A Web server exclusively handles HTTP requests, whereas an application server serves business logic to application programs through any number of protocols.

Let's examine each in more detail.

The Web server

A Web server handles the HTTP protocol. When the Web server receives an HTTP request, it responds with an HTTP response, such as sending back an HTML page. To process a request, a Web server may respond with a static HTML page or image, send a redirect, or delegate the dynamic response generation to some other program such as CGI scripts, JSPs (JavaServer Pages), servlets, ASPs (Active Server Pages), server-side JavaScripts, or some other server-side technology. Whatever their purpose, such server-side programs generate a response, most often in HTML, for viewing in a Web browser.

Understand that a Web server's delegation model is fairly simple. When a request comes into the Web server, the Web server simply passes the request to the program best able to handle it. The Web server doesn't provide any functionality beyond simply providing an environment in which the server-side program can execute and pass back the generated responses. The server-side program usually provides for itself such functions as transaction processing, database connectivity, and messaging.

While a Web server may not itself support transactions or database connection pooling, it may employ various strategies for fault tolerance and scalability such as load balancing, caching, and clustering—features oftentimes erroneously assigned as features reserved only for application servers.

The application server

As for the application server, according to our definition, an application server exposes business logic to client applications through various protocols, possibly including HTTP. While a Web server mainly deals with sending HTML for display in a Web browser, an application server provides access to business logic for use by client application programs. The application program can use this logic just as it would call a method on an object (or a function in the procedural world).

Such application server clients can include GUIs (graphical user interface) running on a PC, a Web server, or even other application servers. The information traveling back and forth between an application server and its client is not restricted to simple display markup. Instead, the information is program logic. Since the logic takes the form of data and method calls and not static HTML, the client can employ the exposed business logic however it wants.

In most cases, the server exposes this business logic through a component API, such as the EJB (Enterprise JavaBean) component model found on J2EE (Java 2 Platform, Enterprise Edition) application servers. Moreover, the application server manages its own resources. Such gate-keeping duties include security, transaction processing, resource pooling, and messaging. Like a Web server, an application server may also employ various scalability and fault-tolerance techniques.

XML現在已經成為一種通用的數據交換格式,平臺的無關性使得很多場合都需要用到XML。本文將詳細介紹用Java解析XML的四種方法。

XML現在已經成為一種通用的數據交換格式,它的平臺無關性,語言無關 性,系統無關性,給數據集成與交互帶來了極大的方便。對于XML本身的語法知識與技術細節,需要閱讀相關的技術文獻,這里面包括的內容有 DOM(Document Object Model),DTD(Document Type Definition),SAX(Simple API for XML),XSD(Xml Schema Definition),XSLT(Extensible Stylesheet Language Transformations),具體可參閱w3c官方網站文檔http://www.w3.org獲取更多信息。

XML在不同的語言里解析方式都是一樣的,只不過實現的語法不同而已。基本的解析方式有兩種,一種叫SAX，另一種叫DOM。SAX是基于事件流的解析,DOM是基于XML文檔樹結構的解析。假設我們XML的內容和結構如下:

<?xml version="1.0" encoding="UTF-8"?> <employees> <employee> <name>ddviplinux</name> <sex>m</sex> <age>30</age> </employee> </employees>

本文使用JAVA語言來實現DOM與SAX的XML文檔生成與解析。
首先定義一個操作XML文檔的接口XmlDocument 它定義了XML文檔的建立與解析的接口。

package com.alisoft.facepay.framework.bean; /** * * @author hongliang.dinghl * 定義XML文檔建立與解析的接口 */ public interface XmlDocument { /** * 建立XML文檔 * @param fileName 文件全路徑名稱 */ public void createXml(String fileName); /** * 解析XML文檔 * @param fileName 文件全路徑名稱 */ public void parserXml(String fileName); }

