Lazy evaluator for attribute values.
The listener of changes in a
The container of highlighted areas and their attributes.
Factory for producing
An iterator through highlights in a
An event object notifying about a change in highlighting of certain area of a document.
The highlight layer defines a set of highlights used for rendering a document.
The context passed to a factory when it is asked to create
This class determines a position of a
The Highlighting SPI is a new way of influencing how text in an editor component
is rendered. The editor framework in Netbeans is an extension of the Swing Text SPI
framework and as such it uses things like
to render a
Document on a screen.
Since the editor framework is primarily designed to support various different types of files in the IDE it has to give module a chance to participate in documents rendering. Modules providing support for different languages usually need to influence colors and fonts of different parts of a source file depending on what code it contains (i.e. syntax coloring) or what other information the module needs presenting to a user (e.g. text annotations, hyperlinking, etc.). This all and more can be achieved by using the Highlighting SPI.
The very basic idea behind the SPI is to render a document as a sandwich of independent layers, which will say what colors and font should be used for rendering particular parts of the document. These parts of the document together with their rendering attributes (i.e. colors or font) are called highlighted areas or highlights. Each layer can provide as many non-overlapping highlights as it likes and each module can provide as many layers as it needs. The implementation behind the SPI will collect all layers registered for a particular document type (i.e. mime type), ask each of them for its highlights, merge those highlights together and finally send them to the draw engine, which will render the document.
The whole SPI is organized around the
class, which is the ultimate thing that modules need to implement in order to provide
a list of highlights for a document. The
HighlightsLayers are created
which should be registered in
MimeLookup under the mime-type of a document
that the layer should be used for. All layers registered for one type of a document
are ordedred according to the
they provide. Besides of
ZOrder the layers provide additional information
about nature of highlights they maintain.
HighlightsLayer class implements
interface, which is the fundamental part of the SPI.
HighlightsContainer interface allows to get a list of highlighs
and to listen on changes in highlights that it contains.
HighlightsLayer there are two other implementations of
this interface and they are
PositionsBag classes allow adding
and removing highlights dynamically. The highlights can be added either one-by-one
or in chunks; each change is reported to listeners.
The registration of
HighlightsLayers has to be done through an
instance of the
HighlightsLayerFactory class. The factory should
be registered in
MimeLookup under the mime-type of documents, which
HighlightsLayer should be used for. For example, if a module
wants to provide
it should implement its own
org.some.module.HLFactory class) and register it in
using its XML layer as it is shown on the example below.
<folder name="Editors"> <folder name="text"> <folder name="x-something"> <file name="org-some-module-HLFactory.instance" /> </folder> </folder> </folder>
HLFactory class will simply return a new instance of
the module's implementation of the
HighlightsLayer class from its
method. The parameter of the
createLayers method provides access to
JTextComponent and its
Document, which the layer
is being created for. The method can create and return multiple
The lifecycle of
HighlightsLayers is tied to the lifecycle of
Document. The infrastructure creates new instances of layers by calling
HighlightsLayerFactory objects every time it needs to
visualize a new
Document. The layers created for one
are not cached or resused in any way. This means that the layers themselvs do not have to take
care about a potential change of a
Document instance in
JTextComponent. The infrastructre will always create a new set of
layers if the
Document instance changes. Therefore the layers can
simply hold their instance of
and treat them as invariants.
The basics of the locking and events model of Swing documents is described in the javadoc of the javax.swing.text.AbstractDocument class. Netbeans documents use the same patterns and so does the Highlighting SPI, because of its tight relation to documents. The fundamentals of the Swing documents locking model are that any changes to a document are done under the document's write lock, the document's listeners are notified synchronously on the mutating thread and have full read access to the document, but can't modify it.
The main functionality of the Highlighting SPI is to maintain highlights
of certain areas of a document. These highlights are specified as a triple of
starting offset, ending offset and a set of attributes. The offsets are usually passed
in and out accross the SPI boundaries in form of
ints and even though
some implementations (e.g.
the esential rule is that any calls in and out from the SPI have to be made
under the document's read lock. Let's have a look on a few examples demonstrating
what this means.
HighlightsLayer.getHighlights()have to be carried on under the read lock of the document, which the
HighlightsLayerwas created for.
HighlightsLayerneeds to notify its listeneres that some of its highlights have changed all the events have to be fired under the layer's document's read lock. Obviously, the listeners are not allowed to modify the document from the event notification methods.
PositionsBagthat modify their content have to be done under the read lock of the document, which the bag was created for. Both bags makes all the changes synchronously on the caller's thread and this even includes firing notification events. Therefore all events fired from
PositionsBagwill be fired under the document's read lock if the mutating thread holds the read lock.
