The output of the program is as follows, displaying the tag values in the file students.xml: Students Vector [Name=Java Boy Course=JSP, Name=Java Girl Course=EJB]. You also saw some examples that reflected common XML parsing requirements. Listing 7-12 shows the Java code where you just define the rules file to be used to create a Digester instance and then parse the XML file using that Digester instance.
Apache Digester can do it for you easily. Forward references would be trickier, but Method objects might possibly be cached, and later invoked when the referenced object is actually created. However, you can have different tag names and property names. Hardly any of the code can be termed as action-oriented code. See the ruby xmldigester (http://rubyforge.net/xmldigester) implementation for an example. Change ), You are commenting using your Google account. However some rules clearly can't sensibly be invoked in a nested manner, eg SetPropertyRule. We'll send you an email containing your password. Configuration Properties. Some email discussion has already occurred on this, and Robert Donkin suggested "named stacks" might be part of the solution. He is also a guest lecturer on Java and J2EE. As you move along, you will see some of these rules in the examples. 199 2 2 gold badges 2 2 silver badges 13 13 bronze badges. So directly or indirectly you should be able to access all the data depicted in Listing 7-4 using a reference to a properly populated Academy class instance. I envisage something like this: Separating out the SAX handler methods would greatly simplify the API that users see: and the methods like characters(), startElement(), etc are only present on the handler object, not the main Digester interface.
Jan 6, 2005 - O'Reilly article by Timothy M. O'Brien about jakarta commons in general, including info on Digester.
Listing 7-9 shows the Java code to specify Digester rules and parse the XML accordingly. All rules are expected to extend the abstract class org.apache.commons.digester.Rule and define specific actions that need to be taken when a certain element occurs. {"serverDuration": 84, "requestCorrelationId": "e925eba52d60a705"}, http://www.generationjava.com/projects/Java2Html.shtml, http://flexc.csail.mit.edu/Harpoon/srcdoc/harpoon/IR/Quads/Quad.html, http://www.mail-archive.com/commons-user@jakarta.apache.org/msg07607.html, http://www.mail-archive.com/commons-user@jakarta.apache.org/msg09115.html, http://marc.theaimsgroup.com/?l=jakarta-commons-dev&m=106866350019676&w=2, API user interacts with to create rules (aka "rule factory methods"), API user interacts with to configure Digester (excluding Rule creation) and initiate parse, API the parser interacts with (SAX handler interface), API the Rule objects interact with (eg accessing the object stack), whenever the Rule is added to a digester (passing associated pattern), Digester "core" class (without factory methods), rename "Rules" --> RuleEngine or RuleMatcher or RuleManager. Consideration needs to be given, though, to resetting the state if a parse fails part-way through, or if a Rule instance is stored in a RuleSet and added to multiple Digester instances, etc. The two files academy.xml and academyRules.xml have to be present in the CLASSPATH, and upon execution of the code, you get the same output as shown in Listing 7-10 that you got using the Java code in Listing 7-9.
This could contain: Factory "add" methods return the newly created Rule object? Pretty cool, eh? That is the way SAX works.
See Digester in action below. In Listing 7-3 you register three patterns and two rules that you want to be fired. Fix problem where xmlrules needs to be manually updated when new rules/features are added to the digester "core". The Java class DigestStudents, shown in Listing 7-3, will pick up the contents of the various XML tags and create a Vector class instance that can hold many instances of the class Student. import org.apache.commons.digester3.Digester; import org.apache.commons.digester3.binder.DigesterLoader; import org.apache.commons.digester3.xmlrules.FromXmlRulesModule; // Create an instance of the Digester from the XML rule set, DigesterLoader digesterLoader = DigesterLoader.newLoader(new FromXmlRulesModule() {. Harshad wrote the books Pro Jakarta Commons (Apress, 2004), Oracle JDeveloper 10g: Empowering J2EE Development (Apress, 2004) and also coauthored Java 2 Enterprise Edition 1.4 Bible (Wiley & Sons, 2003). Use Betwixt BeanWriter to write the java beans to a file and then, use BeanReader to read from that file. Copyright 2000 - 2020, TechTarget 2.If don’t have the java classes, create java classes for corresponding xml file.Or if don’t have xml files, create it as per the java classes.Note- property name,hierarchy in xml and java class should match, otherwise you need to provide mapping in your digester xml rule not mentioned here. The big advantage of using the Digester component instead of other APIs is the presence of element matching patterns. Provide more declared exceptions on various methods. It would be nice for SetProperties and SetNestedProperties rules to automatically map xml attributes and element names like "foo-bar" to bean properties of form "fooBar".