1.DOM生成和解析XML文檔

為 XML 文檔的已解析版本定義了一組接口。解析器讀入整個文檔，然后構建一個駐留內存的樹結構，然后代碼就可以使用 DOM 接口來操作這個樹結構。優點：整個文檔樹在內存中，便于操作；支持刪除、修改、重新排列等多種功能；缺點：將整個文檔調入內存（包括無用的節點），浪費時 間和空間；使用場合：一旦解析了文檔還需多次訪問這些數據；硬件資源充足（內存、CPU）。

package com.alisoft.facepay.framework.bean; 

import java.io.FileInputStream; 

import java.io.FileNotFoundException; 

import java.io.FileOutputStream; 

import java.io.IOException; 

import java.io.InputStream; 

import java.io.PrintWriter; 

import javax.xml.parsers.DocumentBuilder; 

import javax.xml.parsers.DocumentBuilderFactory; 

import javax.xml.parsers.ParserConfigurationException; 

import javax.xml.transform.OutputKeys; 

import javax.xml.transform.Transformer; 

import javax.xml.transform.TransformerConfigurationException; 

import javax.xml.transform.TransformerException; 

import javax.xml.transform.TransformerFactory; 

import javax.xml.transform.dom.DOMSource; 

import javax.xml.transform.stream.StreamResult; 

import org.w3c.dom.Document; 

import org.w3c.dom.Element; 

import org.w3c.dom.Node; 

import org.w3c.dom.NodeList; 

import org.xml.sax.SAXException; 

/** 

* 

* @author hongliang.dinghl 

* DOM生成與解析XML文檔 

*/ 

public class DomDemo implements XmlDocument { 

private Document document; 

private String fileName; 

public void init() { 

try { 

DocumentBuilderFactory factory = DocumentBuilderFactory 

.newInstance(); 

DocumentBuilder builder = factory.newDocumentBuilder(); 

this.document = builder.newDocument(); 

} catch (ParserConfigurationException e) { 

System.out.println(e.getMessage()); 

} 

} 

public void createXml(String fileName) { 

Element root = this.document.createElement("employees"); 

this.document.appendChild(root); 

Element employee = this.document.createElement("employee"); 

Element name = this.document.createElement("name"); 

name.appendChild(this.document.createTextNode("丁宏亮")); 

employee.appendChild(name); 

Element sex = this.document.createElement("sex"); 

sex.appendChild(this.document.createTextNode("m")); 

employee.appendChild(sex); 

Element age = this.document.createElement("age"); 

age.appendChild(this.document.createTextNode("30")); 

employee.appendChild(age); 

root.appendChild(employee); 

TransformerFactory tf = TransformerFactory.newInstance(); 

try { 

Transformer transformer = tf.newTransformer(); 

DOMSource source = new DOMSource(document); 

transformer.setOutputProperty(OutputKeys.ENCODING, "gb2312"); 

transformer.setOutputProperty(OutputKeys.INDENT, "yes"); 

PrintWriter pw = new PrintWriter(new FileOutputStream(fileName)); 

StreamResult result = new StreamResult(pw); 

transformer.transform(source, result); 

System.out.println("生成XML文件成功!"); 

} catch (TransformerConfigurationException e) { 

System.out.println(e.getMessage()); 

} catch (IllegalArgumentException e) { 

System.out.println(e.getMessage()); 

} catch (FileNotFoundException e) { 

System.out.println(e.getMessage()); 

} catch (TransformerException e) { 

System.out.println(e.getMessage()); 

} 

} 

public void parserXml(String fileName) { 

try { 

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 

DocumentBuilder db = dbf.newDocumentBuilder(); 

Document document = db.parse(fileName); 

NodeList employees = document.getChildNodes(); 

for (int i = 0; i < employees.getLength(); i++) { 

Node employee = employees.item(i); 

NodeList employeeInfo = employee.getChildNodes(); 

for (int j = 0; j < employeeInfo.getLength(); j++) { 

Node node = employeeInfo.item(j); 

NodeList employeeMeta = node.getChildNodes(); 

for (int k = 0; k < employeeMeta.getLength(); k++) { 

System.out.println(employeeMeta.item(k).getNodeName() 

+ ":" + employeeMeta.item(k).getTextContent()); 

} 

} 

} 

System.out.println("解析完畢"); 

} catch (FileNotFoundException e) { 

System.out.println(e.getMessage()); 

} catch (ParserConfigurationException e) { 

System.out.println(e.getMessage()); 

} catch (SAXException e) { 

System.out.println(e.getMessage()); 

} catch (IOException e) { 

System.out.println(e.getMessage()); 

