JAXBContext (Java Platform SE 8 )
Keywords: javax.xml.bind.JAXBContext class
Date: 2017-07-29

javax.xml.bind

## Class JAXBContext

- java.lang.Object
- - javax.xml.bind.JAXBContext

-     public abstract class JAXBContext
      extends Object

  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, Section 7.4.1 "Named Packages").
  - `JAXBContext.newInstance( com.acme.foo.Foo.class )`
    The JAXBContext instance is initialized with class(es) passed as parameter(s) and classes that are statically reachable from these class(es). See `newInstance(Class...)` for details.

  SPEC REQUIREMENT: the provider must supply an implementation class containing the following method signatures:

       public static JAXBContext createContext( String contextPath, ClassLoader classLoader, Map<String,Object> properties ) throws JAXBException
       public static JAXBContext createContext( Class[] classes, Map<String,Object> properties ) throws JAXBException

  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.

  ### Discovery of JAXB implementation

  When one of the `newInstance` methods is called, a JAXB implementation is discovered by the following steps.

  1. For each package/class explicitly passed in to the `newInstance(java.lang.String)` method, in the order they are specified, `jaxb.properties` file is looked up in its package, by using the associated classloader — this is `the owner class loader` for a `Class` argument, and for a package the specified `ClassLoader`.

     If such a file is discovered, it is `loaded` as a property file, and the value of the `JAXB_CONTEXT_FACTORY` key will be assumed to be the provider factory class. This class is then loaded by the associated classloader discussed above.

     This phase of the look up allows some packages to force the use of a certain JAXB implementation. (For example, perhaps the schema compiler has generated some vendor extension in the code.)

  2. If the system property `JAXB_CONTEXT_FACTORY` exists, then its value is assumed to be the provider factory class. This phase of the look up enables per-JVM override of the JAXB implementation.
  3. Look for `/META-INF/services/javax.xml.bind.JAXBContext` file in the associated classloader. This file follows the standard service descriptor convention, and if such a file exists, its content is assumed to be the provider factory class. This phase of the look up is for automatic discovery. It allows users to just put a JAXB implementation in a classpath and use it without any furhter configuration.
  4. Finally, if all the steps above fail, then the rest of the look up is unspecified. That said, the recommended behavior is to simply look for some hard-coded platform default JAXB implementation. This phase of the look up is so that JavaSE can have its own JAXB implementation as the last resort.

  Once the provider factory class is discovered, its `public static JAXBContext createContext(String,ClassLoader,Map)` method (see `newInstance(String, ClassLoader, Map)` for the parameter semantics.) or `public static JAXBContext createContet(Class[],Map)` method (see `newInstance(Class[], Map)` for the parameter semantics) are invoked to create a `JAXBContext`.

  Since:
    JAXB1.0
  See Also:
    `Marshaller`, `Unmarshaller`, `7.4.1 "Named Packages" in Java Language Specification`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `JAXB_CONTEXT_FACTORY` The name of the property that contains the name of the class capable of creating new `JAXBContext` objects.

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `JAXBContext()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Deprecated Methods
    Modifier and Type | Method and Description
    --- | ---
    `Binder<Node>` | `createBinder()` Creates a `Binder` for W3C DOM.
    `<T> Binder<T>` | `createBinder(Class<T> domType)` Creates a `Binder` object that can be used for associative/in-place unmarshalling/marshalling.
    `JAXBIntrospector` | `createJAXBIntrospector()` Creates a `JAXBIntrospector` object that can be used to introspect JAXB objects.
    `abstract Marshaller` | `createMarshaller()` Create a `Marshaller` object that can be used to convert a java content tree into XML data.
    `abstract Unmarshaller` | `createUnmarshaller()` Create an `Unmarshaller` object that can be used to convert XML data into a java content tree.
    `abstract Validator` | `createValidator()` Deprecated. since JAXB2.0
    `void` | `generateSchema(SchemaOutputResolver outputResolver)` Generates the schema documents for this context.
    `static JAXBContext` | `newInstance(Class... classesToBeBound)` Obtain a new instance of a `JAXBContext` class.
    `static JAXBContext` | `newInstance(Class[] classesToBeBound, Map<String,?> properties)` Obtain a new instance of a `JAXBContext` class.
    `static JAXBContext` | `newInstance(String contextPath)` Obtain a new instance of a `JAXBContext` class.
    `static JAXBContext` | `newInstance(String contextPath, ClassLoader classLoader)` Obtain a new instance of a `JAXBContext` class.
    `static JAXBContext` | `newInstance(String contextPath, ClassLoader classLoader, Map<String,?> properties)` Obtain a new instance of a `JAXBContext` class.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### JAXB_CONTEXT_FACTORY

