freemarker.cache

Class URLTemplateLoader

java.lang.Object

freemarker.cache.URLTemplateLoader

All Implemented Interfaces:

TemplateLoader

Direct Known Subclasses:

ClassTemplateLoader

public abstract class URLTemplateLoader
extends 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.

Constructor Summary

Constructors

Constructor and Description
URLTemplateLoader()

Method Summary

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 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.
Boolean	getURLConnectionUsesCaches() Getter pair of setURLConnectionUsesCaches(Boolean).
void	setURLConnectionUsesCaches(Boolean urlConnectionUsesCaches) Sets if URLConnection.setUseCaches(boolean) will be called, and with what value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

URLTemplateLoader

public URLTemplateLoader()

Method Detail

findTemplateSource

public Object findTemplateSource(String name)
                          throws IOException

Description copied from interface: TemplateLoader

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 TemplateLoader.getLastModified(Object) or TemplateLoader.getReader(Object, String).

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'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 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!

Throws:

IOException

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.

getLastModified

public long getLastModified(Object templateSource)

Description copied from interface: TemplateLoader

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

Description copied from interface: TemplateLoader

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 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.

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 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

public void closeTemplateSource(Object templateSource)
                         throws IOException

Description copied from interface: TemplateLoader

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 TemplateLoader.findTemplateSource(String).

Specified by:

closeTemplateSource in interface TemplateLoader

Parameters:

templateSource - the template source that should be closed.

Throws:

IOException

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.

getURLConnectionUsesCaches

public Boolean getURLConnectionUsesCaches()

Getter pair of setURLConnectionUsesCaches(Boolean).

Since:

2.3.21

setURLConnectionUsesCaches

public void setURLConnectionUsesCaches(Boolean urlConnectionUsesCaches)

Sets if 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).

Since:

2.3.21