} 

} 

}

2.SAX生成和解析XML文檔

為 解決DOM的問題，出現了SAX。SAX ，事件驅動。當解析器發現元素開始、元素結束、文本、文檔的開始或結束等時，發送事件，程序員編寫響應這些事件的代碼，保存數據。優點：不用事先調入整個 文檔，占用資源少；SAX解析器代碼比DOM解析器代碼小，適于Applet，下載。缺點：不是持久的；事件過后，若沒保存數據，那么數據就丟了；無狀態 性；從事件中只能得到文本，但不知該文本屬于哪個元素；使用場合：Applet;只需XML文檔的少量內容，很少回頭訪問；機器內存少；

Java代碼

package com.alisoft.facepay.framework.bean;   

import java.io.FileInputStream;    

import java.io.FileNotFoundException;    

import java.io.IOException;    

import java.io.InputStream;    



import javax.xml.parsers.ParserConfigurationException;    

import javax.xml.parsers.SAXParser;    

import javax.xml.parsers.SAXParserFactory;    



import org.xml.sax.Attributes;    

import org.xml.sax.SAXException;    

import org.xml.sax.helpers.DefaultHandler;    

/**  

*    

* @author hongliang.dinghl  

* SAX文檔解析  

*/  

public class SaxDemo implements XmlDocument {    



public void createXml(String fileName) {    

System.out.println("<<"+filename+">>");    

}    



public void parserXml(String fileName) {    

SAXParserFactory saxfac = SAXParserFactory.newInstance();    



try {    



SAXParser saxparser = saxfac.newSAXParser();    



InputStream is = new FileInputStream(fileName);    



saxparser.parse(is, new MySAXHandler());    



} catch (ParserConfigurationException e) {    



e.printStackTrace();    



} catch (SAXException e) {    



e.printStackTrace();    



} catch (FileNotFoundException e) {    



e.printStackTrace();    



} catch (IOException e) {    



e.printStackTrace();    



}    



}    



}    



class MySAXHandler extends DefaultHandler {    



boolean hasAttribute = false;    



Attributes attributes = null;    



public void startDocument() throws SAXException {    



System.out.println("文檔開始打印了");    



}    



public void endDocument() throws SAXException {    



System.out.println("文檔打印結束了");    



}    



public void startElement(String uri, String localName, String qName,    



Attributes attributes) throws SAXException {    



if (qName.equals("employees")) {    



return;    



}    



if (qName.equals("employee")) {    



System.out.println(qName);    



}    



if (attributes.getLength() > 0) {    



this.attributes = attributes;    



this.hasAttribute = true;    



}    



}    



public void endElement(String uri, String localName, String qName)    



throws SAXException {    



if (hasAttribute && (attributes != null)) {    



for (int i = 0; i < attributes.getLength(); i++) {    



System.out.println(attributes.getQName(0)    

+ attributes.getValue(0));    



}    



}    



}    



public void characters(char[] ch, int start, int length)    



throws SAXException {    



System.out.println(new String(ch, start, length));    



}    



}  

package com.alisoft.facepay.framework.bean; 

import java.io.FileInputStream; 

import java.io.FileNotFoundException; 

import java.io.IOException; 

import java.io.InputStream; 

import javax.xml.parsers.ParserConfigurationException; 

import javax.xml.parsers.SAXParser; 

import javax.xml.parsers.SAXParserFactory; 

import org.xml.sax.Attributes; 

import org.xml.sax.SAXException; 

import org.xml.sax.helpers.DefaultHandler; 

/** 

* 

* @author hongliang.dinghl 

* SAX文檔解析 

*/ 

public class SaxDemo implements XmlDocument { 

public void createXml(String fileName) { 

System.out.println("<<"+filename+">>"); 

} 

public void parserXml(String fileName) { 

SAXParserFactory saxfac = SAXParserFactory.newInstance(); 

try { 

SAXParser saxparser = saxfac.newSAXParser(); 

InputStream is = new FileInputStream(fileName); 

saxparser.parse(is, new MySAXHandler()); 

} catch (ParserConfigurationException e) { 

e.printStackTrace(); 

} catch (SAXException e) { 

e.printStackTrace(); 

} catch (FileNotFoundException e) { 

e.printStackTrace(); 

} catch (IOException e) { 

e.printStackTrace(); 

