The RePlay Framework  

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                RePlay Framework, https://github.com/replay-framework/replay

RePlay is a fork of the Play1 framework, created by Codeborne in 2017. Forking was needed to make some breaking changes (detailed below) that would not be acceptable on Play1. RePlay is a simplification of the Play1 codebase that aims to improve developer ergonomics. The main differences between Play1 and RePlay are outlined below.

RePlay originally forked Play v1.5.0. Any Play1 improvements that were made since then are ported to RePlay when applicable. Version 2 of the Play Framework (Play2) is significantly different from Play1. It caters for Scala web application projects, and uses Scala internally. Porting a Play1 application to Play2 is really hard and has questionable benefits. RePlay aims to provide a more sensible upgrade path for Play1 applications.

We use Gitter to discuss RePlay development, feel free to join the channel to ask questions or just say hi.

How is RePlay different from Play1?

• Uses standard Java build tooling —Gradle— for dependency management and builds:
  • resulting in better compile times by incremental builds,
  • no dependencies (.jars) in version control (both for the framework's and your own project's repository),
  • no dependency on Ivy (an outdated dependency resolver),
  • no Python scripts (with RePlay one simply uses Gradle or Maven),
  • no "modules" folder (which was a custom dependency management mechanism),
• Removes most built-in Play modules (console, docviewer, grizzly, secure, testrunner) and the ability to serve WebSockets. These were not used by RePlay's users (could be reintroduced if needed).
• The pdf and excel Play1 contrib modules are part of the RePlay project (they are plugins).
• Does not require patches to Hibernate, Javaflow, etc.
• It does not use JBoss Javassist for bytecode manipulating "enhancers", resulting in:
  • shorter application startup times (seriously improves development cycles),
  • and support for other JVM languages, like Kotlin (example project).
• Less "magic", like: the before mentioned "enhancers" and creative use of exceptions for redirecting/responding/returning in controller methods.
• No overuse of static fields/methods throughout your application code; RePlay follows generally accepted OO best practices.
• More actively maintained.
• More up to date dependencies (e.g. Hibernate).
• Promotes dependency injection for decoupling concerns (using Google's Guice as a DI provider like Play2).
• Where possible functionality has been refactored into plugins (more on that below) to increase modularity.
• Removed the VirtualFile class (since RePlay 2.4.0), all resources are simply loaded from the classpath.

Requirements

RePlay requires JDK 17 to be built; it is the lower limit of several of RePlay's dependencies: ECJ (for rendering GroovyTemplates), FlyingSaucer (PDF generation) and Selenide (UI tests). Your project should use a JDK version equal to or greater than 17 that's also supported by Hibernate 6.6 (the version RePlay currently depends on), which are JDK 17, 21, 22 and 23.

Getting started

You need to add RePlay dependencies to your build.gradle (or pom.xml):

dependencies {
  implementation("io.github.replay-framework:framework:2.5.0")
  implementation("io.github.replay-framework:javanet:2.5.0") // you can replace "javanet" by "netty3" or "netty4"
  
  // Optionally:
  implementation("io.github.replay-framework:guice:2.5.0")
  implementation("io.github.replay-framework:fastergt:2.5.0")
  implementation("io.github.replay-framework:liquibase:2.5.0")
  implementation("io.github.replay-framework:pdf:2.5.0")
  implementation("io.github.replay-framework:excel:2.5.0")
  implementation("io.github.replay-framework:ehcache:2.5.0") // or `memcached`, or disable caching by not specifying a caching package. Earlier `memcached=true` setting won't be checked anymore!
}

RePlay does not come with the play command line tool (written in Python 2.7) that it part of Play1. Hence, the play new scaffolding generator is not available in RePlay. To start a new RePlay application make a copy of demo application and work your way up from there.

