tomcat 七 源码分析-3 使用Digester读取xml文件实例化server

接下来tomcat要load了，看下面一些程序片段

Java代码  

1. public   void  load() {  
2.   
3.         long  t1 = System.nanoTime();  
4.         initDirs();  
5.         initNaming();  
6.         Digester digester = createStartDigester();  
7.         ........  
8.        digester.push(this );  
9.        digester.parse(inputSource);  
10.         ........  
11.         getServer().init();  

public void load() {

        long t1 = System.nanoTime();
        initDirs();
        initNaming();
        Digester digester = createStartDigester();
        ........
       digester.push(this);
       digester.parse(inputSource);
        ........
        getServer().init();

 令人费解的如何实例化server的？digester有何作用？原来digester是apache的common项目，作用是讲XML转成Object。tomcat读取配置文件conf\server.xml，实例化server对象。形同：

Java代码  

1. // Configure the actions we will be using   
2. digester.addObjectCreate("Server" ,  
3.                          "org.apache.catalina.core.StandardServer" ,  
4.                          "className" );  
5. digester.addSetProperties("Server" );  
6. digester.addSetNext("Server" ,  
7.                     "setServer" ,  
8.                     "org.apache.catalina.Server" );  

        // Configure the actions we will be using
        digester.addObjectCreate("Server",
                                 "org.apache.catalina.core.StandardServer",
                                 "className");
        digester.addSetProperties("Server");
        digester.addSetNext("Server",
                            "setServer",
                            "org.apache.catalina.Server");

 要读懂这些还真费解,这里写了个小例子。

首先xml文件为

Xml代码  

1. <? xml   version = "1.0" ?>   
2. < catalog   library = "somewhere" >   
3.    < book >   
4.       < author > Author 1 </ author >   
5.       < title > Title 1 </ title >   
6.    </ book >   
7.    < book >   
8.       < author > Author 2 </ author >   
9.       < title > His One Book </ title >   
10.    </ book >   
11.    < book >   
12.       < author > Author 3 </ author >   
13.       < title > His Other Book </ title >   
14.    </ book >   
15. </ catalog >   

<?xml version="1.0"?>
<catalog library="somewhere">
   <book>
      <author>Author 1</author>
      <title>Title 1</title>
   </book>
   <book>
      <author>Author 2</author>
      <title>His One Book</title>
   </book>
   <book>
      <author>Author 3</author>
      <title>His Other Book</title>
   </book>
</catalog>

 Book.java

Java代码  

1. package  com.xiao;  
2.   
3. public   class  Book {  
4.        private  String author;  
5.        private  String title;  
6.   
7.        public  Book() {}  
8.   
9.        public   void  setAuthor( String rhs ) { author = rhs; }  
10.        public   void  setTitle(  String rhs ) { title  = rhs; }  
11.          
12.        public  String getAuthor(  ) {  return  author; }  
13.        public  String getTitle(  ) {  return  title; }  
14.          
15.        public  String toString() {  
16.           return   "Book: Author='"  + author +  "' Title='"  + title +  "'" ;  
17.        }  
18.     }  

package com.xiao;

public class Book {
	   private String author;
	   private String title;

	   public Book() {}

	   public void setAuthor( String rhs ) { author = rhs; }
	   public void setTitle(  String rhs ) { title  = rhs; }
	   
	   public String getAuthor(  ) { return author; }
	   public String getTitle(  ) { return title; }
	   
	   public String toString() {
	      return "Book: Author='" + author + "' Title='" + title + "'";
	   }
	}

Catalog.java

Java代码  

1. package  com.xiao;  
2. import  java.util.Vector;  
3. public   class  Catalog {  
4.    private  Vector<Book> books;  
5.   
6.    public  Catalog() {  
7.       books = new  Vector<Book>();  
8.    }  
9.    public   void  addBook( Book rhs ) {  
10.       books.addElement( rhs );  
11.    }  
12.    public  String toString() {  
13.       String newline = System.getProperty( "line.separator"  );  
14.       StringBuffer buf = new  StringBuffer();  
15.       buf.append( "--- Books ---"  ).append( newline );  
16.       for (  int  i= 0 ; i<books.size(); i++ ){  
17.           Book book  = books.elementAt(i);  
18.          buf.append( book.toString()).append( newline );  
19.       }  
20.       return  buf.toString();  
21.    }  
22. }  

package com.xiao;
import java.util.Vector;
public class Catalog {
   private Vector<Book> books;

   public Catalog() {
      books = new Vector<Book>();
   }
   public void addBook( Book rhs ) {
      books.addElement( rhs );
   }
   public String toString() {
      String newline = System.getProperty( "line.separator" );
      StringBuffer buf = new StringBuffer();
      buf.append( "--- Books ---" ).append( newline );
      for( int i=0; i<books.size(); i++ ){
    	  Book book  = books.elementAt(i);
         buf.append( book.toString()).append( newline );
      }
      return buf.toString();
   }
}

