public abstract class URLTemplateLoader extends Object implements TemplateLoader
getURL(String)
method. Both ClassTemplateLoader
and
WebappTemplateLoader
are (quite trivial) subclasses of this class.Constructor and Description |
---|
URLTemplateLoader() |
Modifier and Type | Method and Description |
---|---|
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 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.
|
protected abstract URL |
getURL(String name)
Given a template name (plus potential locale decorations) retrieves
an URL that points the template source.
|
Boolean |
getURLConnectionUsesCaches()
Getter pair of
setURLConnectionUsesCaches(Boolean) . |
void |
setURLConnectionUsesCaches(Boolean urlConnectionUsesCaches)
Sets if
URLConnection.setUseCaches(boolean) will be called, and with what value. |
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!protected abstract URL getURL(String name)
name
- the name of the sought template, including the locale
decorations.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
protected static String canonicalizePrefix(String prefix)
prefix
- the path prefix to canonicalizepublic Boolean getURLConnectionUsesCaches()
setURLConnectionUsesCaches(Boolean)
.public void setURLConnectionUsesCaches(Boolean urlConnectionUsesCaches)
URLConnection.setUseCaches(boolean)
will be called, and with what value. By default this is
null
; see the behavior then below. The recommended value is false
, so that FreeMarker can always
reliably detect when a template was changed. The default is null
only for backward compatibility,
and certainly will be changed to false
in 2.4.0. As FreeMarker has its own template cache with its
own update delay setting (Configuration.setTemplateUpdateDelay(int)
), setting this to false
shouldn't cause performance problems.
Regarding null
value: By default then URLConnection.setUseCaches(boolean)
won't be called,
and so the default of the URLConnection
subclass will be in effect (usually true
). That's the
2.3.0-compatible mode. However, if Configuration.getIncompatibleImprovements()
is at least 2.3.21, then
when Configuration.getTemplate
is used, null
will mean false
. Note that this 2.3.21 trick
only works if the template is loaded through Configuration.getTemplate
(or TemplateCache
).