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What is an uber jar?
(7 answers)
Closed 3 years ago.
I've heard people say that they create a fat JAR and deploy it. What do they actually mean ?
The different names are just ways of packaging java apps.
Skinny – Contains ONLY the bits you literally type into your code editor, and NOTHING else.
Thin – Contains all of the above PLUS the app’s direct dependencies of your app (db drivers, utility libraries, etc).
Hollow – The inverse of Thin – Contains only the bits needed to run your app but does NOT contain the app itself. Basically a pre-packaged “app server” to which you can later deploy your app, in the same style as traditional Java EE app servers, but with important differences.
Fat/Uber – Contains the bit you literally write yourself PLUS the direct dependencies of your app PLUS the bits needed to run your app “on its own”.
Source: Article from Dzone
The fat jar is the jar, which contains classes from all the libraries, on which your project depends and, of course, the classes of current project.
In different build systems fat jar is created differently, for example, in Gradle one would create it with (instruction):
task fatJar(type: Jar) {
manifest {
attributes 'Main-Class': 'com.example.Main'
}
baseName = project.name + '-all'
from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
with jar
}
In Maven it's being done this way (after setting up regular jar):
<pluginRepositories>
<pluginRepository>
<id>onejar-maven-plugin.googlecode.com</id>
<url>http://onejar-maven-plugin.googlecode.com/svn/mavenrepo</url>
</pluginRepository>
<plugin>
<groupid>org.dstovall</groupid>
<artifactid>onejar-maven-plugin</artifactid>
<version>1.4.4</version>
<executions>
<execution>
<configuration>
<onejarversion>0.97</onejarversion>
<classifier>onejar</classifier>
</configuration>
<goals>
<goal>one-jar</goal>
</goals>
</execution>
</executions>
</plugin>
Fat jar or uber jar is a jar which contains all project class files and resources packed together with all it's dependencies. There are different methods for achieving such effect:
dependencies' jars are copied into main jar and then loaded using special class loader (onejar, spring-boot-plugin:repackage)
dependencies' jars are extracted at the top of main jar hierarchy (maven-assembly-plugin with it's jar-with-dependencies assembly)
dependencies' jars are unpacked at the top of main jar hierarchy and their packages are renamed (maven-shade-plugin with shade goal)
Below sample assembly plugin configuration jar-with-dependencies:
<project>
...
<build>
...
<plugins>
<plugin>
<!-- NOTE: We don't need a groupId specification because the group is
org.apache.maven.plugins ...which is assumed by default.
-->
<artifactId>maven-assembly-plugin</artifactId>
<version>2.6</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<classifier
</configuration>
...
</project>
For more detailed explanation: Uber-JAR at imagej.net
In the case of an executable jar, another way to think about a fat jar is one you can execute by invoking:
java -jar myFatLibrary.jar
without the need for -cp / --classpath, or even double clicking the jar icon.
A fat jar simply contains same classes as a classical jar + classes from all of their runtime dependencies.
With Jeka ( https://jeka.dev) you can achieve it programmatically :
JkPathTreeSet.of(Paths.get("classes")).andZips(
Paths.get("bouncycastle-pgp-152.jar"),
Paths.get("classgraph-4.8.41.jar"),
Paths.get("ivy-2.4.0.jar")
).zipTo(Paths.get("fat.jar"));
or just by parametring Java plugin :
javaPlugin.getProject().getMaker().defineMainArtifactAsFatJar(true);
from the Gradle documentation
In the Java space, applications and their dependencies typically used to be packaged as separate JARs within a single distribution archive. That still happens, but there is another approach that is now common: placing the classes and resources of the dependencies directly into the application JAR, creating what is known as an uber or fat JAR.
here is a demonstrated of uberJar task in build.gradle file:
task uberJar(type: Jar) {
archiveClassifier = 'uber'
from sourceSets.main.output
dependsOn configurations.runtimeClasspath
from {
configurations.runtimeClasspath.findAll { it.name.endsWith('jar') }.collect { zipTree(it) }
}
}
In this case, we’re taking the runtime dependencies of the project — configurations.runtimeClasspath.files — and wrapping each of the JAR files with the zipTree() method. The result is a collection of ZIP file trees, the contents of which are copied into the uber JAR alongside the application classes.
Related
I have a multimodule maven project, as follows:
module: project-assembly;
module: project-implementation;
module: project-application;
module: project-web;
in project-assembly/src/main/assembly/config
i have important configuration files for my project, and i need them to be copied during build process into project-web module into WEB-INF folder.
More important, this has to be done with specific profile.
For example, having a "x" profile, this is the one who needs this files in order to package successfully the project.
is there a way to achieve this? Thanks
You can use the maven-antrun-plugin to copy files between arbitrary folders (ant copy). But I would strongly advise against copying between modules. It is confusing and even more: The build order or the subset of modules that are built are subject to change (depending on the dependencies and also the command line parameters). For this copying, you need to make sure that the build happens in a defined order.
Think about sharing the configuration in another way.
you can use maven resource plugin-
<properties>
<othermodule-dir>...</othermodule-dir>
</properties>
<build>
<resources>
<resource>
<!-- package thumbnail -->
<directory>${sourceDir}</directory>
<targetPath>${othermodule-dir}</targetPath>
<filtering>true</filtering>
</resource>
</resources>
.
.
</build>
I'm trying to create a .bat file to run my generated executable JAR file. I found this method of creating .bat files for running a project. So, I read up on the plugin here and added the following to my pom.xml.
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>appassembler-maven-plugin</artifactId>
<version>1.10</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>assemble</goal>
</goals>
</execution>
</executions>
<configuration>
<assembleDirectory>${assembleDir}</assembleDirectory>
<generateRepository>false</generateRepository>
<repositoryName>lib</repositoryName>
<configurationDirectory>conf</configurationDirectory>
<copyConfigurationDirectory>false</copyConfigurationDirectory>
<programs>
<program>
<mainClass>com.companyname.tests.TestRunner</mainClass>
<id>AutoConfigTest</id>
</program>
</programs>
</configuration>
</plugin>
And, yes, as the name suggests, this JAR contains JUnit test cases.
