I have an interesting task to compile some libraries from project repo.
I get jar with library sources using mvn dependency:sources.
I unpacked java files to src/main/java folder.
I run 'maven clean install'
Some libraries compiles ok, but some don't - some packages not found, because they not in sources jar and not in library pom.xml. Why the authors of libraries do this?
For example try to compile this lib: https://repo1.maven.org/maven2/edu/ucar/netcdf/4.2/
Error: package ucar.unidata.util does not exist. And where and how i must get this package? And why authors not include this to jar or pom file?
The problem is massive, not only this library affected.
Although I do not understand the concrete error you gave, let me state that it is in general not possible to rebuild a jar if you just have the sources jar and the POM.
Lots of things may be missing, like resources, tests and the project structure itself (if it was a multi-module project), and some POMs are "flattened", so that important plugin calls etc. are removed.
So you need to get used to the fact that this may or may not work.
Usually, people just use the jar as it is. If for some reasons (that you are not revealing, although I asked you twice) you need to compile from source, I can (in this order):
Look for a github/gitlab page of the project (often given in the POM, or you find it in google) and draw the project from there.
Fiddle with the sources and POM until you can compile the project (as you would with any broken project). This may or may not succeed.
Don't use the library but write the necessary stuff you need yourself.
Related
Using IntelliJ IDEA, it is often a straight-forward task to check out a project from GitHub and get it to build locally.
Once the base project is imported from GitHub, the IDE will download artifacts which will allow the main project to run. The dependencies can be examined by using File > Project Structure... > Libraries.
So the IDE downloads dependencies to allow running, but not to build from source. The IDE is able to decompile classes, but the IDE will not automatically download the source code for those dependency libraries so that the programmer can alter the code.
This question is about the steps required in the IDE and project configuration such that a selected dependency will be built locally, and thus allow the programmer to alter the code.
What I tried was to import the project on which the main project was dependent, as a separate project, then configure the main project to utilize the local project instead of the downloaded artifact. The first step, downloading the sub-project and getting it to compile, was completed successfully.
So I ended-up with two projects, the main one, and the one on which the main project depended. The task at hand, if this was the appropriate way to get this done, would be to open the main project and take some action to convince the main project to use the local build, rather than the downloaded runtime "jar".
First, I edited the POM.xml to comment out the dependency for the sub project. Checking File > Project Structure... > Libraries, I could see that it was gone, and the build now failed (as expected).
I went to File > Project Structure... > Libraries > + (plus sign) and poked around with New Module, and Import Module, but I was not able to convince the original project to use the locally available sub project. The result from various attempts was that code in the base project was not able to import from the sub project (unable to compile).
What are the specific steps to take in the IDE to get what was a runtime dependency "jar file" to instead to build locally, and use that instead?
Use a SNAPSHOT version for the dependency (you'll need to change this in both your project's pom.xml and the dependency's pom.xml, so if the current version is 2.0.0 change it to 2.0.0-SNAPSHOT)
Then you can edit the dependency's code and run mvn install in the dependency to provide the new version of the dependency to your project.
TLDR: there is no simple and straight-forward way of downloading a project's code and the code of its dependencies to rebuild it in one go as a complete chain.
Your project depends on several other artifacts. From the screenshot, we may assume that this is a maven project, at least we can be sure that there artifacts with compiled classes available for download, because this happends during build. You can view the compiled classes of your dependencies, because Intelli has the capability of decompressing jars and decompiling code, obviously, but the contents you are viewing is read-only.
Sidenote: Maven convention is to create 3 separate jars for each project. One with compiled classes, one with source files only and one with generated documentation. By default intellij may not download these, but you can force it (right-click on pom.xml -> maven -> Download sources and documentation). This will attach the actual source code instead of decompiled classes to your IDE, so it's much easier to understand the code - but still, there is no option to modify it - it's still read-only extract from some jar.
So what if you want to actually edit the source? You have 3 options, all with its own set of problems that need human intelligence to solve:
You extract the decompiled source from classes jar
You extract the attached source from sources jar
You check out git repository of the dependency
Now, beware of the downsides of each approach:
You can be sure that the decompiled source matches your project dependency 1:1. But decompiled code is not easy to read, missing comments, etc. Also, some projects may not ship their build scripts with the classes jar. Anything more complex than mvn clean install may turn out to be a blocker.
You can be reasonably sure the code matches your project dependency, but this actually is not a given. There is a chance of human error, causing the sources to actually not match the compiled classes (build from different revision or whatnot). Much depends on the quality of the project, the discipline put into the build process and care to avoid environment specific configuration that is not part of the source. The larger and older is the project, the less chances are you are able to recompile it successfully using only src jar.
