AbstractImageSessionContext
Date: 2016-04-28

org.apache.xmlgraphics.image.loader.impl

## Class AbstractImageSessionContext

- java.lang.Object
- - org.apache.xmlgraphics.image.loader.impl.AbstractImageSessionContext

- All Implemented Interfaces:
    ImageSessionContext
  Direct Known Subclasses:
    DefaultImageSessionContext

      public abstract class AbstractImageSessionContext
      extends java.lang.Object
      implements ImageSessionContext

  Abstract base class for classes implementing ImageSessionContext. This class provides all the special treatment for Source creation, i.e. it provides optimized Source objects where possible.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static interface` | `AbstractImageSessionContext.FallbackResolver` Implementations of this interface will be used as the mechanism for creating the `Source` that wraps resources.
    `static class` | `AbstractImageSessionContext.RestrictedFallbackResolver` This fallback resolver is to be used in environments where controlling file access is of critical importance.
    `static class` | `AbstractImageSessionContext.UnrestrictedFallbackResolver` An unrestricted resolver that has various contingency mechanisms that access the file-system.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `AbstractImageSessionContext()`
    `AbstractImageSessionContext(AbstractImageSessionContext.FallbackResolver fallbackResolver)`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected static javax.imageio.stream.ImageInputStream` | `createImageInputStream(java.io.InputStream in)`
    `javax.xml.transform.Source` | `getSource(java.lang.String uri)` Returns a Source object for a URI.
    `protected boolean` | `isReusable(javax.xml.transform.Source src)` Indicates whether a Source is reusable.
    `javax.xml.transform.Source` | `needSource(java.lang.String uri)` Returns a Source object for a URI.
    `javax.xml.transform.Source` | `newSource(java.lang.String uri)` Attempts to create a Source object from the given URI.
    `protected abstract javax.xml.transform.Source` | `resolveURI(java.lang.String uri)` Attempts to resolve the given URI.
    `void` | `returnSource(java.lang.String uri, javax.xml.transform.Source src)` Returns a Source object to a pool.
    `static java.io.File` | `toFile(java.net.URL url)` Convert from a `URL` to a `File`.

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

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

    - ### Methods inherited from interface org.apache.xmlgraphics.image.loader.ImageSessionContext

      `getParentContext, getTargetResolution`

- - ### Constructor Detail

    - #### AbstractImageSessionContext

          public AbstractImageSessionContext()

    - #### AbstractImageSessionContext

          public AbstractImageSessionContext(AbstractImageSessionContext.FallbackResolver fallbackResolver)

      Parameters:
        `fallbackResolver` - the fallback resolution mechanism to be used when simply getting an `InputStream` that backs a `Source` isn't possible.

  - ### Method Detail

    - #### resolveURI

          protected abstract javax.xml.transform.Source resolveURI(java.lang.String uri)

      Attempts to resolve the given URI.
      Parameters:
        `uri` - URI to access
      Returns:
        A `Source` object, or null if the URI cannot be resolved.

    - #### newSource

          public javax.xml.transform.Source newSource(java.lang.String uri)

      Attempts to create a Source object from the given URI. If possible this method returns an ImageSource instance which provides the best possible method to access the image.
      Specified by:
        `newSource` in interface `ImageSessionContext`
      Parameters:
        `uri` - URI to access
      Returns:
        A `Source` object, or null if the URI cannot be resolved.

    - #### createImageInputStream

          protected static javax.imageio.stream.ImageInputStream createImageInputStream(java.io.InputStream in)
                                                                                 throws java.io.IOException

      Throws:
        `java.io.IOException`

    - #### toFile

          public static java.io.File toFile(java.net.URL url)

      Convert from a `URL` to a `File`.

      This method will decode the URL. Syntax such as `file:///my%20docs/file.txt` will be correctly decoded to `/my docs/file.txt`.

      Note: this method has been copied over from Apache Commons IO and enhanced to support UNC paths.

      Parameters:
        `url` - the file URL to convert, `null` returns `null`
      Returns:
        the equivalent `File` object, or `null` if the URL's protocol is not `file`
      Throws:
        `java.lang.IllegalArgumentException` - if the file is incorrectly encoded

    - #### getSource

          public javax.xml.transform.Source getSource(java.lang.String uri)

      Returns a Source object for a URI. This method is not guaranteed to return an instance. Implementations normally return already created Sources from a pool (normally populated through the `ImageSessionContext.returnSource(String, Source)` method).
      Specified by:
        `getSource` in interface `ImageSessionContext`
      Parameters:
        `uri` - the URI of the image
      Returns:
        the Source object to load the image from, or null

    - #### needSource

          public javax.xml.transform.Source needSource(java.lang.String uri)
                                                throws java.io.FileNotFoundException

      Returns a Source object for a URI. This method is guaranteed to return a Source object. If the image cannot be found, a `FileNotFoundException` is thrown.
      Specified by:
        `needSource` in interface `ImageSessionContext`
      Parameters:
        `uri` - the URI of the image
      Returns:
        the Source object to load the image from
      Throws:
        `java.io.FileNotFoundException` - if the image cannot be found

    - #### returnSource

          public void returnSource(java.lang.String uri,
                          javax.xml.transform.Source src)

      Returns a Source object to a pool. This is provided in order to reuse a Source object between the preloading and the final loading of an image. Note that not all Source objects can be reused! Non-reusable Sources are discarded.
      Specified by:
        `returnSource` in interface `ImageSessionContext`
      Parameters:
        `uri` - the URI of the image
        `src` - the Source object belonging to the URI

    - #### isReusable

          protected boolean isReusable(javax.xml.transform.Source src)

      Indicates whether a Source is reusable. A Source object is reusable if it's an `ImageSource` (containing an `ImageInputStream`) or a `DOMSource`.
      Parameters:
        `src` - the Source object
      Returns:
        true if the Source is reusable