Learn to use XML engine XQEngine

Author：Eve Cole Update Time：2009-07-07 16:09:39

Recently I have been looking for XML search tools. The application I wrote needs to regularly search some related XML files. My original intention was to see if there is data matching the data I want in the file, but there is Sometimes, I also want to output the data I found. At first, I tried XSLT and XPath, hoping to transform the search problem into a problem that could be solved using XSLT. However, after a period of experimentation, I found that using XSLT did not really solve the search problem I wanted to solve. Because the data I want to output is comma-separated numbers, and XSLT cannot meet this requirement, and XLST cannot provide full-text search functionality. Then I wanted to try using XML Query Language (XQL) to see if I could solve it, so I carefully looked at the implementation of various versions of XQL. Coincidentally, I happened to find a small tool called XQEngine that could solve this problem. , so, in this article I would like to introduce how to use XQEngine to search for the string data you want to find in your XML file.

XQEngine can be found at www.fatdog.com. It is a JavaBean that uses a SAX parser to index one or more XML documents, and then you can perform complex searches in these documents. The search language it uses is a superset of XQL and has a similar syntax to XPath.

The Java class using XQEngine must implement a result() method. After completing the search, the engine will call this method to pass the search results to the result() method. Three formats for displaying data can be used to output the data results. Use command line parameters to specify the search parameters you need. For example, you can specify that a file will not be indexed if it contains the word stop; or you can instruct the engine in the parameters to ignore words that are less than the specified number.

Below, I have given a routine using XQEngine, let us analyze it now. First, the main() method instantiates a search engine: , and then call the setSaxParserName() method to set the full name of the SAX parser. Because we are using the Xerces parser, we need to use "org.apache.xerces.parsers.SAXParser". Then we need to set the search parameters, in this case we will not index numbers or any words less than 3 characters. There will be detailed configuration parameter descriptions in the XQEngine API document you downloaded, so I will not go into details on how to configure the parameters here. Please refer to the relevant documents yourself. Finally, the setDocument() method specifies the XML file that XQEngine will index or search. Of course, if you want to index multiple files, you only need to set several corresponding setDocument() methods.

We can also see from the code below that the XQEngine engine will return search results in three different formats: STANDARD, SUMMARY and CSV (using comma separated values). For simplicity, I have defined one for each return result type. number instead of (1, 2, 3), and then call the setListenerType() method with the corresponding parameters. I will describe each return result type in detail later. There is also a method printSessionState() used to output index and engine information, but I did not write it into the routine, so the above program will only output the search results; in the next step, call the addXQLResultListener() method and pass the Search An instance is used to implement the XQLResultListener interface; then the setQuery method is called with the query string as a parameter, and the engine will start executing the query task. After the query is completed, the engine calls the result() method of the Search class and returns the query results. In the routine I provided, the result() method simply outputs the results.
Code:

import java.io.*;
import com.fatdog.textEngine.XmlEngine;
import com.fatdog.textEngine.exceptions.*;
import com.fatdog.textEngine.query.XQLResultListener;
public class Search implements XQLResultListener
{
public static void main( String[] args )
{
XmlEngine engine = new XmlEngine();
String searchFile = args[0];
String searchType = args[1];
String query = args[2];
try { file://configuration engine
engine.setSaxParserName( "org.apache.xerces.parsers.SAXParser");
engine.setMinIndexableWordLength(3);
engine.setDoIndexNumbers( false );
engine.setDocument( searchFile );

if (searchType.equals("1")) {
engine.setListenerType(
XmlEngine.STANDARD_LISTENER);
}
else if (searchType.equals("2")) {
engine.setListenerType(
XmlEngine.SUMMARY_LISTENER);
}
else {
engine.setListenerType(
XmlEngine.CSV_LISTENER);
}
}
catch( MissingOrInvalidSaxParserException e ){
System.out.println(
"Missing or unavailable SAX parser" );
return;
}
catch(FileNotFoundException e) {
System.out.println(
"Cannot find XML file: ");
return;
}
catch(CantParseDocumentException e) {
System.out.println(
"Cannot parse XML file: ");
return;
}
// engine.printSessionStats();
engine.addXQLResultListener( new Search() );
try {
engine.setQuery( query );
}
catch(InvalidQueryException e) {
System.out.println(
"Unavailable query request: " + e.getMessage() );
return;
}
}
public void results( String xqlResults )
{
System.out.println(xqlResults);
}
}

