I have a java program which is a compiler and executor for Jasper Reports and is called via shell script on our reports server.
I just fixed a bug caused by a missing dependancy, but it took me a while to figure out what was going wrong. Normally, problems caused by the compile process are captured, recorded to a log file and emailed to the relevant person. As this was a NoClassDefFoundError, it basically exited the program and failed in a silent manner from the users perspective.
Is there any way for me to capture errors like this one so that they can also be emailed away? I have the authority to modify the executing shell script.
Typically errors are not caught by application code and are thrown to JVM level where they are printed to STDERR. So, your way to track this error is to redirect STDERR to file:
java -cp YourMain 1>stdout.log 2>stderr.log
You can also put both STDOUT and STDERR together:
java -cp YourMain 1>&2 2>wholelog.log
There is a lot of reference about stream redirection in web. You can take a look there if my examples do not satisfy you. And it a depends on your OS.
Just can catch the error i.e.
try {
numericDefinition = new net.sf.cb2xml.def.BasicNumericDefinition(
binName, binarySizes, SynchronizeAt, usePositive, floatSynchronize, doubleSynchronize
);
} catch (NoClassDefFoundError e) {
System.out.println("Class Not Found: " + e.getMessage());
}
You do need to be very careful of your coding though, it is easy to get NoClassDefFoundError thrown at class initialisation time and not get into to the try .. catch block.
The NoClassDefFoundError will be thrown the first time a class is refereneced which could be when could when a class uses a class which uses a class which uses a class ... which uses a class that references a class that does not exist.
The following may fail with NoClassDefFoundError at class initialization because of the import.
import net.sf.cb2xml.def.BasicNumericDefinition; // could cause the NoClassDefFoundError
...........
try {
numericDefinition = new BasicNumericDefinition(
binName, binarySizes, SynchronizeAt, usePositive, floatSynchronize, doubleSynchronize
);
} catch (NoClassDefFoundError e) {
System.out.println("Class Not Found: " + e.getMessage());
}
Related
My code is giving an error below;
Exception in thread "main" java.lang.NoSuchMethodError:
com/myApp/Client.cypherCBC(Ljava/lang/String;)Ljava/lang/String;
But it's working fine in an another local environment. My code so far is below;
try {
System.out.println("Encrypted CBC passwd : "
+ Client.cypherCBC("CypherThePassword"));
} catch (Exception e) {
e.printStackTrace();
}
This is due to a run-time JAR or class mismatch. the "Client" class which was there at the time you compile your application has a static method "cypherCBC" which gets String parameter, but at run-time class loader has loaded the "Client" class which doesn't have that kind of method (same name with same signature).
if you can debug the application at runtime, put a break-point at the line which exception was thrown, then try to evaluate following expression,
Client.class.getResource("Client.class")
, then you can find where the class has been leaded from, then you can decompile and try to troubleshoot the issue.
I got the same error while running a web application in Weblogic.
The reason for this error is there are two versions of classes are in the environment.To fix this you have to figure out which .class is using at the run time.
I used following to identify which class is loaded at run time.
-verbose:class
There is a duplicate class on your classpath.
So, That is why JVM is getting confused that which one needs to pick because both classes have a same method with a different signature that you are trying to call.
Summary: Loading a jar from a running Java program causes a NoClassDefFoundError caused by a ClassNotFoundException caused by inter-class dependencies (e.g. import statements). How can I get around it?
The problem in more detail:
I am attempting to programmatically load a jar file -- let's call it "Server" -- into the Java Virtual Machine through my own Java program -- let's call it "ServerAPI" -- and use extension and some other tricks to modify the behavior of and interact with Server. ServerAPI depends on Server, but if Server is not present, ServerAPI still has to be able to run and download Server from a website.
To avoid errors caused by ServerAPI loading without satisfying its dependencies from Server, I have made a launcher -- let's call it "Launcher" -- that is intended to download Server and set up ServerAPI as necessary, then load Server and ServerAPI, then run ServerAPI.
However, when I attempt to load jars from Launcher, I get errors caused because the ClassLoaders are unable to resolve the other classes in the file that the class it's loading depends on. In short, if I try to load Class A, it will throw an error if A imports B because I haven't loaded B yet. However, if B also imports A, I'm stuck because I can't figure out how to load two classes at once or how to load a class without the JVM running its validation.
Why all the restrictions have led me to this problem:
I am attempting to modify and add to the behavior of Server, but for complicated legal reasons, I cannot modify the program directly, so I have created ServerAPI that depends on and can tweak the behavior of Server from the outside.
