This page provides some development support in the form of howtos. See also High Level Documentation.
We really recommend reading the book Java by Comparison.
Please read https://github.com/cxxr/better-java
try not to abbreviate names of variables, classes or methods
use lowerCamelCase instead of snake_case
name enums in singular, e.g. Weekday
instead of Weekdays
(except if they represent flags)
Principles:
All Exceptions we throw should be or extend JabRefException
; This is especially important if the message stored in the Exception should be shown to the user. JabRefException
has already implemented the getLocalizedMessage()
method which should be used for such cases (see details below!).
Catch and wrap all API exceptions (such as IOExceptions
) and rethrow them
Example:
try {// ...} catch (IOException ioe) {throw new JabRefException("Something went wrong...",Localization.lang("Something went wrong...", ioe);}
Never, ever throw and catch Exception
or Throwable
Errors should only be logged when they are finally caught (i.e., logged only once). See Logging for details.
If the Exception message is intended to be shown to the User in the UI (see below) provide also a localizedMessage (see JabRefException
).
(Rationale and further reading: https://www.baeldung.com/java-exceptions)
Principle: Error messages shown to the User should not contain technical details (e.g., underlying exceptions, or even stack traces). Instead, the message should be concise, understandable for non-programmers and localized. The technical reasons (and stack traces) for a failure should only be logged.
To show error message two different ways are usually used in JabRef:
showing an error dialog
updating the status bar at the bottom of the main window
TODO: Usage of status bar and Swing Dialogs
Many times there is a need to provide an object on many locations simultaneously. This design pattern is quite similar to Java's Observer, but it is much simpler and readable while having the same functional sense.
EventBus
represents a communication line between multiple components. Objects can be passed through the bus and reach the listening method of another object which is registered on that EventBus
instance. Hence, the passed object is available as a parameter in the listening method.
Any listening method has to be annotated with @Subscribe
keyword and must have only one accepting parameter. Furthermore the object which contains such listening method(s) has to be registered using the register(Object)
method provided by EventBus
. The listening methods can be overloaded by using different parameter types.
post(object)
posts an object through the EventBus
which has been used to register the listening/subscribing methods.
/* Listener.java */import com.google.common.eventbus.Subscribe;public class Listener {private int value = 0;@Subscribepublic void listen(int value) {this.value = value;}public int getValue() {return this.value;}}
/* Main.java */import com.google.common.eventbus.EventBus;public class Main {private static EventBus eventBus = new EventBus();public static void main(String[] args) {Main main = new Main();Listener listener = new Listener();eventBus.register(listener);eventBus.post(1); // 1 represents the passed event// Output should be 1System.out.println(listener.getValue());}}
The event
package contains some specific events which occur in JabRef.
For example: Every time an entry was added to the database a new EntryAddedEvent
is sent through the eventBus
which is located in BibDatabase
.
If you want to catch the event you'll have to register your listener class with the registerListener(Object listener)
method in BibDatabase
. EntryAddedEvent
provides also methods to get the inserted BibEntry
.
JabRef uses the logging facade SLF4j. All log messages are passed internally to log4j2 which handles any filtering, formatting and writing of log messages.
Obtaining a logger for a class:
private static final Log LOGGER = LogFactory.getLog(<ClassName>.class);
If the logging event is caused by an exception, please add the exception to the log message as:
catch (SomeException e) {LOGGER.warn("Warning text.", e);...}
SLF4J also support parameterized logging, e.g. if you want to print out multiple arguments in a log statement use a pair of curly braces. Examples
More information about this topic from the translator side is provided at Translating JabRef Interface.
All labeled UI elements, descriptions and messages shown to the user should be localized, i.e., should be displayed in the chosen language.
JabRef uses ResourceBundles (see Oracle Tutorial) to store key=value
pairs for each String to be localized.
To show an localized String the following org.jabref.logic.l10n.Localization
has to be used. The Class currently provides three methods to obtain translated strings:
public static String lang(String key);public static String lang(String key, String... params);public static String menuTitle(String key, String... params);
The actual usage might look like:
Localization.lang("Get me a translated String");Localization.lang("Using %0 or more %1 is also possible", "one", "parameter");Localization.menuTitle("Used for Menus only");
General hints:
Use the String you want to localize directly, do not use members or local variables: Localization.lang("Translate me");
instead of Localization.lang(someVariable)
(possibly in the form someVariable = Localization.lang("Translate me")
Use %x
-variables where appropriate: Localization.lang("Exported %0 entries.", number)
instead of Localization.lang("Exported ") + number + Localization.lang(" entries.");
Use a full stop/period (".") to end full sentences
The tests check whether translation strings appear correctly in the resource bundles.
Add new Localization.lang("KEY")
to Java file. Run the LocalizationConsistencyTest
under (src/test/org.jabref.logic.
