I am trying to run a java based tool using a command line syntax as the following: java -cp archive.jar archiveFolder.theMainClassName.Although the class I am searching for, a main class, "theMainClassName" is in the archive.jar and in the archiveFolder given at input, I keep getting the error that my class is not seen. Does anybody have any ideas concerning this problem? Thank you in advance
Here's a concrete example of what does work, so you can compare your own situation.
Take this code and put it anywhere, in a file called MainClass.java. (I've assumed a directory called src later. Normally you'd arrange the source to match the package, of course.)
package archiveFolder;
public class MainClass
{
public static void main(String[] args)
{
System.out.println("I'm MainClass");
}
}
Then run each of these commands:
# Compile the source
javac -d . src/MainClass.java
# Build the jar file
jar cf archive.jar archiveFolder
# Remove the unpackaged binary, to prove it's not being used
rm -rf archiveFolder # Or rmdir /s /q archiveFolder on Windows
# Execute the class
java -cp archive.jar achiveFolder.MainClass
The result:
I'm MainClass
How are you building your jar file? Is the code in the appropriate package?
Does theMainClassName class have the following package line at the top:
package archiveFolder
You need the class file to be in the same directory structure as the declared package. So if you had something like:
org/jc/tests/TestClass.class
its source file would have to look like this:
package org.jc.tests;
public class TestClass {
public static void main(String[] args) {
System.out.printf("This is a test class!\n");
}
}
Then you could use the following to create the jar file and run it from the command line (assuming the current directory is at the top level, just above org):
$ jar -cf testJar.jar org/jc/tests/*.class
$ java -cp testJar.jar org.jc.tests.TestClass
Perhaps with java -jar archive.jar?
Of course, it supposes the manifest points to the right class...
You should give the exact message you got, it might shed more light.
EDIT: See Working with Manifest Files: The Basics for information on setting the application entry point (Main class) in your jar manifest file.
Usually this happens when a dependent class (static member) is not found - like this, using log4j:
public class MyClass {
private static Logger log = Logger.getLogger("com.example");
}
The reason is that the initialization of such a static member can be understood as part of the class loading - errors causing the class not to be available (loadable), resulting in the error you described.
Static constructors are another possible reason:
public class MyClass {
static {
// <b>any</b> error caused here will cause the class to
// not be loaded. Demonstrating with stupid typecast.
Object o = new String();
Integer i = (Integer) o;
}
}
I think others have covered some common stuff here. I'd jar tf the jar and make sure the class is listed. I'd also double-check that the class is public and the method is "public static void main(String[] arg)".
Related
I'm putting together some (Python) scripts to help me automate some of my grading of hundreds of simple student Java repos. Not all of them have the same directory structure or naming of files. I've traversed them all and compiled them and if I make assumptions I can run them and test them, etc. But I'd like to know if there's a way I could find the "main" .class that has the main() method in it, so that I don't have to make assumptions about their file naming (which wouldn't work all the time anyway).
I'm aware of reflection, so yes, I know I could write another simple helper Java program to assist me in identifying it myself. But I was wondering if anything already exists (java command line option, tool from the jdk, etc.) to test a .class file to see if it is has the main() method in it.
I was wondering if anything already exists (java command line option, tool from the JDK, etc.) to test a .class file to see if it is has the main() method in it.
There is no tool or option in Java SE that does that directly.
I know I could write another simple helper Java program to assist me ...
It would be simpler to write a shell script that iterates a file tree, finds .class files, calls javap on them, and greps for a method with the appropriate main method signature.
Or you could do something similar on the source code tree.
(In retrospect, you should have set the assignment requirements so that the students had to use a specified class and package name for the class containing their main method. But it is too late for that now ...)
In the C++ days, distributing the headers files to use a shared object file was a big deal. People would get one or the other without both, and there was always the chance you'd get mis-matched versions.
Java fixed that with javap which prints the methods (and other major interfaces) of a compiled .class file.
To test if a class file has a main, run
javap SomeFile.class
which will list all public interfaces. Within that list, see if it has the "main entry point"
public static void main(java.lang.String[])
Now to handle this in mass, simply create a Python script that:
Locates all the relevant classes.
Runs javap on the class.
Reads the output for a method that matches (at the beginning, as there can be a variable number of Exceptions at the end "public static void main(java.lang.String[])
And you'll find all entry points.
