I'm trying to make an Ant build script for my project, which runs fine in Eclipse. When I try to run the exported jar:
java -verbose:class -jar MyProject.jar
I get an unexpected error:
java.lang.NoSuchMethodError: com.employer.MyInterface.myMethod()I
what's really weird about this is debugging attempts like these all appear to be producing expected output (both before the export and after):
System.out.println("1:" + (myObj instanceof MyClass));
System.out.println("2:" + (myObj instanceof MyInterface));
Class c = MyClass.class;
URL myClassURL = c.getProtectionDomain().getCodeSource()
.getLocation();
System.out.println("url: " + myClassURL);
try {
Method[] m = c.getDeclaredMethods();
for (int i = 0; i < m.length; i++) {
System.out.println(m[i].toString());
}
} catch (Throwable e) {
System.err.println(e);
}
System.out.println("gni2:" + myObj.myMethod());
where MyClass implements MyInterface. That is, I can see both the interface and the class in my jar file if I examine it using emacs, I see the class loader load each of them, I see myMethod in getDeclaredMethods, there's only one MyClass.class in the jar, etc.
I've changed this to an Answer your own question because I figured it out while typing up the question. Instead of deleting the question, here's the solution just in case it helps someone else.
The problem ended up being that 2 of the projects that my project depends on have overlapping package+class names. I think a colleague copied code from one project to the other at some point in the past and then only maintained one of them. Eclipse uses the first class it finds based the order in a Build Path setting, whereas Ant overwrites one class with the other based on the order in the build file (and the orders end up being reversed).
Related
I'm using Google OR-tools library (v6.4) for a project (though my question is not specific to this library). This consists of one jar, which has a few native dependencies (a bunch of ".so"/".dylib" object files, depending on the OS). This build for my project is being made on Ubuntu 14.04
The problem I'm facing: On trying to load a specific object file at runtime (using System.load()), I'm getting an UnsatisfiedLinkError with the message as "undefined symbol" (I've added the stacktrace below). However, I am loading the object file defining this symbol just before this, so I'm not sure why this error is being thrown.
I'm loading the dependencies in the following way: The object files are being packed into the jar created by Maven during build, and are being extracted and loaded (using System.load()) at runtime. The method for that is as follows:
public class EnvironmentUtils {
public static void loadResourceFromJar(String prefix, String suffix) {
String tempFilesDirectory = System.getProperty("java.io.tmpdir");
File tempFile = null;
try {
tempFile = new File(tempFilesDirectory + "/" + prefix + suffix);
tempFile.deleteOnExit();
try (final InputStream inputStream = EnvironmentUtils.class.getClassLoader().
getResourceAsStream(prefix+suffix)) {
if (inputStream == null) {
throw new RuntimeException(prefix + suffix + " was not found inside JAR.");
} else {
Files.copy(inputStream, tempFile.toPath(), StandardCopyOption.REPLACE_EXISTING);
}
}
System.load(tempFile.getAbsolutePath());
} catch (Exception e) {
//Log top 10 lines of stack trace
}
}
}
This method is being called inside a static block for all dependencies:
public class DummyClass {
static {
String sharedLibraryExtension = EnvironmentUtils.getSharedLibraryExtension(); //.so for linux, .dylib for Mac
String jniLibraryExtension = EnvironmentUtils.getJniLibraryExtension(); //.so for linux, .jnilib for Mac
EnvironmentUtils.loadResourceFromJar("libfap", sharedLibraryExtension);
EnvironmentUtils.loadResourceFromJar("libcvrptw_lib", sharedLibraryExtension);
EnvironmentUtils.loadResourceFromJar("libortools", sharedLibraryExtension);
EnvironmentUtils.loadResourceFromJar("libdimacs", sharedLibraryExtension);
EnvironmentUtils.loadResourceFromJar("libjniortools", jniLibraryExtension);
}
}
On running System.load() for libdimacs.so, an UnsatisfiedLinkError is thrown. Stacktrace:
java.lang.UnsatisfiedLinkError: /tmp/libdimacs.so: /tmp/libdimacs.so: undefined symbol: _ZN6google14FlagRegistererC1IbEEPKcS3_S3_PT_S5_
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1824)
at java.lang.Runtime.load0(Runtime.java:809)
at java.lang.System.load(System.java:1086)
at com.(PROJECT_NAME).utils.EnvironmentUtils.loadResourceFromJar(EnvironmentUtils.java:78)
at com.(PROJECT_NAME).DummyClass.<clinit>(DummyClass.java:28)
However, this symbol "_ZN6google14FlagRegistererC1IbEEPKcS3_S3_PT_S5_" is present in libortools.so, which is being loaded before libdimacs. I verified this by running the following command:
objdump -t (LIBRARY_PATH)/libortools.so | grep _ZN6google14FlagRegistererC1IbEEPKcS3_S3_PT_S5_
This gave me the following output:
0000000000ce12cc gw F .text 00000091 _ZN6google14FlagRegistererC1IbEEPKcS3_S3_PT_S5_
So it would seem that the symbol should have been defined at the time of the System.load() call, unless there was some issue in loading the containing object file. To check if the object file had been loaded correctly, I used the approach detailed in this solution. Apart from the class detailed in that answer, I added the following lines after System.load() call in EnvironmentUtils.loadResourceFromJar() to print the most recently loaded library name:
public class EnvironmentUtils {
public static void loadResourceFromJar(String prefix, String suffix) {
...
