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Workaround for java.lang.UnsupportedClassVersionError to not show it

After migration to Java 8, my tool throw the follwing exception if somebody try to run it on earlier Java environments.
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/myapp/MyTool: Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)
Is there some way to not show this error, and show nice error message with proposition to upgrade Java.
As I understood I should create some small class like:
public class CheckerJavaVersion {
public static void main(String args[]) {
String sVersion = System.getProperty("java.version");
sVersion = sVersion.substring(0, 3);
Float f = Float.valueOf(sVersion);
if (f.floatValue() < (float) 1.8) {
System.out.println("Please upgrate your Java to 1.8 version");
System.exit(1);
}
}
}
and compile it via older compiler. I need some solution how to run this class firstly before the main method of MyToll class starts.
PS. Aplication is packed in jar.

The problem is that the error occurs when the class is loaded, so you'd either have to use a "starter app" which starts the actual application in a separate process or dynamically load the application after the Java version has been checked.
I didn't test it but what might work is something like this:
public static void main(String args[]) {
if( javaVersionOk ) {
Class.forName("actual.mainclass.name").getMethod("actual.main.method.name").invoke();
}
}
The idea is to access the class via its name and thus make the runtime load and initialize it at that time. I'm not sure, however, if you can delay class loading like that in all cases so you'd have to go on from there.
And btw, IIRC there already are applications/libraries that provide this kind of functionality, I just don't rember their names. So a search might be worth your while.
Edit: you might want to have a look at appstart if not for using it then for inspiration.
Another launcher would be Apache Commons Launcher.
Alternatives:
Alternatively you could just provide a launch script for each platform you want to support , call java -version and check the returned version before launching the application.
Another alternative would be to use JNLP/WebStart locally, which allows you to specify a minimum version and which AFAIK even provides for download/upgrade functionality.

Error using apache -common-validator --java.lang.NoClassDefFoundError: org/apache/commons/digester/Rule

I am using following jars-
commons-validator-1.4.0 ; commons.logging-1.2 ; commons.digester-1.8 ;commons.beanutils-1.8.3
commons.collections-3.2.1
but keeps on getting same error at line -
Caused by: java.lang.ClassNotFoundException: org.apache.commons.digester.Rule
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:216)
This is the code i am writing -
InputStream in = this.getClass().getResourceAsStream("validator-name-required.xml");
// Create an instance of ValidatorResources to initialize from an xml file.
ValidatorResources resources = new ValidatorResources(in);
Please help its been a day i am stuck into this error !! Thanks in advance

Finally i am able to do this. I have used the following jars -
commons-beanutils-1.8.3.jar
commons-collections-3.2.1.jar
commons-digester-1.8.jar
commons-logging-1.1.1.jar
commons-validator-1.4.0.jar
and this works :)

Its look like that "org.apache.commons.digester.Rule" class was not found, Version 2.1 of digester have Rule.class, download this version and try.