Keep in mind that sometimes a single library or JAR file has many entry points, some of which are not intended as the primary entry point.
Well simply calling java -cp . <file> will either completely blow out if the class doesn't have a main method or will run the relevant code. Now, if the code fails to run right and errors out you may see it as the same effect as not having a main method.
public class HasMain {
public static void main(String[] args) {
System.out.println("Hit main");
}
}
public class HasDoIt {
public static void doIt(String[] args) {
System.out.println("Hit doIt");
}
}
public class WillBlowUp {
public static void main(String[] args) {
System.out.println("Hit blowUp");
throw new IllegalStateException("oops");
}
}
Using PowerShell:
PS D:\Development\sandbox> javac HasMain.java
PS D:\Development\sandbox> javac HasDoIt.java
PS D:\Development\sandbox> javac WillBlowUp.java
PS D:\Development\sandbox> java -cp . HasMain
Hit main
PS D:\Development\sandbox> $?
True
PS D:\Development\sandbox> java -cp . HasDoIt
Error: Main method not found in class HasDoIt, please define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
PS D:\Development\sandbox> $?
False
PS D:\Development\sandbox> java -cp . WillBlowUp
Hit blowUp
Exception in thread "main" java.lang.IllegalStateException: oops
at WillBlowUp.main(WillBlowUp.java:4)
PS D:\Development\sandbox> $?
False
So simply checking return values could be a quick way to test if the class has what you want, albeit any exit(1) type return will throw a false-false
I have been trying to run Java with command line arguments, but for some reason the class can not be found. I am very certain the directory is correct. Is there any way to fix this?
CLDemo.java file
public class Demo {
public static void main(String[] args) {
System.out.print("It works!!!");
}
}
You need to do cd out\production before java CLDemo.
The default compile output of IntelliJ IDEA is under out\production folder, and Java needs to run at the corresponding package (folder) of your compile output.
I am using spring framework.
I have an interface And a class In the same package.
My interface is
package soundsystem;
public interface CompactDisc{
void play();
}
My class is
package soundsystem;
import org.springframework.stereotype.*;
#Component
public class Sgtpeppers implements CompactDisc{
private String title = "A Movie";
private String artist = "The Movie is Being Played";
public void play(){
System.out.println("The CD is Played \n"+title+"\n"+artist);
}
}
On Compilation it gives me this error
Sgtpeppers.java:5: error: cannot find symbol
public class Sgtpeppers implements CompactDisc{
^
symbol: class CompactDisc
1 error
The Interface is Compiled First and the .class file is also stored the soundsystem package.
I Think there is something wrong with the javac Command.
The command i used is
javac -d . -cp "spring-framework-5.0.1.RELEASE/libs/*" Sgtpeppers.java
Is this because i changed the classpath?
1) As a general rule, to compile classes, don't perform the task from the directory of a specific package.
Instead, use the root of the application source code as base to run the javac/java command.
By following this simple rule :
2)To compile all classes located in a same package, just specify the package as "source files" :
javac soundsystem/*.java
3)To compile a specific class depending on another compiled class of your source code (in the same package or not), you don't need to specify "." (that represents the current directory) in the classpath as it is the default value.
Java documentation states indeed that :
The default class path is the current directory. Setting the CLASSPATH
variable or using the -classpath command-line option overrides that
default, so if you want to include the current directory in the search
path, then you must include a dot (.) in the new settings.
But if you explicitly set the classpath with another value, the default value is not more used.
And here you did it :
javac -d . -cp "spring-framework-5.0.1.RELEASE/libs/*" Sgtpeppers.java
So you should add explicitly "." in the classpath too.
From the source code root, it would give on Windows :
javac -d . -cp ".;spring-framework-5.0.1.RELEASE/libs/*"
soundsystem/Sgtpeppers.java
For Unix, separator char is :, so it would give :
javac -d . -cp ".:spring-framework-5.0.1.RELEASE/libs/*"
soundsystem/Sgtpeppers.java
I am trying to call an external Java function from Haxe using "extern".
Haxe Code :
extern class Ext
{
public static function test():String;
}
class Sample
{
public static function main()
{
trace(Ext.test());
}
}
Java Code :
public class Ext
{
public static String test()
{
return "Hello";
}
}
Both Sample.hx and Ext.java files are in the same folder.
When I try to execute haxe -main Sample -java Sample, I get the following error.
