public interface TemplateLoader
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.
Modifier and Type | Method and Description |
---|---|
void |
closeTemplateSource(java.lang.Object templateSource)
Closes the template source, releasing any resources held that are only required for reading the template and/or
its metadata.
|
java.lang.Object |
findTemplateSource(java.lang.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(java.lang.Object templateSource)
Returns the time of last modification of the specified template source.
|
java.io.Reader |
getReader(java.lang.Object templateSource,
java.lang.String encoding)
Returns the character stream of a template represented by the specified template source.
|
java.lang.Object findTemplateSource(java.lang.String name) throws java.io.IOException
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.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)
).java.io.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!long getLastModified(java.lang.Object templateSource)
findTemplateSource()
.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.Long.MIN_VALUE
is reserved for internal use.java.io.Reader getReader(java.lang.Object templateSource, java.lang.String encoding) throws java.io.IOException
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.
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.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)
).java.io.IOException
- if an I/O error occurs while accessing the stream.void closeTemplateSource(java.lang.Object templateSource) throws java.io.IOException
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)
.templateSource
- the template source that should be closed.java.io.IOException