I prevented the plugin from unpacking JARs and creating the repo folder and set that to my already generated lib folder, which contains all the JARs(executables and the dependencies). The .bat file is being generated but, when running it, I'm getting the following error.
Error: Could not find or load main class com.companyname.tests.TestRunner
Also, I want the command prompt to stay after execution. In this case it is closing immediately. Maybe its because I'm getting an error. I'm not sure.
So, got into searching again and found this. But as the accepted answer suggests, my pom.xml already contains -
<packaging>jar</packaging>
The assembled directory is -
AutoConfigTest
|
|--bin
| `- contains the .bat file
|--conf
| `- contains the property files and other configuration files
|--lib
`- contains all the JARs
What am I doing wrong here?
Maybe it's related to (from the README.md)
All dependencies and the artifact of the project itself are placed in a generated Maven repository in a defined assemble directory. All artifacts (dependencies + the artifact from the project) are added to the classpath in the generated bin scripts.
In your pom.xml you prevent the generation of that repository. So you need to ensure that the artifact from the project is copied at the expected place.
Assuming following project settings
<groupId>com.companyname</groupId>
<artifactId>Maven-AppAssembler</artifactId>
<version>0.0.1-SNAPSHOT</version>
the artifact is expected to be at (the CLASSPATH setting in the scripts bin/AutoConfigTest)
"$REPO"/com/companyname/Maven-AppAssembler/0.0.1-SNAPSHOT/Maven-AppAssembler-0.0.1-SNAPSHOT.jar
where $REPO resolve to target/appassembler/lib.
I found the issue. #SubOptimal was correct in pointing out that the main class isn't visible to the batch file.
For some reason, the test JAR file (which contains the main class) isn't being added to the classpath variable of the batch file. As a result, whenever I ran the batch file, I was getting the error mentioned in the question.
I went back to the documentation and found this.
Sometimes it happens that you have many dependencies which means having a very long classpath, and becomes too long (in particular on Windows based platforms). This option can help in such situation. If you activate this option, your classpath contains only a classpath wildcard (REPO/*). But be aware that this works only in combination with Java 1.6 and above and with repositoryLayout flat.
So, instead of adding individual JAR files into the path, I added the whole lib directory to the classpath by adding the following to the pom.xml.
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>appassembler-maven-plugin</artifactId>
<version>1.10</version>
...
<configuration>
...
<repositoryLayout>flat</repositoryLayout>
<useWildcardClassPath>true</useWildcardClassPath>
...
</configuration>
...
</plugin>
I could do this because the repository layout of lib was already flat. There were no hierarchies. No other change was required. The batch file now behaves as expected.
Maven 2 is driving me crazy during the experimentation / quick and dirty mock-up phase of development.
I have a pom.xml file that defines the dependencies for the web-app framework I want to use, and I can quickly generate starter projects from that file. However, sometimes I want to link to a 3rd party library that doesn't already have a pom.xml file defined, so rather than create the pom.xml file for the 3rd party lib by hand and install it, and add the dependency to my pom.xml, I would just like to tell Maven: "In addition to my defined dependencies, include any jars that are in /lib too."
It seems like this ought to be simple, but if it is, I am missing something.
Any pointers on how to do this are greatly appreciated. Short of that, if there is a simple way to point maven to a /lib directory and easily create a pom.xml with all the enclosed jars mapped to a single dependency which I could then name / install and link to in one fell swoop would also suffice.
Problems of popular approaches
Most of the answers you'll find around the internet will suggest you to either install the dependency to your local repository or specify a "system" scope in the pom and distribute the dependency with the source of your project. But both of these solutions are actually flawed.
Why you shouldn't apply the "Install to Local Repo" approach
When you install a dependency to your local repository it remains there. Your distribution artifact will do fine as long as it has access to this repository. The problem is in most cases this repository will reside on your local machine, so there'll be no way to resolve this dependency on any other machine. Clearly making your artifact depend on a specific machine is not a way to handle things. Otherwise this dependency will have to be locally installed on every machine working with that project which is not any better.
Why you shouldn't apply the "System Scope" approach
The jars you depend on with the "System Scope" approach neither get installed to any repository or attached to your target packages. That's why your distribution package won't have a way to resolve that dependency when used. That I believe was the reason why the use of system scope even got deprecated. Anyway you don't want to rely on a deprecated feature.
The static in-project repository solution
After putting this in your pom:
<repository>
<id>repo</id>
<releases>
<enabled>true</enabled>
<checksumPolicy>ignore</checksumPolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
<url>file://${project.basedir}/repo</url>
</repository>
for each artifact with a group id of form x.y.z Maven will include the following location inside your project dir in its search for artifacts:
repo/
| - x/
| | - y/
| | | - z/
| | | | - ${artifactId}/
| | | | | - ${version}/
| | | | | | - ${artifactId}-${version}.jar
To elaborate more on this you can read this blog post.
Use Maven to install to project repo
Instead of creating this structure by hand I recommend to use a Maven plugin to install your jars as artifacts. So, to install an artifact to an in-project repository under repo folder execute:
mvn install:install-file -DlocalRepositoryPath=repo -DcreateChecksum=true -Dpackaging=jar -Dfile=[your-jar] -DgroupId=[...] -DartifactId=[...] -Dversion=[...]
If you'll choose this approach you'll be able to simplify the repository declaration in pom to:
<repository>
<id>repo</id>
<url>file://${project.basedir}/repo</url>
</repository>
A helper script
Since executing installation command for each lib is kinda annoying and definitely error prone, I've created a utility script which automatically installs all the jars from a lib folder to a project repository, while automatically resolving all metadata (groupId, artifactId and etc.) from names of files. The script also prints out the dependencies xml for you to copy-paste in your pom.