Rebuild .jar file for netbeans platform

I have a java project (Netbeans platforms and hibernate for ORM).i use hibernate build entities and add this jar file to my project and it work fine, When I add new table to Database and rebuild entities, it has error. the new entities class is not found though I have checked my code, but I don't find any solutions. Please help me(my table name is menu)
this i my code
for (int i = 0; i < table_row; i++) {
Menu menus = (Menu) items.get(i);
objectData[i][0] = menus.getId();
objectData[i][1] = menus.getTitle();
objectData[i][2] = menus.getLevel();
objectData[i][3] = menus.getParentId();
objectData[i][4] = menus.getClassname();
objectData[i][5] = menus.getCategoryId();
objectData[i][6] = menus.getIcon();
objectData[i][7] = menus.getOrder();
objectData[i][8] = menus.getCreated();
objectData[i][9] = menus.getModified();
}
and this is exception
Classes: loaded=3871 total loaded=3871 unloaded 0
INFO [org.netbeans.core.ui.warmup.DiagnosticTask]: Total memory 4,074,373,120
INFO [null]: Total physical memory 4,074,373,120
SEVERE [global]
java.lang.ClassNotFoundException: com.osstech.dbentities.Menu
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:222)
Caused: java.lang.ClassNotFoundException: com.osstech.dbentities.Menu starting from ModuleCL#302d6b3[com.osstech.Systems] with possible defining loaders [ModuleCL#759d36f1[com.osstech.dbentities]] and declared parents [ModuleCL#7f28abd9[org.netbeans.modules.settings], ModuleCL#fcd0400[org.openide.windows], org.netbeans.MainImpl$BootClassLoader#6db17b38, ModuleCL#561ac555[org.netbeans.api.progress], ModuleCL#52b4e7ec[com.osstech.DataAccess], ModuleCL#759d36f1[com.osstech.dbentities], ModuleCL#2716630b[com.osstech.wraplibrary], ModuleCL#6461d2bf[com.osstech.Utilities], ModuleCL#f27bf78[org.openide.awt]]
at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:224)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
Caused: java.lang.NoClassDefFoundError: com/osstech/dbentities/Menu

Need some code to say anything conclusively. But, seems like you have a menu configured in layer.xml called com.osstech.dbentities.Menu. That is mis-configured. when netbeans tries to instanciate this object, it can't find it.

writing a udf in pig kind of like tutorial

I am new to pig.. and am trying to write a udf function.
So basically here is the problem statement.
I have a dummy data like this..
user_id, movie_id, date_time_stamp
So what I am trying to do is this.
if the transaction is between
9 am and 11 am --> breakfast
and so on
So here is my pig script
REGISTER path/myudfs.jar
in = LOAD 'path/input' USING
PigStorage('\\u001') AS (user:long,movie:long, time:chararray);
result = foreach in GENERATE myudfs.time(time);
STORE result INTO 'path/output/time' using PigStorage(',');
Now myudf.jar java code is like this
public class time extends EvalFunc<String>{
public String exec(Tuple input) throws IOException {
if ((input == null) || (input.size() == 0))
return null;
try{
String time = (String) input.get(0) ;
DateFormat df = new SimpleDateFormat("hh:mm:ss.000");
Date date = df.parse(time);
String timeOfDay = getTimeOfDay(date);
return timeOfDay;
} catch (ParseException e) {
//how will I handle when df.parse(time) fails and throws ParseException?
//maybe:
return null;
}
}
So it takes in the tuple and returns a string... (I am new to java also..)
After this i try to run this script as
pig -f time.pig
It returns an error
2012-11-12 08:33:08,214 [main] INFO
org.apache.pig.backend.hadoop.executionengine.HExecutionEngine - Connecting to
hadoop file system at: maprfs:///
2012-11-12 08:33:08,353 [main] INFO
org.apache.pig.backend.hadoop.executionengine.HExecutionEngine - Connecting to
map-reduce job tracker at: maprfs:///
2012-11-12 08:33:08,767 [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1069:
Problem resolving class version numbers for class myudfs.time
Some one posted on pig mailing list is that my PIG_CLASSPATH is not set and that i should point it to /path/hadoop/conf
I did that.. so now $echo PIG_CLASSPATH --> /path/hadoop/conf
But i get the same error
Please advise.
Thanks
Edit 1: On looking into the log, the error trace is:
Caused by: java.lang.UnsupportedClassVersionError: myudfs/time : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at org.apache.pig.impl.PigContext.resolveClassName(PigContext.java:427)
... 27 more
is this like a java issue?

