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

q9989

　　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();

　　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");
　　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>
　　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 + "'";
}
}
　　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();
}
}
　　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);
}
}

　　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());
}
}

　　部分解释以及在代码注释里。