          public static final String JAXB_CONTEXT_FACTORY

      The name of the property that contains the name of the class capable of creating new `JAXBContext` objects.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### JAXBContext

          protected JAXBContext()

  - ### Method Detail

    - #### newInstance

          public static JAXBContext newInstance(String contextPath)
                                         throws JAXBException

      Obtain a new instance of a `JAXBContext` class.

      This is a convenience method to invoke the `newInstance(String,ClassLoader)` method with the context class loader of the current thread.

      Throws:
        `JAXBException` - if an error was encountered while creating the `JAXBContext` such as
        1. failure to locate either ObjectFactory.class or jaxb.index in the packages
        2. an ambiguity among global elements contained in the contextPath
        3. failure to locate a value for the context factory provider property
        4. mixing schema derived packages from different providers on the same contextPath

    - #### newInstance

          public static JAXBContext newInstance(String contextPath,
                                                ClassLoader classLoader)
                                         throws JAXBException

      Obtain a new instance of a `JAXBContext` class.

      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, Section 7.4.1 "Named Packages").

      Every package listed on the contextPath must meet one or both of the following conditions otherwise a `JAXBException` will be thrown:

      1. it must contain ObjectFactory.class
      2. 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 `<jaxb:globalBindings valueClass="false">`, 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.

      The steps involved in discovering the JAXB implementation is discussed in the class javadoc.

      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
        1. failure to locate either ObjectFactory.class or jaxb.index in the packages
        2. an ambiguity among global elements contained in the contextPath
        3. failure to locate a value for the context factory provider property
        4. mixing schema derived packages from different providers on the same contextPath

    - #### newInstance

          public static JAXBContext newInstance(String contextPath,
                                                ClassLoader classLoader,
                                                Map<String,?> properties)
                                         throws JAXBException

      Obtain a new instance of a `JAXBContext` class.

      This is mostly the same as `newInstance(String, ClassLoader)`, but this version allows you to pass in provider-specific properties to configure the instantiation of `JAXBContext`.

      The interpretation of properties is up to implementations. Implementations should throw `JAXBException` if it finds properties that it doesn't understand.

      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. Can be null, which means the same thing as passing in an empty map.
      Returns:
        a new instance of a `JAXBContext`
      Throws:
        `JAXBException` - if an error was encountered while creating the `JAXBContext` such as
        1. failure to locate either ObjectFactory.class or jaxb.index in the packages
        2. an ambiguity among global elements contained in the contextPath
        3. failure to locate a value for the context factory provider property
        4. mixing schema derived packages from different providers on the same contextPath
      Since:
        JAXB2.0

    - #### newInstance

          public static JAXBContext newInstance(Class... classesToBeBound)
                                         throws JAXBException

      Obtain a new instance of a `JAXBContext` class.

      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, Section 7.4.1 "Named Packages").

      The steps involved in discovering the JAXB implementation is discussed in the class javadoc.

