Interface TemplateLoader

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      void closeTemplateSource​(Object templateSource)
      Closes the template source, releasing any resources held that are only required for reading the template and/or its metadata.
      Object findTemplateSource​(String name)
      Finds the template in the backing storage and returns an object that identifies the storage location where the template can be loaded from.
      long getLastModified​(Object templateSource)
      Returns the time of last modification of the specified template source.
      Reader getReader​(Object templateSource, String encoding)
      Returns the character stream of a template represented by the specified template source.
    • Method Detail

      • findTemplateSource

        Object findTemplateSource​(String name)
                           throws IOException
        Finds the template in the backing storage and returns an object that identifies the storage location where the template can be loaded from. See the return value for more information.
        Parameters:
        name - The name of the template, already localized and normalized by the cache. It is completely up to the loader implementation to interpret the name, however it should expect to receive hierarchical paths where path components are separated by a slash (not backslash). Backslashes (or any other OS specific separator character) are not considered as separators by FreeMarker, and thus they will not be replaced with slash before passing to this method, so it's up to the template loader to handle them (say, be throwing and exception that tells the user that the path (s)he has entered is invalid, as (s)he must use slash -- typical mistake of Windows users). The passed names are always considered relative to some loader-defined root location (often referred as the "template root directory"), and will never start with a slash, nor will they contain a path component consisting of either a single or a double dot -- these are all resolved by the template cache before passing the name to the loader. As a side effect, paths that trivially reach outside template root directory, such as ../my.ftl, will be rejected by the template cache, so they never reach the template loader. Note again, that if the path uses backslash as path separator instead of slash as (the template loader should not accept that), the normalization will not properly happen, as FreeMarker (the cache) recognizes only the slashes as separators.
        Returns:
        An object representing the template source, which can be supplied in subsequent calls to getLastModified(Object) and getReader(Object, String), when those are called on the same TemplateLoader. null must be returned if the source for the template doesn't exist; don't throw exception then! The exact type of this object is up to the TemplateLoader implementation. As this object is possibly used as hash key in caches, and is surly compared with another template source for equality, it must have a proper Object.equals(Object) and Object.hashCode()) implementation. Especially, template sources that refer to the same physical source must be equivalent, otherwise template caching can become inefficient. This is only expected from Object.equals(Object) when the compared template sources came from the same TemplateLoader instance. Also, it must not influence the equality if the source is open or closed (closeTemplateSource(Object)).
        Throws:
        IOException - When an error occurs that makes it impossible to find out if the template exists, or to access the existing template. Don't throw exception if the template doesn't exist, instead return with null then!
      • getLastModified

        long getLastModified​(Object templateSource)
        Returns the time of last modification of the specified template source. This method is called after findTemplateSource().
        Parameters:
        templateSource - an object representing a template source, obtained through a prior call to findTemplateSource(String). This must be an object on which closeTemplateSource(Object) wasn't applied yet.
        Returns:
        the time of last modification of the specified template source, or -1 if the time is not known.
      • getReader

        Reader getReader​(Object templateSource,
                         String encoding)
                  throws IOException
        Returns the character stream of a template represented by the specified template source. This method is possibly called for multiple times for the same template source object, and it must always return a Reader that reads the template from its beginning. Before this method is called for the second time (or later), its caller must close the previously returned Reader, and it must not use it anymore. That is, this method is not required to support multiple concurrent readers for the same source templateSource object.

        Typically, this method is called if the template is missing from the cache, or if after calling findTemplateSource(String) and getLastModified(Object) it was determined that the cached copy of the template is stale. Then, if it turns out that the encoding parameter used doesn't match the actual template content (based on the #ftl encoding=... header), this method will be called for a second time with the correct encoding parameter value.

        Parameters:
        templateSource - an object representing a template source, obtained through a prior call to findTemplateSource(String). This must be an object on which closeTemplateSource(Object) wasn't applied yet.
        encoding - the character encoding used to translate source bytes to characters. Some loaders may not have access to the byte representation of the template stream, and instead directly obtain a character stream. These loaders should ignore the encoding parameter.
        Returns:
        A Reader representing the template character stream. It's the responsibility of the caller (which is TemplateCache usually) to close() it. The Reader is not required to work after the templateSource was closed (closeTemplateSource(Object)).
        Throws:
        IOException - if an I/O error occurs while accessing the stream.
      • closeTemplateSource

        void closeTemplateSource​(Object templateSource)
                          throws IOException
        Closes the template source, releasing any resources held that are only required for reading the template and/or its metadata. This is the last method that is called by the TemplateCache for a template source, except that Object.equals(Object) is might called later too. TemplateCache ensures that this method will be called on every object that is returned from findTemplateSource(String).
        Parameters:
        templateSource - the template source that should be closed.
        Throws:
        IOException