Java

First some kudos and credits to the below. None of the material in this post is original, and I have documented it for my personal learning. Please refer to the below original (and superior) articles. ZeroTurnaround’s Jevgeni Kabanov awesome and most practical Do You Really Get Classloaders? Oracle’s A Sundararajan Understanding Java class loading All the way from 1996 by Chuck Mcmanis The basics of Java classloaders Hello java.lang.ClassLoader A Java class is loaded (i.e. born into the JVM) by a concrete implementation of java.lang.ClassLoader. If a class must be class loaded, what loads the java.lang.ClassLoader class itself (i.e. who loads the loader)? It turns out that there is a bootstrap classloader wired into the JVM. The bootstrap loader loads java.lang.ClassLoader in additional to many other Java platform classes (e.g. java.lang.*) into memory. The essential API: ...

Struts, the famous Java MVC web framework of the late 90’s and early 00’s that pioneered well structured server side web logic. Many Java based enterprise applications developed during this era (a metric s#!t ton) still make heavy use of Struts 1.x today. Apache Struts 1 is a discontinued open-source web application framework for developing Java EE web applications. It complements the Servlet API to encourage developers to adopt a model–view–controller (MVC) architecture. It was originally created by Craig McClanahan and donated to the Apache Foundation in May, 2000. ...

Thrown into a large, legacy EE code base, I needed to create new SOAP web services, and update some existing ones. To make life interesting, there lacked a repeatable process (e.g. via Ant or Maven) for processing WSDL’s and generating the associated JAXWS and JAXB source code artifacts in a consistent manner. First things first, a repeatable and scriptable procedure. wsimport to the rescue. wsimport has been around so long now, the com.sun.tools.ws.ant.WsImport Ant task is guarenteed to be kicking around in your environment. It’s also a best practice to use the vendor specific wrapper to wsimport, in my case WebSphere. ...

On the hunt for an sporadic DB2 SQL Error -805, I took a dive into some logs. It had been rearing its ugly head for weeks now, and starting to impact our business area. The call stack pointed straight to the bad patch of code, the Java EE solution contains a programmatic TimerService, responsible for shuffling data from one database to other; a rudimentary replication solution in other words. The specific source database in this case happened to be DB2 running on AIX. No big deal. Except that the code has proven to be flakey under load. That is, the code was transferring ~500,000 records daily, but was choking for ~100,000 records, the lions share of the load and failures seemed to pertain to BLOB data. ...

Font rendering in IntelliJ on Linux looks horrid. Any Java based application does for that matter. I can’t take it anymore. I just burnt 30 minutes looking into solutions. Fastest option, run it on the Linux optimised JVM tuxjdk. tuxjdk is a series of patched to OpenJDK to enhance user experience with Java-based and Swing-based tools (NetBeans, Idea, Android Studio, etc) Instructions (for me) next time this happens: Download tuxjdk and unpack it in /usr/lib/jvm, e.g. /usr/lib/jvm/jdk-8u25-tuxjdk-b01 Run IntelliJ like this; export IDEA_JDK=/usr/lib/jvm/jdk-8u25-tuxjdk-b01/ & ./idea.sh ...

In my current project we use IBM’s version of Eclipse. On a Windows 7 VM. The VM crashes weekly. Not only has this made me paranoid about loosing my work (I stash my changes in version control like a demon), it seems to corrupt my RAD/Eclipse instance. Starting RAD produces the useful “An error has occured” error message: !SESSION 2015-09-02 10:53:50.331 ----------------------------------------------- eclipse.buildId=unknown java.fullversion=JRE 1.7.0 IBM J9 2.6 Windows 7 amd64-64 Compressed References 20140313_192258 (JIT enabled, AOT enabled) J9VM - R26_Java726_SR6_20140313_1318_B192258 JIT - r11.b05_20131003_47443.02 GC - R26_Java726_SR6_20140313_1318_B192258_CMPRSS J9CL - 20140313_192258 BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_AU Framework arguments: -product com.ibm.rational.rad.product.v80.ide Command-line arguments: -os win32 -ws win32 -arch x86_64 -product com.ibm.rational.rad.product.v80.ide !ENTRY org.eclipse.equinox.app 0 0 2015-09-02 10:53:52.658 !MESSAGE Product com.ibm.rational.rad.product.v80.ide could not be found. !ENTRY org.eclipse.osgi 4 0 2015-09-02 10:53:54.131 !MESSAGE Application error !STACK 1 java.lang.RuntimeException: No application id has been found. at org.eclipse.equinox.internal.app.EclipseAppContainer.startDefaultApp(EclipseAppContainer.java:242) at org.eclipse.equinox.internal.app.MainApplicationLauncher.run(MainApplicationLauncher.java:29) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:88) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55) at java.lang.reflect.Method.invoke(Method.java:618) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584) at org.eclipse.equinox.launcher.Main.run(Main.java:1438) at org.eclipse.equinox.launcher.Main.main(Main.java:1414) The error log isn’t much help. Something somewhere is corrupt. Asking Eclipse to clean itself seems to fix things: ...