The Highlighting SPI does not use any special threads and any processing it
does is always done on the caller's thread. This means that the above described
constraints hardly cause any limitation for practical use. The majority of
things happening around a document are done from within
which hold the document's read lock anyway.
The Highlighting SPI is generally thread-safe meaning that any implementation behind the SPI can be used simultaneously from multiple threads if not stated otherwise. This doesn't change in any way the rule of acquiring a read lock before calling the SPI. Swing documents generally allow access for multiple readers that can run concurrently.
Since there can be multiple layers suplying highlights for one document and the
highlights can generally overlap it is important to sort the layers according
to their Z-order. For this purpose each layer has to supply an appropriate
ZOrder maintains a position of a layer
relatively to other layers as a simple integer number. The higher the number
the higher (more visible) the layer is in the z-order hierarchy.
Instances of the
ZOrder class are immutable making it
impossible to dynamically change a position of a layer in the z-order stack
created for a document.
ZOrder class contains several predefined constants,
which can be used as well-known positions. These constants are called z-order
racks and are meant to be used as a starting point for positioning a layer. An
exact z-order can then be specified by choosing an integer position of the layer
within a rack. The racks are listed below in their respective z-order.
TOP_RACK- the top most rack
SHOW_OFF_RACK- layers providing short-lived highlights that can temporarily override highlights from other layers. An example can be text selection or text search layers.
DEFAULT_RACK- the rack for general layers
CARET_RACK- layers that highlight a caret
SYNTAX_RACK- layers providing syntax or semantic highlighting of text
BOTOM_RACK- the bottom rack
The Highlighting SPI uses
javax.swing.text.AttributeSet to define
attributes for particular highlights. These attributes can be anything,
which the editor's drawing engine understands and can render. Usually the
attribute names are constants from
org.netbeans.api.editor.settings.EditorStyleConstants. The values
depend on the meaning of each particular attribute, but they usually are instances
Boolean.FALSE and similar.
Since there can be more highlighting layers participating on one document and
they can provide highlights that overlap the infrastructure will merge attributes
AttributeSets provided for areas with overlapping highlights.
The merging is done in the order defined by
ZOrders of the participating
layers, which means that if two layers provide an attribute with the same name
then the merged
AttributeSet will contain the attribute from the
layer, which is placed higher in the z-order hierarchy.
There are two important rules for using
AttributeSets, which should
be carefully followed by all highlighting layer implementations. Violating these
rules may potentialy break the rendering of a document or may cause performance
AttributeSets should always be treated as immutable objects. Once you create an
AttibuteSetand use it for a highlight you should not modify it. Your modification is most likely to be ignored or can have unpredictable results.
AttributeSetfor each of those highlights when all of them would in fact be the same. Instead you should always create one instance of
AttributeSetand share it among all highlights that render the same text category (e.g. token or token category, etc.).
AttributeSets used for highlighting are often created by calling
and it is a responsibility of this class to prevent excesive creation of
AttributeSets it provides. However, if your highlighting layer creates
AttributeSets they should always be cached and reused. You can
use methods from the
class for creating immutable
The Netbeans editor as any other modern editor allows selecting blocks of text and highlighting them to a user for easier identification. We call this functionality caret selection services and it includes things as simple as marking a block of text that the user selected for copy/paste operation or highlighting a line where the caret is placed to more complex ones such as highlighting occurences of a text that the user search for using the 'Find dialog', etc.
This functionality usually only needs to create one highlight and update it
depending on the caret movements/selection notified from
The more complex cases may need to create several highlights (e.g. to show the
text being searched for). Generally, the highlights are created independently on the
text changes in the document itself (e.g. the caret move or searching for a text).
However, they have to survive editing the document (e.g. the highlighted occurences
of the searched text have to remain highlighted when other parts of the document
The caret selection highlights are generally short-lived and have higher importance than other highlights (e.g. syntax or semantic coloring). They usually change the background color to highlight the selection, but also retain as much of a visual appearance of the highlighted text as possible.
This type of a document coloring shows 'words' or characters in different colors to indicate their meaning in the structure of the text document. This is very popular with highly structured documents such as source code files, scripts, SGML-like documents, etc. It's usually not used for plain text documents containing text in a human language.
Syntax highlighting in Netbeans editor is based on a lexical analysis done by lexer plug-ins registered for various types of documents. The lexers are written using the APIs provided by the Lexer module. During the lexical analysis text gets split into tokens of different types and categories. Each token type or category can have defined its own coloring information such as font and foreground and background colors, etc. Tokens know their position in text (i.e. offset and length), which information can then be used for creating highlights.
