I am writing an application that must update parts of an already existing xml file based on a set of files in a directory. An example of this xml file can be seen below:
http://izpack.org/documentation/sample-install-definition.html
In the below scope a list of files is added and its specified if they should be "parsable" (used for parameter substitution):
<packs>
<pack name="Main Application" required="yes" installGroups="New Application" >
<file src="post-install-tasks.bat" targetdir="$INSTALL_PATH"/>
<file src="build.xml" targetdir="$INSTALL_PATH"/>
<parsable targetfile="$INSTALL_PATH/post-install-tasks.bat"/>
<parsable targetfile="$INSTALL_PATH/build.xml"/>
</pack>
</packs>
Now the number of files that must be added to this scope can change each time the application is run. To make this possible I have considered the following approach:
1) Read the whole xml into a org.w3c.dom.*; Document and add nodes based on result from reading the directory.
2) Somehow add the content from a .properties file to the scope. This way its possible to update the filelist without recompiling the code.
3) ??
Any suggestions on a good approach to this kind of task?
if there's a chance that your XML configuration might be of significant size, then it is really not good to go ahead with a DOM based approach [due to the associated memory footprint of loading a large XML document]
you should take a look at StaX. it has a highly optimised approach for both parsing and writing XML documents.
3) Overwrite the old file with your new, modified version. The DOM parsers keep comments intact, but you could end up with formatting differences. In order to write to a file, do:
Source source = new DOMSource(doc);
File file = new File(filename);
Result result = new StreamResult(file);
Transformer xformer = TransformerFactory.newInstance().newTransformer();
xformer.transform(source, result);
Related
I have created a simple XML file to which I am writing some tweets that i collect on every batch run. I want the file to be appended rather than rewritten on every batch run. At the moment it is overwriting the current document on every batch run.
Can help me out with this please !!
Use this:
FileWriter writer = new FileWriter(file,true);
that will open the file in append mode.
Please note that it might cause a problem, if you have:
<root>
<sometag></sometag>
</root>
and then you append the same structure again, the next time you read the file you'll get:
<root>
<sometag></sometag>
</root>
<root>
<sometag></sometag>
</root>
which is not valid. So if you need to parse this xml later, you'll have to do it this way:
Read entire xml content.
Add new element to document object (using DOM parser)
write updated document to file (overriding old data).
I need to validate XML Schema Instance (XSD) documents which are programmatically generated so I'm using the following Java snippet, which works fine:
SchemaFactory factory = SchemaFactory.newInstance(
XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema xsdSchema = factory.newSchema( // Reads URL every time...
new URL("http://www.w3.org/2001/XMLSchema.xsd"));
Validator xsdValidator = xsdSchema.newValidator();
xsdValidator.validate(new StreamSource(schemaInstanceStream));
However, when I save the XML Schema definition file locally and refer to it this way:
Schema schema = factory.newSchema(
new File("test/xsd/XMLSchema.xsd"));
It fails with the following exception:
org.xml.sax.SAXParseException: schema_reference.4: Failed to read schema document 'file:/Users/foo/bar/test/xsd/XMLSchema.xsd', because 1) could not find the document; 2) the document could not be read; 3) the root element of the document is not <xsd:schema>.
I've ensured that the file exists and is readable by doing exists() and canRead() assertions on the File object. I've also downloaded the file with a couple different utilities (web browser, wget) to ensure that there is no corruption.
Any idea why I can validate XSD instance documents when I generate the schema from the HTTP URL but I get the above exception when trying to generate from a local file with the same contents?
[Edit]
To elaborate, I've tried multiple forms of factory.newSchema(...) using Readers and InputStreams (instead of the File directly) and still get exactly the same error. Moreover, I've dumped the file contents before using it or the various input streams to ensure it's the right one. Quite vexing.
Full Answer
It turns out that there are three additional files referenced by XML Schema which must be also stored locally and XMLSchema.xsd contains an import statement whose schemaLocation attribute must be changed. Here are the files that must be saved in the same directory:
XMLSchema.xsd - change schemaLocation to "xml.xsd" in the "import" element for XML Namespace.