Hot tip, logging helps understand how a piece of software works, long after it has left the cosy confines of the debugger. Logging SOAP message bodies can be really handy, when the thing that is interacting with your software is out of your control (i.e. a vendor or trading partner). And if you’re using web services, the likehood of this is high. Running JAX-WS web services in our servlet container, needed a quick and easy way to acheive this. Welcome to the wonderful world of SOAPHandler’s. ...

A useful starting place logback setup. I needed a way to roll logs not only by date, but also by size, to prevent behemoth log files from being generated. The marvellousSizeAndTimeBasedFNATP triggering policy (which comes out of the box) will gzip roll logs based on date, and then size too. So your logs directory ends up looking something like this: fooapp.log fooapp_2015-08-22.0.log.zip fooapp_2015-08-22.1.log.zip fooapp_2015-08-22.2.log.zip fooapp_2015-08-23.0.log.zip fooapp_2015-08-24.0.log.zip ... Here’s a sample logback.xml configuration that: ...

I was dealing with an application that stores image binary data in DB2. DB2 tooling (e.g. IBM Data Studio) didn’t seem to offer a convenient way of extracting images out of the box. I wasn’t suprised. It turns out dragging them out via JDBC was the path of least resistance. Ensure that you give your JDBC driver enough hints about the heavy nature of the result set that is coming back. For DB2 ResultSet.TYPE_FORWARD_ONLY and ResultSet.CONCUR_READ_ONLY worked well. ...

Following the routine restart of a WebSphere app server earlier this week, our application refused to start back up. This was an annoying suprise, as the environments are normally incredibly stable. The logs highlighted that a darker force was at play: [15/07/15 13:38:00:581 EST] 000000a9 StandaloneEJB I StandaloneEJBLifeCycle startApplication OpenWebBeans Container is starting... [15/07/15 13:38:00:589 EST] 000000a9 ObserverMetho I ObserverMethodImpl notify Cannot send event to bean in non-active context : [-43735604,Name:null,WebBeans Type:EXTENSION,APITypes:[java.lang.Object,org.apache.webbeans.jsf.scopes.Jsf2ScopesExtension,javax.enterprise.inject.spi.Extension],Qualifiers:[javax.enterprise.inject.Default]] [15/07/15 13:38:00:958 EST] 000000a9 ApplicationMg E WSVR0101W: An error occurred starting, ZizzledApp [15/07/15 13:38:00:959 EST] 000000a9 ApplicationMg A WSVR0217I: Stopping application: ZizzledApp [15/07/15 13:38:00:972 EST] 000000a9 WSEJBIntercep E CWOWB0102E: A JCDI error has occurred: <null> [15/07/15 13:38:00:977 EST] 000000a9 WSEJBIntercep E CWOWB0102E: A JCDI error has occurred: <null> [15/07/15 13:38:01:003 EST] 000000a9 ServletWrappe I com.ibm.ws.webcontainer.servlet.ServletWrapper doDestroy SRVE0253I: [ZizzledApp] [/ZizzledAppService/v1] [ZizzledAppServiceImpl]: Destroy successful. [15/07/15 13:38:01:039 EST] 000000a9 SharedEJBRunt I WSVR0041I: Stopping EJB jar: ZizzledAppEJB.jar [15/07/15 13:38:01:099 EST] 000000a9 SharedEJBRunt I WSVR0059I: EJB jar stopped: ZizzledAppEJB.jar [15/07/15 13:38:01:137 EST] 000000a9 ApplicationMg A WSVR0220I: Application stopped: ZizzledApp [15/07/15 13:38:01:208 EST] 000000a9 CompositionUn E WSVR0194E: Composition unit WebSphere:cuname=ZizzledApp in BLA WebSphere:blaname=ZizzledApp failed to start. [15/07/15 13:38:01:234 EST] 000000a9 FfdcProviderW com.ibm.ws.ffdc.impl.FfdcProvider logIncident FFDC1003I: FFDC Incident emitted on /var/logs/WebSphere8/ffdc/bencode02_9315bb77_15.07.15_13.38.01.2112090578995796253353.txt com.ibm.ws.runtime.component.CompositionUnitMgrImpl 679 [15/07/15 13:38:01:269 EST] 000000a9 DMAdapter I com.ibm.ws.ffdc.impl.DMAdapter getAnalysisEngine FFDC1009I: Analysis Engine using data base: /usr/WebSphere8/AppServer/properties/logbr/ffdc/adv/ffdcdb.xml [15/07/15 13:38:01:338 EST] 000000a9 FfdcProviderW com.ibm.ws.ffdc.impl.FfdcProvider logIncident FFDC1003I: FFDC Incident emitted on /var/logs/WebSphere8/ffdc/bencode02_9315bb77_15.07.15_13.38.01.235306456357083187192.txt com.ibm.ws.management.AdminServiceImpl.invoke 679 Wanting more details than an error occurred starting, tried my luck with the FFDC logs listed toward the end of the log: ...