 CreateCatalog.java

Java代码  

1. package  com.xiao;  
2. import  java.io.IOException;  
3. import  org.apache.tomcat.util.digester.Digester;  
4. import  org.xml.sax.SAXException;  
5.   
6. public   class  CreateCatalog {  
7.     protected   Catalog ct;  
8.       
9.     public   void  SetCatalog(Catalog ol){  
10.           
11.         ct = ol;  
12.     }  
13.       
14.     public  Catalog GetCatalog(){  
15.           
16.         return   this .ct;  
17.     }  
18.     public  String toString() {  
19.           
20.         return  ct.toString();  
21.         }  
22.       
23.     public  Digester createStartDigester() throws  IOException, SAXException  
24.     {  
25.         Digester digester = new  Digester();  
26.         digester.setValidating( false  );  
27.         //解析XML时，遇到catalog，就实例化一个com.xiao.Catalog对象，并且压栈   
28.         digester.addObjectCreate( "catalog" ,  "com.xiao.Catalog" );  
29.         //对catalog，调用栈的次top对象(现在还没有压入,父对象)的SetCatalog函数。   
30.         //passing the element that is on the top of the stack, which must be of type com.xiao.Catalog   
31.         //This is the rule that causes the parent/child relationship to be created.   
32.         digester.addSetNext("catalog" ,  "SetCatalog" ,  "com.xiao.Catalog" );  
33.           
34.         digester.addObjectCreate( "catalog/book" , "com.xiao.Book" );  
35.           
36.         //对rule，调用当前top object的setAuthor函数，参数个数为1   
37.         digester.addCallMethod("catalog/book/author" ,  "setAuthor" , 1 );  
38.         //对rule，添加第一个参数值   
39.         digester.addCallParam("catalog/book/author" ,  0 );  
40.         digester.addCallMethod("catalog/book/title" ,  "setTitle" , 1 );  
41.         digester.addCallParam("catalog/book/title" ,  0 );  
42.         //此时次top的object就是com.xiao.Catalog，调用它的addBook函数，将com.xiao.Book传入   
43.         digester.addSetNext("catalog/book" ,  "addBook" ,  "com.xiao.Book" );  
44.           
45.         return  (digester);  
46.     }  
47. }  

package com.xiao;
import java.io.IOException;
import org.apache.tomcat.util.digester.Digester;
import org.xml.sax.SAXException;

public class CreateCatalog {
	protected  Catalog ct;
	
	public void SetCatalog(Catalog ol){
		
		ct = ol;
	}
	
	public Catalog GetCatalog(){
		
		return this.ct;
	}
	public String toString() {
		
		return ct.toString();
		}
	
	public Digester createStartDigester()throws IOException, SAXException
	{
		Digester digester = new Digester();
		digester.setValidating( false );
		//解析XML时，遇到catalog，就实例化一个com.xiao.Catalog对象，并且压栈
		digester.addObjectCreate( "catalog", "com.xiao.Catalog");
		//对catalog，调用栈的次top对象(现在还没有压入,父对象)的SetCatalog函数。
		//passing the element that is on the top of the stack, which must be of type com.xiao.Catalog
		//This is the rule that causes the parent/child relationship to be created.
		digester.addSetNext("catalog", "SetCatalog", "com.xiao.Catalog");
		
		digester.addObjectCreate( "catalog/book","com.xiao.Book");
		
		//对rule，调用当前top object的setAuthor函数，参数个数为1
		digester.addCallMethod("catalog/book/author", "setAuthor",1);
		//对rule，添加第一个参数值
		digester.addCallParam("catalog/book/author", 0);
		digester.addCallMethod("catalog/book/title", "setTitle",1);
		digester.addCallParam("catalog/book/title", 0);
		//此时次top的object就是com.xiao.Catalog，调用它的addBook函数，将com.xiao.Book传入
		digester.addSetNext("catalog/book", "addBook", "com.xiao.Book");
		
		return (digester);
	}
}

 TestDigester.java

Java代码  

1. package  com.xiao;  
2.   
3. import  org.apache.tomcat.util.digester.Digester;  
4. import  org.xml.sax.InputSource;  
5. import  org.xml.sax.SAXException;  
6.   
7. import  java.io.*;  
8. public   class  TestDigester {  
9.       
10.     public   static   void  main(String[] args)  throws  IOException, SAXException  {  
11.         // TODO Auto-generated method stub   
12.         CreateCatalog cc = new  CreateCatalog();  
13.         Digester digester = cc.createStartDigester();     
14.         String configFile = "xiapingtest/ts.xml" ;     
15.         InputSource inputSource = null ;  
16.         InputStream inputStream = null ;  
17.         File file = new  File(System.getProperty( "user.dir" ),configFile);  
18.         inputSource = new  InputSource( "file://"  + file.getAbsolutePath());  
19.         inputStream = new  FileInputStream(file);  
20.         inputSource.setByteStream(inputStream);  
21.         //在加入CreateCatalog对象，这个是第一个压入的对象   
22.         digester.push(cc);  
23.         //处理xml文件，逐个加入对象   
24.         digester.parse(inputSource);          
25.         System.out.println(cc.toString());  
26.     }  
27.   
28. }  

package com.xiao;

import org.apache.tomcat.util.digester.Digester;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import java.io.*;
public class TestDigester {
	
	public static void main(String[] args) throws IOException, SAXException  {
		// TODO Auto-generated method stub
		CreateCatalog cc = new CreateCatalog();
		Digester digester = cc.createStartDigester();	
		String configFile = "xiapingtest/ts.xml";	
		InputSource inputSource = null;
		InputStream inputStream = null;
		File file = new File(System.getProperty("user.dir"),configFile);
		inputSource = new InputSource("file://" + file.getAbsolutePath());
		inputStream = new FileInputStream(file);
		inputSource.setByteStream(inputStream);
		//在加入CreateCatalog对象，这个是第一个压入的对象
		digester.push(cc);
		//处理xml文件，逐个加入对象
		digester.parse(inputSource);		
		System.out.println(cc.toString());
	}

}

 部分解释以及在代码注释里。