} 

} 

} 

class MySAXHandler extends DefaultHandler { 

boolean hasAttribute = false; 

Attributes attributes = null; 

public void startDocument() throws SAXException { 

System.out.println("文檔開始打印了"); 

} 

public void endDocument() throws SAXException { 

System.out.println("文檔打印結束了"); 

} 

public void startElement(String uri, String localName, String qName, 

Attributes attributes) throws SAXException { 

if (qName.equals("employees")) { 

return; 

} 

if (qName.equals("employee")) { 

System.out.println(qName); 

} 

if (attributes.getLength() > 0) { 

this.attributes = attributes; 

this.hasAttribute = true; 

} 

} 

public void endElement(String uri, String localName, String qName) 

throws SAXException { 

if (hasAttribute && (attributes != null)) { 

for (int i = 0; i < attributes.getLength(); i++) { 

System.out.println(attributes.getQName(0) 

+ attributes.getValue(0)); 

} 

} 

} 

public void characters(char[] ch, int start, int length) 

throws SAXException { 

System.out.println(new String(ch, start, length)); 

} 

}

3.DOM4J生成和解析XML文檔

DOM4J 是一個非常非常優秀的Java XML API，具有性能優異、功能強大和極端易用使用的特點，同時它也是一個開放源代碼的軟件。如今你可以看到越來越多的 Java 軟件都在使用 DOM4J 來讀寫 XML，特別值得一提的是連 Sun 的 JAXM 也在用 DOM4J。

Java代碼

package com.alisoft.facepay.framework.bean;   

import java.io.File;    

import java.io.FileWriter;    

import java.io.IOException;    

import java.io.Writer;    

import java.util.Iterator;    



import org.dom4j.Document;    

import org.dom4j.DocumentException;    

import org.dom4j.DocumentHelper;    

import org.dom4j.Element;    

import org.dom4j.io.SAXReader;    

import org.dom4j.io.XMLWriter;    

/**  

*    

* @author hongliang.dinghl  

* Dom4j 生成XML文檔與解析XML文檔  

*/  

public class Dom4jDemo implements XmlDocument {    



public void createXml(String fileName) {    

Document document = DocumentHelper.createDocument();    

Element employees=document.addElement("employees");    

Element employee=employees.addElement("employee");    

Element name= employee.addElement("name");    

name.setText("ddvip");    

Element sex=employee.addElement("sex");    

sex.setText("m");    

Element age=employee.addElement("age");    

age.setText("29");    

try {    

Writer fileWriter=new FileWriter(fileName);    

XMLWriter xmlWriter=new XMLWriter(fileWriter);    

xmlWriter.write(document);    

xmlWriter.close();    

} catch (IOException e) {    



System.out.println(e.getMessage());    

}    





}    





public void parserXml(String fileName) {    

File inputXml=new File(fileName);    

SAXReader saxReader = new SAXReader();    

try {    

Document document = saxReader.read(inputXml);    

Element employees=document.getRootElement();    

for(Iterator i = employees.elementIterator(); i.hasNext();){    

Element employee = (Element) i.next();    

for(Iterator j = employee.elementIterator(); j.hasNext();){    

Element node=(Element) j.next();    

System.out.println(node.getName()+":"+node.getText());    

}    



}    

} catch (DocumentException e) {    

System.out.println(e.getMessage());    

}    

System.out.println("dom4j parserXml");    

}   

}  

4.JDOM生成和解析XML  

為減少DOM、SAX的編碼量，出現了JDOM；優點：20-80原則，極大減少了代碼量。使用場合：要實現的功能簡單，如解析、創建等，但在底層，JDOM還是使用SAX（最常用）、DOM、Xanan文檔。

    

package com.alisoft.facepay.framework.bean;    



import java.io.FileNotFoundException;    

import java.io.FileOutputStream;    

import java.io.IOException;    

import java.util.List;    



import org.jdom.Document;    

import org.jdom.Element;    