However, for more complicated legal reasons, Server and ServerAPI cannot simply be downloaded together. Launcher (see above) has to be downloaded with ServerAPI, then Launcher needs to download Server. Finally, ServerAPI can be run using Server as a dependency. That's why this problem is so complex.
This problem will also apply to a later part of the project, which will involve a plugin-based API interface that needs to be able to load and unload plugins from jar files while running.
Research I have already done on this problem:
I have read through and failed to be helped by:
this question, which only addresses the issue of a single method and does not address inter-class dependency errors;
this question, which will not work because I cannot shut down and restart the program every time a jar is loaded or unloaded (mainly for the plugin part I briefly mentioned);
this question, which only works for situations where the dependencies are present when the program starts;
this question, which has the same problem as #2;
this question, which has the same problem as #3;
this article, from which I learned about the hidden loadClass(String, boolean) method, but trying with true and false values did not help;
this question, which has the same problem as #1;
and more. Nothing has worked.
//EDIT:
Attempts I have made so far:
I have tried using URLClassLoaders to load the jar using the JarEntries from the JarFile similar to this question. I tried this both by using and calling a URLClassLoader's loadClass(String) method and by making a class that extends URLClassLoader so that I could utilize loadClass(String, boolean resolve) to try to force the ClassLoader to resolve all the classes it loads. Both ways, I got this same error:
I couldn't find the class in the JarEntry!
entry name="org/apache/logging/log4j/core/appender/db/jpa/converter/ContextMapAttributeConverter.class"
class name="org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapAttributeConverter"
java.lang.NoClassDefFoundError: javax/persistence/AttributeConverter
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:455)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:367)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at Corundum.launcher.CorundumClassLoader.load(CorundumClassLoader.java:52)
at Corundum.launcher.CorundumLauncher.main(CorundumLauncher.java:47)
Caused by: java.lang.ClassNotFoundException: javax.persistence.AttributeConverter
at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 12 more
//END EDIT
//EDIT 2:
Here is a sample of the code that I used to load a class while trying to resolve it. This was inside a class that I made that extends URLClassLoader. On the line beginning with Class<?> clazz = loadClass(, I have tried using true and false as the boolean argument; both attempts resulted in the same error above.
public boolean load(ClassLoadAction class_action, FinishLoadAction end_action) {
// establish the jar associated with this ClassLoader as a JarFile
JarFile jar;
try {
jar = new JarFile(jar_path);
} catch (IOException exception) {
System.out.println("There was a problem loading the " + jar_path + "!");
exception.printStackTrace();
return false;
}
// load each class in the JarFile through its JarEntries
Enumeration<JarEntry> entries = jar.entries();
if (entries.hasMoreElements())
for (JarEntry entry = entries.nextElement(); entries.hasMoreElements(); entry = entries.nextElement())
if (!entry.isDirectory() && entry.getName().endsWith(".class"))
try {
/* this "true" in the line below is the whole reason this class is necessary; it makes the URLClassLoader this class extends "resolve" the class,
* meaning it also loads all the classes this class refers to */
Class<?> clazz = loadClass(entry.getName().substring(0, entry.getName().length() - 6).replaceAll("/", "."), true);
class_action.onClassLoad(this, jar, clazz, end_action);
} catch (ClassNotFoundException | NoClassDefFoundError exception) {
try {
close();
} catch (IOException exception2) {
System.out.println("There was a problem closing the URLClassLoader after the following " + exception2.getClass().getSimpleName() + "!");
exception.printStackTrace();
}
try {
jar.close();
} catch (IOException exception2) {
System.out.println("There was a problem closing the JarFile after the following ClassNotFoundException!");
exception.printStackTrace();
}
System.out.println("I couldn't find the class in the JarEntry!\nentry name=\"" + entry.getName() + "\"\nclass name=\""
+ entry.getName().substring(0, entry.getName().length() - 6).replaceAll("/", ".") + "\"");
exception.printStackTrace();
return false;
}
// once all the classes are loaded, close the ClassLoader and run the plugin's main class(es) load() method(s)
try {
jar.close();
} catch (IOException exception) {
System.out.println("I couldn't close the URLClassLoader used to load this jar file!\njar file=\"" + jar.getName() + "\"");
exception.printStackTrace();
return false;
}
end_action.onFinishLoad(this, null, class_action);
System.out.println("loaded " + jar_path);
// TODO TEST
try {
close();
} catch (IOException exception) {
System.out.println("I couldn't close the URLClassLoader used to load this jar file!\njar file=\"" + jar_path + "\"");
exception.printStackTrace();
return false;
}
return true;
}
//END EDIT 2
I realize that there must be a simple solution to this, but for the life of me I cannot seem to find it. Any help would make me eternally grateful. Thank you.