Subprojects in RePlay's replay-tests/ folder show how to do certain things in RePlay (like using LiquiBase and Hibernate backed applications (in liquibase-app), Kotlin (in helloworld-kotlin), some more advanced controller techniques (in criminals) a multi-module application (in multi-module-app) and dependency injection with Guice (in dependency-injection)).

Documentation for RePlay is found in (or referred to from) this README.

NOTE: Due to its small community, RePlay is not likely the best choice for a new project. Same holds true for Play1 and even Play2 (when not using Scala). RePlay primarily caters to maintainers of Play1-based applications. This README contains an extensive guide for porting Play1 applications to RePlay.

Documentation

For a large part the documentation of Play1 may be used as a reference. Keep the differences between Play1 and RePlay (outlined above) in mind, in order to know what parts of the Play1 documentation to ignore.

API docs for the RePlay framework package are generated with ./gradlew :framework:javadoc after which they are found in the /framework/build/docs/javadoc/ folder. The javadoc.io project provides online access to the Javadoc documentation of RePlay.

Development flow (hot-swapping)

RePlay does not come with the play command line tool, which is used to start a Play1 application in development mode (i.e.: with play run) providing auto-compilation and hot-swapping of code changes.

Developers of RePlay applications need to set up an IDE to get a good development flow.

These steps set up a hot-swapping development flow with IntelliJ IDEA for the criminals RePlay example application:

0. Clone the replay repository
1. Use IntelliJ IDEA to File > Open... the replay project (not Import) by selecting the root of this project's repository
2. In File > Settings... > Build, Excecution, Deployment > Compiler > Java Compiler fill the Additional command line parameters with the value: -parameters (also found in the build.gradle file, it put the method argument names in the bytecode by which the framework auto-binds params at run time)
3. In File > Settings... > Build, Excecution, Deployment > Buitl Tools > Gradle set both Build and run using and Run test using to IntelliJ IDEA (makes restarting and hot-swapping much faster)
4. Go to Run -> Edit Configurations..., click the + (Add New Configuration) in the top-right corner and select "Application"
5. Fill in the following details, and click OK:

• Name: Criminals (how this run/debug configuration shows up in the IntelliJ UI)
• JDK/JRE: select one you prefer (Java 17 seems to work fine)
• Use classpath of module: criminals.main
• Main class: replay.replay-tests.criminals.Application (the package name, criminals should match the package that contains you Application class in app/)
• VM options (shown with Modify options drop-down item Add VM options): -XX:+ShowCodeDetailsInExceptionMessages (for more helpful errors) (applicable only for Java 14+)

Now a "Run/Debug Configuration" with the name of your app shows up in the top-right of the screen. You can press the "Run" button (with the green play icon) to start the application from the IDE.

To run the application in debug mode press the "Debug" button (with a little bug icon, next to the "Run" button) and all should work.

When in debug mode you can use CTRL-SHIFT-F9 to "Reload Changed Classes" (as IntelliJ calls hot-swapping). This only works when class/method signatures were not changed. If hot-swapping failed, you will see a notification in IDEA after which you need to restart the application. To fully restart the project in debug mode use SHIFT-F9, or press the bug icon button again.

Finally, in File -> Settings... -> Build, Execution, Deployment -> Build Tools -> Gradle set both Build and run using and Run test using to IntelliJ IDEA. This should make restarting and hot-swapping much (5-30x) faster!

Deploying

The ./gradlew jar command produces the build/libs/appname.jar file.

The following should start your application from the command line (possibly adding additional flags):

java -cp "build/classes/java/main:build/libs/*:build/lib/*" appname.Application

Replace appname with the name of the package your Application class resides in. The classpath string (after -cp) contains three parts:

1. The first bit points to the folder with the application's .class files (build/classes/java/main) built by the Gradle build script, as that's what RePlay (and Play1 as well) use instead of the copies of these files as found in the application's JAR file.
2. The second bit (build/libs/*) points the application JAR file as build by Gradle (e.g.: ./gradlew jar).
3. The last bit (build/lib/*) points to the dependencies of the project as installed by Gradle (should be last, or they may overshadow project definitions).