Include the dependencies in your target package
When you'll have your in-project repository created you'll have solved a problem of distributing the dependencies of the project with its source, but since then your project's target artifact will depend on non-published jars, so when you'll install it to a repository it will have unresolvable dependencies.
To beat this problem I suggest to include these dependencies in your target package. This you can do with either the Assembly Plugin or better with the OneJar Plugin. The official documentaion on OneJar is easy to grasp.
For throw away code only
set scope == system and just make up a groupId, artifactId, and version
<dependency>
<groupId>org.swinglabs</groupId>
<artifactId>swingx</artifactId>
<version>0.9.2</version>
<scope>system</scope>
<systemPath>${project.basedir}/lib/swingx-0.9.3.jar</systemPath>
</dependency>
Note: system dependencies are not copied into resulted jar/war
(see How to include system dependencies in war built using maven)
You may create local repository on your project
For example if you have libs folder in project structure
In libs folder you should create directory structure like: /groupId/artifactId/version/artifactId-version.jar
In your pom.xml you should register repository
<repository>
<id>ProjectRepo</id>
<name>ProjectRepo</name>
<url>file://${project.basedir}/libs</url>
</repository>
and add dependency as usual
<dependency>
<groupId>groupId</groupId>
<artifactId>artifactId</artifactId>
<version>version</version>
</dependency>
That is all.
For detailed information: How to add external libraries in Maven (archived)
Note: When using the System scope (as mentioned on this page), Maven needs absolute paths.
If your jars are under your project's root, you'll want to prefix your systemPath values with ${basedir}.
This is what I have done, it also works around the package issue and it works with checked out code.
I created a new folder in the project in my case I used repo, but feel free to use src/repo
In my POM I had a dependency that is not in any public maven repositories
<dependency>
<groupId>com.dovetail</groupId>
<artifactId>zoslog4j</artifactId>
<version>1.0.1</version>
<scope>runtime</scope>
</dependency>
I then created the following directories repo/com/dovetail/zoslog4j/1.0.1 and copied the JAR file into that folder.
I created the following POM file to represent the downloaded file (this step is optional, but it removes a WARNING) and helps the next guy figure out where I got the file to begin with.
<?xml version="1.0" encoding="UTF-8" ?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.dovetail</groupId>
<artifactId>zoslog4j</artifactId>
<packaging>jar</packaging>
<version>1.0.1</version>
<name>z/OS Log4J Appenders</name>
<url>http://dovetail.com/downloads/misc/index.html</url>
<description>Apache Log4j Appender for z/OS Logstreams, files, etc.</description>
</project>
Two optional files I create are the SHA1 checksums for the POM and the JAR to remove the missing checksum warnings.
shasum -b < repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.jar \
> repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.jar.sha1
shasum -b < repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.pom \
> repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.pom.sha1
Finally I add the following fragment to my pom.xml that allows me to refer to the local repository
<repositories>
<repository>
<id>project</id>
<url>file:///${basedir}/repo</url>
</repository>
</repositories>
This is how we add or install a local jar
<dependency>
<groupId>org.example</groupId>
<artifactId>iamajar</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${project.basedir}/lib/iamajar.jar</systemPath>
</dependency>
i gave some default groupId and artifactId because they are mandatory :)
You really ought to get a framework in place via a repository and identifying your dependencies up front. Using the system scope is a common mistake people use, because they "don't care about the dependency management." The trouble is that doing this you end up with a perverted maven build that will not show maven in a normal condition. You would be better off following an approach like this.
Maven install plugin has command line usage to install a jar into the local repository, POM is optional but you will have to specify the GroupId, ArtifactId, Version and Packaging (all the POM stuff).
Using <scope>system</scope> is a terrible idea for reasons explained by others, installing the file manually to your local repository makes the build unreproducible, and using <url>file://${project.basedir}/repo</url> is not a good idea either because (1) that may not be a well-formed file URL (e.g. if the project is checked out in a directory with unusual characters), (2) the result is unusable if this project’s POM is used as a dependency of someone else’s project.
Assuming you are unwilling to upload the artifact to a public repository, Simeon’s suggestion of a helper module does the job. But there is an easier way now…
The Recommendation
Use non-maven-jar-maven-plugin. Does exactly what you were asking for, with none of the drawbacks of the other approaches.
I found another way to do this, see here from a Heroku post
To summarize (sorry about some copy & paste)
Create a repo directory under your root folder:
yourproject
+- pom.xml
+- src
+- repo
Run this to install the jar to your local repo directory
mvn deploy:deploy-file -Durl=file:///path/to/yourproject/repo/ -Dfile=mylib-1.0.jar -DgroupId=com.example -DartifactId=mylib -Dpackaging=jar -Dversion=1.0
Add this your pom.xml:
<repositories>
<!--other repositories if any-->
<repository>
<id>project.local</id>
<name>project</name>
<url>file:${project.basedir}/repo</url>
</repository>
</repositories>
<dependency>
<groupId>com.example</groupId>
<artifactId>mylib</artifactId>
<version>1.0</version>
</dependency>
What seems simplest to me is just configure your maven-compiler-plugin to include your custom jars. This example will load any jar files in a lib directory.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<includes>
<include>lib/*.jar</include>
</includes>
</configuration>
</plugin>
After having really long discussion with CloudBees guys about properly maven packaging of such kind of JARs, they made an interesting good proposal for a solution:
Creation of a fake Maven project which attaches a pre-existing JAR as a primary artifact, running into belonged POM install:install-file execution. Here is an example of such kinf of POM:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<version>2.3.1</version>
<executions>
<execution>
<id>image-util-id</id>
<phase>install</phase>
<goals>
<goal>install-file</goal>
</goals>
<configuration>
<file>${basedir}/file-you-want-to-include.jar</file>
<groupId>${project.groupId}</groupId>
<artifactId>${project.artifactId}</artifactId>
<version>${project.version}</version>
<packaging>jar</packaging>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
But in order to implement it, existing project structure should be changed. First, you should have in mind that for each such kind of JAR there should be created different fake Maven project (module). And there should be created a parent Maven project including all sub-modules which are : all JAR wrappers and existing main project. The structure could be :
root project (this contains the parent POM file includes all sub-modules with module XML element) (POM packaging)
JAR 1 wrapper Maven child project (POM packaging)
JAR 2 wrapper Maven child project (POM packaging)
main existing Maven child project (WAR, JAR, EAR .... packaging)
When parent running via mvn:install or mvn:packaging is forced and sub-modules will be executed. That could be concerned as a minus here, since project structure should be changed, but offers a non static solution at the end
The problem with systemPath is that the dependencies' jars won't get distributed along your artifacts as transitive dependencies. Try what I've posted here: Is it best to Mavenize your project jar files or put them in WEB-INF/lib?
