When do you use jaxb

When a portion of a document is skipped, the unmarshaller notifies a ValidationEventHandler , so it allows you to see what's going on. Also consider installing a Schema object to the unmarshaller, so that the unmarshaller performs a schema validation while unmarshalling. JAXBContext "knows" a set of classes, and if it doesn't know a class that it's supposed to know, then the unmarshaller may fail to perform as you expected. It will output the list of classes it knows. If a class is not in this list, the unmarshaller will never return an instance of that class.

Make you see all the classes you expect to be returned from the unmarshaller in the list. When dealing with a large schema that spans across a large number of classes and packages, this is one possible cause of a problem. If you are binding classes that are generated from XJC, then the easiest way to include all the classes is to specify the generated ObjectFactory class es.

Because of the "strange" way that element default values in XML Schema work, people often get confused about their behavior. This section describes how this works. When a class has an element property with the default value, and if the document you are reading is missing the element, then the unmarshaller does not fill the field with the default value.

Instead, the unmarshaller fills in the field when the element is present but the content is missing. This is consistent with the XML Schema spec, where it essentially states that the element defaults do not kick in when the element is absent, so unfortunately we can't change this behavior.

Depending on your expectation, using a field initializer may achieve what you are looking for. Alternatively, attribute default values work in a way that agrees with the typical expectation, so consider using that. Also, see Element default values and marshalling. This is the typical use case, but in some situations this is not desirable. When a document is large, it's usually because there's repetitive parts in it.

Perhaps it's a purchase order with a large list of line items, or perhaps it's an XML log file with large number of log entries. Your program acts on a single chunk, and then throws it away. In this way, you'll be only keeping at most one chunk in memory, which allows you to process large documents.

See the streaming-unmarshalling example and the partial-unmarshalling example in the JAXB RI distribution for more about how to do this. The streaming-unmarshalling example has an advantage that it can handle chunks at arbitrary nest level, yet it requires you to deal with the push model JAXB unmarshaller will " push " new chunk to you and you'll need to process them right there.

In contrast, the partial-unmarshalling example works in a pull model which usually makes the processing easier , but this approach has some limitations in databinding portions other than the repeated part. The techniques discussed above can be used to handle this case as well, since they let you unmarshal chunks one by one.

By default, a JAXB marshaller uses random namespace prefixes such as ns1 , ns2 , While this is perfectly valid XML wrt the schema, for human readability, you might want to change them to something that makes more sense. See the namespace-prefix sample in the distribution for more details. Because of a "strange" way element default values in XML Schema work, people often get confused about its behavior.

When a class has an element property with the default value, and if a value is null, then the marshaller will not produce the corresponding element in XML:. This is consistent with the XML Schema spec, where it essentially states that the element defaults do not kick in when the element is absent.

Attribute default values do not have this problem, so if you can change the schema, changing it to an attribute is usually a better idea. Alternatively, depending on your expectation, setting the field to a default value in Java may achieve what you are looking for. Also, see Element default values and unmarshalling. So perhaps you have a class like this:. There're seven Marshaller.

If you are writing to a file, a socket, or memory, then you should use the version that takes OutputStream. Unless you change the target encoding to something else default is UTF-8 , there's a special marshaller codepath for OutputStream , which makes it run really fast. You can also write to Writer , but in this case you'll be responsible for encoding characters, so in general you need to be careful. This is bit unintuitive, but you'll do it like this:.

And after the method invocation you get a complete DOM tree that represents the marshalled document. The version that takes ContentHandler is useful when you need a custom formatting needs like you want each attribute to be in new line, etc , but otherwise they are not very interesting if you are writing a whole document.

This changes the behaviors of the marshaller so that it works better in this situation. If you are writing to an OutputStream or Writer and generally sending it to someone else, you can do something like this:. Like I mentioned, this is probably the fastest, even though println isn't very pretty. The downside of this approach is that if the ancestor elements declare the namespaces, JAXB won't be able to take advantage of them.

You can also marshal an object as a subtree of an existing DOM tree. To do this, you pass the Element object as the second parameter, and the marshaller will marshal an object as a child of this node. StAX is also very convenient for doing this sort of things.

Finally, you can marshal an object as a subtree into ContentHandler , but it requires a fair amount of SAX programming experience, and it goes beyond the scope of this entry. Another common use case is where you have an object that doesn't have XmlRootElement on it. JAXB allows you to marshal it like this:. You can actually use it with a class that has XmlRootElement , and that simply renames the root element name.

At the first glance the second Point. In this example, both the class and the instance are Point , so you won't see xsi :type. But if they are different, you'll see it. This can be also used to marshal a simple object, like String or an integer. But unfortunately it cannot be used to marshal objects like List or Map , as they aren't handled as the first-class citizen in the JAXB world.

For example, dom4j has DocumentResult that extends Result , so you can do:. This amounts to looking at the same XML by using different schema, and again this is much more efficient than going through ByteArrayOutputStream.

In this section, we'll discuss the possible causes and how to resolve this. The 1 cause of extra namespace declarations is due to the DOM mapping. Note that the two namespace declarations are copied over, but c is not because it's overridden.

Also not that JAXB is not touching the whitespace in document. This copying of namespace declarations is necessary to preserve the infoset in the input document. Now, imagine what happens when you marshal this back to XML. Despite the fact that in this example neither b nor c prefixes are in use, JAXB cannot delete them, because it doesn't know if those attributes are significant to the application or not.

Therefore, this could end up producing XML with "extra namespace declarations" like:. Resolving this problem is not possible in the general case, but sometimes one of the following strategy works:. In such a case, adding explicit type attribute avoids the use of DOM, so things will work as expected.

