     //包名别名
     xstream.aliasPackage("org.thoughtworks", "cn.tjpu.zhw.xml");
     System.out.println(xstream.toXML(teamBlog));
}

运行结果如下：

<org.thoughtworks.Blog>
  <writer>
    <name>Guilherme Silveira</name>
  </writer>
  <entries>
    <org.thoughtworks.Entry>
      <title>first</title>
      <description>My first blog entry.</description>
    </org.thoughtworks.Entry>
    <org.thoughtworks.Entry>
      <title>tutorial</title>
      <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
    </org.thoughtworks.Entry>
  </entries>
</org.thoughtworks.Blog>