A detailed introduction to the comparison of several ways to parse XML files

We often need to parse XML files at work. I was asked about some expanded knowledge in the interview a few days ago, which was surprising. If there is no satisfactory answer, I will record it and study it.

Features: DOM needs to load XML files into memory at one time.
SAX does not require a one-time load, and analysis can start immediately instead of waiting for all data to be processed.
JDOM makes extensive use of Java’s collection objects, which greatly improves the work efficiency of Java programmers. 28 Principles.
DOM4J is currently the most used, and our project is also using DOM4j for parsing.

1) DOM (JAXP Crimson parser)
DOM is the official W3C standard for representing XML documents in a platform- and language-independent way. DOM is a collection of nodes or pieces of information organized in a hierarchical structure. This hierarchy allows developers to search the tree for specific information. Analyzing this structure typically requires loading the entire document and constructing the hierarchy before any work can be done. Because it is based on information hierarchy, DOM is considered tree-based or object-based. DOM, and tree-based processing in general, has several advantages. First, because the tree is persistent in memory, it can be modified so that the application can make changes to the data and structures. It can also navigate up and down the tree at any time, rather than a one-time process like SAX. DOM is also much simpler to use. 2) SAX

The advantages of SAX processing are very similar to the advantages of streaming media. Analysis can start immediately instead of waiting for all data to be processed. Also, since the application just checks the data as it is read, there is no need to store the data in memory. This is a huge advantage for large documents. In fact, the application doesn't even have to parse the entire document; it can stop parsing when a certain condition is met. In general, SAX is also much faster than its replacement, DOM.

Choose DOM or SAX? For developers who need to write their own code to process XML documents, choosing a DOM or SAX parsing model is a very important design decision. DOM uses a tree structure to access XML documents, while SAX uses the
event
model. The DOM parser converts the XML document into a tree containing its content, and can traverse the tree. The advantage of using DOM to parse the model is that programming is easy. Developers only need to call the tree-building instructions, and then use navigation
API
s to access the required tree nodes to complete the task. Elements in the tree can be easily added and modified. However, since the entire XML document needs to be processed when using the DOM parser, the performance and memory requirements are relatively high, especially when encountering large XML files. Due to its traversal capabilities, DOM parsers are often used in services where XML documents need to change frequently. The SAX parser adopts an event-based model. It can trigger a series of events when parsing XML documents. When a given tag is found, it can activate a callback method and tell the method to formulate The tag has been found. SAX usually has lower memory requirements because it allows developers to decide which tags to process. Especially when developers only need to process part of the data contained in the document, SAX's scalability is better reflect. But coding is more difficult when using a SAX parser, and it is difficult to access multiple different data in the same document at the same time. 3) JDOM www.jdom.org

The purpose of JDOM is to be a Java-specific document model that simplifies interaction with XML and is faster than using DOM. JDOM has been heavily promoted and promoted since it was the first Java-specific model. It is being considered for eventual use as a "Java Standard Extension" via "Java Specification Request JSR-102". JDOM development has been started since the early 2000s.

There are two main differences between JDOM and DOM. First, JDOM only uses concrete classes and not
interfaces
. This simplifies the API in some ways, but also limits flexibility. Second, the API makes extensive use of the Collections class, simplifying its use for Java developers who are already familiar with these classes.

The JDOM documentation states that its purpose is to "solve 80% (or more) Java/XML problems using 20% ​​(or less) effort" (assuming 20% ​​based on the learning curve). JDOM is certainly useful for most Java/XML applications, and most developers find the API much easier to understand than DOM. JDOM also includes fairly extensive checks on program behavior to prevent users from doing anything that doesn't make sense in XML. However, it still requires that you understand XML well enough to do more than the basics (or even understand the errors in some cases). This may be more meaningful work than learning DOM or JDOM interfaces.

JDOM itself does not contain a parser. It typically uses a SAX2 parser to parse and validate input XML documents (although it can also take previously constructed DOM representations as input). It contains converters to output JDOM representations into SAX2 event streams, DOM models, or XML text documents. JDOM is open source released under a variant of the Apache license.

4) DOM4J dom4j.sourceforge.net

Although DOM4J represents a completely independent development result, initially, it was an intelligent branch of JDOM. It incorporates many features beyond basic XML document representation, including integrated XPath support, XML Schema support, and event-based processing for large or streaming documents. It also provides options to build document representations with parallel access capabilities through the DOM4J API and standard DOM interfaces. It has been under development since the second half of 2000. To support all these features, DOM4J uses interfaces and abstract basic class methods. DOM4J makes heavy use of the Collections class in the API, but in many cases it also provides alternatives that allow for better performance or a more direct coding approach. The direct benefit is that although DOM4J pays the price of a more complex API, it provides much greater flexibility than JDOM.

While adding flexibility, XPath integration, and the goal of processing large documents, DOM4J's goals are the same as JDOM: ease of use and intuitive operation for Java developers. It also aims to be a more complete solution than JDOM, achieving the goal of handling essentially all Java/XML problems. While accomplishing that goal, it places less emphasis than JDOM on preventing incorrect application behavior.

DOM4J is a very, very excellent Java XML API with excellent performance, powerful functions and extreme ease of use. It is also an open source software. Nowadays you can see that more and more Java software is using DOM4J to read and write XML. It is particularly worth mentioning that even Sun's JAXM is also using DOM4J.

