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。