)
Tests fail. In the test output a snippet is generated which must be added to the English translation file.
Add snippet to English translation file located at src/main/resources/l10n/JabRef_en.properties
Please do not add translations for other languages directly in the properties. They will be overwritten by Crowdin
Add the new Language to the Language enum in https://github.com/JabRef/jabref/blob/master/src/main/java/org/jabref/logic/l10n/Language.java
Create an empty <locale code>.properties file
Configure the new language in Crowdin
If the language is a variant of a language zh_CN
or pt_BR
it is necessary to add a language mapping for Crowdin to the crowdin.yml file in the root. Of course the properties file also has to be named according to the language code and locale.
We try to build a cleanup mechanism based on formatters. The idea is that we can register these actions in arbitrary places, e.g., onSave, onImport, onExport, cleanup, etc. and apply them to different fields. The formatters themself are independent of any logic and therefore easy to test.
Example: NormalizePagesFormatter
Drag and Drop makes usage of the Dragboard. For JavaFX the following tutorial is helpful. Note that the data has to be serializable which is put on the dragboard. For drag and drop of Bib-entries between the maintable and the groups panel, a custom Dragboard is used, CustomLocalDragboard
which is a generic alternative to the system one.
For accessing or putting data into the Clipboard use the ClipboardManager
.
JabRefFrame
and BasePanel
are the two main classes. You should never directly call them, instead pass them as parameters to the class.
Optional<Path> file = FileHelper.expandFilename(database, fileText, preferences.getFilePreferences());
String path
Can be the files name or a relative path to it. The Preferences should only be directly accessed in the GUI. For the usage in logic pass them as parameter
@comment{jabref-meta: fileDirectory:<directory>
“fileDirectory” is determined by Globals.pref.get(“userFileDir”) (which defaults to “fileDirectory”
There is also “fileDirectory-<username>”, which is determined by Globals.prefs.get(“userFileDirIndividual”)
Used at DatabasePropertiesDialog
model
and logic
must not know JabRefPreferences
. See ProxyPreferences
for encapsulated preferences and https://github.com/JabRef/jabref/pull/658 for a detailed discussion.
See https://github.com/JabRef/jabref/blob/master/src/main/java/org/jabref/logic/preferences/TimestampPreferences.java (via https://github.com/JabRef/jabref/pull/3092) for the current way how to deal with preferences.
Defaults should go into the model package. See Comments in this Commit
Imagine you want to test the method format(String value)
in the class BracesFormatter
which removes double braces in a given string.
Placing: all tests should be placed in a class named classTest
, e.g. BracesFormatterTest
.
Naming: the name should be descriptive enough to describe the whole test. Use the format methodUnderTest_ expectedBehavior_context
(without the dashes). So for example formatRemovesDoubleBracesAtBeginning
. Try to avoid naming the tests with a test
prefix since this information is already contained in the class name. Moreover, starting the name with test
leads often to inferior test names (see also the Stackoverflow discussion about naming).
Test only one thing per test: tests should be short and test only one small part of the method. So instead of
testFormat() {assertEqual("test", format("test"));assertEqual("{test", format("{test"));assertEqual("test", format("test}}"));}
we would have five tests containing a single assert
statement and named accordingly (formatDoesNotChangeStringWithoutBraces
, formatDoesNotRemoveSingleBrace
, , etc.). See JUnit AntiPattern for background.
Do not just test happy paths, but also wrong/weird input.
It is recommend to write tests before you actually implement the functionality (test driven development).
Bug fixing: write a test case covering the bug and then fix it, leaving the test as a security that the bug will never reappear.
Do not catch exceptions in tests, instead use the assertThrows(Exception.class, ()->doSomethingThrowsEx())
feature of junit-jupiter to the test method.
Use assertEquals(Collections.emptyList(), actualList);
instead of assertEquals(0, actualList.size());
to test whether a list is empty.
Similarly, use assertEquals(Arrays.asList("a", "b"), actualList);
to compare lists instead of
assertEquals(2, actualList.size());assertEquals("a", actualList.get(0));assertEquals("b", actualList.get(1));
Use the assertEquals
methods in BibtexEntryAssert
to check that the correct BibEntry is returned.
If you need a temporary file in tests, then add the following Annotation before the class:
@ExtendWith(TempDirectory.class)class TestClass{@BeforeEachvoid setUp(@TempDirectory.TempDir Path temporaryFolder){}}
to the test class. A temporary file is now created by Files.createFile(path)
. Using this pattern automatically ensures that the test folder is deleted after the tests are run. See the junit-pioneer doc for more details.
