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五、使用別名(Alias)

首先，有這樣一段Java代碼：

Java代碼

1. import java.util.ArrayList;
2. import java.util.List;
4. import com.thoughtworks.xstream.XStream;
6. public class XStreamTest2 {
7. public static void main(String[] args) {
8. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
9. teamBlog.add(new Entry("first","My first blog entry."));
10. teamBlog.add(new Entry("tutorial",
11. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
13. XStream xstream = new XStream();
14. System.out.println(xstream.toXML(teamBlog));
15. }
17. }
18. class Blog {
19. private Author writer;
20. private List entries = new ArrayList();
22. public Blog(Author writer) {
23. this.writer = writer;
24. }
26. public void add(Entry entry) {
27. entries.add(entry);
28. }
30. public List getContent() {
31. return entries;
32. }
33. }
35. class Author {
36. private String name;
37. public Author(String name) {
38. this.name = name;
39. }
40. public String getName() {
41. return name;
42. }
43. }
45. class Entry {
46. private String title, description;
47. public Entry(String title, String description) {
48. this.title = title;
49. this.description = description;
50. }
51. }

對於上面這段代碼，現在我要將一個Blog對象轉換成為XML字符串，產生的結果是：

Xml代碼

1. <cn.tjpu.zhw.xml.Blog>
2. <writer>
3. <name>Guilherme Silveira</name>
4. </writer>
5. <entries>
6. <cn.tjpu.zhw.xml.Entry>
7. <title>first</title>
8. <description>My first blog entry.</description>
9. </cn.tjpu.zhw.xml.Entry>
10. <cn.tjpu.zhw.xml.Entry>
11. <title>tutorial</title>
12. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
13. </cn.tjpu.zhw.xml.Entry>
14. </entries>
15. </cn.tjpu.zhw.xml.Blog>

但是，我要將一個Blog對象轉換成為下面的XML字符串的形式：

Xml代碼

1. <blog author="Guilherme Silveira">
2. <entry>
3. <title>first</title>
4. <description>My first blog entry.</description>
5. </entry>
6. <entry>
7. <title>tutorial</title>
8. <description>
9. Today we have developed a nice alias tutorial. Tell your friends! NOW!
10. </description>
11. </entry>
12. </blog>

該怎麽辦呢？

這就需要用到別名轉換方法了！

下面我們就一步步的調整代碼：

1，給類起別名

需求：將節點cn.tjpu.zhw.xml.Blog、cn.tjpu.zhw.xml.Entry重命名為blog和entry

添加代碼：

Java代碼

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

即main方法如下：

Java代碼

1. public static void main(String[] args) {
2. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
3. teamBlog.add(new Entry("first","My first blog entry."));
4. teamBlog.add(new Entry("tutorial",
5. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
7. XStream xstream = new XStream();
8. xstream.alias("blog", Blog.class);
9. xstream.alias("entry", Entry.class);
10. System.out.println(xstream.toXML(teamBlog));
11. }

運行結果如下：

Xml代碼

1. <blog>
2. <writer>
3. <name>Guilherme Silveira</name>
4. </writer>
5. <entries>
6. <entry>
7. <title>first</title>
8. <description>My first blog entry.</description>
9. </entry>
10. <entry>
11. <title>tutorial</title>
12. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
13. </entry>
14. </entries>
15. </blog>

2，給字段其別名

需求：將writer節點重命名為author節點

添加代碼：

Java代碼

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

即main方法為：

Java代碼

1. public static void main(String[] args) {
2. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
3. teamBlog.add(new Entry("first","My first blog entry."));
4. teamBlog.add(new Entry("tutorial",
5. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
7. XStream xstream = new XStream();
8. xstream.alias("blog", Blog.class);
9. xstream.alias("entry", Entry.class);
10. xstream.aliasField("author", Blog.class, "writer");
11. System.out.println(xstream.toXML(teamBlog));
12. }

運行結果如下：

Xml代碼

1. <blog>
2. <author>
3. <name>Guilherme Silveira</name>
4. </author>
5. <entries>
6. <entry>
7. <title>first</title>
8. <description>My first blog entry.</description>
9. </entry>
10. <entry>
11. <title>tutorial</title>
12. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
13. </entry>
14. </entries>
15. </blog>

3，使用隱式集合(Implicit Collection)

隱式集合：當你不想將一個集合的根節點呈現出來的時候，它就是一個隱式集合。

數組、Collection、Map都可以成為隱式集合。

需求：隱藏entries節點

添加代碼：

Java代碼

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

則main方法如下：

Java代碼

1. public static void main(String[] args) {
2. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
3. teamBlog.add(new Entry("first","My first blog entry."));
4. teamBlog.add(new Entry("tutorial",
5. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
7. XStream xstream = new XStream();
8. xstream.alias("blog", Blog.class);
9. xstream.alias("entry", Entry.class);
10. xstream.aliasField("author", Blog.class, "writer");
11. xstream.addImplicitCollection(Blog.class, "entries");
12. System.out.println(xstream.toXML(teamBlog));
13. }

