剛剛學了一下Digester如何解析xml檔案,是以記錄下來,友善以後檢視。
一般用來讀取xml檔案的工具包有DOM、SAX和JDOM等,但用過的人都知道,它們屬于比較底層的API,寫起來代碼量很大,而且如果修改了xml檔案的格式,代碼也要做大幅度的改動。而使用Apache Jakarta的Digester,解析XML檔案非常友善且不需要過多的關心底層的具體解析過程。Digester本來僅僅是Jakarta Struts中的一個工具,用于處理struts-config.xml配置檔案。顯然,将XML檔案轉換成相應的Java對象是一項很通用的功能,這個工具理應具有更廣泛的用途,是以很快它就在Jakarta Commons項目(用于提供可重用的Java元件庫)中有了一席之地。Digester由"事件"驅動,通過調用預定義的規則操作對象棧,将XML檔案轉換為Java對象。
工作原理如下: Digester底層采用SAX(Simple API for XML)析XML檔案,是以很自然的,對象轉換由"事件"驅動,在周遊每個節點時,檢查是否有比對模式,如果有,則執行規則定義的操作,比如建立特定的Java對象,或調用特定對象的方法等。此處的XML元素根據比對模式(matching pattern)識别,而相關操作由規則(rule)定義。
如下xml代碼,右邊是左邊元素對應的比對模式:
[xhtml] view plain copy
- <datasources> 'datasources'
- <datasource> 'datasources/datasource'
- <name/> 'datasources/datasource/name'
- <driver/> 'datasources/datasource/driver'
- </datasource>
- <datasource> 'datasources/datasource'
- <name/> 'datasources/datasource/name'
- <driver/> 'datasources/datasource/driver'
- </datasource>
- </datasources>
例子1:
下面介紹解析xml檔案的代碼
下面是存放位址及編碼的xml檔案viewcache.xml(片段):
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- <?xml version="1.0" encoding="UTF-8" ?>
- <viewcache>
- <areas>
- <area>
- <id>1098</id>
- <parentId>1001</parentId>
- <areaType>province</areaType>
- <name>北京</name>
- <ordering>1867</ordering>
- </area>
- <area>
- <id>1099</id>
- <parentId>1098</parentId>
- <areaType>capital</areaType>
- <name>北京</name>
- <ordering>1868</ordering>
- <phoneArea>010</phoneArea>
- </area>
- <area>
- <id>4476</id>
- <parentId>1099</parentId>
- <areaType>county</areaType>
- <name>北京市朝陽區</name>
- <ordering>1869</ordering>
- <phoneArea>010</phoneArea>
- </area>
- <area>
- <id>4477</id>
- <parentId>1099</parentId>
- <areaType>county</areaType>
- <name>北京市崇文區</name>
- <ordering>1870</ordering>
- <phoneArea>010</phoneArea>
- </area>
- <area>
- <id>4478</id>
- <parentId>1099</parentId>
- <areaType>county</areaType>
- <name>北京市大興區</name>
- <ordering>1871</ordering>
- <phoneArea>010</phoneArea>
- </area>
- </areas>
- </viewcache>
此xml檔案分3層結構,分别為:
<viewcache>節點 其下包含1個<areas>節點
<areas>節點 其下包含多個<area>節點
<area>節點,其下包含各種資訊節點 : 如:<id> 、<name>等。
我們的操作目标是把area中的資訊節點的内容提取出來。
把每個<arrea>看做為一個對象,<area>中資訊節點的内容為對象中的元素。
設定一個類Area.java 其内容如下:
[java] view plain copy
- public class Area {
- private int id;
- private String name;
- private String areaType;
- private int parentId;
- private int ordering;
- private String zip;
- private String phoneArea;
- public int getOrdering() {
- return ordering;
- }
- public void setOrdering(int ordering) {
- this.ordering = ordering;
- }
- public String getAreaType() {
- return areaType;
- }
- public void setAreaType(String areaType) {
- this.areaType = areaType;
- }
- public int getId() {
- return id;
- }
- public void setId(int id) {
- this.id = id;
- }
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- public int getParentId() {
- return parentId;
- }
- public void setParentId(int parentId) {
- this.parentId = parentId;
- }
- public String getZip() {
- return zip;
- }
- public void setZip(String zip) {
- this.zip = zip;
- }
- public String getPhoneArea() {
- return phoneArea;
- }
- public void setPhoneArea(String phoneArea) {
- this.phoneArea = phoneArea;
- }
- }
建立一個ViewCache類,用來儲存解析後的所有對象:
[java] view plain copy
- public class ViewCache {
- private List areaList = new ArrayList();
- public List getAreaList() {
- return areaList;
- }
- public void setAreaList(List areaList) {
- this.areaList = areaList;
- }
- // 供Digester調用的方法
- public void addArea(Area area) {
- this.areaList.add(area);
- }
- }
建立一個類AreaDigester,對xml檔案進行解析:
[java] view plain copy
public class AreaDigester {
public ViewCache digester() throws Exception {
Digester digester = new Digester();
digester.setValidating(false);
digester.addObjectCreate("viewcache/areas", ViewCache.class);
// 指明比對模式和要建立的類