Then declare dependencies as usual.
And please read the footer note.
If you want a quick and dirty solution, you can do the following (though I do not recommend this for anything except test projects, maven will complain in length that this is not proper).
Add a dependency entry for each jar file you need, preferably with a perl script or something similar and copy/paste that into your pom file.
#! /usr/bin/perl
foreach my $n (#ARGV) {
$n=~s#.*/##;
print "<dependency>
<groupId>local.dummy</groupId>
<artifactId>$n</artifactId>
<version>0.0.1</version>
<scope>system</scope>
<systemPath>\${project.basedir}/lib/$n</systemPath>
</dependency>
";
A quick&dirty batch solution (based on Alex's answer):
libs.bat
#ECHO OFF
FOR %%I IN (*.jar) DO (
echo ^<dependency^>
echo ^<groupId^>local.dummy^</groupId^>
echo ^<artifactId^>%%I^</artifactId^>
echo ^<version^>0.0.1^</version^>
echo ^<scope^>system^</scope^>
echo ^<systemPath^>${project.basedir}/lib/%%I^</systemPath^>
echo ^</dependency^>
)
Execute it like this: libs.bat > libs.txt.
Then open libs.txt and copy its content as dependencies.
In my case, I only needed the libraries to compile my code, and this solution was the best for that purpose.
To install the 3rd party jar which is not in maven repository use maven-install-plugin.
Below are steps:
Download the jar file manually from the source (website)
Create a folder and place your jar file in it
Run the below command to install the 3rd party jar in your local maven repository
mvn install:install-file -Dfile= -DgroupId=
-DartifactId= -Dversion= -Dpackaging=
Below is the e.g one I used it for simonsite log4j
mvn install:install-file
-Dfile=/Users/athanka/git/MyProject/repo/log4j-rolling-appender.jar -DgroupId=uk.org.simonsite -DartifactId=log4j-rolling-appender -Dversion=20150607-2059 -Dpackaging=jar
In the pom.xml include the dependency as below
<dependency>
<groupId>uk.org.simonsite</groupId>
<artifactId>log4j-rolling-appender</artifactId>
<version>20150607-2059</version>
</dependency>
Run the mvn clean install command to create your packaging
Below is the reference link:
https://maven.apache.org/guides/mini/guide-3rd-party-jars-local.html
A strange solution I found:
using Eclipse
create simple (non-maven) java project
add a Main class
add all the jars to the classpath
export Runnable JAR (it's important, because no other way here to do it)
select Extract required libraries into generated JAR
decide the licence issues
tadammm...install the generated jar to your m2repo
add this single dependency to your other projects.
cheers,
Balint
Even though it does not exactly fit to your problem, I'll drop this here. My requirements were:
Jars that can not be found in an online maven repository should be in the SVN.
If one developer adds another library, the other developers should not be bothered with manually installing them.
The IDE (NetBeans in my case) should be able find the sources and javadocs to provide autocompletion and help.
Let's talk about (3) first: Just having the jars in a folder and somehow merging them into the final jar will not work for here, since the IDE will not understand this. This means all libraries have to be installed properly. However, I dont want to have everyone installing it using "mvn install-file".
In my project I needed metawidget. Here we go:
Create a new maven project (name it "shared-libs" or something like that).
Download metawidget and extract the zip into src/main/lib.
The folder doc/api contains the javadocs. Create a zip of the content (doc/api/api.zip).
Modify the pom like this
Build the project and the library will be installed.
Add the library as a dependency to your project, or (if you added the dependency in the shared-libs project) add shared-libs as dependency to get all libraries at once.
Every time you have a new library, just add a new execution and tell everyone to build the project again (you can improve this process with project hierachies).
For those that didn't find a good answer here, this is what we are doing to get a jar with all the necessary dependencies in it. This answer (https://stackoverflow.com/a/7623805/1084306) mentions to use the Maven Assembly plugin but doesn't actually give an example in the answer. And if you don't read all the way to the end of the answer (it's pretty lengthy), you may miss it. Adding the below to your pom.xml will generate target/${PROJECT_NAME}-${VERSION}-jar-with-dependencies.jar
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.4.1</version>
<configuration>
<!-- get all project dependencies -->
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<!-- MainClass in mainfest make a executable jar -->
<archive>
<manifest>
<mainClass>my.package.mainclass</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<!-- bind to the packaging phase -->
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
I alluded to some python code in a comment to the answer from #alex lehmann's , so am posting it here.
def AddJars(jarList):
s1 = ''
for elem in jarList:
s1+= """
<dependency>
<groupId>local.dummy</groupId>
<artifactId>%s</artifactId>
<version>0.0.1</version>
<scope>system</scope>
<systemPath>${project.basedir}/manual_jars/%s</systemPath>
</dependency>\n"""%(elem, elem)
return s1
This doesn't answer how to add them to your POM, and may be a no brainer, but would just adding the lib dir to your classpath work? I know that is what I do when I need an external jar that I don't want to add to my Maven repos.