Decoupling the lexers and making them pluggable lets the syntax highlighting be very flexible. A single layer based on the Lexer API can colorify all sorts of documents providing that there is a lexer registered for each type of a document.
Generally a syntax analysis is very fast and syntax highlighting immediately reflects changes done in text. The syntax highlighting layer is usually at the bottom of the hierarchy of highlighting layers.
In fact semantic coloring regardless of the language it is provided for is very similar to syntax coloring. Words or groups of characters are highlighted depending on their meaning in the text. The difference is in the amount of information that is needed to make this type of coloring meaningful. While with syntax coloring all the information needed is in the text itself in semantic coloring parts of text can be colored depending on information found in a completely different document (e.g. in another source file, library, project, etc.).
Semantic highlighting is highly dependent on the type of a document and therefore
is usually provided on case-by-case basis and only for the most important types
of documents (i.e. those most frequenty used such as java files in Netbeans). Also,
semantic coloring is generally not very fast, because of the amount of information
that is sometimes needed to gather before a document can be colored. Therefore,
while all the effort is made to make semantic coloring reflect text changes as
soon as possible, it is generally done asynchronously outside of the documents
event model and highlights are created as soon as they are available. The tokens
created during the semantic analysis always contain token's position within
the text in some form (i.e. either offset or
are available they should be accepted and re-used by the Highlighting SPI.
The language embedding is supported by Lexer API and therefore there is no problem with supporting it for syntax coloring. For semantic coloring all the work lies on the highlighting layers providing semantic coloring support for a particular language. These layers have to be prepared to provide highlights for parts of a document, which does not contain text in the language they support, but which contains some embedded parts in that language. The Highlighting infrastructure will scan the document for all languages it contains and then it will create appropriate highlighting layers. The layers can be added dynamically as user inserts parts of text in a new language. The layers, however, may not be removed immediately when the last part of text in a language they suppor is removed. Therefore the layers should be prepared to provide no highlights if there is no text they recognize.
In certain situations
are used for other purposes than editing. For example debugger may want to show
JEditorPane for adding a new watch, where a user could write a piece
of java code that should evaluated. This pane should use basically the same layers
so that the entered code looks like properly colored and formatted java code.
However, it is not desirable to use exactly the same layers as for an ordinary
java editor, because some highlightings have a little value in this context or
could even be disturbing. There is no point in highlighting the row with the caret,
because watches are essentially one-line expressions. There is also a little point
in showing text-search related highlights, because hardly anybody will use text
search in these simple expressions anyway. On the other hand it makes sense to
highlight selected text if user selects some.
There can be a whole range of usecases where modules need to show an editor pane, but do not want to use a particular set of highlighting layers, which are registered for the mime type of text that the module is trying to display and which would normally be used for an ordinary editor pane. These usecases are very specific for each module and its way of implementing some features.
The editor insfrastructure supports this usecase through allowing modules to
set special properties on the editor pane that they want to use for displaying text.
The properties are called
The value of those properties can be
of regular expressions that will be used for finding the matching layers by evaluating
each regular expression against the layer's type id. The exact interpretation of those
two properties is described below.
HighlightsLayerIncludes- Defines the set of layers that will be used for rendering text in an editor pane that defines this property. Every layer, which type Id matches at least one of the regular expressions defined by this property, will be included for rendering. The default value is
null, which means that all registered layers will be used.
HighlightsLayerExcludes- Defines the set of layers that will not be used for rendering. Every layer, which type Id matches at least one of the regular expressions defined by this property, will be excluded from rendering. The default value is
null, which means that no layer will be excluded.
The filters defined by those two properties are used in the same order as they were listed above. That is the includes are used first and whatever layers they includ are then filtered by the excludes filter. The result is then used for rendering text in an editor component, which defined those properties.
The example below shows how to disable the caret row highlighting layer
JEditorPane pane = new JEditorPane(); pane.putClientProperty( "HighlightsLayerExcludes", "^org\\.netbeans\\.modules\\.editor\\.lib2\\.highlighting\\.CaretRowHighlighting$" );
The main usecases described above are certainly not the only usecases of the Highlighting SPI. In general the SPI can be used for binding any type of information to parts of text in a document. While this information should have limited size to keep a good performance of Netbeans editor it can be pretty much anything. Information provided in highlights is currently used only by the editor's drawing engine, which provides a limited set of features useful mostly for rendering text. Some other uses could be for example text annotations, hyperlinking, showing icons in text, etc.
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