freemarker.cache

Class URLTemplateLoader

Implemented Interfaces:
TemplateLoader
Known Direct Subclasses:
ClassTemplateLoader

public abstract class URLTemplateLoader
extends java.lang.Object
implements TemplateLoader

This is an abstract template loader that can load templates whose location can be described by an URL. Subclasses only need to override the getURL(String) method. Both ClassTemplateLoader and WebappTemplateLoader are (quite trivial) subclasses of this class.
Version:
$Id: URLTemplateLoader.java,v 1.14 2003/01/29 08:01:17 szegedia Exp $
Author:
Attila Szegedi

Method Summary

protected static String
canonicalizePrefix(String prefix)
Can be used by subclasses to canonicalize URL path prefixes.
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.
protected abstract URL
getURL(String name)
Given a template name (plus potential locale decorations) retrieves an URL that points the template source.

Method Details

canonicalizePrefix

protected static String canonicalizePrefix(String prefix)
Can be used by subclasses to canonicalize URL path prefixes.
Parameters:
prefix - the path prefix to canonicalize
Returns:
the canonicalized prefix. All backslashes are replaced with forward slashes, and a trailing slash is appended if the original prefix wasn't empty and didn't already end with a slash.

closeTemplateSource

public void closeTemplateSource(Object templateSource)
            throws IOException
Specified by:
closeTemplateSource in interface TemplateLoader
Parameters:
templateSource - the template source that should be closed.

findTemplateSource

public Object findTemplateSource(String name)
            throws IOException
Specified by:
findTemplateSource in interface TemplateLoader
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 is 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 reffered as the "template root direcotry"), 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 normalisation 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 TemplateLoader.getLastModified(Object) and TemplateLoader.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!

getLastModified

public long getLastModified(Object templateSource)
Returns the time of last modification of the specified template source. This method is called after findTemplateSource().
Specified by:
getLastModified in interface TemplateLoader
Parameters:
templateSource - an object representing a template source, obtained through a prior call to TemplateLoader.findTemplateSource(String).
Returns:
the time of last modification of the specified template source, or -1 if the time is not known.

getReader

public Reader getReader(Object templateSource,
                        String encoding)
            throws IOException
Returns the character stream of a template represented by the specified template source. This method is called after getLastModified() if it is determined that a cached copy of the template is unavailable or stale.
Specified by:
getReader in interface TemplateLoader
Parameters:
templateSource - an object representing a template source, obtained through a prior call to TemplateLoader.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 will - quite naturally - ignore the encoding parameter.
Returns:
a reader representing the template character stream. The framework will call close().

getURL

protected abstract URL getURL(String name)
Given a template name (plus potential locale decorations) retrieves an URL that points the template source.
Parameters:
name - the name of the sought template, including the locale decorations.
Returns:
an URL that points to the template source, or null if it can determine that the template source does not exist.