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package javax.xml.bind;

import org.w3c.dom.Node;

import java.util.Collections;

import java.util.Map;

import java.util.Properties;

/**

 * The {@code 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.

 *

 * <p>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:

 *

 * <ul>

 * <li>{@link #newInstance(String, ClassLoader) JAXBContext.newInstance( "com.acme.foo:com.acme.bar" )} <br>

 * 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").

 * </li>

 * <li>{@link #newInstance(Class...) JAXBContext.newInstance( com.acme.foo.Foo.class )} <br>

 * The JAXBContext instance is initialized with class(es)

 * passed as parameter(s) and classes that are statically reachable from

 * these class(es). See {@link #newInstance(Class...)} for details.

 * </li>

 * </ul>

 *

 * <p><i>

 * 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 {@code jaxb.properties} file in

 * each package containing schema derived classes.  The property file must

 * contain a property named {@code javax.xml.bind.context.factory} whose

 * value is the name of the class that implements the {@code createContext}

 * APIs.</i>

 *

 * <p><i>

 * The class supplied by the provider does not have to be assignable to

 * {@code javax.xml.bind.JAXBContext}, it simply has to provide a class that

 * implements the {@code createContext} APIs.</i>

 *

 * <p><i>

 * In addition, the provider must call the

 * {@link DatatypeConverter#setDatatypeConverter(DatatypeConverterInterface)

 * 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.</i>

 *

 * <a name="Unmarshalling"></a>

 * <h3>Unmarshalling</h3>

 * <p>

 * The {@link 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 {@code JAXBContext} object

 * allows the merging of global elements and type definitions across a set of schemas (listed

 * in the {@code contextPath}). Since each schema in the schema set can belong

 * to distinct namespaces, the unification of schemas to an unmarshalling

 * context must 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 {@code contextPath}.  For example:

 *

 * <pre>

 *      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

 * </pre>

 *

 * <p>

 * 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 {@code ObjectFactory} classes that exist in each of

 * java packages contained in the {@code 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 {@code com.acme.foo}

 * that contains a schema derived interface named {@code PurchaseOrder}.  In

 * order to create objects of that type, the client application would use the

 * factory method like this:

 *

 * <pre>

 *       com.acme.foo.PurchaseOrder po =

 *           com.acme.foo.ObjectFactory.createPurchaseOrder();

 * </pre>

 *

 * <p>

 * Once the client application has an instance of the the schema derived object,

 * it can use the mutator methods to set content on it.

 *

 * <p>

 * For more information on the generated {@code ObjectFactory} classes, see

 * Section 4.2 <i>Java Package</i> of the specification.

 *

 * <p>

 * <i>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

 * {@code newInstance( javaContentInterface )} method</i>

 *

 * <h3>Marshalling</h3>

 * <p>

 * The {@link 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 {@code unmarshal}

 * operation.  Clients can marshal a java content tree back to XML data

 * to a {@code java.io.OutputStream} or a {@code java.io.Writer}.  The

 * marshalling process can alternatively produce SAX2 event streams to a

 * registered {@code 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.

 *

 * <p>

 * Here is a simple example that unmarshals an XML document and then marshals

 * it back out:

 *

 * <pre>

 *        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 );

 * </pre>

 *

 *

 * <h3>Validation</h3>

 * <p>

 * Validation has been changed significantly since JAXB 1.0.  The {@link 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 {@code Validator}

 * will still work properly when deployed with the JAXB 1.0 runtime system.

 *

 * In JAXB 2.0, the {@link Unmarshaller} has included convenince methods that expose

 * the JAXP 1.3 {@link javax.xml.validation} framework.  Please refer to the

 * {@link Unmarshaller#setSchema(javax.xml.validation.Schema)} API for more

 * information.

 *

 *

 * <h3>JAXB Runtime Binding Framework Compatibility</h3>

 * <p>

 * 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 ({@code 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.

 *

 *

 * <h3>Discovery of JAXB implementation</h3>

 * <p>

 * To create an instance of {@link JAXBContext}, one of {@code JAXBContext.newInstance(...)} methods is invoked. After

 * JAX-B implementation is discovered, call is delegated to appropriate provider's method {@code createContext(...)}

 * passing parameters from the original call.

 * <p>

 * JAX-B implementation discovery happens each time {@code JAXBContext.newInstance} is invoked. If there is no user

 * specific configuration provided, default JAX-B provider must be returned.

 * <p>

 * Implementation discovery consists of following steps:

 *

 * <ol>

 *

 * <li>

 * Packages/classes explicitly passed in to the {@link #newInstance} method are processed in the order they are

 * specified, until {@code jaxb.properties} file is looked up in its package, by using the associated classloader —

 * this is {@link Class#getClassLoader() the owner class loader} for a {@link Class} argument, and for a package

 * the specified {@link ClassLoader}.