關于JAXP，DOM，SAX，JDOM，DOM4J的一些想法

這些API是XSLT的關鍵部分，它們構建在DOM和SAX解析器基礎上。

Sun在XML領域總是后知后覺，等到Sun重視XML的時候，XML的API早就滿天飛了，尤其是IBM具有非常大的領先優勢。不過Sun是規范 的制訂者，于是參考WOffice:smarttags" />3C的標準制訂了JAXP規范。JAXP不像Xerces和Crimon那樣，它只是一個spec，本身是不做任何事情的，它的作用就是提出一 個統一的接口，讓其它的XML API都來遵循JAXP編程，那么用JAXP寫出來的程序，底層的API可以任意切換。

具體來說JAXP包括了幾個工廠類，這就是JDK1.4里面的Javax.xml.parsers 包，用來尋找符合DOM標準的XML API實現類的位置；此外JAXP還包括一整套interface，這就是JDK1.4里面的org.w3c.dom那幾個包。工廠類負責加載DOM的實 現類。

當你嚴格采用JAXP編程的時候，是遵循W3C的DOm標準的，那么在JAXP底層你實際上可以任意切換不同的DOM實現，例如Xerces，或者Crimon，再或者其它，切換方法就是配置jaxp.properties。因此JAXP就是一些標準接口而已。

JAXP應用程序 -> JAXP接口 -> Xerces DOM實現 -> Xerces DOM/SAX 解析器
JAXP應用程序 -> JAXP接口 -> Crimson DOM實現 -> Crimson DOM/SAX 解析器
JAXP應用程序 -> JAXP接口 -> Crimson DOM實現 -> Xerces DOM/SAX 解析器

W3C的DOM標準API難用的讓人想撞墻，于是有一幫人開發Java專用的XML API目的是為了便于使用，這就是jdom的由來，開發到一半的時候，另一部分人又分了出來，他們有自己的想法，于是他們就去開發dom4j，形成了今天 這樣兩個API，至于他們之間的性能，功能之比較看看上面我推薦的文章就知道了，jdom全面慘敗。

jdom 相當于上面的 JAXP接口 ＋ Xerces DOM實現部分，它本身沒有解析器，它可以使用Xerces或者Crimson的解析器即
JAXP應用程序 -> JAXP接口 -> Xerces DOM實現 -> Crimson DOM/SAX 解析器 或 Xerces DOM/SAX 解析器

jdom應用程序 -> jdom API -> Xerces/Crimson解析器
dom4j應用程序 -> dom4j API -> Xerces/Crimson解析器
dom4j應用程序 -> dom4j API -> Alfred2解析器

因此可以看出采用dom4j/jdom編寫的應用程序，已經不具備可移植性了。

Sun是JAXP標準的制訂者，甚至很執著的在JDK1.4里面綁定Crimson DOM實現和解析器，然后可笑的是，Sun自己的JAXM RI竟然不是用JAXP寫出來的，而是dom4j

我的舉例：

1．   僅僅是XSL轉換。XMLàHTML，通過XSL

Import javax.xml.transform.TransformerFactory;

Import javax.xml.transform.Transformer;

Import javax.xml.stream.StreamSource;

Import javax.xml.stream.StreamResult;

import java.io.FileOutputStream;

TransformerFactory transFactory = TransformerFactory.newInstance();

Transform transformer = transFacyory.newTransformer(new StreamSource(XMLSheetName));

Transformer.transform(new StreamSource(XMLFileName),new StreamResult(new FileOutputStream(outputURL)));

這里的stream是一個DOM對象。
我感覺這個就是JAXP應用程序 -> JAXP接口 -> Xerces DOM實現 -> Xerces DOM/SAX 解析器,不知道對不對。

2．遍歷XML，通過DOM。不僅僅是XSL轉換。中間有對XML元素內容的操作。
Import javax.xml.transform.TransformerFactory;

Import javax.xml.transform.Transformer;

Import javax.xml.stream.StreamSource;

Import javax.xml.stream.StreamResult;

import java.io.FileOutputStream;

//Xerces解析器來完成DOM遍歷XML.DOMParser是Xerces包的一部分。

Import org.apache.xerces.parsers.DOMParser;

Import org.w3c.dom.Document;

Import org.w3c.dom.NodeList;

//DOM遍歷XML

DOMParser parser = new DOMParser();

Parser.parse(XMLFileName);//解析并在內存中創建XML樹。

Document document = parser.getDocument();//通過Document對象，可以使用內存中的樹。

NodeList products = document.getElementByTagName(“product_id”);

Int num_products = products.getLength();