Hope this helps.
What works in our project is what Archimedes Trajano wrote, but we had in our .m2/settings.xml something like this:
<mirror>
<id>nexus</id>
<mirrorOf>*</mirrorOf>
<url>http://url_to_our_repository</url>
</mirror>
and the * should be changed to central. So if his answer doesn't work for you, you should check your settings.xml
I just wanted a quick and dirty workaround... I couldn't run the script from Nikita Volkov: syntax error + it requires a strict format for the jar names.
I made this Perl script which works with whatever format for the jar file names, and it generates the dependencies in an xml so it can be copy pasted directly in a pom.
If you want to use it, make sure you understand what the script is doing, you may need to change the lib folder and the value for the groupId or artifactId...
#!/usr/bin/perl
use strict;
use warnings;
open(my $fh, '>', 'dependencies.xml') or die "Could not open file 'dependencies.xml' $!";
foreach my $file (glob("lib/*.jar")) {
print "$file\n";
my $groupId = "my.mess";
my $artifactId = "";
my $version = "0.1-SNAPSHOT";
if ($file =~ /\/([^\/]*?)(-([0-9v\._]*))?\.jar$/) {
$artifactId = $1;
if (defined($3)) {
$version = $3;
}
`mvn install:install-file -Dfile=$file -DgroupId=$groupId -DartifactId=$artifactId -Dversion=$version -Dpackaging=jar`;
print $fh "<dependency>\n\t<groupId>$groupId</groupId>\n\t<artifactId>$artifactId</artifactId>\n\t<version>$version</version>\n</dependency>\n";
print " => $groupId:$artifactId:$version\n";
} else {
print "##### BEUH...\n";
}
}
close $fh;
The solution for scope='system' approach in Java:
public static void main(String[] args) {
String filepath = "/Users/Downloads/lib/";
try (Stream<Path> walk = Files.walk(Paths.get(filepath))) {
List<String> result = walk.filter(Files::isRegularFile)
.map(x -> x.toString()).collect(Collectors.toList());
String indentation = " ";
for (String s : result) {
System.out.println(indentation + indentation + "<dependency>");
System.out.println(indentation + indentation + indentation + "<groupId>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</groupId>");
System.out.println(indentation + indentation + indentation + "<artifactId>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</artifactId>");
System.out.println(indentation + indentation + indentation + "<version>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</version>");
System.out.println(indentation + indentation + indentation + "<scope>system</scope>");
System.out.println(indentation + indentation + indentation + "<systemPath>" + s + "</systemPath>");
System.out.println(indentation + indentation + "</dependency>");
}
} catch (IOException e) {
e.printStackTrace();
}
}
Maven 2 is driving me crazy during the experimentation / quick and dirty mock-up phase of development.
I have a pom.xml file that defines the dependencies for the web-app framework I want to use, and I can quickly generate starter projects from that file. However, sometimes I want to link to a 3rd party library that doesn't already have a pom.xml file defined, so rather than create the pom.xml file for the 3rd party lib by hand and install it, and add the dependency to my pom.xml, I would just like to tell Maven: "In addition to my defined dependencies, include any jars that are in /lib too."
It seems like this ought to be simple, but if it is, I am missing something.
Any pointers on how to do this are greatly appreciated. Short of that, if there is a simple way to point maven to a /lib directory and easily create a pom.xml with all the enclosed jars mapped to a single dependency which I could then name / install and link to in one fell swoop would also suffice.
Problems of popular approaches
Most of the answers you'll find around the internet will suggest you to either install the dependency to your local repository or specify a "system" scope in the pom and distribute the dependency with the source of your project. But both of these solutions are actually flawed.
Why you shouldn't apply the "Install to Local Repo" approach
When you install a dependency to your local repository it remains there. Your distribution artifact will do fine as long as it has access to this repository. The problem is in most cases this repository will reside on your local machine, so there'll be no way to resolve this dependency on any other machine. Clearly making your artifact depend on a specific machine is not a way to handle things. Otherwise this dependency will have to be locally installed on every machine working with that project which is not any better.
Why you shouldn't apply the "System Scope" approach
The jars you depend on with the "System Scope" approach neither get installed to any repository or attached to your target packages. That's why your distribution package won't have a way to resolve that dependency when used. That I believe was the reason why the use of system scope even got deprecated. Anyway you don't want to rely on a deprecated feature.
The static in-project repository solution
After putting this in your pom:
<repository>
<id>repo</id>
<releases>
<enabled>true</enabled>
<checksumPolicy>ignore</checksumPolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
<url>file://${project.basedir}/repo</url>
</repository>
for each artifact with a group id of form x.y.z Maven will include the following location inside your project dir in its search for artifacts:
repo/
| - x/
| | - y/
| | | - z/
| | | | - ${artifactId}/
| | | | | - ${version}/
| | | | | | - ${artifactId}-${version}.jar
To elaborate more on this you can read this blog post.
Use Maven to install to project repo
Instead of creating this structure by hand I recommend to use a Maven plugin to install your jars as artifacts. So, to install an artifact to an in-project repository under repo folder execute:
mvn install:install-file -DlocalRepositoryPath=repo -DcreateChecksum=true -Dpackaging=jar -Dfile=[your-jar] -DgroupId=[...] -DartifactId=[...] -Dversion=[...]
If you'll choose this approach you'll be able to simplify the repository declaration in pom to:
<repository>
<id>repo</id>
<url>file://${project.basedir}/repo</url>
</repository>
A helper script
Since executing installation command for each lib is kinda annoying and definitely error prone, I've created a utility script which automatically installs all the jars from a lib folder to a project repository, while automatically resolving all metadata (groupId, artifactId and etc.) from names of files. The script also prints out the dependencies xml for you to copy-paste in your pom.