2... Comparison

1) DOM4J has the best performance, even Sun's JAXM is also using DOM4J. Currently, many open source projects use DOM4J extensively. For example, the famous Hibernate also uses DOM4J to read XML
configuration files
. If portability is not considered, then use DOM4J. 2) JDOM and DOM performed poorly during performance testing, and memory overflowed when testing 10M documents. It is also worth considering using DOM and JDOM in the case of small documents. Although the developers of JDOM have stated that they expect to focus on performance issues before the official release, from a performance point of view, it really has nothing to recommend. In addition, DOM is still a very good choice. DOM implementation is widely used in many
programming languages
. It is also the basis for many other XML-related standards, and since it is officially recommended by the W3C (as opposed to the non-standard based Java model), it may also be required in certain types of projects (such as in JavaScript uses DOM). 3) SAX performs better, which depends on its specific parsing method - event
driven
. A SAX detects the incoming XML stream, but does not load it into memory (of course when the XML stream is read, some documents will be temporarily hidden in memory). 3. The basic usage of the four xml operation methods
method xml file:

＜?xml version="1.0" encoding="GB2312"?＞ 
＜RESULT＞ 
＜VALUE＞ 
　　 ＜NO＞A1234＜/NO＞ 
　　 ＜ADDR＞XX号＜/ADDR＞ 
＜/VALUE＞ 
＜VALUE＞ 
　　 ＜NO＞B1234＜/NO＞ 
　 　＜ADDR＞XX组＜/ADDR＞ 
＜/VALUE＞ 
＜/RESULT＞

1) DOM

import java.io.*; 
import java.util.*; 
import org.w3c.dom.*; 
import javax.xml.parsers.*; 

public class MyXMLReader{ 
　public static void main(String arge[]){ 

　　long lasting =System.currentTimeMillis(); 
　　try{ 
　　　File f=new File("data_10k.xml"); 
　　　DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance(); 
　　　DocumentBuilder builder=factory.newDocumentBuilder(); 
　　　Document doc = builder.parse(f); 
　　　NodeList nl = doc.getElementsByTagName("VALUE"); 
　　　for (int i=0;i＜nl.getLength();i++){ 
　　　　System.out.print("车牌号码:" + doc.getElementsByTagName("NO").item(i).getFirstChild().getNodeValue()); 
　　　　System.out.println("车主地址:" + doc.getElementsByTagName("ADDR").item(i).getFirstChild().getNodeValue()); 
　 　} 
　　}catch(Exception e){ 
　　　e.printStackTrace(); 
}

2 ) SAX

import org.xml.sax.*; 
import org.xml.sax.helpers.*; 
import javax.xml.parsers.*; 

public class MyXMLReader extends DefaultHandler { 

　java.util.Stack tags = new java.util.Stack(); 
　public MyXMLReader() { 
　　super(); 
} 

　public static void main(String args[]) { 
　　long lasting = System.currentTimeMillis(); 
　　try { 
　　　SAXParserFactory sf = SAXParserFactory.newInstance(); 
　　　SAXParser sp = sf.newSAXParser(); 
　　　MyXMLReader reader = new MyXMLReader(); 
　　　sp.parse(new InputSource("data_10k.xml"), reader); 
　　} catch (Exception e) { 
　　　e.printStackTrace(); 
　　} 

　　System.out.println("运行时间：" + (System.currentTimeMillis() - lasting) + "毫秒");} 
　　public void characters(char ch[], int start, int length) throws SAXException { 
　　String tag = (String) tags.peek(); 
　　if (tag.equals("NO")) { 
　　　System.out.print("车牌号码：" + new String(ch, start, length)); 
} 
if (tag.equals("ADDR")) { 
　　System.out.println("地址:" + new String(ch, start, length)); 
} 
} 

　　public void startElement(String uri,String localName,String qName,Attributes attrs) { 
　　tags.push(qName);} 
}

3) JDOM

import java.io.*; 
import java.util.*; 
import org.jdom.*; 
import org.jdom.input.*; 

public class MyXMLReader { 

　public static void main(String arge[]) { 
　　long lasting = System.currentTimeMillis(); 
　　try { 
　　　SAXBuilder builder = new SAXBuilder(); 
　　　Document doc = builder.build(new File("data_10k.xml")); 
　　　Element foo = doc.getRootElement(); 
　　　List allChildren = foo.getChildren(); 
　　　for(int i=0;i＜allChildren.size();i++) { 
　　　　System.out.print("车牌号码:" + ((Element)allChildren.get(i)).getChild("NO").getText()); 
　　　　System.out.println("车主地址:" + ((Element)allChildren.get(i)).getChild("ADDR").getText()); 
　　　} 
　　} catch (Exception e) { 
　　　e.printStackTrace(); 
} 

}

4) DOM4J

import java.io.*; 
import java.util.*; 
import org.dom4j.*; 
import org.dom4j.io.*; 

public class MyXMLReader { 

　public static void main(String arge[]) { 
　　long lasting = System.currentTimeMillis(); 
　　try { 
　　　File f = new File("data_10k.xml"); 
　　　SAXReader reader = new SAXReader(); 
　　　Document doc = reader.read(f); 
　　　Element root = doc.getRootElement(); 
　　　Element foo; 
　　　for (Iterator i = root.elementIterator("VALUE"); i.hasNext() { 
　　　　foo = (Element) i.next(); 
　　　　System.out.print("车牌号码:" + foo.elementText("NO")); 
　　　　System.out.println("车主地址:" + foo.elementText("ADDR")); 
　　　} 
　　} catch (Exception e) { 
　　　e.printStackTrace(); 
} 
)

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