XMLSchema.dtd - as is.
datatypes.dtd - as is.
xml.xsd - as is.
Thanks to #Blaise Doughan and #Tomasz Nurkiewicz for their hints.
I assume you are trying to load XMLSchema.xsd. Please also download XMLSchema.dtd and datatypes.dtd and put them in the same directory. This should push you a little bit further.
UPDATE
Is XMLSchema.xsd importing any other schemas by relative paths that are not on the local file systen?
Your relative path may not be correct wrt your working directory. Try entering a fully qualified path to eliminate the possibility that the file can not be found.
org.xml.sax.SAXParseException: schema_reference.4: Failed to read
schema document 'file:/Users/foo/bar/test/xsd/XMLSchema.xsd', because
1) could not find the document; 2) the document could not be read; 3)
the root element of the document is not .
I am currently using the standard javax.xml.transform library to transform my XML to CSV using XSL. My XSL file is large - at around 950 lines. My XML files can be quite large also.
It was working fine in the prototype stage with a fraction of the XSL in place at around 50 lines or so. Now in the 'final system' when it performs the transform it comes up with the error Branch target offset too large for short.
private String transformXML() {
String formattedOutput = "";
try {
TransformerFactory tFactory = TransformerFactory.newInstance();
Transformer transformer =
tFactory.newTransformer( new StreamSource( xslFilename ) );
StreamSource xmlSource = new StreamSource(new ByteArrayInputStream( xmlString.getBytes() ) );
ByteArrayOutputStream baos = new ByteArrayOutputStream();
transformer.transform( xmlSource, new StreamResult( baos ) );
formattedOutput = baos.toString();
} catch( Exception e ) {
e.printStackTrace();
}
return formattedOutput;
}
I came across a few postings on this error but not too sure what to do.
Am I doing anything wrong code wise?
Are there any alternative 3rd Party transformers available that could do this?
Thanks,
Andez
Try Saxon instead.
Your code would stay the same. All you would need to do is set javax.xml.transform.TransformerFactory to net.sf.saxon.TransformerFactoryImpl in the JVM's system properties.
Use saxon. offtop: if you use the same stylesheet to transform many XML files, you might want to consider templates (pre-compiled stylesheets):
javax.xml.transform.Templates style = tFactory.newTemplates(xslSource);
style.newTransformer().transform(...);
I came across a post on the net that mentioned apache XALAN. So I added the jars to my project. Everything has started working since even though I do not directly reference any XALAN classes in my code. As far as I can tell it still should use the jaxax.xml classes.
Not too sure what is happening there. But it is working.
As an alternative to Saxon, you can split up your large template into smaller templates.
Template definitions contained in XSLT stylesheets are compiled by SAP
JVM's XSLT compiler "Xalan" into Java methods for faster execution of
transformations. Java bytecode branch instructions contained in these
Java methods are limited to 32K offsets. Large template definitions
can now lead to very large Java methods, where the branch offset would
need to be larger than 32K. Therefore these stylesheets cannot be
compiled to Java methods and therefore cannot be used for
transformations.
Solution
Since each template definition of an XSLT stylesheet is compiled into
a separate Java method, using multiple smaller templates can be used
as solution. A very large template can be broken into multiple smaller
templates by using the "call-template" element.
It is described in-depth in this article Size limitation for XSLT stylesheets.
Sidenote: I would only recommend this as a last resort if saxon is not available, as this requires quite a few changes to your xsl file.
I don't need to read complex XML files. I just want to read the following configuration file with a simplest XML reader
<config>
<db-host>localhost</db-host>
<db-port>3306</db-port>
<db-username>root</db-username>
<db-password>root</db-password>
<db-name>cash</db-name>
</config>
How to read the above XML file with a XML reader through Java?