Troubleshooting

You may find some warnings for "illegal reflective access" when running the application. These are safe to ignore up until JVM version 17.

With this flag --add-opens java.base/java.lang=ALL-UNNAMED these warnings from guice may be suppressed (this will be fixed in a future version of guice).

To suppress the "illegal reflective access" warnings from netty you could use io.github.replay-framework:netty4 instead of io.github.replay-framework:netty3.

Plugins

Play1 installs some plugins out-of-the-box which you can disable in your project. The plugins that Play1 enables by default will need to be explicitly added to your RePlay project's play.plugins file. The ability to disable plugins is no longer needed (and has therefor been removed).

Some Play1 plugins do not have a RePlay equivalent, such as: play.plugins.EnhancerPlugin (RePlay does not do byte-code "enhancing" by design), play.ConfigurationChangeWatcherPlugin, play.db.Evolutions and play.plugins.ConfigurablePluginDisablingPlugin (no longer needed as just explained).

The RePlay project comes with the following plugins:

• play.data.parsing.TempFilePlugin¹ — Creates temporary folders for file parsing and deletes them after request completion.
• play.data.validation.ValidationPlugin¹ — Adds validation on controller methods parameters based on annotations.
• play.db.DBPlugin¹ — Sets up the Postgres, MySQL or H2 data source based on the configuration values.
• play.db.jpa.JPAPlugin¹ — Initialises required JPA EntityManagerFactories.
• play.i18n.MessagesPlugin¹ — The internationalization system for UI strings.
• play.jobs.JobsPlugin¹ — Simple cron-style or out-of-request-cycle jobs runner.
• play.libs.WS¹ — Simple HTTP client (to make webservices requests).
• play.modules.excel.Plugin — Installs the Excel spreadsheet rendering plugin (requires the io.github.replay-framework:pdf library). In Play1 this is available as a community plugin.
• play.modules.gtengineplugin.GTEnginePlugin² — Installs the Groovy Templates engine for rendering views (requires the io.github.replay-framework:fastergt library).
• play.modules.logger.RequestLogPlugin — logs every request with response type+status
• play.modules.logger.RePlayLogoPlugin — Shows the RePlay logo at application startup
• play.plugins.PlayStatusPlugin¹ — Installs the authenticated /@status endpoint.
• play.plugins.security.AuthenticityTokenPlugin — Add automatic validation of a form's authenticityToken to mitigate CSRF attacks. In Play1 the checkAuthenticity() method is built into the Controller class and needs to be explicitly called.

¹) This plugin is installed by default in Play1 (no entry in the play.plugins file needed).

²) Built into the Play1 framework (not as a plugin), shipped as a plugin in RePlay.

A community plugin for creating PDFs exists for Play1. In RePlay this functionality is part of the main project and available as a regular library (no longer a plugin) named io.github.replay-framework:pdf.

RePlay projects put play.plugins file in conf/. The syntax of the play.plugins file remains the same.

Write your own plugins by extending play.PlayPlugin is still possible, porting one of the many Play1 modules to RePlay should be straightforward or not needed at all.

Porting a Play1 application to RePlay

Porting a Play1 application to RePlay requires quite some work, depending on the size of the application. The work will be significantly less than porting the application to Play2 or a currently popular Java MVC framework (like Spring Boot).

A serious part of the work stems from the removal of Play1's "Enhancers", these use JBoss Javassist to apply runtime bytecode manipulation which add methods and intercept method calls or member field access. Removing the enhancers gives RePlay many of its benefits: quick builds, reduce start-up times, allow non-Java JVM language interop, reduce magic, make mocking easier and results in more idiomatic Java code.

It is advised to perform the porting work as much as possible while still being based on Play1. This allows you to break up the effort in smaller "testable" steps making the effort more incremental and thereby greatly reducing the complexity of actual switch to RePlay. Where this is possible the guide below points this out with a TIP.