digester.addObjectCreate("viewcache/areas/area", Area.class);
// 設定對象屬性,與xml檔案對應,不設定則是預設
digester.addBeanPropertySetter("viewcache/areas/area/id", "id");
digester.addBeanPropertySetter("viewcache/areas/area/parentId", "parentId");
digester.addBeanPropertySetter("viewcache/areas/area/name", "name");
digester.addBeanPropertySetter("viewcache/areas/area/areaType", "areaType");
digester.addBeanPropertySetter("viewcache/areas/area/ordering", "ordering");
digester.addBeanPropertySetter("viewcache/areas/area/zip", "zip");
digester.addBeanPropertySetter("viewcache/areas/area/phoneArea", "phoneArea");
// 當移動到下一個标簽中時的動作
digester.addSetNext("viewcache/areas/area", "addArea");
ViewCache vc = null;
try {
File file = new File("viewcache.xml");
BufferedReader read = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
StringBuffer sb = new StringBuffer();
String content = "";
while((content=read.readLine()) != null){
sb.append(content);
}
vc = (ViewCache) digester.parse(new StringReader(sb.toString()));
} catch (IOException e) {
throw new Exception(e);
} catch (SAXException e) {
throw new Exception(e);
}
return vc;
}
}
調用AreaDigester的digester方法,即可把解析後的所有位址對象,存放在ViewCache的list中。
例子2:
要解析的xml檔案books.xml如下:
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- <?xml version="1.0" encoding="UTF-8" ?>
- <library name="alibaba圖書館">
- <book title ="thinking in java" author="xxx">
- <chapter>
- <no>第一章</no>
- <caption>第一章的标題</caption>
- </chapter>
- <chapter>
- <no>第二章</no>
- <caption>第二章的标題</caption>
- </chapter>
- </book>
- <book title="effective java" author="yyy">
- <chapter>
- <no>第一章</no>
- <caption>第一章的标題</caption>
- </chapter>
- </book>
- </library>
Library類如下:
[java] view plain copy
- public class Library {
- private String name;
- private List<Book> bookList = new ArrayList<Book>();
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- public List<Book> getBookList() {
- return bookList;
- }
- public void addBook(Book book) {
- bookList.add(book);
- }
- }
Book類如下:
[java] view plain copy
- public class Book {
- private String title;
- private String author;
- private List<Chapter> chapters = new ArrayList<Chapter>();
- public void setBookInfo(String title, String author) {
- this.title = title;
- this.author = author;
- }
- public void addChapter(Chapter chapter) {
- this.chapters.add(chapter);
- }
- public String getTitle() {
- return title;
- }
- public void setTitle(String title) {
- this.title = title;
- }
- public String getAuthor() {
- return author;
- }
- public void setAuthor(String author) {
- this.author = author;
- }
- public List<Chapter> getChapters() {
- return chapters;
- }
- public void setChapters(List<Chapter> chapters) {
- this.chapters = chapters;
- }
- }
Chapter類如下:
[java] view plain copy
- public class Chapter {
- private String no;
- private String caption;
- public String getNo() {
- return no;
- }
- public void setNo(String no) {
- this.no = no;
- }
- public String getCaption() {
- return caption;
- }
- public void setCaption(String caption) {
- this.caption = caption;
- }
- }
解析xml的類如下:
[java] view plain copy
- public class MainTest {
- public static void main(String[] args) {
- // 建立一個Digester對象
- Digester digester = new Digester();
- //指定它不要用DTD驗證XML文檔的合法性——這是因為我們沒有為XML文檔定義DTD
- digester.setValidating(false);
- // 從library标簽開始解析,并建立一個Library對象做為根對象
- digester.addObjectCreate("library", Library.class);
- // 根據library标簽屬性值設定對象的屬性,一次可以設定多個屬性
- digester.addSetProperties("library");
- // 也可以用下面的方法,指定propertyName
- // digester.addSetProperties("library", "name", "name");
- // -----第1層元素開始
- digester.addObjectCreate("library/book", Book.class);
- //digester.addSetProperties("library/book");
- // 可以用以下三條語句代替
- digester.addCallMethod("library/book", "setBookInfo", 2);
- digester.addCallParam("library/book", 0, "title");
