Seeking Advice on Legacy Application Migration Strategy

[Wejden Mrabti]

Hello GWT Community,

I'm currently working on a large legacy application stack, using Java 8, Hibernate version 5.3.20.Final, and Hibernate Search 5.11.5.Final. Our frontend technology stack includes GWT version 2.8.2 and GXT version 2.3.1a-gwt22. Fontend and backend arent well de-coupled.

In my initial approach to modernize the application, I began by migrating Hibernate to version 6.2, assuming it would be the easiest step. However, I encountered an issue where Hibernate 6.2 requires transitioning to Jakarta Persistence. When attempting to compile parts of my codebase, I received the following error:

java.lang.UnsupportedClassVersionError: jakarta/persistence/Transient has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

This suggests that I need to execute my code with JDK 11. However, when attempting to do so, I encountered the following issue:

[ERROR] Found resouce but unrecognized URL format: 'jrt:/java.sql/javax/sql/DataSource.class' java.lang.NoClassDefFoundError: javax/sql/DataSource

After reviewing your discussions in the GWT contributors group, I'm questioning whether starting with the Hibernate migration is the right approach. Should I instead prioritize migrating Java or perhaps GWT? I would greatly appreciate your insights and advice based on your experiences.

Thank you,

WM

[Jens]

I would first focus on upgrading Java, GWT and possibly GXT if it is incompatible with newest GWT. The DataSource error will go away once you upgrade GWT because newer GWT versions use a newer Jetty. Keep in mind that in newest GWT the use of embedded Jetty as appliction server during development has been deprecated. It is preferred to use a local jetty installation, a docker container or launching jetty via a build tool plugin (maven / gradle).

Once you have upgraded to latest GWT you have the possibility to use GWT 2.11-jakarta if you need to switch to Jakarta.

GWT itself only supports Hibernate 4 validation. So if the application uses Hibernate validation in GWT as well, then you likely need to use https://gitlab.com/ManfredTremmel/gwt-bean-validators

-- J.

[Wejden Mrabti]

thank  you @jens for your answer 

I started by  upgrading gwt Only  from version 2.8.2 To 2.10.0 and I kept java 8 .

I my jetty-env.xml file  i had  org.eclipse.jetty.webapp.WebAppContext as a configurationClass, so It cause fd ollowing error when launching java.lang.ClassNotFoundException: org.eclipse.jetty.webapp.WebAppContext

at java.lang.ClassLoader.findClass(ClassLoader.java:523)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at org.eclipse.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:487)
at com.google.gwt.dev.shell.jetty.JettyLauncher$WebAppContextWithReload$WebAppClassLoaderExtension.loadClass(JettyLauncher.java:458)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at org.eclipse.jetty.util.Loader.loadClass(Loader.java:64)
at org.eclipse.jetty.xml.XmlConfiguration$JettyXmlConfiguration.nodeClass(XmlConfiguration.java:477)
at org.eclipse.jetty.xml.XmlConfiguration$JettyXmlConfiguration.configure(XmlConfiguration.java:417)
at org.eclipse.jetty.xml.XmlConfiguration.configure(XmlConfiguration.java:364)
at org.eclipse.jetty.plus.webapp.EnvConfiguration.lambda$configure$0(EnvConfiguration.java:120)
at org.eclipse.jetty.webapp.WebAppClassLoader.runWithServerClassAccess(WebAppClassLoader.java:138)
at org.eclipse.jetty.plus.webapp.EnvConfiguration.configure(EnvConfiguration.java:118)
at org.eclipse.jetty.webapp.WebAppContext.configure(WebAppContext.java:498)
at org.eclipse.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1409)
at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:910)
at org.eclipse.jetty.servlet.ServletContextHandler.doStart(ServletContextHandler.java:288)
at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:524)
at com.google.gwt.dev.shell.jetty.JettyLauncher$WebAppContextWithReload.doStart(JettyLauncher.java:568)
at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:73)
at org.eclipse.jetty.util.component.ContainerLifeCycle.start(ContainerLifeCycle.java:169)
at org.eclipse.jetty.util.component.ContainerLifeCycle.doStart(ContainerLifeCycle.java:110)
at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:97)
at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:73)
at org.eclipse.jetty.util.component.ContainerLifeCycle.start(ContainerLifeCycle.java:169)
at org.eclipse.jetty.server.Server.start(Server.java:423)
at org.eclipse.jetty.util.component.ContainerLifeCycle.doStart(ContainerLifeCycle.java:110)
at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:97)
at org.eclipse.jetty.server.Server.doStart(Server.java:387)
at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:73)
at com.google.gwt.dev.shell.jetty.JettyLauncher.start(JettyLauncher.java:776)
at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:636)
at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:898)
at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:705)
at com.google.gwt.dev.DevMode.main(DevMode.java:432)
Suppressed: java.lang.ClassNotFoundException: org.eclipse.jetty.webapp.WebAppContext
at java.net.URLClassLoader.findClass(URLClassLoader.java:387)
at org.eclipse.jetty.webapp.WebAppClassLoader.findClass(WebAppClassLoader.java:629)
at org.eclipse.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:511)
... 31 more

[Jens]

Then the very first thing to do is stop using the embedded Jetty of GWT DevMode as application server. The embedded Jetty in GWT DevMode does some ClassLoader hacks and it often causes issues for people using the embedded Jetty as application server. That is the reason why GWT 2.11 has deprecated the use of embedded Jetty except for demo purposes. If you search for "jetty-web.xml" or "jetty-env.xml" on Github GWT issues then you will already find some issues with the above stack trace.

So you should find a solution to run a dedicated servlet container (jetty, tomcat, etc) that fits your workflow. 

GWT has updated its Getting Started instructions (https://www.gwtproject.org/gettingstarted-v2.html) to use the recommended project layout and a dedicated servlet container via Maven plugin. The core essence is to split the legacy project layout into three projects (client, shared, server) with dedicated classpaths and use a build tool to build a *.war file (or an exploded war folder) and then deploy this file/folder to a dedicated servlet container of your choice. The dedicated servlet container can then be configured as you like, usually as closely to your production server as possible.

Personally I don't like launching a servlet container via a build tool so I use a jetty docker container and a shell script to deploy the webapp.

-- J.