//XSL轉化器

TransformerFactory transFactory = TransformerFactory.newInstance();

Transform transformer = transFacyory.newTransformer(new StreamSource(XMLSheetName));

Transformer.transform(new StreamSource(XMLFileName),new StreamResult(new FileOutputStream(outputURL)));

我感覺XSL轉化和對XML對象的操作是兩個過程?？梢苑謩e對待。最重要的是對對象的操作。這也就是為什么有DOM,JDOM,DOM4J。轉化好像只需要JAXP就可以了，關心的是StreamSource和StreamResult。這兩個是DOM對象。

3．JDOM使用，生成Document內容并保存到XML文件。
import org.jdom.Element;
import org.jdom.Document;//和Import org.w3c.dom.Document對比一下。一個是JAXP的一個是JDOM的Document

import org.jdom.output.XMLOutputter;

Element root = Element(“orders”);

root.addContent(“ ”);

org.jdom.Document document = new Document(root);//創建JDOM樹。

FileOutputStream outStream = new FileOutputStream(XMLFileName);

XMLOutputter outToFile = new XMLOutputter();

outToFile.output(document,outStream);

outStream.flush();

outStream.close();

jdom應用程序 -> jdom API -> Xerces/Crimson解析器
VS
JAXP應用程序 -> JAXP接口 -> Xerces DOM實現 -> Xerces DOM/SAX 解析器

這里的沒有Transform的過程，直接把Document的內容存到XML中。沒有XSL轉化，沒有XSL文件。

JDOM提供了幾種輸出方法。這里XMLOutputter是保存到文件，輸出一個實際的XML流。還有DOMOutputter,在內存中創建一個傳統的DOM樹。還有SAXOutputter，創建一串SAX事件以便被其他對象讀取。

4．JDOM使用，讀取已有的XML然后生成Document，修改Document
import org.jdom.Element;
import org.jdom.Document;

import org.jdom.output.XMLOutputter;
    import org.jdom.input.SAXBuilder;

    SAXBuilder builder = new SAXBuilder();
    Document document = builder.build(XMLFileName);

Element order = Element(“orders”);

orders.addAttribute(“order_id”,session_id);

Element root = document.getRootElement();//root是已經存在的根元素。

Root.addContent(order);//在根元素里增加orders元素。

//把document保存到文件中。

FileOutputStream outStream = new FileOutputStream(XMLFileName);

XMLOutputter outToFile = new XMLOutputter();

outToFile.output(document,outStream);

outStream.flush();

outStream.close();

即使創建一個DOM式的結構，這里仍使用SAXBuilder來做這這件事情。

DOMBuilder和SAXBuilder中的”DOM”和”SAX”指的是用于建立文檔的方法，而不是生成的內容。

5．XSL轉換,能把DOM對象轉化成輸出，也可以向上面所舉例的把XMLFileName的流轉化成輸出的流（文件或屏幕顯示）。但是不能把JDOM對象轉化，所以需要把JDOM轉化成DOM對象，然后再輸出。
import org.jdom.Element;
import org.jdom.Document;

import org.jdom.output.XMLOutputter;
    import org.jdom.input.SAXBuilder;  
    //XSL轉化需要的包
import org.jdom.output.DOMOutputter;//對比org.jdom.output.XMLOutputter;
Import javax.xml.transform.TransformerFactory;

Import javax.xml.transform.Transformer;

Import javax.xml.transform.DOMSource;//對比Import javax.xml.stream.StreamSource;

Import javax.xml.stream.StreamResult;

   org.w3c.dom.Document DOMDoc;
   DOMOutputter DomOut = DOMOutputter();
   DOMDoc = DomOut.output(org.jdom.Document);//把jdom的document轉化成DOM的document

   TransformFactory transFactory = TransformFactory.newInstance();
   Transformer transformer = transFactory.newTransformer(new DOMSource(DOMDoc));//感覺錯了，應該是XSL文件。
   Transformer.transform(new DOMSource(DOMDoc),new StreamResult(out));

//對比以前的轉化，是從文件到文件，現在是DOM樹到屏幕輸出。
TransformerFactory transFactory = TransformerFactory.newInstance();

Transform transformer = transFacyory.newTransformer(new StreamSource(XMLSheetName));