System.load(tempFile.getAbsolutePath());
final String[] libraries = ClassScope.getLoadedLibraries(ClassLoader.getSystemClassLoader());
System.out.println(libraries[libraries.length - 1]);
}
}
The output (till just before the UnsatisfiedLinkError) is as follows:
/tmp/libfap.so
/tmp/libcvrptw_lib.so
/tmp/libortools.so
So libortools.so seems to be loading correctly, which means the symbol should be loaded in memory. The exact same code is working perfectly with the corresponding Mac (".dylib") dependencies (Built on MacOS Sierra 10.12.5). Would appreciate any advice on resolving this. Thank you.
I'm apologize that the java artifact may be broken currently...
you can use c++filt to demangle the symbol ;)
c++filt _ZN6google14FlagRegistererC1IbEEPKcS3_S3_PT_S5_
google::FlagRegisterer::FlagRegisterer<bool>(char const*, char const*, char const*, bool*, bool*)
In fact gflag has recently change its namespace from google:: to gflags:: and glog or protobobuf? try to find the correct one and I guess it failed...
note: Still not completely sure whose is the bad guy who use the google:: namespace since libortools merge all its static dependencies but I guess now you understand the bug...
note2: I have a patch in mizux/shared branch https://github.com/google/or-tools/commit/805bc0600f4b5645114da704a0eb04a0b1058e28#diff-e8590fe6fb5044985c8bf8c9e73c0d88R114
warning: this branch is currently broken and not ready yet. I'm trying ,for unix, to move from static to dynamic dependencies, so I need to fix all rpath, transitives deps etc... and in the process I also had to fix this issue (that I didn't reproduced while using static dependencies)
If too long to finish (we should create a release 6.7.2 or 6.8 (i.e. new artifact) by the end of May 2018) which maybe only contains this fix and not my branch...
I am trying to start a new process with Runtime.exec() from my javafx application.
The new process is my javafx application (but in a new process, the "parent" one will still be open).
So I run javaw via the exec method and tell it my classpath. And here is my problem: the classpath contains whitespaces, so I need to quote every path. But I retrieve the path at runtime via java.class.path (since it is the same application).
Do I need to process the string and quote everything or is there an easy way to get this to work?
Here is the code:
public static void startInNewProcess() {
try {
Runtime r = Runtime.getRuntime();
File javaPath = new File(System.getProperty("java.home"), "bin/javaw");
File classPath = new File(System.getProperty("java.class.path"));
System.out.println("java loc: " + javaPath.toString());
System.out.println("classpath: " + classPath);
Process p = r.exec(javaPath.toString() + " -classpath " + classPath.getPath());
} catch (Exception e) {
e.printStackTrace();
}
}
I get the following string as classpath:
classpath: C:\Users\kwilhelm\git\ResourcePlaner\bin;C:\Program Files (x86)\eclipse\plugins\org.eclipse.fx.ide.css.jfx8_2.0.0.201506111511.jar;C:\Users\kwilhelm\git\ResourcePlaner\lib\itextpdf-5.5.6-javadoc.jar;C:\Users\kwilhelm\git\ResourcePlaner\lib\itextpdf-5.5.6-sources.jar;C:\Users\kwilhelm\git\ResourcePlaner\lib\itextpdf-5.5.6.jar;C:\Users\kwilhelm\git\ResourcePlaner\lib\controlsfx-8.40.9.jar
But javaw gives the error that it can't find mainclass "Files", so it can't handle the whitespace in the path.
So is there a way to get the classpath with quotes?
Is there a better solution?
Any help is apreciated
And here is my problem: the classpath contains whitespaces, so I need to quote every path.
Actually, no you don't.
And in fact, if you do attempt to quote every path, it is likely to mess up bigtime, because exec doesn't understand shell quoting.
What you actually need to do is this:
Process p = r.exec(new String[] {javaPath.toString(),
"-classpath",
classPath.getPath()});
This tells exec exactly where the boundaries of the command arguments are, so that it doesn't need to try (and fail) to figure it out for itself.
In fact, that still isn't right. You also need to add:
any other JVM options that the cloned instance needs,
a class name, and
any arguments required after the classname.