The following list breaks down the porting effort into tasks:

• Port the dependency specification from conf/dependencies.yml (Ivy2 format) to build.gradle (Gradle format).
• Ensure that app/play.plugins file (or the file where the play.plugins.descriptor configuration property is pointing) is on the classpath (e.g. sourceSets.main.resources { srcDir 'app' }) and add all plugins you need explicitly (see the section on "Plugins").
• Add the app/<appname>/Application.java and app/<appname>/Module.java (see the RePlay example project and multi-module-app test and RePlay example project for inspiration).
• Play1 recommends to subclass from db.Model, which is deprecated in RePlay. Instead, implement a base model as part of your project as seen in replay-test/liquibase-app. This give you more flexibility in configuring Hibernate handling of the id column.
• Play1's PropertiesEnhancer was removed.
  • This enhancer reduces the boilerplate needed to make classes adhere to the "Java Bean" standard. In short: a bean is a Java class that (1) implements java.io.Serializable, (2) implements public getter/setter methods for accessing the state, and (3) implements the default constructor (a public constructor that takes no arguments). All @Entity annotated classes (e.g. model classes) should adhere to the Bean standard. Play1's PropertiesEnhancer creates the default constructor in case it is absent, creates getter/setter methods and rewrites direct access to Entities' public member fields (e.g.: obj.memberField; and obj.memberField = newValue;) to calls to the corresponding getter/setter methods.
  • In for a large part the model code still works: adherence to the Java Bean standard is not strictly enforced.
  • In some cases the model code does not work without Play1's PropertiesEnhancer:
    • Runtime errors for lacking default constructors: simply implement them for all @Entity annotated classes. In most cases adding public ClassName() {} suffices. IntelliJ can help with that.
    • In some cases a member field's getter needs to be implemented and used (instead of the member field access) for Hibernate to work. IntelliJ can do this per file, right-click a file and Refactor > Encapsulate fields, where you pick all public non-static fields.
    • Since Groovy maps direct field access to use the getters and setters, your template code should still work.
  • TIP: By setting play.propertiesEnhancer.enabled=false in conf/application.conf of a Play1 project, this work required can be performed on the Play1 based version of the application.
  • TIP2: Use IntelliJ's Refactor -> Encapsulate Fields... on all @Entity annotated classes to have them generated for you.
  • TIP3: For the id field on play.db.jpa.Model only encapsulate with a getter. To do so copy the Model class into your project, string replace all import play.db.jpa.Model to point to your copy of the class, run Refactor -> Encapsulate Fields... on your own class (only generate the getter!), finally remove your class and string replace the imports back to what they were.
• Play1's JPAEnhancer was removed.

  • In RePlay, entity classes (they in Play1 extend Model) have to implement create, count, find*, all and delete* methods themselves.

    • TIP: Reimplement these methods using the methods found in RePlay's play.db.jpa.JPARepository.

  • TIP: By adding the following lines to conf/application.conf of a Play1 project, the work required can be performed on the Play1 based version of the application.

    plugins.disable.0=play.db.jpa.JPAPlugin
    plugins.disable.1=play.modules.jpastats.JPAStatsPlugin
    

  • TIP: Split the files in app/models/ into entities (e.g. a User class with the Hibernate entity definition) and repositories (e.g. a UserRepository class with the static methods for retrieving User entities from the database).

public class UserRepo {

  static findById(final long id) {
    return JPARepository.from(User.class).findById(id);
  }
}

