I'm writing an import function of XML files to my Java application. I am using XOM to parse the XML files. The code for parsing the XML is not easy to understand, it is some hardcoded .getChild(3) and so on. It is hard to follow the code compared to the declarative XML document.
Isn't there a more maintainable way to parse XML documents to Java objects? I would like to have it in a more declarative way, where I can specify what tags corresponds to what Java classes.
Have a look at JAX/B - fairly simple annotation-based approach. It's a standard Java API.
There are tools to generate Annotated Java classes from XSDs or sample XML files. I describe my use of it in my blog
I really like Simple for converting XML to Java.
Have a look at Apache Commons Digester.
Agreed JAXB (JSR-222) is the best solution. Note that JAXB is a spec meaning you have a choice of implementations:
http://bdoughan.blogspot.com/2010/07/jaxb-xml-binding-standard.html
Standard JAXB allows you to specify the mappings by means of annotations, MOXy JAXB also allows you to specify your metadata via XML:
http://wiki.eclipse.org/EclipseLink/Examples/MOXy/EclipseLink-OXM.XML
If you want a maintainable solution you need to break the one-to-one relationship between XML elements found in almost all XML binding solutions, and use XPath based mapping used in MOXy:
http://bdoughan.blogspot.com/2010/07/xpath-based-mapping.html
parse google geocode with xstream
The Simple XML framework uses annotations on field and method declarations as well as on class definitions to map XML to Java and back. Its many times more lightweight than JAXB (which pulls in tonnes of dependencies). In fact it has no external dependencies at all. And its faster too. I tried JAXB many times, but found the annotations and functionality awkward and cumbersome. Check out the Tutorial.
Check Castor XML Mapping
Here is documentation for same : http://www.castor.org/xml-mapping.html
I finally found XStream that was easy to use and parses the XML in a declarative way.
Related
I am trying to find a good serialization library in java world. What I need:
1. It can serialize/deserialize object into xml, of course.
2. It has to use xml definition and code can be generated by any clients. I don't want to share code with my clients. I would rather share xml definition and let them generate code from it.
I found JAXB can do No1, but I am not sure if it can adopt No2. Is there anything else I can use.
Thanks a lot.
You can use JAXB for both the requirement, it can serialize/deserialize ( or we can say Unmarshal and Marshal). The JAXB classes generated from an XML Schema are POJOs with the standard JAXB annotations. As part of Metro there is a project for JAXB providing reference implementation. JSR 222 is developed by JCP for JAXB. You can have a look at these for more details.
It has to use xml definition and code can be generated by any clients.
You can generate an XML schema from a JAXB model. This XML schema can be considered the XML definition:
How to generate xsd file using java code?
And a JAXB model can be generated from an XML schema.
http://blog.bdoughan.com/2010/09/processing-atom-feeds-with-jaxb.html
Not sure that I understand your second requirement, but xstream might be the answer
http://x-stream.github.io/
I am looking for a easy to implement xml to java binding. The problem I am facing that there is more than one xml file, and I need to create one object tree from these files.
JAXB is not helping for two reason : the xmls are not usually have any schema, and second JAXB does not offer any solution for combining them.
I tried smooks too, but it also doesn't offer any multiple XML digestion system.
Does anybody have any idea?
You can do this in JAXB using an initialized XmlAdapter. Below is a link to answer I gave to a similar question:
Using JAXB to cross reference XmlIDs from two XML files
Note:
JAXB implementations (Metro, EclipseLink MOXy, Apache JaxMe) do not require an XML schema:
http://wiki.eclipse.org/EclipseLink/Examples/MOXy/GettingStarted
If you use JAXB, I suggest creating your own XSDs for the XML files your need to use. That'll help you document what you thought the schema was at the time, and help identify any future issues due to change at the source.
Then, create a class or classes that deserialize the individual documents into the JAXB-generated classes and then build the object you want from those objects.
Even if you don't use JAXB, I'd still recommend using this kind of pattern to isolate the transformation from XML to Java and keep the part of your app that knows about XML in one place, away from your business logic.
I've used XMLBeans before. Really easy and flexible to use, should be able to help you a great deal.
In Java for XML marshalling/unmarshalling one can use JAXB, JIBX, CASTOR, ADB etc.
But out of these which is most generic & commonly used? Or is there any other utility available?
The standard is the JAXB (JSR 222), and the famous project with this name is the reference implementation. Unlike JAXB 1.0, JAXB 2.0 RI is quite good, and I've used it a lot. Other libraries implements the JAXB standard (I think tha Castor and JiBX, but I have no experience with them).
I've also use XStream, which was very easy and simple - it has a proprietary API though.
I don't know of any benchmark other than https://bindmark.dev.java.net/old-index.html - notice it is a 4 year old one. perhaps you can take it's ideas or any usable code it may have and run some tests yourself.
I personally use XMLBeans. I like it more than JAXB (and I am biased in favour of things from Sun since they should be more "standard"). I cannot speak to the commonly used part of it though.
JAXB is preferred because of following reasons:
No extra jaxb libraries are required if you are using JDK1.6 or above, because JAXB is bundled in JDK 1.6.
The jaxbMarshaller.unmarshal() contains a lot of overloaded methods, find one that suit yours.
JAXB is pretty easy to understand and operate. what it requires is couple of annotations like #XmlRootElement and #XmlAccessorType along with four lines of code
Modifying XML files in Java is much easier using JAXB as compared to other XML parsers like DOM and SAX because you only deal with POJOs
JAXB is more memory efficient than DOM or SAX parser.
JAXB doesn't require XML schema to work. Though you can use XML Schema for generating corresponding Java classes and its pretty useful if you have large and complex XML Schema which will result in huge number of classes but for simple usage you can just annotate your object with relevant XML annotations provided by JAXB package i.e. java.xml.binding and you are good to go.