Embarassingly, I found that the answer was that the error message was telling the truth. javax.persistence.AttributeConverter, the class that the loader was claiming was not present, was not in the jar.
I fixed the issue by loading only the main class and the ClassLoader all references classes, essentially loading all the classes in the jar that are used in the program, which is all I need.
Now, I could have sworn that I checked for this before and found that class; I figure I must have actually checked the Apache open source repository for the class rather than the actual Server when I checked that. I can't remember.
In any case, AttributeConverter is missing. I don't know how or why they managed to compile a jar with missing dependencies, but I guess their main processes never use that part of the code, so it never threw errors.
I'm sorry to have wasted everyone's time...including my own. I have been stuck on this problem for a while now.
Moral of this story:
If you're trying to load an executable jar, don't bother loading all the classes in a jar unless you actually have to. Just load the main class; that will load everything the program needs to run.
//EDIT:
I have now started having the same error, but it does not appear until I attempt to call a method from a loaded class. The question is apparently still open. Please downvote and disregard this answer.
I am getting a compilation error to my code in StateMachine.java class in a Codename One project:
error: cannot find symbol
getRuntime().
symbol: method exec(String)
location: class Runtime
the full statement is;
try {
Runtime.getRuntime().exec("cmd.exe /c start dir ");
} catch (IOException e) {
System.out.println("Print this");
}
and is running fine in a plain Java project.
What am i missing?
//===============================================
ADD: ..and to
try {
Process p = Runtime.getRuntime().exec("cmd /c dir A*");
} catch (IOException e) {
System.out.println("Print this");
}
I'm also getting an compiler error saying
error: cannot find symbol
Process
symbol: class Process
location: class StateMachine
seems to be blocking the OS/backend reach-- but how, what's the "mentality" behind?
We don't support Runtime.exec and it will obviously not work on a mobile phone where you have neither cmd nor access to other processes running on the device due to process isolation. E.g. iOS maintains a private file system per process so sharing files becomes a problem.
You can use Display.getInstance().execute() to run things like the browser but obviously cmd will never work on a device regardless of the technology you choose.
I am trying to set up sphinx, i am following this tutorial.
When i copy and paste the code of hello world from "sphinx4-0.1alpha-src"; i get an error on line:
} catch (InstantiationException e) {
Error says Unreachable catch block for InstantiationException.
This exception is never thrown from the try statement body.
I mean i have not written this code, and even in the video there is this line but no error comes up. I know that it is not a big deal and if i run the program and click avoid the error, it runs properly.
[I am using Eclipse "eclipse-standard-kepler-SR1-win32-x86_64" on a windows 8 machine]
List of files in that folder:
build.xml
hello.gram
helloworld.config.xml
HelloWorld.java
helloworld.Manifest
README.html
Ques - why do i see this error at all?
(I think there is not a problem in the code as it is alpha edition of sphnix)
It could be because this exception is never declared to be thrown from your try{} block, just remove last catch block
Please, consider the following snippet which is being run from Eclipse.
Even though the external jar file does not exist no Exception is thrown and process is not null. Why is it so?
try {
Process process = Runtime.getRuntime().exec("java -jar NonExisting.jar");
if (process == null)
System.out.println("process = null");
else
System.out.println(process);
} catch (IOException e) {
System.err.println(e);
}
It prints
java.lang.ProcessImpl#1a4d139
If I run it manully from command line then there is an error:
C:\Users\workspace\Project\src>java -jar NonExisting.jar
Error: Unable to access jarfile NonExisting.jar
Process.waitFor() gives you the exit code of the spawned process, and is likely returning a non-zero (i.e. error) value. You should check this value, and collect the stdout/err at the same time (see here for more info). stderr will likely report an error.
All you're currently doing is confirming that the process has been invoked. The process then tries/fails to load the jar file, and that's when it exists and reports an error.
The process was created and finished. You should check the return value of the Process object. An exception will be thrown if there is a problem with the creation of the new process, so here you don't get an exception.
Whoa, this is quite ugly :-) Why dont you start the Main Methd of the jar in a new thread? Well you should check the exit status of the process:
http://en.wikipedia.org/wiki/Exit_status
http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/Process.htm
You are basically forking the process so you cannot get exceptions or anything java specific from this, you need to deal with the new process, like any other OS specific app.