Okay, we have written a program using XQEngine, so let's run this code. Before compiling this code, we need to download XQEngine and the SAX parser. I downloaded the Xerces parser from xml.apache.org. The operating system I use is Windows 2000 Professional, and the JDK is version 1.3. OK, after you have done this, follow me to set up CLASSPATH. Modify CLASSPATH in "Environment Variables" and add "c:xqlXQEngine.jar;c: xqlantlr.jar; c:xercesxerces.jar". Now the code can be compiled, but in order to run the program, we also need an XML file. I used the web.xml file in Apache Tomcat as a demonstration. As I introduced before, we use 1, 2, and 3 to replace the three return query result formats:

1. Use STANDARD_LISTENER (number 1) and the query item "//welcome-file-list/welcome-file", C:xqlxql1>java Search web.xml 1 "//welcome-file-list/welcome-file "

Parser.installSaxParser:

<org.apache.xerces.parsers.SAXParser>
installed successfully
1: indexing web.xml
Query: ( // ( / welcome-file-list welcome-file ) )
3 hit(s) for file://welcome-file-list/welcome-file
＜?xml version="1.0"?＞
<xql:result
query="//welcome-file-list/welcome-file"
hitCount="3"
elemCount="3"
docCount="1"
xmlns:xql="http://www.fatdog.com/ Standard_Listener.html">
＜welcome-file＞
index.jsp
＜/welcome-file＞
＜welcome-file＞
index.html
＜/welcome-file＞
＜welcome-file＞
index.htm
＜/welcome-file＞
＜/xql:result＞

In the above example, the query item requires finding all "welcome-file" sub-elements of any "welcome-file-list" element. Please note that the search results are basically excerpted from the original XML document, and the relationship between the search results and the original document cannot be established. The return type of SUMMARY_LISTENER(2) is somewhat different. It includes a "docID" number and an "elemlx" number, so that the result can be associated with the original document.

The following is an example of returned results:

C:xqlxql1>java Search web.xml 2
"//welcome-file-list/welcome-file"
Parser.installSaxParser: <org.apache.xerces.parsers.SAXParser>
installed successfully

1: indexing web.xml

Query: ( // ( / welcome-file-list welcome-file ) )

3 hit(s) for file://welcome-file-list/welcome-file

＜?xml version="1.0"?＞
<xql:result
query="//welcome-file-list/welcome-file"
hitCount="3"
elemCount="3"
docCount="1"
xmlns:xql="http://www.fatdog.com/
Summary_Listener.html">
＜welcome-file xql:docID="0" xql:elemIx="270"/＞
＜welcome-file xql:docID="0" xql:elemIx="271"/＞
＜welcome-file xql:docID="0" xql:elemIx="272"/＞
＜/xql:result＞

I have also said before that for my application, the most important thing is to return results separated by commas, so CSV_LISTENER(3) is very useful. It can return a result separated by commas, as follows :

C:xqlxql1>java Search web.xml 3
"//welcome-file-list/welcome-file"
Parser.installSaxParser:
<org.apache.xerces.parsers.SAXParser>
installed successfully

1: indexing web.xml

Query: ( // ( / welcome-file-list welcome-file ) )

3 hit(s) for file://welcome-file-list/welcome-file

3,3,1,0
0,270,welcome-file
0,271,welcome-file
0,272,welcome-file

Of course, XQEngine also has many powerful functions. I can't introduce them one by one here. The documentation it comes with has a wealth of source programs and usage methods. You can learn to use them by yourself. Of course, if you are willing, you can You can even develop a GUI program. The document comes with a GUI-based search program: SwingQueryDemo. You can take a look and study it.