I use CASTOR mapping and IMHO it is very easy to use provided you are familiar with XML. All you need to do is to create Java objects and map them to the XMl using a mapping file. The mapping file is required if your XML is a complex one. If it is a simple and straight forward XML, CASTOR will itself look for respective Java class which matches the XML element name [Castor uses Java's Reflection APIs to do this].
Java has annotations and that is good. However, some developers feel that it is best to annotate code with metadata using xml files - others prefer annotations but would use metadata to override annotations in source code.
I am writing a Java framework that uses annotations. The question is: is there a standard way to define and parse metadata from xml files. I think this is something every framework that uses annotations could benefit from but I can seem to find something like this on the Internet.
Must I roll my own xml parsing/validation or has someone already done something like this?
There is not a standard way, but here are some Java frameworks who does it:
JPA - check ejb-3_0-fr-spec-persistence.pdf
Spring Framework
TestNG - as written above, though I think it focuses to much on the annotation side rather than the actual configuration he tries to achieve
Seam Framework
I wrote the Annox library which does exactly what you need. With Annox you can read arbitrary annotations from XML.
It's not exactly what you want, but the backport175 project has an implementation of annotations for Java versions before Java 5.
It has some of the functionality you search in that it will read both its own style implementations and "real" annotations if they are present. Maybe this can be used as a starting point to build a more general framework.
Use JAXB http://java.sun.com/developer/technicalArticles/WebServices/jaxb/
You would write the xsd for your metadata file, generate JAXB classes that can help you parse the xml files.
What's the simplest-to-use techonlogy available to save an arbitrary Java object graph as an XML file (and to be able to rehydrate the objects later)?
The easiest way here is to serialize the object graph.
Java 1.4 has built in support for serialization as XML.
A solution I have used successfully is XStream (http://x-stream.github.io/)- it's a small library that will easily allow you to serialize and deserialize to and from XML.
The downside is you can only very limited define the resulting XML; which might not be neccessary in your case.
Apache digester is fairly easy: http://commons.apache.org/digester/
JAXB is newer and comes with annotation goodness: https://jaxb.dev.java.net
XStream by the folks at Thoughtworks has a simple API and even deals with things like duplicate and circular references. It seems to be actively developed and is well documented.
http://x-stream.github.io/
Use java.beans.XMLEncoder. Its API is very simple (actually a little too simple; it'd be nice to wire it to a SAX ContentHandler), but it works on many graphs out of the box, and it's easy to create your own persistence delegate for any odd-ball classes you might encounter.
The syntax used by XMLDecoder allows
you to invoke any method, instance
or static, including constructors,
so it's extremely flexible.
Other encoders name
elements and attributes after class
and field names, so there's no fixed schema for the result. The XMLEncoder's
XML follows a simple DTD and can
easily be validated or transformed,
even when you've never seen the
types it uses.
You can assign objects an
identifier, and reference them
throughout the graph.
You can refer to constants defined
in classes or interfaces.
And, it's built into Java SE, so you don't need to ship an extra library.
Simple
Although XStream and JAXB can serialize an some object graphs succssfully they can not handle very complex graphs. The most powerful solution for large complex graphs is Simple XML Serialization. It can handle any graph. Also, it’s fast and simple to use without any dependencies.
To quote the Simple project page:
Simple is a high performance XML serialization and configuration framework for Java. Its goal is to provide an XML framework that enables rapid development of XML configuration and communication systems. This framework aids the development of XML systems with minimal effort and reduced errors. It offers full object serialization and deserialization, maintaining each reference encountered. In essence it is similar to C# XML serialization for the Java platform, but offers additional features for interception and manipulation.
The Simple API is, well, simple! It's really good. http://simple.sourceforge.net/
You can also use XStream: http://www.ibm.com/developerworks/library/x-xstream/index.html
JAX-B is part of the standard APIs and really easy to use.
If you need control over the XML that gets generated, I recommend taking a look at Betwixt (http://commons.apache.org/betwixt/) - it adds a lot of functionality to Apache's digester (Digester is good for building object graphs from XML, but is not so good for generating them).
If you really don't care about the XML that gets generated (just that it can be deserialized in the future), then the XMLEncoder/Decoder classes built into Java or good - as long as the objects you are serializing follow the JavaBean specification. The biggest area I've run into problems with the XMLEncoder/Decoder solution is if you have a bean that returns an immutable list for one of it's properties - the encoder doesn't handle that situation very well.
If you need to control the structure of the XML, the XStream is a good choice. You can use annotations to define precisely the structure/mapping of the XML and your objects.
I'd second (or third) XStream. It reads and writes XML without needing any special binding configuration or placing lots of extraneous syntax in the XML.
I put together a list with a lot of xml serialization libraries and its license
XStream is very simple http://x-stream.github.io/
XStream is a simple library to serialize objects to XML and back again.
java.beans.XMLEncoder perhaps?
Jackson
The Jackson Project is a processing and binding library for XML, JSON, and some other formats.
… Jackson is a suite of data-processing tools for Java (and the JVM platform), including the flagship streaming JSON parser / generator library, matching data-binding library (POJOs to and from JSON) and additional data format modules to process data encoded in Avro, BSON, CBOR, CSV, Smile, (Java) Properties, Protobuf, XML or YAML; and even the large set of data format modules to support data types of widely used data types such as Guava, Joda, PCollections and many, many more…
If you are really only interested in serializing your objects to a file and then deserializing them later, then you might check out YAML instead of XML. YAML is much easier to work with than XML and the output files are very human-readable (which may or may not be a requirement). Check out yaml.org for more information. I've used JYAML successfully on a recent project.