C:\Users\ila5\Desktop\CPP>haxe -main Sample -java Sample
haxelib run hxjava hxjava_build.txt --haxe-version 3201 --feature-level 1
javac.exe "-sourcepath" "src" "-d" "obj" "-g:none" "#cmd"
src\haxe\root\Sample.java:33: error: cannot find symbol
haxe.Log.trace.__hx_invoke2_o(0.0, haxe.root.Ext.test(), 0.0, new haxe.lang.DynamicObject(new java.lang.String[]{"className", "fileName", "methodName"}, new java.lang.Object[]{"Sample", "Sample.hx", "main"}, new java.lang.String[]{"lineNumber"}, new double[]{((double) (((double) (10) )) )}));
^
symbol: class Ext
location: package haxe.root
1 error
Compilation error
Native compilation failed
Error: Build failed
I would like to understand why the build failed. Any ideas?
I am not sure you might need to reference your Java code with -lib or something else?
But generally with Java target it's much simpler to just use a jar file. By typing haxe --help you will see the relevant command listed, I have never had a need to hand write externs for the Java target.
-java-lib <file> : add an external JAR or class directory library
The reason it fails is explained here
https://groups.google.com/forum/#!topic/haxelang/EHeoGN_Ppvg
I tried setting up with class paths and various options but did not get a solution, I think it's just a bit fiddly to do externs on the java target by hand. Really it's better to use Java compiler to create jars and let haxe auto generate the externs unless you get an issue then report it to hxJava repository.
Use -java-lib.
# build.sh
haxe Main.hx -main Main -java-lib javalib/ -java out
,
// ./Main.hx
import external.*;
class Main {
public static function main() {
trace(external.ExternalClass.myFunction());
}
}
,
// ./javalib/external/ExternalClass.java
package external;
public class ExternalClass {
public static String myFunction() {
return "External Java function";
}
}
,
./javalib/external/ExternalClass.class is the output of javac ExternalClass.java
I have built a DLL which I am attempting to wrap Java code with, however I am having some troubles with running my Java program. I wrote a simple test DLL and Java program and am producing the same error, and although there are plenty of resources regarding NoClassDefFoundError online I can't seem to solve mine with any troubleshooting methods.
Here is my D:\Test1.Java file
public class Test1 {
static {
//System.loadLibrary("HeyLand");
System.load("D://HeyLand.dll");
}
public native void displayHeyLand();
public static void main (String[] args) {
Test1 t = new Test1();
t.displayHeyLand();
}
}
After compiling, attempting to run D:\Test1.classresults in the following:
D:\>java Test1.class
Exception in thread "main" java.lang.NoClassDefFoundError: Test1.class
Caused by: java.lang.ClassNotFoundException: Test1.class
at java.net.URLClassLoader.findClass(URLClassLoader.java:434)
at java.lang.ClassLoader.loadClass(ClassLoader.java:660)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:358)
at java.lang.ClassLoader.loadClass(ClassLoader.java:626)
Could not find the main class: Test1.class. Program will exit.
Why I am stumped :
1. I have set my classpath to be D:\, so I believe my class definition would be in the classpath, and I do not see how my compile-time and run-time classpaths could be any different.
2. I don't see how this could have anything to do with static initialization, and I believe the exception would look different.
Perhaps I'm just missing something incredibly simple, I am very newbie with Java.
Any help is greatly appreciated!
The classpath environmental variable is taking precedence over that in the java run command. You need to specify the class location (as well as removing the .class file extension)
java -cp . Test1
Java normal syntax for executing class file is
Java [<options>....} <class-name> [<arguments>....]
For example
java com.package.name.Test1
here how compiler works
1. Compiler search for complete class name
2. Load that class
3. check for main method - in the same class
4. Call main method with passed arguments in command line string.
Now following are the possibilities why your class may not found main method.
1 - forgot to include package name
I am new developer in java but I found when I run application using eclips or intellJ editor it gives different path and package name and execute code as I noticed it on command line edior. So make sure you are including package name
For example:
java com.package.name.Test1 instead of
java Test1
2. File name or pathname rather then class name
As I noticed output file is in different location. That why class file path was different.
java Test1.class
java com/package/name/Test1.class
3. Typo
also I noticed you are using
static {
//System.loadLibrary("HeyLand");
System.load("D://HeyLand.dll");
}
Is this function ? or constructor? If it is function then where is name of the function? You cant write code without any reference in classs