The wildcard processing mode " strict " would force a typed binding, and thereby eliminate any DOM mapping. You might be able to manulally go into the DOM tree and remove unnecessary namespace declarations, if your application knows what are necessary and what are not.

Schemagen tools by default come in as CLI, ant task, and Maven plugin. These interfaces allow you to invoke schemagen functionality from your program. If the classes you'd like to generate schema from are already available as java. The CLI interface public static int com.

You can pass in all the schemagen command-line arguments as a string array, and get the exit code as an int value. Messages are sent to System. Ant task can be invoked very easily from a non-Ant program. The schemagen ant task is defined in the SchemaGenTask class,. The above two interfaces are built on top of externally committed contracts, so they'll evolve only in a compatibile way. The downside is that the amount of control you can exercise over them would be limited.

But be warned that those interfaces are subject to change in the future versions, despite our best effort to preserve them. Most of those interfaces are defined and well-documented in the com. You can see how the schemagen tools are eventually calling into this API at the implementaion of SchemaGenerator class. This section discusses how you can change the generated XML schema.

For changes that also affect the infoset such as changing elements to attributes, namespaces, etc. As of JAXB 2. The JAXB project is currently lacking resources to attack this problem, and therefore looking for volunteers to work on this project.

The basic idea would be to define enough annotations to cover the basic constraint facets such as length, enumerations, pattern, etc. The schema generator would have to be then extended to honor those annotations and generate schemas accordingly. If you are interested in picking up this task, let us know! Required to compile against JAXB. Minimum requirement to compile is jaxb-api. If a client application is running on an environment where JAXB runtime is provided, jaxb-api is all that is needed.

If client application needs to include the runtime, e. To generate JAXB classes from schema community maven-jaxb2-plugin can be used. Alternatively to community plugins, there are tooling artifacts jaxb-xjc and jaxb-jxc, which can be used for java from XML schema generation and vice versa.

See also xml schema compiler usage. Where are schemagen and xjc command line scripts available in JavaSE prior to 11? These are included only in the zip distribution.

Starting from 2. There are only a few things to be aware of. JAXB does reflectively access private members of the class, so client application if loaded from module path needs to "open" packages containing jaxb classes to JAXB. Module java. Similar to endorsed mechanism prior to Java 9, starting from 9 there is an "upgrade module" mechanism which can replace content of JDK module. JavaSE bundled java. Since java. No RI-specific vendor extensions are supported: This is so that portability across different JavaSE 6 implementations will be guaranteed.

Therefore, if you develop an application that uses JAXB 2. If you'd like to reduce the footprint of your application by taking advantage of a JAXB implementation in JavaSE, you can take the following steps:.

You will no longer have to ship jaxb-api. This doesn't require any change to your code. When you do this, be sure to test your application since it's not very easy to find all such dependencies. Each version of JavaSE 6, 7, 8, There are several ways to achieve this:. Place the jaxb-api. Do not put other JAXB jars into the endorsed directory. And put jaxb-impl, jaxb-core to classpath of your application. This would affect any other applications that use this JRE, and it's easy.

On the other hand, in various scenarios you may not be able to alter the JRE. Use the system property java. The directory must not contain any other jaxb artifacts like jaxb-impl. This allows you use to use different version of JAXB for different applications. No matter which approach you take, make sure not to include jar files other than jaxb-api. Doing so, for example including jaxb-xjc. See the endorsed directory mechanism for more details.

JavaSE has never shipped an Ant task implementation, so we are just following that tradition. Actually, while XStream is ok, it's not really simpler, since both are very simple.

And Digester is NOT simple, just simplistic. Someone please mention JAXB Between that an a few XmlAdapter classes, I can map any schema to any existing Java structure. Also note that you CAN do code-first: start with beans, generate schema iff you need it.

What is JAXB? LostMohican LostMohican 2, 7 7 gold badges 27 27 silver badges 37 37 bronze badges. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. Now live: A fully responsive profile. Linked See more linked questions. Related Hot Network Questions. Stack Overflow works best with JavaScript enabled. Accept all cookies Customize settings.

This is primarily intended to be used to produce a wrapper XML element around collections. So, it must be used with collection property. Subscribe to get new post notifications, industry updates, best practices, and much more. Directly into your inbox, for free. The problem i am facing, is that my xml annotations are getting ignored, hence attributes are also appearing as elements. I am using spring boot. In my model class how do I map two different xml elements to one variable?

Try XmlElements. A blog about Java and its related technologies, the best practices, algorithms, interview questions, scripting languages, and Python. About Me. Contact Us. Privacy policy. Without JAXB is it possible? I am using spring restservices with JAXB. No, JAXB is not required. You can use MOXy as well.

Idea is that you need to use some interface which is capable of marshaling and unmarshalling. OR, you can directly build your XML object and send in response. Other wise we can directly send our java object in the form of xml or json form as our wish. I have some confusion in web services while doing conversions like this.

I think it can be achieved by using a bindings file but I am not aware of the exact configuration to put in this file. Can you help? Hi, how can I run this without maven? I used the same thing in STS and it worked fine? Can you help me? Thank you. I want to have the Employees class to be a property of the Department class, so that the root node is the Department and the XML looks like:. How you are generating the class? This SA thread has good information.

Let me know if something else you want to know? Tags are in small letters. Use jaxb with namespaces. But in the unmarshalling example, you never defined getID and getFirstName so how would this work?

The problem is to unmarshal it. Whatever I try, it is not possible to unmarshal it. Can i send you a mail or something describing the problem?