- digester.addCallParam("library/book", 1, "author");
- // -----第2層元素開始
- digester.addObjectCreate("library/book/chapter", Chapter.class);
- digester.addBeanPropertySetter("library/book/chapter/no");
- // digester.addBeanPropertySetter("library/book/chapter/no", "no");
- // digester.addBeanPropertySetter("library/book/chapter/caption");
- // 下面的方法,可以用來代替上一句,作用是一樣的
- digester.addCallMethod("library/book/chapter/caption", "setCaption", 0);
- // addSetNext()是說在再次遇到比對節點後, 調用目前對象(Chapter類的對象)的父對象(Book類的對象)的方法,方法參數是目前層元素的對象
- digester.addSetNext("library/book/chapter", "addChapter");
- // -----第2層元素結束
- digester.addSetNext("library/book", "addBook");
- // -----第1層元素結束
- try {
- // 解析XML檔案,并得到ROOT元素
- Library library = (Library) digester.parse(MainTest.class.getResourceAsStream("books.xml"));
- System.out.println(" 圖書館: " + library.getName());
- System.out.println(" 共藏書: " + library.getBookList().size() + " 本 ");
- System.out.println(" ***************************** ");
- for (Book book : library.getBookList()) {
- System.out.println(" 書名: " + book.getTitle() + " 作者: " + book.getAuthor());
- System.out.println(" ------------------------------ ");
- // 顯示章節
- System.out.println(" 共 " + book.getChapters().size() + " 章 ");
- for (Chapter chapter : book.getChapters()) {
- System.out.println(chapter.getNo() + ": " + chapter.getCaption());
- }
- System.out.println(" ------------------------------ ");
- }
- } catch (IOException e) {
- e.printStackTrace();
- } catch (SAXException e) {
- e.printStackTrace();
- }
- }
- }
例子3:
Digester解析xml的規則,除了在java類中描述設定之外,還可以把解析規則放在xml檔案中。以例子2中的代碼為例,規則在books-rule.xml檔案中,内容如下:(The DTD is distributed in the
commons-digester.jar
. It can be found at
org/apache/commons/digester/xmlrules/digester-rules.dtd,通過檢視DTD檔案,可以知道有哪些标簽可以使用
)
[xhtml] view plain copy
- <?xml version="1.0" encoding="UTF-8" ?>
- <!DOCTYPE digester-rules PUBLIC
- "-//Jakarta Apache //DTD digester-rules XML V1.0//EN"
- "digester-rules.dtd">
- <digester-rules>
- <object-create-rule pattern="library" classname="com.alibaba.chj.digester.Library" />
- <set-properties-rule pattern="library">
- <alias attr-name="name" prop-name="name" />
- </set-properties-rule>
- <pattern value="library/book">
- <object-create-rule classname="com.alibaba.chj.digester.Book" />
- <set-properties-rule />
- <pattern value="chapter">
- <object-create-rule classname="com.alibaba.chj.digester.Chapter" />
- <bean-property-setter-rule pattern="no" propertyname="no" />
- <bean-property-setter-rule pattern="caption" propertyname="caption" />
- <set-next-rule methodname="addChapter" />
- </pattern>
- <set-next-rule methodname="addBook" />
- </pattern>
- </digester-rules>
解析xml類的代碼,修改為:
[java] view plain copy
- public class MainTest {
- public static void main(String[] args) {
- try {
- Digester digester = DigesterLoader.createDigester(DigesterXmlRuleTest.class.getResource("books-rule.xml"));
- Library library = (Library) digester.parse(DigesterXmlRuleTest.class.getResourceAsStream("books.xml"));
- System.out.println(" 圖書館: " + library.getName());
- System.out.println(" 共藏書: " + library.getBookList().size() + " 本 ");
- System.out.println(" ***************************** ");
- for (Book book : library.getBookList()) {
- System.out.println(" 書名: " + book.getTitle() + " 作者: " + book.getAuthor());
- System.out.println(" ------------------------------ ");
- // 顯示章節
- System.out.println(" 共 " + book.getChapters().size() + " 章 ");
- for (Chapter chapter : book.getChapters()) {
- System.out.println(chapter.getNo() + ": " + chapter.getCaption());
- }
- System.out.println(" ------------------------------ ");
- }
- } catch (IOException e) {
- e.printStackTrace();
- } catch (SAXException e) {
- e.printStackTrace();
- }
- }
- }
用于規則放在xml檔案中,是以解析的類,顯得更加簡潔一些。