A sane man's approach. You should have your build scripts, readmes, tutorials, etc. Except, of course, if we are talking some obscure company internal project with zero effort put in its maintenance. Surely, there are the same issues as before: not all projects are rebuilt easily on any environment. There may be steps upon steps required for your workstation to be configured as expected. Hopefully, self-respecting open-source java projects are easy to build, but again - not a given - not all project are open-source, not all are self-respecting.
Important note: When checking out the git repo of your dependency - you must also make sure that you are using correct revision. If the project is maintained with respect for git tags/branches naming convention - you are in luck. Not a given by any means.
All the above is enough to discourage any attempts to automatically decompose dependencies to compilable units by your IDE, and all the burden is put into you. So let's assume the best - our dependency is a simple, self-contained java application that is easily built using simple mvn clean install. You have it checked out in a separate project in your IDE. You identified correct git revision that matches version your project depends on.
Now let's apply your little change and test it. First thing you want to do is change pom.xml of your project to use a made up version of your dependency. It should be a -SNAPSHOT version for clarity and tidiness. You may of course build your modified dependency with real release version - but please be wary of how maven manages dependencies. If you install version 1.0 yourself - it stays in your local repo forever. You will forget about it, and will be using your fake 1.0 version when building all other dependent projects unless you manually locate and remove it from repo. So stick to 1.1-SNAPSHOT.
Now every time you need to apply a small fix to your dependency, execute mvn clean install in its repo, then make sure your actual project depends on the correct new SNAPSHOT version, execute your maven clean install and that's it.
Note that all this has very little to do with Intellij. You are not expected to modify any library paths, advanced project settings, or links to jars. Stick to modifying pom.xml and you are set.
When working maven project , maven sometimes generate classes folder in target directory. Sometimes it doesn't(may be create and delete immediately) ?.
What are the cases when it happen and when it doesn't ?.
It depends on your project configuration. For general, the project packaging type will be one key factor. Like "pom" type or "bom" type, these types are just for describing a project meta like dependencies management, general plugin configurations and etc, which does not contain source code to do compiling. For jar package which contains source code, it will generate classes with compiling with default configuration of maven-compiler-plugin.
But for maven and its plugins, they are having many flexible ways to do configuration to change their abilities. For example, for compiling, you can even change your source code folder location and compilation location by using build-helper-maven-plugin. So this is still depending on your pom configurations.
For build-helper-maven-plugin, see https://www.mojohaus.org/build-helper-maven-plugin/usage.html for more details.
I have read numerous posts regarding this, and I was still not able to find a clear-cut answer.
We have the need to use a proprietary SDK in our maven project and this SDK contains ~315 jar files that are needed for around 30 lines of code (SAP product). Every answer I read dealt with adding individual jars to your local maven repo. That is fine and I understand that, but is it possible to add an entire directory of libraries. These libraries are only needed for compiling the project since they are already on the classpath of the target server (They would all be scoped as provided in a pom).
I've tagged Netbeans 8 since that is the IDE I am using, so if anyone knows a hack to get a maven project in netbeans compiled using libraries on Netbeans classpath that would be a good solution as well...
JAR's are just java .class organized in folders and Zipped. Extract all those 315 JARs to somewhere, thus merging all of their content, and then Zip it again to one single fat JAR file. Add this fat JAR to your local repository as you have read elsewhere.
This other question can help you with the JAR merging thing: How to combine two Jar files
Although there are many messy workarounds for this, the ideal would be to let the compilation fail and search for the missing compile jars using a search utility like agent ransack you can search within the jars in that directory for the missing classes referenced in the compiler errors. As you find the jars you need, add them as dependencies with the scope of provided.
A less clean option would be to zip all of the jars, use the dependency plugin to unpack them to a folder and add that folder to the classpath of the build, then remove them or exclude them from the final package.
I know that there is a Git plugin for Eclipse ("Egit"), but I like to do Git stuff on the command line, and I like to code in Eclipse, so I want to keep them separate.
I cloned a Git repo (I don't think its important, but for good measure, it was https://github.com/spinscale/dropwizard-jobs.git). I then opened up Eclipse (Juno) and created a new Java project, and selected the root of the cloned repo as the base path to my project. Eclipse asked me if I wanted to associate the project with the Java facet, and I clicked 'OK'.
