What are the possible causes of a "java.lang.Error: Unresolved compilation problem"?
Additional information:
I have seen this after copying a set of updated JAR files from a build on top of the existing JARs and restarting the application. The JARs are built using a Maven build process.
I would expect to see LinkageErrors or ClassNotFound errors if interfaces changed. The above error hints at some lower level problem.
A clean rebuild and redeployment fixed the problem. Could this error indicate a corrupted JAR?
(rewritten 2015-07-28)
Summary: Eclipse had compiled some or all of the classes, and its compiler is more tolerant of errors.
Long explanation:
The default behavior of Eclipse when compiling code with errors in it, is to generate byte code throwing the exception you see, allowing the program to be run. This is possible as Eclipse uses its own built-in compiler, instead of javac from the JDK which Apache Maven uses, and which fails the compilation completely for errors. If you use Eclipse on a Maven project which you are also working with using the command line mvn command, this may happen.
The cure is to fix the errors and recompile, before running again.
The setting is marked with a red box in this screendump:
try to clean the eclipse project
you just try to clean maven by command
mvn clean
and after that following command
mvn eclipse:clean eclipse:eclipse
and rebuild your project....
Your compiled classes may need to be recompiled from the source with the new jars.
Try running "mvn clean" and then rebuild
The major part is correctly answered by Thorbjørn Ravn Andersen.
This answer tries to shed light on the remaining question: how could the class file with errors end up in the jar?
Each build (Maven & javac or Eclipse) signals in its specific way when it hits a compile error, and will refuse to create a Jar file from it (or at least prominently alert you). The most likely cause for silently getting class files with errors into a jar is by concurrent operation of Maven and Eclipse.
If you have Eclipse open while running a mvn build, you should disable Project > Build Automatically until mvn completes.
EDIT:
Let's try to split the riddle into three parts:
(1) What is the meaning of "java.lang.Error: Unresolved compilation
problem"
This has been explained by Thorbjørn Ravn Andersen. There is no doubt that Eclipse found an error at compile time.
(2) How can an eclipse-compiled class file end up in jar file created
by maven (assuming maven is not configured to used ecj for
compilation)?
This could happen either by invoking Maven with no or incomplete cleaning. Or, an automatic Eclipse build could react to changes in the filesystem (done by Maven) and re-compile a class, before Maven proceeds to collect class files into the jar (this is what I meant by "concurrent operation" in my original answer).
(3) How come there is a compile error, but mvn clean succeeds?
Again several possibilities: (a) compilers don't agree whether or not the source code is legal, or (b) Eclipse compiles with broken settings like incomplete classpath, wrong Java compliance etc. Either way a sequence of refresh and clean build in Eclipse should surface the problem.
I had this error when I used a launch configuration that had an invalid classpath. In my case, I had a project that initially used Maven and thus a launch configuration had a Maven classpath element in it. I had later changed the project to use Gradle and removed the Maven classpath from the project's classpath, but the launch configuration still used it. I got this error trying to run it. Cleaning and rebuilding the project did not resolve this error. Instead, edit the launch configuration, remove the project classpath element, then add the project back to the User Entries in the classpath.
I got this error multiple times and struggled to work out. Finally, I removed the run configuration and re-added the default entries. It worked beautifully.
Just try to include package name in eclipse in case if you forgot it
Import all packages before using it, EX: import java.util.Scanner before using Scanner class.
These improvements might work and it will not give Java: Unresolved compilation problem anymore.
Also make sure to check compiler compliance level and selected jdk version is same
As a weird case, I encountered such an exception where the exception message (unresolved compilation bla bla) was hardcoded inside of generated class' itself. Decompiling the class revealed this.
I had the same issue using the visual studio Code. The root cause was backup java file was left in the same directory.
Removed the backup java file
When the build failed, selected the Fix it, it cleaned up the cache and restarted the workSpace.
I am build a gradle project and run compileJava task everything is ok. But i right click one java file and 'Compile xxxx.java', i get some error.
Error:(3, 25) java: package com.jpf.ms.entity not exists
...
IDEA version: 14.1.4
Make sure your settings.build references that package, and refresh your dependencies as shown here before running gradle tasks.
I use JUnit for the test,when I change some codes, I must make project manually, it can't auto compile like maven. If I doesn't make project it is the last time code.
Can anybody tell me why? Thanks a lot!
Actually I need change the before launch 'make' to 'sbt action',then I run or debug project it can auto compile in SBT project.
I have read questions: this and that. They suggest to modify sbt file. But I want run sbt clean assembly without tests and do not modify sbt build files. Is it possible with sbt? In maven there is -DskipTest=true parameter, is there analog for sbt?
For any properties you need to change on the command line, prepend them with "set ", and wrap them in quotes.
Example for Windows:
sbt "set test in assembly := {}" clean assembly
Example for Mac:
sbt 'set test in assembly := {}' clean assembly
I have a apache_mod.c which is supposed to be updated for continuous integration
I would like to use Maven to compile this module for generating apache_mod.so
Then packaging it in .jar
I can't find how to compile the apache_mod.c with Maven to get apache_mod.so because it seems that an Apache2 module needs to be compiled with apxs2 command which already put the *.so file in /usr/lib/apache2/modules.
So, do you have any idea how to compile apache_mod.c with Maven in order to get apache_mod.so to package it?
I don't think that putting *.so (shared object) into jar archive is correct solution, but to answer your question how to compile native c or c++ files using maven, you can use the native plugin http://mojo.codehaus.org/maven-native/native-maven-plugin/. Also, the apxs2 is just wrapper around gcc, so you don't have to use apxs2 to build apache module. You can just use gcc.
Seems I tried to do two things in one.
Generating *.so and packaging it are two different things.
So here is the process :
Having a Maven project compiling and generating *.so
Having a Maven Assembly to package *.so and others files and *.war
Seems Boris has been definitly right. Using Maven native plugin allow to compile *.c in *.so then Maven assembly plugin is used to package it.
Thanks for all.