 *

 * <p>

 * If such a resource is discovered, it is {@link Properties#load(InputStream) loaded} as a property file, and

 * the value of the {@link #JAXB_CONTEXT_FACTORY} key will be assumed to be the provider factory class. If no value

 * found, {@code "javax.xml.bind.context.factory"} is used as a key for backwards compatibility reasons. This class is

 * then loaded by the associated class loader discussed above.

 *

 * <p>

 * 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.)

 *

 * <li>

 * If the system property {@link #JAXB_CONTEXT_FACTORY} exists, then its value is assumed to be the provider

 * factory class. If no such property exists, properties {@code "javax.xml.bind.context.factory"} and

 * {@code "javax.xml.bind.JAXBContext"} are checked too (in this order), for backwards compatibility reasons. This phase

 * of the look up enables per-JVM override of the JAXB implementation.

 *

 * <li>

 * Provider of {@link javax.xml.bind.JAXBContextFactory} is loaded using the service-provider loading

 * facilities, defined by the {@link java.util.ServiceLoader} class, to attempt

 * to locate and load an implementation of the service using the {@linkplain

 * java.util.ServiceLoader#load(java.lang.Class) default loading mechanism}: the service-provider loading facility

 * will use the {@linkplain java.lang.Thread#getContextClassLoader() current thread's context class loader}

 * to attempt to load the context factory. If the context class loader is null, the

 * {@linkplain ClassLoader#getSystemClassLoader() system class loader} will be used.

 * <br>

 * In case of {@link java.util.ServiceConfigurationError service

 * configuration error} a {@link javax.xml.bind.JAXBException} will be thrown.

 *

 * <li>

 * Look for resource {@code /META-INF/services/javax.xml.bind.JAXBContext} using provided class loader.

 * Methods without class loader parameter use {@code Thread.currentThread().getContextClassLoader()}.

 * If such a resource exists, its content is assumed to be the provider factory class.

 *

 * This configuration method is deprecated.

 *

 * <li>

 * 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 Java SE can have its own JAXB implementation as the last resort.

 * </ol>

 *

 * <p>

 * Once the provider factory class is discovered, context creation is delegated to one of its

 * {@code createContext(...)} methods.

 *

 * For backward compatibility reasons, there are two ways how to implement provider factory class:

 * <ol>

 *     <li>the class is implementation of {@link javax.xml.bind.JAXBContextFactory}. It must also implement no-arg

 *     constructor. If discovered in other step then 3, new instance using no-arg constructor is created first.

 *     After that, appropriate instance method is invoked on this instance.

 *     <li>the class is not implementation of interface above and then it is mandated to implement the following

 *     static method signatures:

 * <pre>

 *

 * 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

 * </pre>

 *      In this scenario, appropriate static method is used instead of instance method. This approach is incompatible

 *      with {@link java.util.ServiceLoader} so it can't be used with step 3.

 * </ol>

 * <p>

 * There is no difference in behavior of given method {@code createContext(...)} regardless of whether it uses approach

 * 1 (JAXBContextFactory) or 2 (no interface, static methods).

 *

 * @apiNote

 * Service discovery method using resource {@code /META-INF/services/javax.xml.bind.JAXBContext} (described in step 4)

 * is supported only to allow backwards compatibility, it is strongly recommended to migrate to standard

 * {@link java.util.ServiceLoader} mechanism (described in step 3). The difference here is the resource name, which

 * doesn't match service's type name.

 * <p>

 * Also using providers implementing interface {@link JAXBContextFactory} is preferred over using ones defining

 * static methods, same as {@link JAXBContext#JAXB_CONTEXT_FACTORY} property is preferred over property

 * {@code "javax.xml.bind.context.factory"}

 *

 * @implNote

 * Within the last step, if Glassfish AS environment detected, its specific service loader is used to find factory class.

 *

 * @author <ul><li>Ryan Shoemaker, Sun Microsystems, Inc.</li>

 *             <li>Kohsuke Kawaguchi, Sun Microsystems, Inc.</li>

 *             <li>Joe Fialli, Sun Microsystems, Inc.</li></ul>

 *

 * @see Marshaller

 * @see Unmarshaller

 * @see <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-7.html#jls-7.4.1">S 7.4.1 "Named Packages"

 *      in Java Language Specification</a>

 *

 * @since 1.6, JAXB 1.0

 */

public abstract class JAXBContext {

    /**

     * The name of the property that contains the name of the class capable

     * of creating new {@code JAXBContext} objects.

