JAXB: How to marshal objects in lists?
Solution 1
On the records property add:
@XmlElementWrapper(name="records")
@XmlElement(name="data")
For more information on JAXB and collection properties see:
Solution 2
This is in response to your second question disquised an answer:
Both approaches will generate the same XML. My recommendation is go with the model that is best for your application. For me that is generally using @XmlElementWrapper/@XmlElement. Since "records" is just there to organize the "data" elements it doesn't really deserve its own class.
I lead the MOXy JAXB implementation and we offer an XPath-based mapping extension to go beyond what is capable with @XmlElementWrapper:
- http://bdoughan.blogspot.com/2010/07/xpath-based-mapping.html
- http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html
Solution 3
In response to your second question:
Is this the recommended way to create a Java class structure
according to the XML file structure above?
Technically speaking, introducing an extra Records
class to solve your JAXB issue is unnecessary and redundant work, because JAXB does not need it. The
@XmlElementWrapper
and @XmlElement
name
property have been designed to solve your issue.
From your comments to Blaise's answer, I maintain a tutorial with operational examples explaining how do deal with generic classes such as List, etc.. when unmarshalling.
rmv
Updated on July 05, 2022Comments
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rmv almost 2 years
Perhaps a stupid question: I have a
List
of type<Data>
which I want to marshal into a XML file. This is my classDatabase
containing anArrayList
...@XmlRootElement public class Database { List<Data> records = new ArrayList<Data>(); public List<Data> getRecords() { return records; } public void setRecords(List<Data> records) { this.records = records; } }
...and this is class Data:
// @XmlRootElement public class Data { String name; String address; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } }
Using the following test class...
public class Test { public static void main(String args[]) throws Exception { Data data1 = new Data(); data1.setName("Peter"); data1.setAddress("Cologne"); Data data2 = new Data(); data2.setName("Mary"); data2.setAddress("Hamburg"); Database database = new Database(); database.getRecords().add(data1); database.getRecords().add(data2); JAXBContext context = JAXBContext.newInstance(Database.class); Marshaller marshaller = context.createMarshaller(); marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); marshaller.marshal(database, new FileWriter("test.xml")); } }
...I got the result:
<database> <records> <address>Cologne</address> <name>Peter</name> </records> <records> <address>Hamburg</address> <name>Mary</name> </records> </database>
But that's not what I was expecting, i.e. all tags for
<Data>
objects are missing. I am looking for a way to export the data in the following structure, but I don't know how to achieve this:<database> <records> <data> <address>Cologne</address> <name>Peter</name> </data> <data> <address>Hamburg</address> <name>Mary</name> </data> </records> </database>
One additional question: if I want to deal with the problem without using
@XmlElementWrapper
and@XmlElement
annotations, I can introduce an intermediary classpublic class Records { List<Data> data = new ArrayList<Data>(); public List<Data> getData() { return data; } public void setData(List<Data> data) { this.data = data; } }
used by the modified base class
@XmlRootElement public class Database { Records records = new Records(); public Records getRecords() { return records; } public void setRecords(Records records) { this.records = records; } }
in a slightly modified
Test
class:... Database database = new Database(); database.getRecords().getData().add(data1); database.getRecords().getData().add(data2); ...
The result also is:
<database> <records> <data> <address>Cologne</address> <name>Peter</name> </data> <data> <address>Hamburg</address> <name>Mary</name> </data> </records> </database>
Is this the recommended way to create a Java class structure according to the XML file structure above?
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rmv over 13 yearsCool, that's it! Thanks a lot.
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rmv over 13 yearsIt's really quite impressive what's going on in this area. I think i need some time to get in touch with this new mapping technique. Can you give me a first hint, how to read exported XML data into the class structure again? If i use @XmlElementWrapper/@XmlElement for the export, the import program complains that the corresponding classes are (obviously :-) not existing...
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bdoughan over 13 yearsThe import (unmarshal) should just work, what exception are you getting?
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rmv over 13 yearsI think i got an exception that class 'Records' could not be find. But to be sure, i will verify it by an example tomorrow...
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rmv over 13 yearsYes, you are right, unmarshalling works as expected! --- JAXBContext context = JAXBContext.newInstance(Database.class); Unmarshaller unmarshaller = context.createUnmarshaller(); Database database = (Database) unmarshaller.unmarshal(new File("test.xml"));
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bdoughan over 12 years@LawrenceTierney - The following article on
@XmlAccessorType
may help with annotating fields or properties (getter/setter): blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html -
Alkanshel over 6 yearsI would have posted this on your blog but it seems like only team members can respond there. Thank you for your sample code, but is there a cleaner way to do this now in 2017 without the boilerplate classes and strict typing?
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Roberto over 5 years@XmlelementWrapper is not applicable to type - compilation error message. What's wrong?