      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):
        1. No JAXB implementation was discovered
        2. Classes use JAXB annotations incorrectly
        3. Classes have colliding annotations (i.e., two classes with the same type name)
        4. The JAXB implementation was unable to locate provider-specific out-of-band information (such as additional files generated at the development time.)
        `IllegalArgumentException` - if the parameter contains `null` (i.e., `newInstance(null);`)
      Since:
        JAXB2.0

    - #### newInstance

          public static JAXBContext newInstance(Class[] classesToBeBound,
                                                Map<String,?> properties)
                                         throws JAXBException

      Obtain a new instance of a `JAXBContext` class.

      An overloading of `newInstance(Class...)` to configure 'properties' for this instantiation of `JAXBContext`.

      The interpretation of properties is up to implementations. Implementations should throw `JAXBException` if it finds properties that it doesn't understand.

      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.
        `properties` - provider-specific properties. Can be null, which means the same thing as passing in an empty map.
      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):
        1. No JAXB implementation was discovered
        2. Classes use JAXB annotations incorrectly
        3. Classes have colliding annotations (i.e., two classes with the same type name)
        4. The JAXB implementation was unable to locate provider-specific out-of-band information (such as additional files generated at the development time.)
        `IllegalArgumentException` - if the parameter contains `null` (i.e., `newInstance(null,someMap);`)
      Since:
        JAXB2.0

    - #### createUnmarshaller

          public abstract Unmarshaller createUnmarshaller()
                                                   throws JAXBException

      Create an `Unmarshaller` object that can be used to convert XML data into a java content tree.
      Returns:
        an `Unmarshaller` object
      Throws:
        `JAXBException` - if an error was encountered while creating the `Unmarshaller` object

    - #### createMarshaller

          public abstract Marshaller createMarshaller()
                                               throws JAXBException

      Create a `Marshaller` object that can be used to convert a java content tree into XML data.
      Returns:
        a `Marshaller` object
      Throws:
        `JAXBException` - if an error was encountered while creating the `Marshaller` object

    - #### createValidator

          public abstract Validator createValidator()
                                             throws JAXBException

      Deprecated. since JAXB2.0
      `Validator` has been made optional and deprecated in JAXB 2.0. Please refer to the javadoc for `Validator` for more detail.

      Create a `Validator` object that can be used to validate a java content tree against its source schema.

      Returns:
        a `Validator` object
      Throws:
        `JAXBException` - if an error was encountered while creating the `Validator` object

    - #### createBinder

          public <T> Binder<T> createBinder(Class<T> domType)

      Creates a `Binder` object that can be used for associative/in-place unmarshalling/marshalling.
      Parameters:
        `domType` - select the DOM API to use by passing in its DOM Node class.
      Returns:
        always a new valid `Binder` object.
      Throws:
        `UnsupportedOperationException` - if DOM API corresponding to `domType` is not supported by the implementation.
      Since:
        JAXB2.0

    - #### createBinder

          public Binder<Node> createBinder()

      Creates a `Binder` for W3C DOM.
      Returns:
        always a new valid `Binder` object.
      Since:
        JAXB2.0

    - #### createJAXBIntrospector

          public JAXBIntrospector createJAXBIntrospector()

      Creates a `JAXBIntrospector` object that can be used to introspect JAXB objects.
      Returns:
        always return a non-null valid `JAXBIntrospector` object.
      Throws:
        `UnsupportedOperationException` - Calling this method on JAXB 1.0 implementations will throw an UnsupportedOperationException.
      Since:
        JAXB2.0

    - #### generateSchema

          public void generateSchema(SchemaOutputResolver outputResolver)
                              throws IOException

      Generates the schema documents for this context.
      Parameters:
        `outputResolver` - this object controls the output to which schemas will be sent.
      Throws:
        `IOException` - if `SchemaOutputResolver` throws an `IOException`.
        `UnsupportedOperationException` - Calling this method on JAXB 1.0 implementations will throw an UnsupportedOperationException.
      Since:
        JAXB 2.0

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