To find the jar version, open the jar using winzip (or similar) and look for manifest.mf. There should be a line in there that says 'Created-By' and this will give the version of java that was used to build the jar.
This needs to be older or equal to the version of java you are using to build your app. If you are doing this at the command line type:
java -version
or in eclipse go to
project(menu) > properties (menu item) > java build path (in list) > libraries (tab)
and take a look at the version that you are using for the JDK/JRE (you may be able to tell this from the directory, if not then go to that directory and do java -version).
Chances are you'll need to update the version of java you have in eclipse.

java.lang.NoClassDefFoundError: Could not initialize class java.net.ProxySelector

I'm running into a problem with a java app constantly throwing:
java.lang.NoClassDefFoundError: Could not initialize class java.net.ProxySelector.
I am running Suse Linux 10.3 and running java 1.6.0. My CLASSPATH is set to
/usr/lib/jvm/jre-1.6.0-openjdk/lib.
No other users seem to be having this error so I'm assuming its my setup. For those wondering the app is yamj (http://code.google.com/p/moviejukebox/)
Any ideas as to what maybe missing or what I maybe doing wrong?
Edit the full trace of the error is as follows:
java.lang.NoClassDefFoundError: Could not initialize class java.net.ProxySelector
at sun.net.www.protocol.http.HttpURLConnection$5.run(HttpURLConnection.java:736)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:732)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:672)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:997)
at com.moviejukebox.thetvdb.tools.XMLHelper.getEventReader(XMLHelper.java:19)
at com.moviejukebox.thetvdb.model.Mirrors.(Mirrors.java:30)
at com.moviejukebox.thetvdb.TheTVDB.(TheTVDB.java:37)
at com.moviejukebox.plugin.TheTvDBPlugin.(TheTvDBPlugin.java:57)
at sun.reflect.GeneratedConstructorAccessor2.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
at java.lang.Class.newInstance0(Class.java:372)
at java.lang.Class.newInstance(Class.java:325)
at com.moviejukebox.plugin.DatabasePluginController.getMovieDatabasePlugin(DatabasePluginController.java:96)
at com.moviejukebox.plugin.DatabasePluginController.access$000(DatabasePluginController.java:30)
at com.moviejukebox.plugin.DatabasePluginController$1.initialValue(DatabasePluginController.java:44)
at com.moviejukebox.plugin.DatabasePluginController$1.initialValue(DatabasePluginController.java:39)
at java.lang.ThreadLocal.setInitialValue(ThreadLocal.java:160)
at java.lang.ThreadLocal.get(ThreadLocal.java:150)
at com.moviejukebox.plugin.DatabasePluginController.scan(DatabasePluginController.java:70)
at com.moviejukebox.MovieJukebox.updateMovieData(MovieJukebox.java:1051)
at com.moviejukebox.MovieJukebox.access$100(MovieJukebox.java:80)
at com.moviejukebox.MovieJukebox$4.call(MovieJukebox.java:613)
at com.moviejukebox.MovieJukebox$4.call(MovieJukebox.java:600)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java

ProxySelector is an abstract class. Are you trying to instantiate it directly?

My CLASSPATH is set to
/usr/lib/jvm/jre-1.6.0-openjdk/lib.
don't think that should be in your CLASSPATH
try clearing the CLASSPATH and running it

Firstly, you shouldn't have to put "/usr/lib/jvm/jre-1.6.0-openjdk/lib" on your classpath. The "java" command should put all of the standard J2SE libraries on the bootclasspath without you doing anything.
Second, it would help if you gave us the full stacktrace, not just the exception message. I suspect that the real problem is that java.net.ProxySelector (or something it depends on) is failing during static initialization. But only a stacktrace would confirm that.

Since it's second result in google search on this error, I want to post this piece of code I found at some forum that helped me with the same exception. Cannot explain in details - it was just a quick test project for me, so I didn't have time for deeper investigation.
static {
try {
Class c = Class.forName("sun.net.spi.DefaultProxySelector");
if (c != null && ProxySelector.class.isAssignableFrom(c)) {
theProxySelector = (ProxySelector) c.newInstance();
}
} catch (Exception e) {
theProxySelector = null;
}
}