Building a Custom Text Editor with JFace Text

The Java Developer's Guide to Eclipse

In Chapter 26, Building a Custom Text Editor with JFace Text, you learned how JFace Text provides a framework for creating, displaying, and editing text documents. The framework is domain-independent, extensible and rich with support for building editors of syntax-oriented text, such as programming language source, XML, HTML, and SQL. It is not surprising, then, that Eclipse’s default text editor and Java editor are built using this framework.

To begin, import the example project, com.ibm.jdg2e.editor.jfacetext.sql. It demonstrates key features of the JFace Text framework, as shown below.

SQL editor

Running the Example

In the Plug-in Development perspective, launch the runtime Workbench (Run > Run As > Eclipse Application).
Create a new project in the workspace of the runtime Workbench.
Copy the test.sql file from the com.ibm.jdg2e.editor.jfacetext.sql project in the development (host) workspace into the new project in the runtime workspace.
Open the test.sql file.
Use the the content assist; type the first few letters of the SELECT keyword ("sel") and then Ctrl+Space, and the content proposals will appear.
Type in the word where in lower case. Notice the color syntax highlighting:
Select Edit > Content Format and notice that "where" is turned to uppercase "WHERE".
Define a code folding region by selecting some of the SQL Editor's text. Then select Define Folding Region from the editor's context menu. When collapsed, the folded region is denoted by the small triangle in the left vertical ruler.

Roadmap of the Example

The SQL Editor implements three editor customizations:

SQL keywords are available using content assist.
Using syntax highlighting, SQL keywords are colorized.
The formatter folds all SQL keywords to upper case.

The implementation phases begins with the creation of an editor with only the basic text editing functions. Here are the highlights of the basic text editing implementation.

The SQLEditor class extends AbstractDecoratedTextEditor. Look into the SQLEditor constructor.
The SQLEditorDocumentParticipant is a subclass of FileDocumentProvider.
The SQLPartitionScanner class extending the RuleBasedPartionScanner. Look at the action contributor that extends TextEditorActionContributor.
The SQLEditorContributor class, implements IDocumentSetupParticipant.
Look for the menu item string resources in the plug-in properties files.
Look at the method createActions method in the SQLEditor. Also the class overrides the following methods:
contributeToMenu – contributes actions to the menu
contributeToToolBar – contributes actions to the toolbar
See the SQL editor extension in the plug-in manifest file.

Basic Editor Classes

Class (All)	Description
`SQLEditor`	This class is responsible for configuring the SQL editor.
`SQLEditorContributor`	Manages the installation and deinstallation of actions for the SQL editor.
`SQLEditorDocumentParticipant`	This is the expected class for extensions provided for the `org.eclipse.core.filebuffers.documentSetup` extension point.
`SQLEditorPlugin`	The main plug-in class.
`SQLEditorSourceViewerConfiguration`	This class defines the editor add-ons; content assist, content formatter, highlighting, auto-indent strategy, double click strategy.

Content Assistant

In this part of the implementation, a content assistant provides completion proposals for SQL keywords. Here are the highlights of the contents assist implementation.

ISQLSyntax implements an interface that encapsulates the SQL syntax.
The content processor class implements theIContentAssistProcessorand implements the ISQLSyntax interfaces.
The SQLDoubleClickStrategy implements the double click handler.
The SQLCompletionProcessor computes the content assist proposals in the computeCompletionProposals method.
The SQLSourceViewerConfiguration class extends SourceViewerConfiguration. The key method is getContentAssitant, which returns an instance of the SQLCompletionProcessor class.

SQL Specific Implementations

Class (All)	Description
`ISQLSyntax`	Contains the SQL syntax words (upper and lower cases).
`SQLCodeScanner`	The `SQLCodeScanner` is a `RuleBaseScanner`.This class finds SQL comments and keywords, as the user edits the document. It is "programmed" with a sequence of rules that evaluates and returns the offset and the length of the last found token.
`SQLCompletionProcessor`	The SQL content assist processor. This content assist processor proposes completions and computes context information for a SQL content type.
`SQLDoubleClickStrategy`	Process double clicks in the SQL content.
`SQLPartitionScanner`	The `SQLPartitionScanner` is a `RulesBasedPartitionScanner`. The SQL document partitions are computed dynamically as events signal that the document has changed. The document partitions are based on tokens that represent comments and SQL code sections.

Syntax Highlighting

This part of the implementation adds the syntax highlighting of SQL keywords. Here are the highlights of this phase of development.

The SQLWordDetector implements ISQLSyntax (a locally defined interface) and an IWordDetector interfaces.
The SQLWhitespaceDetector implements the IWhitespaceDetector interface.
The SQLCodeScanner extends the RuleBasedScanner and implements ISQLSyntax.
The method getPresentationReconciler enables highlighting in the SQLSourceViewerConfiguration class.

SQL Plug-in Utilities

Class (All)	Description
`ColorProvider`	Colors used in the SQL editor.
`SQLWhiteSpaceDetector`	A class that determines if character is a SQL white space character.
`SQLWordDetector`	Determines whether a given character is valid as part of a SQL keywords in the current context.
`WordPartDetector`	Scans and detects parts of a word.

Content Formatting

This part of the implementation adds the content formatting of SQL keywords. Here are the highlights of this phase of development.

The SQLWordStrategy class that implements IFormattingStrategy and ISQLSyntax.
The getContentFormatter method of the class SQLSourceViewerConfiguration, returns the formatting strategy.

Formatting Specific Implementation

Class (All)	Description
`SQLWordStrategy`	The formatting strategy that converts SQL keywords to upper case.

Class Diagram

The classes involved in the solution and their relationships are shown in the figure below (click a class to see more information).