This project has a large dependency tree (if you like, check out its 4 POM files). I don't use Maven to build (I use Gradle) so I just ran a script that resolves the dependencies of these POMs into a directory, and then I created a lib directory in this Eclipse project and copied all the JARs into it. I then added all these JARs to the project's classpath.
I am now seeing 10 errors in the Problems view in Eclipse, and they're all similar errors:
The type ApplicationStartTestJob is already defined ApplicationStartTestJob.java /dropwizard-jobs/dropwizard-jobs-core/src/test/java/de/spinscale/dropwizard/jobs line 10 Java Problem
The type ApplicationStartTestJob is already defined ApplicationStartTestJob.java /dropwizard-jobs/dropwizard-jobs-guice/src/test/java/de/spinscale/dropwizard/jobs line 10 Java Problem
8 more all like this, etc.
Sure enough, when I expand the entire project, I see it has the following structure:
dropwizard-jobs/
dropwizard-jobs-core/
src/test/java/
de.spinscale.dropwizard.jobs
ApplicationStartTestJob.java
dropwizard-jobs-guice
src/test/java/
de.spinscale.dropwizard.jobs
ApplicationStartTestJob.java
dropwizard-jobs-spring
src/test/java/
de.spinscale.dropwizard.jobs
ApplicationStartTestJob.java
So it seems that the maintainers of this project like to rename their unit tests with the exact same package/class names, and for some reason, Eclipse sees them as all belonging inside the same package. To test this I renamed dropwizard-jobs-core/src/main/java/de.spinscale.dropwizard.jobs.ApplicationStartTest to something else, and did the same for dropwizard-jobs-guice/src/main/java/de.spinscale.dropwizard.jobs.ApplicationStartTest and sure enough, all the errors associated with ApplicationStartTest being already defined went away.
So my suspicion is confirmed: The intention of these subfolders (dropwizard-jobs-core, dropwizard-jobs-guice and dropwizard-jobs-spring) is that they are sub-projects with separate classpaths. Eclipse thinks all of these source folders are part of the same project, and so it is lumping all of their classes into the same classpath. Since each subproject uses the same unit test naming conventions (same package/class names for each subproject), Eclipse see multiple classes in the same package as having the same name.
OK, good! I figured out the problem. But what's the solution? Ideally I would be able to keep all of these inside the same project, but perhaps modify the .classpath file or do something similar that instruct Eclipse to keep the subprojects separated from a classpath perspective. Any ideas?
SImply download eclipse m2e plugin, then import the project(considering you have already checked-out at your workstation), and do spend sometime learning MAVEN commands. here you can find an pverview of maven parent project and modules. Maven parent pom vs modules pom
One possible solution would be to introduce maven, which allows to naturally define a parent project and sub-projects in a multi-module maven project.
You can actually test that configuration outside of Eclipse, and then use M2Eclipse in order to import parent and its dependencies, at the same time (as commented in this answer) in your Eclipse.
Actually, the M2Eclipse project itself has guice test project, which you can use as model for your own guive subproject, in the repo sonatype/m2eclipse-guice, with an adequate pom.xml.
I've seen a lot of projects, even from big companies like Elephant Bird (Twitter) and Akela (Mozilla) that offer source and ask you to compile it yourself instead of also offering jars. Is there some benefit to compiling in your own environment instead of just downloading a jar someone else has compiled?
Dependencies are not in the same location or even have the same version on every machine. It is simpler to detect where they are at compile-time.
If there is any native code (sometimes just for optimization) in a project, there are probably platform-dependent flags that need to be set at compile-time.
The short answer is dependency management. Most public OSS Java projects offer jars by publishing them to Maven Central. You are expected to use a build system like Gradle, Ivy, or Maven to manage your dependencies - these tools will automatically download the library you want along with any of its dependent libraries and be smart about it, caching it on your local filesystem so if a library is shared across multiple libraries it won't be downloaded twice.
As for the example projects you listed, Elephant Bird is available via Maven Central whereas Akela tells you exactly how to create your own jar (perhaps it's not quite far along enough to justify going through the rigmarole of publishing to Maven Central):
Building
To make a jar you can do:
mvn package
To make a Hadoop MapReduce job jar with no defined main class in the manifest:
mvn assembly:assembly
Without an automatic build system its hard to maintain a current version of the jar file online. Including the jar file in the repository is generally not a good idea as users who clone it don't need the compiled jar, they want the code. So unless the publisher explicitly adds a jar file to a download location outside of the sourcecode repository and updates this file every time the application changes you have to compile it yourself. Automatic Build systems can help a publisher to provide a current compiled jar to it's users but for smaller projects it's not always sufficient to go through the trouble of setting one up.