The classname is mandatory. (You left it out, and that is why the java command was outputting its help message!)
My current java project is using methods and variables from another project (same package). Right now the other project's jar has to be in the classpath to work correctly. My problem here is that the name of the jar can and will change because of increasing versions, and because you cannot use wildcards in the manifest classpath, it's impossible to add it to the classpath. So currently the only option of starting my application is using the -cp argument from the command line, manually adding the other jar my project depends on.
To improve this, I wanted to load the jar dynamically and read about using the ClassLoader. I read a lot of examples for it, however I still don't understand how to use it in my case.
What I want is it to load a jar file, lets say, myDependency-2.4.1-SNAPSHOT.jar, but it should be able to just search for a jar file starting with myDependency- because as I already said the version number can change at anytime. Then I should just be able to use it's methods and variables in my Code just like I do now (like ClassInMyDependency.exampleMethod()).
Can anyone help me with this, as I've been searching the web for a few hours now and still don't get how to use the ClassLoader to do what I just explained.
Many thanks in advance
(Applies to Java version 8 and earlier).
Indeed this is occasionally necessary. This is how I do this in production. It uses reflection to circumvent the encapsulation of addURL in the system class loader.
/*
* Adds the supplied Java Archive library to java.class.path. This is benign
* if the library is already loaded.
*/
public static synchronized void loadLibrary(java.io.File jar) throws MyException
{
try {
/*We are using reflection here to circumvent encapsulation; addURL is not public*/
java.net.URLClassLoader loader = (java.net.URLClassLoader)ClassLoader.getSystemClassLoader();
java.net.URL url = jar.toURI().toURL();
/*Disallow if already loaded*/
for (java.net.URL it : java.util.Arrays.asList(loader.getURLs())){
if (it.equals(url)){
return;
}
}
java.lang.reflect.Method method = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{java.net.URL.class});
method.setAccessible(true); /*promote the method to public access*/
method.invoke(loader, new Object[]{url});
} catch (final java.lang.NoSuchMethodException |
java.lang.IllegalAccessException |
java.net.MalformedURLException |
java.lang.reflect.InvocationTargetException e){
throw new MyException(e);
}
}
I needed to load a jar file at runtime for both java 8 and java 9+. Here is the method to do it (using Spring Boot 1.5.2 if it may relate).
public static synchronized void loadLibrary(java.io.File jar) {
try {
java.net.URL url = jar.toURI().toURL();
java.lang.reflect.Method method = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{java.net.URL.class});
method.setAccessible(true); /*promote the method to public access*/
method.invoke(Thread.currentThread().getContextClassLoader(), new Object[]{url});
} catch (Exception ex) {
throw new RuntimeException("Cannot load library from jar file '" + jar.getAbsolutePath() + "'. Reason: " + ex.getMessage());
}
}
I am starting to switch from a well-known Java build system to Gradle to build all my projects, and after barely two hours into it I have already been able to publish a new version of one of my projects without a problem -- a breeze.
But now I encounter a difficulty. In short, I need to replicate the functionality of this Maven plugin which generates the necessary files for a ServiceLoader-enabled service.
In short: given a base class foo.bar.MyClass, it generates a file named META-INF/services/foo.bar.MyClass whose content is a set of classes in the current project which implement that interface/extend that base class. Such a file would look like:
com.mycompany.MyClassImpl
org.othercompany.MyClassImpl
In order to do this, it uses I don't know what as a classloader, loads the Class objects for com.myCompany.MyClassImpl or whatever and checks whether this class implements the wanted interface.
I am trying to do the same in Gradle. Hours of googling led me to this plugin, but after discussing with its author a little, it appears this plugin is able to merge such files, not create them. So, I have to do that myself...
And I am a real beginner both with Gradle and Groovy, which does not help! Here is my current code, link to the full build.gradle here; output (which I managed to get somehow; doesn't work from a clean dir) shown below (and please bear with me... I do Java, and I am final happy; Groovy is totally new to me):
/*
* TEST CODE
*/
final int CLASS_SUFFIX = ".class".length();
final URLClassLoader classLoader = this.class.classLoader;
// Where the classes are: OK
final File classesDir = sourceSets.main.output.classesDir;
final String basePath = classesDir.getCanonicalPath();
// Add them to the classloader: OK
classLoader.addURL(classesDir.toURI().toURL())
// Recurse over each file
classesDir.eachFileRecurse {
// You "return" from a closure, you do not "continue"...
