tomcat 7 源码分析-3 使用Digester读取xml文件实例化server

tomcat 7 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

 

 public   void  load() {

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

 

 // 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" );

        // 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   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 >

<?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

 

 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 +  "'" ;
        }
     }

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

 

 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();
    }
 }

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

 

 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);
     }
 }

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

 

 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());
     }

 }

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。