Package freemarker.cache

Interface TemplateLoader

All Known Subinterfaces:
StatefulTemplateLoader
All Known Implementing Classes:
ByteArrayTemplateLoader, ClassTemplateLoader, FileTemplateLoader, MultiTemplateLoader, StringTemplateLoader, URLTemplateLoader, WebappTemplateLoader, WebappTemplateLoader
public interface TemplateLoader
FreeMarker loads template "files" through objects that implement this interface, thus the templates need not be real files, and can come from any kind of data source (like classpath, servlet context, database, etc). While FreeMarker provides a few TemplateLoader implementations out-of-the-box, it's normal for embedding frameworks to use their own implementations.

To set the TemplateLoader used by FreeMaker, use Configuration.setTemplateLoader(TemplateLoader).

Implementations of this interface should be thread-safe.

Implementations should override Object.toString() to show information about from where the TemplateLoader loads the templates. For example, for a template loader that loads template from database table toString could return something like "MyDatabaseTemplateLoader(user=\"cms\", table=\"mail_templates\")". This string will be shown in TemplateNotFoundException exception messages, next to the template name.

For those who has to dig deeper, note that the TemplateLoader is actually stored inside the TemplateCache of the Configuration, and is normally only accessed directly by the TemplateCache, and templates are get via the TemplateCache API-s.

  • Method Summary

    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 Details

    • 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 (template root directory relative path) 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, by throwing an 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 (the template file), 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 for the specified template source, or -1 if the time is not known. This value meant to be milliseconds since the epoch, but in fact FreeMarker doesn't care what it means, it only cares if it changes, in which case the template needs to be reloaded (even if the value has decreased). -1 is not special in that regard either; if you keep returning it, FreeMarker won't reload the template (as far as it's not evicted from the cache from some other reason). Note that Long.MIN_VALUE is reserved for internal use.

    • 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.

      Unlike findTemplateSource(String), this method must not tolerate if the template is not found, and must throw IOException in that case.

      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; not null. 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