if (!isPotentialClass(it))
return;
// Transform into a class name
final String path = it.getAbsolutePath();
final String name = path.substring(basePath.length() + 1);
final String className = name.substring(0, name.length() - CLASS_SUFFIX)
.replace('/', '.');
// Try and load it
try {
classLoader.loadClass(className);
println(className);
} catch (NoClassDefFoundError ignored) {
println("failed to load " + className + ": " + ignored);
}
}
boolean isPotentialClass(final File file)
{
return file.isFile() && file.name.endsWith(".class")
}
The output:
com.github.fge.msgsimple.InternalBundle
failed to load com.github.fge.msgsimple.bundle.MessageBundle: java.lang.NoClassDefFoundError: com/github/fge/Frozen
failed to load com.github.fge.msgsimple.bundle.MessageBundleBuilder: java.lang.NoClassDefFoundError: com/github/fge/Thawed
com.github.fge.msgsimple.bundle.PropertiesBundle$1
com.github.fge.msgsimple.bundle.PropertiesBundle
com.github.fge.msgsimple.provider.MessageSourceProvider
com.github.fge.msgsimple.provider.LoadingMessageSourceProvider$1
com.github.fge.msgsimple.provider.LoadingMessageSourceProvider$2
com.github.fge.msgsimple.provider.LoadingMessageSourceProvider$3
com.github.fge.msgsimple.provider.LoadingMessageSourceProvider$Builder
com.github.fge.msgsimple.provider.LoadingMessageSourceProvider
com.github.fge.msgsimple.provider.MessageSourceLoader
com.github.fge.msgsimple.provider.StaticMessageSourceProvider$Builder
com.github.fge.msgsimple.provider.StaticMessageSourceProvider$1
com.github.fge.msgsimple.provider.StaticMessageSourceProvider
com.github.fge.msgsimple.source.MessageSource
com.github.fge.msgsimple.source.MapMessageSource$Builder
com.github.fge.msgsimple.source.MapMessageSource$1
com.github.fge.msgsimple.source.MapMessageSource
com.github.fge.msgsimple.source.PropertiesMessageSource
com.github.fge.msgsimple.locale.LocaleUtils
com.github.fge.msgsimple.serviceloader.MessageBundleFactory
com.github.fge.msgsimple.serviceloader.MessageBundleProvider
:compileJava UP-TO-DATE
The problem is in the two first lines: Frozen and Thawed are in a different project, which is in the compile classpath but not in the classpath I managed to grab so far... As such, these classes cannot even load.
How do I modify that code so as to have the full compile classpath availabe? Is my first question. Second question: how do I plug that code, when it works, into the build process?
Here are some hints:
Create a new URLClassLoader, rather than reusing an existing one.
Initialize the class loader with sourceSets.main.compileClasspath (which is an Iterable<File>) rather than classesDir.
Turn the code into a Gradle task class. For more information, see "Writing a simple task class" in the Gradle User Guide.
Ideally, you'd use a library like ASM to analyze the code, rather than using a class loader. To avoid the case where you cannot load a class because it internally references a class that's not on the compile class path, you may want to initialize the class loader with sourceSets.main.runtimeClasspath instead.
Im using Java SDK 1.7 on Windows 7 via cmd.exe . Up until a few hours ago everything was working correctly when suddenly I was unable to run my compiled class files, consistently presented with the error in the title.
I seem to be able to compile my My.java file however I am unable to run the resulting class file (My.class). I am constantly given the error "Error: Could not find or load main class My.class". I have tried this with multiple other class files all resulting in the same problem.
My 'Path' environment variable is set to "C:\Program Files (x86)\Java\jdk1.7.0_05\bin" if you were wondering
I have tried reinstalling, creating and setting a classpath variable (no luck), and even directly using the
java -cp . My.class
command.
I have tried these posts all to no avail, hence why I'm posting:
Error: Could not find or load main class
Error: Could not find or load main class- Novice
Could not find or load main class
Java 1.7.0_03 Error: Could not find or load main class
If it makes any difference my code is :
import javax.swing.JOptionPane;
class My {
public static void main(String[] args) {
final double x = 3.2;
int i = (int)x;
double m = 0;
if (x < 4) {
String saySomething = JOptionPane.showInputDialog(i);
System.out.println(saySomething);
}
else {
String saySomething = JOptionPane.showInputDialog(i);
System.out.println("Hello World");
}
while (m < 10) {
System.out.print(" While Loop ");
m++;
};
for (i=1; i < 10; i++) {
System.out.println("For Loop");
};
}
}
You should specify the classname instead of the file of the class to load. The difference is a simple matter of removing the .class extension.
I would use an IDE and you shouldn't get these issues. Compile and run is just a click of the mouse.
BTW to run your program from the command line
java -cp . My
You don't add .class
Position yourself in a directory of your project (you need to have src and bin directories there, assuming you keep sources in src and binaries in bin)
java -cp bin My
I myself was facing the same problem. It was happening because I was being remiss in typing the name of the class properly. In my instance, I was typing
java doubler
instead of
java Doubler