運行結果：

Xml代碼

1. <blog>
2. <author>
3. <name>Guilherme Silveira</name>
4. </author>
5. <entry>
6. <title>first</title>
7. <description>My first blog entry.</description>
8. </entry>
9. <entry>
10. <title>tutorial</title>
11. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
12. </entry>
13. </blog>

4，給XML屬性起別名

需求：將writer節點，改成blog節點的authot屬性

添加代碼：

Java代碼

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

即main方法如下：

Java代碼

1. public static void main(String[] args) {
2. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
3. teamBlog.add(new Entry("first","My first blog entry."));
4. teamBlog.add(new Entry("tutorial",
5. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
7. XStream xstream = new XStream();
8. xstream.alias("blog", Blog.class);
9. xstream.alias("entry", Entry.class);
10. xstream.useAttributeFor(Blog.class, "writer");
11. xstream.aliasField("author", Blog.class, "writer");
12. xstream.addImplicitCollection(Blog.class, "entries");
13. System.out.println(xstream.toXML(teamBlog));
14. }

但是運行的結果卻是不是預想的那樣：

Xml代碼

1. <blog>
2. <author>
3. <name>Guilherme Silveira</name>
4. </author>
5. <entry>
6. <title>first</title>
7. <description>My first blog entry.</description>
8. </entry>
9. <entry>
10. <title>tutorial</title>
11. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
12. </entry>
13. </blog>

可以看到，運行的結果根本就沒有變化，為什麽？

因為，還缺少一個轉換器，XML節點的屬性是一個String字符串，但是Author類不是字符串，這就需要一個轉換器將Author對象轉換成一個String對象、同時能夠將String對象反轉換為Author對象：

Java代碼

1. //定義一個轉換器，如果使用，則需要在使用時註冊到對應的XStream對象中
2. class AuthorConverter implements SingleValueConverter {
3. /*該方法用於從Author對象中提取一個String字符串*/
4. public String toString(Object obj) {
5. return ((Author) obj).getName();
6. }
7. /*該方法用於從一個String字符串生成Author對象*/
8. public Object fromString(String name) {
9. return new Author(name);
10. }
11. /*該方法告訴XStream對象，該轉換器可以轉換哪種類型的對象*/
12. public boolean canConvert(Class type) {
13. return type.equals(Author.class);
14. }
15. }

新的main方法如下：

Java代碼

1. public class XStreamTest2 {
2. public static void main(String[] args) {
3. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
4. teamBlog.add(new Entry("first","My first blog entry."));
5. teamBlog.add(new Entry("tutorial",
6. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
8. XStream xstream = new XStream();
9. xstream.alias("blog", Blog.class);
10. xstream.alias("entry", Entry.class);
11. //設置XML節點的屬性
12. xstream.useAttributeFor(Blog.class, "writer");
13. //註冊轉換器
14. xstream.registerConverter(new AuthorConverter());
15. xstream.aliasField("author", Blog.class, "writer");
16. xstream.addImplicitCollection(Blog.class, "entries");
17. System.out.println(xstream.toXML(teamBlog));
18. }
19. }

到此為止，運行的結果就會真正的向預期的那樣：

Xml代碼

1. <blog author="Guilherme Silveira">
2. <entry>
3. <title>first</title>
4. <description>My first blog entry.</description>
5. </entry>
6. <entry>
7. <title>tutorial</title>
8. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
9. </entry>
10. </blog>

5，使用包名別名

需求：有時候需要事項不同包裏面的相同類名的節點之間的相互映射，這時就需要改變一下包名了

添加代碼：

Java代碼

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

即更改main方法：

Java代碼

1. public static void main(String[] args) {
2. Blog teamBlog = new Blog(new Author("Guilherme Silveira"));
3. teamBlog.add(new Entry("first","My first blog entry."));
4. teamBlog.add(new Entry("tutorial",
5. "Today we have developed a nice alias tutorial. Tell your friends! NOW!"));
7. XStream xstream = new XStream();
8. //包名別名
9. xstream.aliasPackage("org.thoughtworks", "cn.tjpu.zhw.xml");
10. System.out.println(xstream.toXML(teamBlog));
11. }

運行結果如下：

Xml代碼

1. <org.thoughtworks.Blog>
2. <writer>
3. <name>Guilherme Silveira</name>
4. </writer>
5. <entries>
6. <org.thoughtworks.Entry>
7. <title>first</title>
8. <description>My first blog entry.</description>
9. </org.thoughtworks.Entry>
10. <org.thoughtworks.Entry>
11. <title>tutorial</title>
12. <description>Today we have developed a nice alias tutorial. Tell your friends! NOW!</description>
13. </org.thoughtworks.Entry>
14. </entries>
15. </org.thoughtworks.Blog>

使用XStream是實現XML與Java對象的轉換(2)--別名