Module org.apache.sis.metadata
Package org.apache.sis.xml

# Class MarshallerPool

Object
MarshallerPool

public class MarshallerPool extends Object
Creates and configures `Marshaller` or `Unmarshaller` objects for use with SIS. Users fetch (un)marshallers by calls to the `acquireMarshaller()` or `acquireUnmarshaller()` methods, and can restitute the (un)marshaller to the pool after usage like below:

    Marshaller marshaller = pool.acquireMarshaller();
    marshaller.marchall(...);
    pool.recycle(marshaller);

## Configuring (un)marshallers

The (un)marshallers created by this class can optionally by configured with the SIS-specific properties defined in the `XML` class, in addition to JAXB standard properties.

## Thread safety

The same `MarshallerPool` instance can be safely used by many threads without synchronization on the part of the caller. Subclasses should make sure that any overridden methods remain safe to call from multiple threads.

Since:
  0.3
See Also:
  - `XML`
  - JAXB Performance and thread-safety

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected final JAXBContext`
  `context`
  The JAXB context to use for creating marshaller and unmarshaller.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `MarshallerPool(JAXBContext context, Map<String,?> properties)`
  Creates a new factory using the given JAXB context.
  `MarshallerPool(Map<String,?> properties)`
  Creates a new factory using the SIS default `JAXBContext` instance.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Marshaller`
  `acquireMarshaller()`
  Returns a JAXB marshaller from the pool.
  `Unmarshaller`
  `acquireUnmarshaller()`
  Returns a JAXB unmarshaller from the pool.
  `protected Marshaller`
  `createMarshaller()`
  Creates an configures a new JAXB marshaller.
  `protected Unmarshaller`
  `createUnmarshaller()`
  Creates an configures a new JAXB unmarshaller.
  `void`
  `recycle(Marshaller marshaller)`
  Declares a marshaller as available for reuse.
  `void`
  `recycle(Unmarshaller unmarshaller)`
  Declares a unmarshaller as available for reuse.

  ### Methods inherited from class Object

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

- ## Field Details

  - ### context

    protected final JAXBContext context
    The JAXB context to use for creating marshaller and unmarshaller.
    See Also:
      - `createMarshaller()`
      - `createUnmarshaller()`

- ## Constructor Details

  - ### MarshallerPool

    public MarshallerPool(Map<String,?> properties) throws JAXBException
    Creates a new factory using the SIS default `JAXBContext` instance. The `properties` map is optional. If non-null, then the keys can be `XML` constants or the names of any other properties recognized by both `Marshaller` and `Unmarshaller` implementations.

    Tip: if the properties for the `Marshaller` differ from the properties for the `Unmarshaller`, then consider overriding the `createMarshaller()` or `createUnmarshaller()` methods instead.

    Parameters:
      `properties` - the properties to be given to the (un)marshaller, or `null` if none.
    Throws:
      `JAXBException` - if the JAXB context cannot be created.

  - ### MarshallerPool

    public MarshallerPool(JAXBContext context, Map<String,?> properties) throws JAXBException
    Creates a new factory using the given JAXB context. The `properties` map is optional. If non-null, then the keys can be `XML` constants or the names of any other properties recognized by both `Marshaller` and `Unmarshaller` implementations.

    Tip: if the properties for the `Marshaller` differ from the properties for the `Unmarshaller`, then consider overriding the `createMarshaller()` or `createUnmarshaller()` methods instead.

    Parameters:
      `context` - the JAXB context.
      `properties` - the properties to be given to the (un)marshaller, or `null` if none.
    Throws:
      `JAXBException` - if the marshaller pool cannot be created.

- ## Method Details

  - ### acquireMarshaller

    public Marshaller acquireMarshaller() throws JAXBException
    Returns a JAXB marshaller from the pool. If there is no marshaller currently available in the pool, then this method will create a new one.

    This method shall be used as below:

        Marshaller marshaller = pool.acquireMarshaller();
        marshaller.marchall(...);
        pool.recycle(marshaller);

    Note that `recycle(Marshaller)` shall not be invoked in case of exception, since the marshaller may be in an invalid state.
    Returns:
      a marshaller configured for formatting OGC/ISO XML.
    Throws:
      `JAXBException` - if an error occurred while creating and configuring a marshaller.

  - ### acquireUnmarshaller

    public Unmarshaller acquireUnmarshaller() throws JAXBException
    Returns a JAXB unmarshaller from the pool. If there is no unmarshaller currently available in the pool, then this method will create a new one.

    This method shall be used as below:

        Unmarshaller unmarshaller = pool.acquireUnmarshaller();
        Unmarshaller.unmarchall(...);
        pool.recycle(unmarshaller);

    Note that `recycle(Unmarshaller)` shall not be invoked in case of exception, since the unmarshaller may be in an invalid state.
    Returns:
      a unmarshaller configured for parsing OGC/ISO XML.
    Throws:
      `JAXBException` - if an error occurred while creating and configuring the unmarshaller.

  - ### recycle

    public void recycle(Marshaller marshaller)
    Declares a marshaller as available for reuse. The caller should not use anymore the given marshaller after this method call, since the marshaller may be re-used by another thread at any time after recycle.

    #### Cautions

    - Do not invoke this method if the marshaller threw an exception, since the marshaller may be in an invalid state. In particular, this method should not be invoked in a `finally` block.
    - Do not invoke this method twice for the same marshaller, unless the marshaller has been obtained by a new call to `acquireMarshaller()`. In case of doubt, it is better to not recycle the marshaller at all.
    Note that this method does not close any output stream. Closing the marshaller stream is caller's or JAXB responsibility.
    Parameters:
      `marshaller` - the marshaller to return to the pool.

  - ### recycle

    public void recycle(Unmarshaller unmarshaller)
    Declares a unmarshaller as available for reuse. The caller should not use anymore the given unmarshaller after this method call, since the unmarshaller may be re-used by another thread at any time after recycle.

    #### Cautions

    - Do not invoke this method if the unmarshaller threw an exception, since the unmarshaller may be in an invalid state. In particular, this method should not be invoked in a `finally` block.
    - Do not invoke this method twice for the same unmarshaller, unless the unmarshaller has been obtained by a new call to `acquireUnmarshaller()`. In case of doubt, it is better to not recycle the unmarshaller at all.
    Note that this method does not close any input stream. Closing the unmarshaller stream is caller's or JAXB responsibility.
    Parameters:
      `unmarshaller` - the unmarshaller to return to the pool.

  - ### createMarshaller

    protected Marshaller createMarshaller() throws JAXBException
    Creates an configures a new JAXB marshaller. This method is invoked only when no existing marshaller is available in the pool. Subclasses can override this method if they need to change the marshaller configuration.
    Returns:
      a new marshaller configured for formatting OGC/ISO XML.
    Throws:
      `JAXBException` - if an error occurred while creating and configuring the marshaller.
    See Also:
      - `context`
      - `acquireMarshaller()`

  - ### createUnmarshaller

    protected Unmarshaller createUnmarshaller() throws JAXBException
    Creates an configures a new JAXB unmarshaller. This method is invoked only when no existing unmarshaller is available in the pool. Subclasses can override this method if they need to change the unmarshaller configuration.
    Returns:
      a new unmarshaller configured for parsing OGC/ISO XML.
    Throws:
      `JAXBException` - if an error occurred while creating and configuring the unmarshaller.
    See Also:
      - `context`
      - `acquireUnmarshaller()`