public class MultiTemplateLoader extends Object implements StatefulTemplateLoader
TemplateLoader
that uses a set of other loaders to load the templates.
On every request, loaders are queried in the order of their appearance in the
array of loaders provided to the constructor. However, if a request for some template
name was already satisfied in the past by one of the loaders, that Loader is queried
first (a soft affinity).
This class is not thread-safe. If it's accessed from multiple
threads concurrently, proper synchronization must be provided by the callers.
Note that TemplateCache
, the natural user of this class, provides the
necessary synchronizations when it uses this class, so then you don't have to worry
this.
Constructor and Description |
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MultiTemplateLoader(TemplateLoader[] loaders)
Creates a new multi template Loader that will use the specified loaders.
|
Modifier and Type | Method and Description |
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void |
closeTemplateSource(Object templateSource)
Closes the template source.
|
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.
|
void |
resetState()
Invoked by
Configuration.clearTemplateCache() to instruct this
template loader to throw away its current state and start afresh. |
String |
toString()
Show class name and some details that are useful in template-not-found errors.
|
public MultiTemplateLoader(TemplateLoader[] loaders)
loaders
- the loaders that are used to load templates.public Object findTemplateSource(String name) throws IOException
TemplateLoader
findTemplateSource
in interface TemplateLoader
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.TemplateLoader.getLastModified(Object)
and TemplateLoader.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 (TemplateLoader.closeTemplateSource(Object)
).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!public long getLastModified(Object templateSource)
TemplateLoader
findTemplateSource()
.getLastModified
in interface TemplateLoader
templateSource
- an object representing a template source, obtained
through a prior call to TemplateLoader.findTemplateSource(String)
.public Reader getReader(Object templateSource, String encoding) throws IOException
TemplateLoader
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 TemplateLoader.findTemplateSource(String)
and TemplateLoader.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.
getReader
in interface TemplateLoader
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 should ignore the encoding parameter.TemplateCache
usually) to
close()
it.IOException
- if an I/O error occurs while accessing the stream.public void closeTemplateSource(Object templateSource) throws IOException
TemplateLoader
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 TemplateLoader.findTemplateSource(String)
.closeTemplateSource
in interface TemplateLoader
templateSource
- the template source that should be closed.IOException
public void resetState()
StatefulTemplateLoader
Configuration.clearTemplateCache()
to instruct this
template loader to throw away its current state and start afresh.resetState
in interface StatefulTemplateLoader