Sometimes it is necessary to load a specific resource or to access the resource directory
Path resourceDir = Paths.get(MSBibExportFormatTestFiles.class.getResource("MsBibExportFormatTest1.bib").toURI()).getParent();
When the directory is needed, it is important to first point to an actual existing file. Otherwise the wrong directory will be returned.
If you modify preference, use following pattern to ensure that the stored preferences of a developer are not affected:
Or even better, try to mock the preferences and insert them via dependency injection.
@Testpublic void getTypeReturnsBibLatexArticleInBibLatexMode() {// Mock preferencesPreferencesService mockedPrefs = mock(PreferencesService.class);GeneralPreferences mockedGeneralPrefs = mock(GeneralPReferences.class);// Switch to BibLatex modewhen(mockedPrefs.getGeneralPrefs()).thenReturn(mockedGeneralPrefs);when(mockedGeneralPrefs.getDefaultBibDatabaseMode()).thenReturn(BibDatabaseMode.BIBLATEX);// Now testEntryTypes biblatexentrytypes = new EntryTypes(mockedPrefs);assertEquals(BibLatexEntryTypes.ARTICLE, biblatexentrytypes.getType("article"));}
To test that a preferences migration works successfully, use the mockito method verify
. See PreferencesMigrationsTest
for an example.
Global variables should be avoided. Try to pass them as dependency.
Database.addDatabaseChangeListener does not work as the DatabaseChangedEvent does not provide the field information. Therefore, we have to use BibtexEntry.addPropertyChangeListener(VetoableChangeListener listener)
You can normalize the authors using org.jabref.model.entry.AuthorList.fixAuthor_firstNameFirst(String)
. Then the authors always look nice. The only alternative containing all data of the names is org.jabref.model.entry.AuthorList.fixAuthor_lastNameFirst(String)
. The other fix...
methods omit data (like the von parts or the junior information).
Benchmarks can be executed by running the jmh
gradle task (this functionality uses the JMH Gradle plugin)
Best practices:
Read test input from @State
objects
Return result of calculations (either explicitly or via a BlackHole
object)
Try out the YourKit JAva Profiler.
When creating an equals
method follow:
Use the ==
operator to check if the argument is a reference to this object. If so, return true
.
Use the instanceof
operator to check if the argument has the correct type. If not, return false
.
Cast the argument to the correct type.
For each “significant” field in the class, check if that field of the argument matches the corresponding field of this object. If all these tests succeed, return true
otherwise, return false
.
When you are finished writing your equals method, ask yourself three questions: Is it symmetric? Is it transitive? Is it consistent?
Also, note:
Always override hashCode
when you override equals (hashCode
also has very strict rules) (Item 9 ofEffective Java)
Don’t try to be too clever
Don’t substitute another type for Object
in the equals declaration
Always try to use the methods from the nio-package. For interoperability, they provide methods to convert between file and path. https://docs.oracle.com/javase/tutorial/essential/io/path.html Mapping between old methods and new methods https://docs.oracle.com/javase/tutorial/essential/io/legacy.html#mapping
The following expressions can be used in FXML attributes, according to the official documentation
Type | Expression | Value point to | Remark |
Location |
| path relative to the current FXML file | |
Resource |
| key in ResourceBundle | |
Attribute variable |
| named control or variable in controller (may be path in the namespace) | resolved only once at load time |
Expression binding |
| expression, for example | changes to source are propagated |
Bidirectional expression binding |
| expression | changes are propagated in both directions (not yet implemented in JavaFX, see feature request) |
Event handler |
| name of the event handler method in the controller | |
Constant |
| constant (here | |
All radio buttons that should be grouped together need to have a ToggleGroup defined in the FXML code Example:
<VBox><fx:define><ToggleGroup fx:id="citeToggleGroup"/></fx:define><children><RadioButton fx:id="inPar" minWidth="-Infinity" mnemonicParsing="false"text="%Cite selected entries between parenthesis" toggleGroup="$citeToggleGroup"/><RadioButton fx:id="inText" minWidth="-Infinity" mnemonicParsing="false"text="%Cite selected entries with in-text citation" toggleGroup="$citeToggleGroup"/><Label minWidth="-Infinity" text="%Extra information (e.g. page number)"/><TextField fx:id="pageInfo"/></children></VBox>
All dialogs should be displayed to the user via DialogService
interface methods. DialogService
provides methods to display various dialogs (including custom ones) to the user. It also ensures the displayed dialog opens on the correct window via initOwner()
(for cases where the user has multiple screens). The following code snippet demonstrates how a custom dialog is displayed to the user:
dialogService.showCustomDialog(new DocumentViewerView());
If an instance of DialogService
is unavailable within current class/scope in which the dialog needs to be displayed, DialogService
can be instantiated via the code snippet shown as follows:
DialogService dialogService = Injector.instantiateModelOrService(DialogService.class);