Include the dependencies in your target package
When you'll have your in-project repository created you'll have solved a problem of distributing the dependencies of the project with its source, but since then your project's target artifact will depend on non-published jars, so when you'll install it to a repository it will have unresolvable dependencies.
To beat this problem I suggest to include these dependencies in your target package. This you can do with either the Assembly Plugin or better with the OneJar Plugin. The official documentaion on OneJar is easy to grasp.
For throw away code only
set scope == system and just make up a groupId, artifactId, and version
<dependency>
<groupId>org.swinglabs</groupId>
<artifactId>swingx</artifactId>
<version>0.9.2</version>
<scope>system</scope>
<systemPath>${project.basedir}/lib/swingx-0.9.3.jar</systemPath>
</dependency>
Note: system dependencies are not copied into resulted jar/war
(see How to include system dependencies in war built using maven)
You may create local repository on your project
For example if you have libs folder in project structure
In libs folder you should create directory structure like: /groupId/artifactId/version/artifactId-version.jar
In your pom.xml you should register repository
<repository>
<id>ProjectRepo</id>
<name>ProjectRepo</name>
<url>file://${project.basedir}/libs</url>
</repository>
and add dependency as usual
<dependency>
<groupId>groupId</groupId>
<artifactId>artifactId</artifactId>
<version>version</version>
</dependency>
That is all.
For detailed information: How to add external libraries in Maven (archived)
Note: When using the System scope (as mentioned on this page), Maven needs absolute paths.
If your jars are under your project's root, you'll want to prefix your systemPath values with ${basedir}.
This is what I have done, it also works around the package issue and it works with checked out code.
I created a new folder in the project in my case I used repo, but feel free to use src/repo
In my POM I had a dependency that is not in any public maven repositories
<dependency>
<groupId>com.dovetail</groupId>
<artifactId>zoslog4j</artifactId>
<version>1.0.1</version>
<scope>runtime</scope>
</dependency>
I then created the following directories repo/com/dovetail/zoslog4j/1.0.1 and copied the JAR file into that folder.
I created the following POM file to represent the downloaded file (this step is optional, but it removes a WARNING) and helps the next guy figure out where I got the file to begin with.
<?xml version="1.0" encoding="UTF-8" ?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.dovetail</groupId>
<artifactId>zoslog4j</artifactId>
<packaging>jar</packaging>
<version>1.0.1</version>
<name>z/OS Log4J Appenders</name>
<url>http://dovetail.com/downloads/misc/index.html</url>
<description>Apache Log4j Appender for z/OS Logstreams, files, etc.</description>
</project>
Two optional files I create are the SHA1 checksums for the POM and the JAR to remove the missing checksum warnings.
shasum -b < repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.jar \
> repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.jar.sha1
shasum -b < repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.pom \
> repo/com/dovetail/zoslog4j/1.0.1/zoslog4j-1.0.1.pom.sha1
Finally I add the following fragment to my pom.xml that allows me to refer to the local repository
<repositories>
<repository>
<id>project</id>
<url>file:///${basedir}/repo</url>
</repository>
</repositories>
This is how we add or install a local jar
<dependency>
<groupId>org.example</groupId>
<artifactId>iamajar</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${project.basedir}/lib/iamajar.jar</systemPath>
</dependency>
i gave some default groupId and artifactId because they are mandatory :)
You really ought to get a framework in place via a repository and identifying your dependencies up front. Using the system scope is a common mistake people use, because they "don't care about the dependency management." The trouble is that doing this you end up with a perverted maven build that will not show maven in a normal condition. You would be better off following an approach like this.
Maven install plugin has command line usage to install a jar into the local repository, POM is optional but you will have to specify the GroupId, ArtifactId, Version and Packaging (all the POM stuff).
Using <scope>system</scope> is a terrible idea for reasons explained by others, installing the file manually to your local repository makes the build unreproducible, and using <url>file://${project.basedir}/repo</url> is not a good idea either because (1) that may not be a well-formed file URL (e.g. if the project is checked out in a directory with unusual characters), (2) the result is unusable if this project’s POM is used as a dependency of someone else’s project.
Assuming you are unwilling to upload the artifact to a public repository, Simeon’s suggestion of a helper module does the job. But there is an easier way now…
The Recommendation
Use non-maven-jar-maven-plugin. Does exactly what you were asking for, with none of the drawbacks of the other approaches.
