The JAXBContext class provides the client's entry point to the
JAXB API. It provides an abstraction for managing the XML/Java binding
information necessary to implement the JAXB binding framework operations:
unmarshal, marshal and validate.
A client application normally obtains new instances of this class using
one of these two styles for newInstance methods, although there are other
specialized forms of the method available:
JAXBContext.newInstance( "com.acme.foo:com.acme.bar" )
The JAXBContext instance is initialized from a list of colon
separated Java package names. Each java package contains
JAXB mapped classes, schema-derived classes and/or user annotated
classes. Additionally, the java package may contain JAXB package annotations
that must be processed. (see JLS 3rd Edition, Section 7.4.1. Package Annotations).
The following JAXB 1.0 requirement is only required for schema to
java interface/implementation binding. It does not apply to JAXB annotated
classes. JAXB Providers must generate a jaxb.properties file in
each package containing schema derived classes. The property file must
contain a property named javax.xml.bind.context.factory whose
value is the name of the class that implements the createContext
APIs.
The class supplied by the provider does not have to be assignable to
javax.xml.bind.JAXBContext, it simply has to provide a class that
implements the createContext APIs.
In addition, the provider must call the
DatatypeConverter.setDatatypeConverter api prior to any client
invocations of the marshal and unmarshal methods. This is necessary to
configure the datatype converter that will be used during these operations.
Unmarshalling
The Unmarshaller class provides the client application the ability
to convert XML data into a tree of Java content objects.
The unmarshal method allows for
any global XML element declared in the schema to be unmarshalled as
the root of an instance document.
Additionally, the unmarshal method allows for an unrecognized root element that
has an xsi:type attribute's value that references a type definition declared in
the schema to be unmarshalled as the root of an instance document.
The JAXBContext object
allows the merging of global elements and type definitions across a set of schemas (listed
in the contextPath). Since each schema in the schema set can belong
to distinct namespaces, the unification of schemas to an unmarshalling
context should be namespace independent. This means that a client
application is able to unmarshal XML documents that are instances of
any of the schemas listed in the contextPath. For example:
JAXBContext jc = JAXBContext.newInstance( "com.acme.foo:com.acme.bar" );
Unmarshaller u = jc.createUnmarshaller();
FooObject fooObj = (FooObject)u.unmarshal( new File( "foo.xml" ) ); // ok
BarObject barObj = (BarObject)u.unmarshal( new File( "bar.xml" ) ); // ok
BazObject bazObj = (BazObject)u.unmarshal( new File( "baz.xml" ) ); // error, "com.acme.baz" not in contextPath
The client application may also generate Java content trees explicitly rather
than unmarshalling existing XML data. For all JAXB-annotated value classes,
an application can create content using constructors.
For schema-derived interface/implementation classes and for the
creation of elements that are not bound to a JAXB-annotated
class, an application needs to have access and knowledge about each of
the schema derived ObjectFactory classes that exist in each of
java packages contained in the contextPath. For each schema
derived java class, there is a static factory method that produces objects
of that type. For example,
assume that after compiling a schema, you have a package com.acme.foo
that contains a schema derived interface named PurchaseOrder. In
order to create objects of that type, the client application would use the
factory method like this:
com.acme.foo.PurchaseOrder po =
com.acme.foo.ObjectFactory.createPurchaseOrder();
Once the client application has an instance of the the schema derived object,
it can use the mutator methods to set content on it.
For more information on the generated ObjectFactory classes, see
Section 4.2 Java Package of the specification.
SPEC REQUIREMENT: the provider must generate a class in each
package that contains all of the necessary object factory methods for that
package named ObjectFactory as well as the static
newInstance( javaContentInterface ) method
Marshalling
The Marshaller class provides the client application the ability
to convert a Java content tree back into XML data. There is no difference
between marshalling a content tree that is created manually using the factory
methods and marshalling a content tree that is the result an unmarshal
operation. Clients can marshal a java content tree back to XML data
to a java.io.OutputStream or a java.io.Writer. The
marshalling process can alternatively produce SAX2 event streams to a
registered ContentHandler or produce a DOM Node object.
Client applications have control over the output encoding as well as
whether or not to marshal the XML data as a complete document or
as a fragment.
Here is a simple example that unmarshals an XML document and then marshals
it back out:
JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
// unmarshal from foo.xml
Unmarshaller u = jc.createUnmarshaller();
FooObject fooObj = (FooObject)u.unmarshal( new File( "foo.xml" ) );
// marshal to System.out
Marshaller m = jc.createMarshaller();
m.marshal( fooObj, System.out );
Validation
Validation has been changed significantly since JAXB 1.0. The Validator
class has been deprecated and made optional. This means that you are advised
not to use this class and, in fact, it may not even be available depending on
your JAXB provider. JAXB 1.0 client applications that rely on Validator
will still work properly when deployed with the JAXB 1.0 runtime system.
In JAXB 2.0, the Unmarshaller has included convenince methods that expose
the JAXP 1.3 javax.xml.validation framework. Please refer to the
Unmarshaller.setSchema(javax.xml.validation.Schema) API for more
information.
JAXB Runtime Binding Framework Compatibility
The following JAXB 1.0 restriction only applies to binding schema to
interfaces/implementation classes.
Since this binding does not require a common runtime system, a JAXB
client application must not attempt to mix runtime objects (JAXBContext,
Marshaller, etc. ) from different providers. This does not
mean that the client application isn't portable, it simply means that a
client has to use a runtime system provided by the same provider that was
used to compile the schema.
This is a convenience method for the
newInstance method. It uses
the context class loader of the current thread. To specify the use of
a different class loader, either set it via the
Thread.setContextClassLoader() api or use the
newInstance method.