• refresh() has been removed from play.db.jpa.GenericModel; simply replace occurrences with: JPA.em().refresh(entityYouWantToRefresh)
• JPA.setRollbackOnly() becomes JPA.em().getTransaction().setRollbackOnly()
• play.Logger has been slimmed down (and renamed to PlayLoggingSetup). In RePlay it merely initializes the slf4j logger within the framework, it cannot be used for actual logging statements (e.g. Logger.warn(...)).
  • Where the Logger of Play1 uses the String.format interpolation (with %s, %d, etc.), the slf4j uses {} for interpolation (which is a bit faster).
  • TIP: You can already replace the use of play.Logger with the slf4j logger in your Play1 application.
  • In RePlay logging is done as follows (common Java idiom):

import org.slf4j.Logger; // replace `import play.Logger;` with these
import org.slf4j.LoggerFactory;

public class YourClassThatNeedsLogging {
  // the following line allows quick access to the logger within this class' context
  private static final Logger logger = LoggerFactory.getLogger(YourClassThatNeedsLogging.class);

  public YourClassThatNeedsLogging(int i) {
    logger.debug("Constructor invoked with param: {}", i);  // example logging statement
  }
  // ...
}

• Play.classloader is removed; replace it with CurrentClass.class.getClassLoader().
• play.libs.Crypto has been slimmed down and is now called Crypter.
  • TIP: You can simply copy the play.libs.Crypto file from Play1 into your project.
• play.libs.WS has been split up into the play.libs.ws package containing the classes that have been split out.
• Router.absolute() now takes a param. Fix this by passing it Router.absolute(Http.Request.current()).
• IO.readFileAsString() now needs an additional Charset argument (usually StandardCharsets.UTF_8 suffices).
• play.cache.Cache.get(...) only takes one argument, removing additional arguments is usually enough.
• play.Plugin changed some of the method signatures.
• play.data.binding.TypeBinder changed some of the method signatures.
• play.jobs.Job requires overriding of doJobWithResult() instead of doJob(). If the job does no return value the subclass should be parameterized over Void, and return null. For example:

@OnApplicationStart
public class LoadMenuJob extends Job<Void> {

  @Override
  public Void doJobWithResult() {
    // ...
    return null;
  }
}

• The play.mvc.Mailer class was dropped, use the play.libs.Mail class instead.
  • TIP: Copy RePlay's play.libs.Mail class into your Play1 project and port over the mail logic while your application is still running on top of Play1.
  • Here an example of a simple text mail:

public class TextMails extends Mail {

  public static void welcomeNewUSer(final User user, final Organization organization) {
    TextEmail email = new TextEmail(); // subclass of a `org.apache.commons.mail.*` class
    email.setFrom("[email protected]");
    email.addRecipient(user.getEmailAddress());
    email.setSubject(
      String.format("Welcome %s! Follow the link in this mail to active your account.",
        organization.name));
    email.setMsg(
      TemplateLoader.load("app/mails/text/welcomeNonTrialInternal.txt"))
        .render(Map.of("user", user, "org", organization));
    send(email);
  }
}