I found another way to do this, see here from a Heroku post
To summarize (sorry about some copy & paste)
Create a repo directory under your root folder:
yourproject
+- pom.xml
+- src
+- repo
Run this to install the jar to your local repo directory
mvn deploy:deploy-file -Durl=file:///path/to/yourproject/repo/ -Dfile=mylib-1.0.jar -DgroupId=com.example -DartifactId=mylib -Dpackaging=jar -Dversion=1.0
Add this your pom.xml:
<repositories>
<!--other repositories if any-->
<repository>
<id>project.local</id>
<name>project</name>
<url>file:${project.basedir}/repo</url>
</repository>
</repositories>
<dependency>
<groupId>com.example</groupId>
<artifactId>mylib</artifactId>
<version>1.0</version>
</dependency>
What seems simplest to me is just configure your maven-compiler-plugin to include your custom jars. This example will load any jar files in a lib directory.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<includes>
<include>lib/*.jar</include>
</includes>
</configuration>
</plugin>
After having really long discussion with CloudBees guys about properly maven packaging of such kind of JARs, they made an interesting good proposal for a solution:
Creation of a fake Maven project which attaches a pre-existing JAR as a primary artifact, running into belonged POM install:install-file execution. Here is an example of such kinf of POM:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<version>2.3.1</version>
<executions>
<execution>
<id>image-util-id</id>
<phase>install</phase>
<goals>
<goal>install-file</goal>
</goals>
<configuration>
<file>${basedir}/file-you-want-to-include.jar</file>
<groupId>${project.groupId}</groupId>
<artifactId>${project.artifactId}</artifactId>
<version>${project.version}</version>
<packaging>jar</packaging>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
But in order to implement it, existing project structure should be changed. First, you should have in mind that for each such kind of JAR there should be created different fake Maven project (module). And there should be created a parent Maven project including all sub-modules which are : all JAR wrappers and existing main project. The structure could be :
root project (this contains the parent POM file includes all sub-modules with module XML element) (POM packaging)
JAR 1 wrapper Maven child project (POM packaging)
JAR 2 wrapper Maven child project (POM packaging)
main existing Maven child project (WAR, JAR, EAR .... packaging)
When parent running via mvn:install or mvn:packaging is forced and sub-modules will be executed. That could be concerned as a minus here, since project structure should be changed, but offers a non static solution at the end
The problem with systemPath is that the dependencies' jars won't get distributed along your artifacts as transitive dependencies. Try what I've posted here: Is it best to Mavenize your project jar files or put them in WEB-INF/lib?
Then declare dependencies as usual.
And please read the footer note.
If you want a quick and dirty solution, you can do the following (though I do not recommend this for anything except test projects, maven will complain in length that this is not proper).
Add a dependency entry for each jar file you need, preferably with a perl script or something similar and copy/paste that into your pom file.
#! /usr/bin/perl
foreach my $n (#ARGV) {
$n=~s#.*/##;
print "<dependency>
<groupId>local.dummy</groupId>
<artifactId>$n</artifactId>
<version>0.0.1</version>
<scope>system</scope>
<systemPath>\${project.basedir}/lib/$n</systemPath>
</dependency>
";
A quick&dirty batch solution (based on Alex's answer):
libs.bat
#ECHO OFF
FOR %%I IN (*.jar) DO (
echo ^<dependency^>
echo ^<groupId^>local.dummy^</groupId^>
echo ^<artifactId^>%%I^</artifactId^>
echo ^<version^>0.0.1^</version^>
echo ^<scope^>system^</scope^>
echo ^<systemPath^>${project.basedir}/lib/%%I^</systemPath^>
echo ^</dependency^>
)
Execute it like this: libs.bat > libs.txt.
Then open libs.txt and copy its content as dependencies.
In my case, I only needed the libraries to compile my code, and this solution was the best for that purpose.
To install the 3rd party jar which is not in maven repository use maven-install-plugin.
Below are steps:
Download the jar file manually from the source (website)
Create a folder and place your jar file in it
Run the below command to install the 3rd party jar in your local maven repository
mvn install:install-file -Dfile= -DgroupId=
-DartifactId= -Dversion= -Dpackaging=
Below is the e.g one I used it for simonsite log4j
mvn install:install-file
-Dfile=/Users/athanka/git/MyProject/repo/log4j-rolling-appender.jar -DgroupId=uk.org.simonsite -DartifactId=log4j-rolling-appender -Dversion=20150607-2059 -Dpackaging=jar
In the pom.xml include the dependency as below
<dependency>
<groupId>uk.org.simonsite</groupId>
<artifactId>log4j-rolling-appender</artifactId>
<version>20150607-2059</version>
</dependency>
Run the mvn clean install command to create your packaging
Below is the reference link:
https://maven.apache.org/guides/mini/guide-3rd-party-jars-local.html
A strange solution I found:
using Eclipse
create simple (non-maven) java project
add a Main class
add all the jars to the classpath
export Runnable JAR (it's important, because no other way here to do it)
select Extract required libraries into generated JAR
decide the licence issues
tadammm...install the generated jar to your m2repo
add this single dependency to your other projects.
cheers,
Balint
Even though it does not exactly fit to your problem, I'll drop this here. My requirements were:
Jars that can not be found in an online maven repository should be in the SVN.
If one developer adds another library, the other developers should not be bothered with manually installing them.
The IDE (NetBeans in my case) should be able find the sources and javadocs to provide autocompletion and help.
Let's talk about (3) first: Just having the jars in a folder and somehow merging them into the final jar will not work for here, since the IDE will not understand this. This means all libraries have to be installed properly. However, I dont want to have everyone installing it using "mvn install-file".
In my project I needed metawidget. Here we go:
Create a new maven project (name it "shared-libs" or something like that).
Download metawidget and extract the zip into src/main/lib.
The folder doc/api contains the javadocs. Create a zip of the content (doc/api/api.zip).
Modify the pom like this
Build the project and the library will be installed.
Add the library as a dependency to your project, or (if you added the dependency in the shared-libs project) add shared-libs as dependency to get all libraries at once.
Every time you have a new library, just add a new execution and tell everyone to build the project again (you can improve this process with project hierachies).
For those that didn't find a good answer here, this is what we are doing to get a jar with all the necessary dependencies in it. This answer (https://stackoverflow.com/a/7623805/1084306) mentions to use the Maven Assembly plugin but doesn't actually give an example in the answer. And if you don't read all the way to the end of the answer (it's pretty lengthy), you may miss it. Adding the below to your pom.xml will generate target/${PROJECT_NAME}-${VERSION}-jar-with-dependencies.jar
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.4.1</version>
<configuration>
<!-- get all project dependencies -->
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<!-- MainClass in mainfest make a executable jar -->
<archive>
<manifest>
<mainClass>my.package.mainclass</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<!-- bind to the packaging phase -->
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
I alluded to some python code in a comment to the answer from #alex lehmann's , so am posting it here.
def AddJars(jarList):
s1 = ''
for elem in jarList:
s1+= """
<dependency>
<groupId>local.dummy</groupId>
<artifactId>%s</artifactId>
<version>0.0.1</version>
<scope>system</scope>
<systemPath>${project.basedir}/manual_jars/%s</systemPath>
</dependency>\n"""%(elem, elem)
return s1
This doesn't answer how to add them to your POM, and may be a no brainer, but would just adding the lib dir to your classpath work? I know that is what I do when I need an external jar that I don't want to add to my Maven repos.