Throws:
JAXBException - if an error was encountered while creating the
JAXBContext such as
failure to locate either ObjectFactory.class or jaxb.index in the packages
an ambiguity among global elements contained in the contextPath
failure to locate a value for the context factory provider property
mixing schema derived packages from different providers on the same contextPath
The client application must supply a context path which is a list of
colon (':', \u003A) separated java package names that contain
schema-derived classes and/or fully qualified JAXB-annotated classes.
Schema-derived
code is registered with the JAXBContext by the
ObjectFactory.class generated per package.
Alternatively than being listed in the context path, programmer
annotated JAXB mapped classes can be listed in a
jaxb.index resource file, format described below.
Note that a java package can contain both schema-derived classes and
user annotated JAXB classes. Additionally, the java package may
contain JAXB package annotations that must be processed. (see JLS 3rd Edition,
Section 7.4.1. "Package Annotations").
Every package listed on the contextPath must meet one or both of the
following conditions otherwise a JAXBException will be thrown:
it must contain ObjectFactory.class
it must contain jaxb.index
Format for jaxb.index
The file contains a newline-separated list of class names.
Space and tab characters, as well as blank
lines, are ignored. The comment character
is '#' (0x23); on each line all characters following the first comment
character are ignored. The file must be encoded in UTF-8. Classes that
are reachable, as defined in newInstance(Class...), from the
listed classes are also registered with JAXBContext.
Constraints on class name occuring in a jaxb.index file are:
Must not end with ".class".
Class names are resolved relative to package containing
jaxb.index file. Only classes occuring directly in package
containing jaxb.index file are allowed.
Fully qualified class names are not allowed.
A qualified class name,relative to current package,
is only allowed to specify a nested or inner class.
To maintain compatibility with JAXB 1.0 schema to java
interface/implementation binding, enabled by schema customization
,
the JAXB provider will ensure that each package on the context path
has a jaxb.properties file which contains a value for the
javax.xml.bind.context.factory property and that all values
resolve to the same provider. This requirement does not apply to
JAXB annotated classes.
If there are any global XML element name collisions across the various
packages listed on the contextPath, a JAXBException
will be thrown.
Mixing generated interface/impl bindings from multiple JAXB Providers
in the same context path may result in a JAXBException
being thrown.
Parameters:
contextPath - list of java package names that contain schema
derived class and/or java to schema (JAXB-annotated)
mapped classes
classLoader - This class loader will be used to locate the implementation
classes.
Returns:
a new instance of a JAXBContext
Throws:
JAXBException - if an error was encountered while creating the
JAXBContext such as
failure to locate either ObjectFactory.class or jaxb.index in the packages
an ambiguity among global elements contained in the contextPath
failure to locate a value for the context factory provider property
mixing schema derived packages from different providers on the same contextPath
This is mostly the same as newInstance(String, ClassLoader),
but this version allows you to pass in provider-specific properties to configure
the instanciation of JAXBContext.
The interpretation of properties is up to implementations.
Parameters:
contextPath - list of java package names that contain schema derived classes
classLoader - This class loader will be used to locate the implementation classes.
properties - provider-specific properties
Returns:
a new instance of a JAXBContext
Throws:
JAXBException - if an error was encountered while creating the
JAXBContext such as
failure to locate either ObjectFactory.class or jaxb.index in the packages
an ambiguity among global elements contained in the contextPath
failure to locate a value for the context factory provider property
mixing schema derived packages from different providers on the same contextPath
The client application must supply a list of classes that the new
context object needs to recognize.
Not only the new context will recognize all the classes specified,
but it will also recognize any classes that are directly/indirectly
referenced statically from the specified classes. Subclasses of
referenced classes nor @XmlTransient referenced classes
are not registered with JAXBContext.
For example, in the following Java code, if you do
newInstance(Foo.class), the newly created JAXBContext
will recognize both Foo and Bar, but not Zot or FooBar:
class Foo {
@XmlTransient FooBar c;
Bar b;
}
class Bar { int x; }
class Zot extends Bar { int y; }
class FooBar { }
Therefore, a typical client application only needs to specify the
top-level classes, but it needs to be careful.
Note that for each java package registered with JAXBContext,
when the optional package annotations exist, they must be processed.
(see JLS 3rd Edition, Section 7.4.1. "Package Annotations").
Parameters:
classesToBeBound - list of java classes to be recognized by the new JAXBContext.
Can be empty, in which case a JAXBContext that only knows about
spec-defined classes will be returned.
Returns:
A new instance of a JAXBContext. Always non-null valid object.
Throws:
JAXBException - if an error was encountered while creating the
JAXBContext, such as (but not limited to):
No JAXB implementation was discovered
Classes use JAXB annotations incorrectly
Classes have colliding annotations (i.e., two classes with the same type name)
The JAXB implementation was unable to locate
provider-specific out-of-band information (such as additional
files generated at the development time.)
The interpretation of properties is implementation specific.
Parameters:
classesToBeBound - list of java classes to be recognized by the new JAXBContext.
Can be empty, in which case a JAXBContext that only knows about
spec-defined classes will be returned.
Returns:
A new instance of a JAXBContext. Always non-null valid object.
Throws:
JAXBException - if an error was encountered while creating the
JAXBContext, such as (but not limited to):
No JAXB implementation was discovered
Classes use JAXB annotations incorrectly
Classes have colliding annotations (i.e., two classes with the same type name)
The JAXB implementation was unable to locate
provider-specific out-of-band information (such as additional
files generated at the development time.)
Submit a bug or feature For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
javax.xml.bind.JAXBContext