You will then store all the Student instances created in an instance of the java.util.Vector class for further processing. DigestXMLJavaAcademy Class (Java Code Using Rules Defined in XML). But I don’t like this trick unless you are in hurry. Contribute to apache/commons-digester development by creating an account on GitHub. I also think the APIs for preconfiguring Rules or RuleSet objects and then reusing them are rather inconsistent, and need some review/fixing. asked Mar 27 at 4:36. Ideally, xmlrules would "auto-detect" rules/features at runtime. ( Log Out / Everybody knows the advantages of using XML, but I doubt many people are able to write a piece of code that parses an XML file and picks up the value of a certain XML tag. Apache Digester can do it for you easily. So you will just continue with the Digester experiments.
Possibly this could be an extension to the existing CallParamRule, but that rule has so many options already! This is an easy and developer-friendly usage to precisely convey the tag to which you want to refer. Any better ideas would be welcome.
Refactor the CallParamRule to break out the separate pieces of functionality into separate rules. Joran uses "Interpreter" --> "SaxHandler", and "ExecutionContext" --> "!Digester" sans "SaxHandler", with "ExecutionContext.getHandler" to get the saxhandler if necessary. Safe information transfer is a must for modern organizations, but not all secure data transmission methods are equal. The scenario for this example is that you are presented with an XML file containing the details of all the students attending the various courses at your training institute. So have loaded the catalogs object with the xml data. it would be nice to to get a method on bar's object called with the reference to the previously-created foo as a parameter. Transforming an XML document into a corresponding hierarchy of Java bean objects is a fairly easy using Apache Digester. It would be nice to confirm that anything ANT variables can do can also be handled using this framework. These classes are Academy, Student, Course, and Teacher. Provide a standard mechanism for inter-rule communication. Provide "mini-digester" distribution? How Amazon launched the warehouse robotics industry, You push any initial objects on the object stack using the Digester’s. You can also use the wildcard * if you want to have a more generalized matching. Apache Digester can do it for you easily. Adding a Digester.setBeanUtilsBean(beanUtilsBean) method would allow users to control this behaviour on a per-digester-instance level. The Digester also depends on the following Commons components: Because Digester uses SAX to do the parsing, XML processing with Digester happens in an event-driven manner. In the current (1.6) version, the best option is probably to create a configured Rules object and a configured !SAXParser object and keep these cached for reuse but recreate a new Digester object each time. This is currently (v1.6) fairly unsafe. Does anyone have any examples of when WithDefaultsRulesWrapper would actually be useful?
The Digester component comes with a set of rule implementations that extend the Rule class; you can find them in the package org.apache.commons.digester. Harshad Oak has a master's degree in computer management and is a Sun Certified Java Programmer and a Sun Certified Web Component Developer. In Listing 7-3 you used ObjectCreateRule to create an instance of the Student class, and you used BeanPropertySetterRule to set the properties of the class. Create a free website or blog at WordPress.com. Digester uses the apache jakarta commons-logging library; see the documentation for that library for more information. Implement a SetPropertyRule variant that allows the data to be in the body text. InputStream input = Digester.class.getClass().getResourceAsStream(“/com/tatu/resources/chain-config.xml”); Done. Their (sole) implicit action does this: How could we implement this in Digester? New Amazon grocery stores run on computer vision, apps. ( Log Out / Do not worry about the syntax because you will look at that in detail later in this article. One problem that has plagued XML development is the complexity of parsing and using XML.
It would be nice to have methods that are guaranteed to be called at the following times: It would be nice to define more formally what exceptions Rule objects can throw and when. Fix ugly logging mess. http://www.wilson.co.uk/xml/minml2.htm. This new rule acts like CallMethodRule except that it calls the target methods as soon as all the necessary parameters are available. You have java classes and corresponding xml files. It's time to learn test-driven development with... Assistive technology ensures that all customers can access software easily. Allow rules to match attribute values: All development seems to revolve around XML these days. So a requirement for Digester is the presence of an XML parser conforming to Java API for XML Processing (JAXP) version 1.1 or later. This is much more intuitive in a number of scenarios; the code is a fair bit more complicated than CallMethodRule however. The reason is that when associated with patterns involving wildcards, or where a single rule instance is associated with multiple different patterns, rule objects can be invoked in a "nested" manner, with their methods being invoked in the order "begin (begin body end) body end".