freemarker.cache

Interface TemplateLoader

All Known Subinterfaces:

StatefulTemplateLoader

All Known Implementing Classes:

ClassTemplateLoader, FileTemplateLoader, MultiTemplateLoader, StringTemplateLoader, URLTemplateLoader, 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 template-not-found 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 and Description
void	closeTemplateSource(Object templateSource) Closes the template source.
Object	findTemplateSource(String name) Finds the object that acts as the source of the template with the given name.
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 object that acts as the source of the template with the given name. This method is called by the TemplateCache when a template is requested, before calling either getLastModified(Object) or getReader(Object, String).

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). Null must be returned if the source for the template can not be found (do not throw FileNotFoundException!). The returned object may will be compared with a cached template source object for equality, using the equals method. Thus, objects returned for the same physical source must be equivalent according to equals method, otherwise template caching can become very ineffective!

Throws:

IOException

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).

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 passed doesn't match the actual template content, 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).

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 (TemplateCache usually) to close() it.

Throws:

IOException - if an I/O error occurs while accessing the stream.

closeTemplateSource

void closeTemplateSource(Object templateSource)
                  throws IOException

Closes the template source. This is the last method that is called by the TemplateCache for a template source. 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