• Port the controller classes over to RePlay. This is likely the biggest task of the porting effort and cannot be performed from your Play1 application like some other porting tasks.
  • Since play.result.Result no longer extends Exception, your controllers should return Result instead of throwing it. In Play1 the controller methods that trigger the request's response (like render(...), renderText(...) and renderJSON(...)) throw an exception. By this exception the rest of the method will not be executed (which may confuse IDEs). In RePlay this is considered abuse of the exception system, and the good old return statement is used to achieve the same. The following changes are needed to adapt Play1 code to this:
    • Make all action methods (the ones pointed at by conf/routes) non-static. You may need to remove the static keyword from some non-action methods as well.
    • Make all action methods return play.mvc.Result instead of void (as RePlay does use exceptions for responding to requests). Some examples of what needs to change:
      • renderJson(...); becomes return new RenderJson(...);.
      • render(...); becomes return new View(...);, with slightly different arguments e.g.:
        • render(token); becomes return new View("path/to/ControllerName/template.html", Map.of("order", order, "token", token));, or return new View("...").with(("order", order).with("token", token);. The second style allows null values to be passed to the template.
      • notFoundIfNull(token); becomes if (token == null) return new NotFound("Token missing");.
      • Triggering redirects using the bytecode mingled Play1 idiom Controller.actionMethod(...); or just actionMethod() (in the same class) becomes return Redirect(...); where the path is provided as first argument. Alternatively the RedirectToAction class can be used with a string pointing to controller methods (like in Play1).
    • Methods annotated with @Before and @After also return Result, and should return null to signify continuation (e.g. to the next @Before annotated method or to the controller action method itself).
      • In RePlay the priority annotation-argument is removed from that annotation.
    • Sometimes private methods that return a value in Play1 also can trigger a response, because responses are triggered by exceptions in Play1. This is no longer allowed using RePlay and thus the code that triggers responses (actual controller code) should be separated from code that merely handles values (probably not controller code). In these cases it would be nice if Java already had multiple return values (through sum-types).
    • Private methods with a void return type that trigger responses in Play1 (by throwing exceptions) need to return Result in replay. In case these private methods do not trigger a response they should return null in the RePlay scenario. The call sites of those methods need the following bit of code to pass through Result objects: var result = privateMethod(); if (result != null) return result;. This ensures the rest of the method is evaluated.
  • Http.Request.current() becomes request (as in Play1 many things are static that are not in RePlay).
  • params.flash(); becomes params.flash(flash); (this stores the render params in the cookie to survive a redirect).
  • TIP: Start by moving your controller classes to an unported/ folder, and move them one-by-one back to controller/ while porting. Ensure that git understand files were moved to allow merging in changes from Play1-based branches of your application.
• Validation.valid(obj) needs an additional String as parameter to which the validation results are bound, and thus becomes: Validation.valid("obj", obj)
• Check, CheckWith, CheckWithCheck and Equals have been removed from the play.data.validation package.
  • They have been removed in favour of calling validation methods explicitly from the body of controller methods (opposed to configuring validations through annotations). This allows much needed control over your application's response in case of validation errors.
  • TIP: Copy those files from Play1 into your project to ease the porting effort (maybe except Equals as it has so many dependencies).
• The params.get() method now always returns a String, use parseXYZ() methods (like Boolean.parseBoolean()) to convert results.
• Writing directly to the stream response.out, e.g. a final call to ImageIO.write(outputImage, "png", response.out) with a Play1 codebase, needs an additional return new Ok() with RePlay.
• While porting the controllers you will find some changes to the views (templates) are required too:
  • In some cases the full package path needs to be provided, e.g.: Play.configuration.getProperty("key") becomes play.Play.configuration.getProperty("key").
• Due to changed encrypting/signing of CookieSessionStore all active sessions are logged out when migrating from Play1 to RePlay. This means that running the Play1 version of the app side-by-side with the RePlay version is not possible (all users get logged out all the time).
• As of September 2024, Play1 brings Hibernate 5.6 while RePlay upgraded to 6.4. This may result in some problems:
  • Hibernate 6.4 is stricter when it comes to mapping columns to properties. This results in a NonUniqueDiscoveredSqlAliasException thrown when a column name occurs twice (e.g. the id column) when mapping the result of a query with joins to an entity.
  • Hibernate changed the "generation strategy" for MySQL, hence you may want to implement jpa.Model yourself which is fully supported in RePlay.

Multi-module applications

RePlay doesn't support using other RePlay applications as modules, like Play1 (see issue #290)! To mimic that feature, a new application.conf property play.classes.scanJars was introduced.

Just define your RePlay modules as a dependencies, and put their jar names in application.conf as comma separated:

play.classes.scanJars=my-fancy-dependency*.jar,my-other-dep-*.jar

The * wildcard is only for easy matching the versioned jar names.

For more details, see the multi-module-app example!

Licence

The RePlay Framework is distributed under MIT license.

The Play1 Framework, that RePlay forked, is distributed under Apache 2 licence.