     */

    public static final String JAXB_CONTEXT_FACTORY = "javax.xml.bind.JAXBContextFactory";

    protected JAXBContext() {

    }

    /**

     * Create a new instance of a {@code JAXBContext} class.

     *

     * <p>

     * This is a convenience method to invoke the

     * {@link #newInstance(String,ClassLoader)} method with

     * the context class loader of the current thread.

     *

     * @throws JAXBException if an error was encountered while creating the

     */

    public static JAXBContext newInstance( String contextPath )

            throws JAXBException {

        //return newInstance( contextPath, JAXBContext.class.getClassLoader() );

        return newInstance( contextPath, getContextClassLoader());

    }

    /**

     * Create a new instance of a {@code JAXBContext} class.

     *

     * <p>

     * The client application must supply a context path which is a list of

     * colon (':', \u005Cu003A) 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

     * {@code 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").

     * </p>

     *

     * <p>

     * Every package listed on the contextPath must meet <b>one or both</b> of the

     * following conditions otherwise a {@code JAXBException} will be thrown:

     * </p>

     * <ol>

     *   <li>it must contain ObjectFactory.class</li>

     *   <li>it must contain jaxb.index</li>

     * </ol>

     *

     * <p>

     * <b>Format for jaxb.index</b>

     * <p>

     * 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 {@link #newInstance(Class...)}, from the

     * listed classes are also registered with JAXBContext.

     * <p>

     * Constraints on class name occuring in a {@code jaxb.index} file are:

     * <ul>

     *   <li>Must not end with ".class".</li>

     *   <li>Class names are resolved relative to package containing

     *       {@code jaxb.index} file. Only classes occuring directly in package

     *       containing {@code jaxb.index} file are allowed.</li>

     *   <li>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.</li>

     * </ul>

     *

     * <p>

     * To maintain compatibility with JAXB 1.0 schema to java

     * interface/implementation binding, enabled by schema customization

     * {@code <jaxb:globalBindings valueClass="false">},

     * the JAXB provider will ensure that each package on the context path

     * has a {@code jaxb.properties} file which contains a value for the

     * {@code javax.xml.bind.context.factory} property and that all values

     * resolve to the same provider.  This requirement does not apply to

     * JAXB annotated classes.

     *

     * <p>

     * If there are any global XML element name collisions across the various

     * packages listed on the {@code contextPath}, a {@code JAXBException}

     * will be thrown.

     *

     * <p>

     * Mixing generated interface/impl bindings from multiple JAXB Providers

     * in the same context path may result in a {@code JAXBException}

     * being thrown.

     *

     * <p>

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

     *

     * @param classLoader

     *      This class loader will be used to locate the implementation

     *      classes.

     *

     * @return a new instance of a {@code JAXBContext}

     * @throws JAXBException if an error was encountered while creating the

     */

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

        return newInstance(contextPath,classLoader,Collections.<String,Object>emptyMap());

    }

    /**

     * Create a new instance of a {@code JAXBContext} class.

     *

     * <p>

     * This is mostly the same as {@link JAXBContext#newInstance(String, ClassLoader)},

     * but this version allows you to pass in provider-specific properties to configure

     * the instantiation of {@link JAXBContext}.

     *

     * <p>

     * The interpretation of properties is up to implementations. Implementations must

     * throw {@code JAXBException} if it finds properties that it doesn't understand.

     *

     * @param classLoader

     *      This class loader will be used to locate the implementation classes.

     * @param properties

     *      provider-specific properties. Can be null, which means the same thing as passing

     *      in an empty map.

     *

     * @return a new instance of a {@code JAXBContext}

     * @throws JAXBException if an error was encountered while creating the

     *                       {@code JAXBContext} such as

     * <ol>

     *   <li>failure to locate either ObjectFactory.class or jaxb.index in the packages</li>

     *   <li>an ambiguity among global elements contained in the contextPath</li>

     *   <li>failure to locate a value for the context factory provider property</li>

     *   <li>mixing schema derived packages from different providers on the same contextPath</li>

     * </ol>

     * @since 1.6, JAXB 2.0

     */

    public static JAXBContext newInstance( String contextPath,

                                           ClassLoader classLoader,

                                           Map<String,?>  properties  ) throws JAXBException {

        return ContextFinder.find(

                        /* The default property name according to the JAXB spec */

                JAXB_CONTEXT_FACTORY,

                        /* the context path supplied by the client app */

                contextPath,

                        /* class loader to be used */

                classLoader,

                properties );

    }

// TODO: resurrect this once we introduce external annotations

//    /**