I like jdom:
SAXBuilder parser = new SAXBuilder();
Document docConfig = parser.build("config.xml");
Element elConfig = docConfig.getRootElement();
String host = elConfig.getChildText("host");
Since you want to parse config files, I think commons-configuration would be the best solution.
Commons Configuration provides a generic configuration interface which enables a Java application to read configuration data from a variety of sources (including XML)
You could use a simple DOM parser to read the xml representation.
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
dom = db.parse("config.xml");
If you just need a simple solution that's included with the Java SDK (since 5.0), check out the XPath package. I'm sure others perform better, but this was all I needed. Here's an example:
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.xml.sax.InputSource;
...
try {
XPath xpath = XPathFactory.newInstance().newXPath();
InputSource inputSource = new InputSource("strings.xml");
// result will equal "Save My Changes" (see XML below)
String result = xpath.evaluate("//string", inputSource);
}
catch(XPathExpressionException e) {
// do something
}
strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="saveLabel">Save My Changes</string>
</resources>
There are several XML parsers for Java. One I've used and found particularly developer friendly is JDOM. And by developer friendly, I mean "java oriented" (i.e., you work with objects in your program), instead of "document oriented", as some other tools are.
I would recommend Commons Digester, which allows you to parse a file without writing reams of code. It uses a series of rules to determine what action is should perform when encountering a given element or attribute (a typical rule might be to create a particular business object).
For a similar use case in my application I used JaxB. With Jaxb, reading XML files is like interacting with Java POJOs. But to use JAXB you need to have the xsd for this xml file. You can look for more info here
If you want to be able to read and write objects to XML directly, you can use XStream
Although I have not tried XPath yet as it has just come to my attention now, I have tried a few solutions and have not found anything that works for this scenario.
I decided to make a library that fulfills this need as long as you are working under the assumptions mentioned in the readme. It has the advantage that it uses SAX to parse the entire file and return it to the user in the form of a map so you can lookup values as key -> value.
https://github.com/daaso-consultancy/ConciseXMLParser
If something is missing kindly inform me of the missing item as I only develop it based on the needs of others and myself.
I need your expertise once again. I have a java class that searches a directory for xml files (displays the files it finds in the eclipse console window), applies the specified xslt to these and sends the output to a directory.
What I want to do now is create an xml containing the file names and file format types. The format should be something like;
<file>
<fileName> </fileName>
<fileType> </fileType>
</file>
<file>
<fileName> </fileName>
<fileType> </fileType>
</file>
Where for every file it finds in the directory it creates a new <file>.
Any help is truely appreciated.
Use an XML library. There are plenty around, and the third party ones are almost all easier to use than the built-in DOM API in Java. Last time I used it, JDom was pretty good. (I haven't had to do much XML recently.)
Something like:
Element rootElement = new Element("root"); // You didn't show what this should be
Document document = new Document(rootElement);
for (Whatever file : files)
{
Element fileElement = new Element("file");
fileElement.addContent(new Element("fileName").addContent(file.getName());
fileElement.addContent(new Element("fileType").addContent(file.getType());
}
String xml = XMLOutputter.outputString(document);
Have a look at DOM and ECS. The following example was adapted to you requirements from here:
XMLDocument document = new XMLDocument();
for (File f : files) {
document.addElement( new XML("file")
.addXMLAttribute("fileName", file.getName())
.addXMLAttribute("fileType", file.getType())
)
);
}
You can use the StringBuilder approach suggested by Vinze, but one caveat is that you will need to make sure your filenames contain no special XML characters, and escape them if they do (for example replace < with <, and deal with quotes appropriately).
In this case it probably doesn't arise and you will get away without it, however if you ever port this code to reuse in another case, you may be bitten by this. So you might want to look at an XMLWriter class which will do all the escaping work for you.
Well just use a StringBuilder :
StringBuilder builder = new StringBuilder();
for(File f : files) {
builder.append("<file>\n\t<fileName>").append(f.getName).append("</fileName>\n)";
[...]
}
System.out.println(builder.toString());