Hope this helps.
What works in our project is what Archimedes Trajano wrote, but we had in our .m2/settings.xml something like this:
<mirror>
<id>nexus</id>
<mirrorOf>*</mirrorOf>
<url>http://url_to_our_repository</url>
</mirror>
and the * should be changed to central. So if his answer doesn't work for you, you should check your settings.xml
I just wanted a quick and dirty workaround... I couldn't run the script from Nikita Volkov: syntax error + it requires a strict format for the jar names.
I made this Perl script which works with whatever format for the jar file names, and it generates the dependencies in an xml so it can be copy pasted directly in a pom.
If you want to use it, make sure you understand what the script is doing, you may need to change the lib folder and the value for the groupId or artifactId...
#!/usr/bin/perl
use strict;
use warnings;
open(my $fh, '>', 'dependencies.xml') or die "Could not open file 'dependencies.xml' $!";
foreach my $file (glob("lib/*.jar")) {
print "$file\n";
my $groupId = "my.mess";
my $artifactId = "";
my $version = "0.1-SNAPSHOT";
if ($file =~ /\/([^\/]*?)(-([0-9v\._]*))?\.jar$/) {
$artifactId = $1;
if (defined($3)) {
$version = $3;
}
`mvn install:install-file -Dfile=$file -DgroupId=$groupId -DartifactId=$artifactId -Dversion=$version -Dpackaging=jar`;
print $fh "<dependency>\n\t<groupId>$groupId</groupId>\n\t<artifactId>$artifactId</artifactId>\n\t<version>$version</version>\n</dependency>\n";
print " => $groupId:$artifactId:$version\n";
} else {
print "##### BEUH...\n";
}
}
close $fh;
The solution for scope='system' approach in Java:
public static void main(String[] args) {
String filepath = "/Users/Downloads/lib/";
try (Stream<Path> walk = Files.walk(Paths.get(filepath))) {
List<String> result = walk.filter(Files::isRegularFile)
.map(x -> x.toString()).collect(Collectors.toList());
String indentation = " ";
for (String s : result) {
System.out.println(indentation + indentation + "<dependency>");
System.out.println(indentation + indentation + indentation + "<groupId>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</groupId>");
System.out.println(indentation + indentation + indentation + "<artifactId>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</artifactId>");
System.out.println(indentation + indentation + indentation + "<version>"
+ s.replace(filepath, "").replace(".jar", "")
+ "</version>");
System.out.println(indentation + indentation + indentation + "<scope>system</scope>");
System.out.println(indentation + indentation + indentation + "<systemPath>" + s + "</systemPath>");
System.out.println(indentation + indentation + "</dependency>");
}
} catch (IOException e) {
e.printStackTrace();
}
}
We use Jenkins which use md5 fingerprinting to identify artifacts and whether the artifact has changed since the last build. Unfortunately Maven builds always generate binary different artifacts.
Therefore I am looking into making Maven generate the same jar artifact for the same set of input files regardless of where and when they were built, which amongst other things mean that the entries in the jar file must be sorted - not only in the index, but in the order they are written to the jar file.
After examining maven-jar-plugin which use maven-assembly-plugin, my conclusions are that they do not collect all files to be written in memory before writing them all at once, but write one at a time. This mean that it may be better to postprocess the generated jar instead of changing the current behavior so I at that time can sort the entries, zero the timestamps, etc.
I am unfamiliar with writing Maven plugins, so my question is, how should I write a plugin which Maven knows how to tell where the artifact-jar-in-progress is located and how I hook it up in my pom.xml?
(At first I need this to work for jar files, but war files would be nice too).
As mentioned, this can be done based on something similar to maven-shade-plugin. I went ahead and wrote a simple plugin to add this capability -- see https://github.com/manouti/jar-timestamp-normalize-maven-plugin (available on the Central repo).
The behavior is based on the shade plugin. It consists of a single goal called normalize which can be bound to the package lifecycle phase and configured in the project's POM:
<plugins>
<plugin>
<groupId>com.github.manouti</groupId>
<artifactId>jar-timestamp-normalize-maven-plugin</artifactId>
<version>1.0-SNAPSHOT</version>
<executions>
<execution>
<id>jar-normalize</id>
<goals>
<goal>normalize</goal>
</goals>
<phase>package</phase>
</execution>
</executions>
</plugin>
</plugins>
A few notes about the plugin:
The artifact under build is accessed via project#getArtifact() where project is a org.apache.maven.project.MavenProject.
Normalization consists of mainly three steps:
Setting the last modified time of all Jar entries to a specific timestamp (default value is 1970-01-01 00:00:00AM but can be changed via -Dtimestamp system property).
Reordering (alphabetically) of attributes in the manifest except for Manifest-Version which always comes first.
Removing comments from the pom.properties file which contain a timestamp that causes the Jar to differ from one build to another.
Once invoked, the goal will generate the output file next to the original artifact (named artifactId-version-normalized.jar), i.e. in the project.build.directory directory.
To create maven plugin project
mvn archetype:generate \
-DgroupId=sample.plugin \
-DartifactId=hello-maven-plugin \
-DarchetypeGroupId=org.apache.maven.archetypes \
-DarchetypeArtifactId=maven-archetype-plugin
invoke this command it will generate a skeleton project with a class called MyMojo.java
write your stuff inside execute() method, and install that plugin to your repository by mvn clean install
then attach its execution with your project, in your project pom.xml
<build>
<plugins>
<plugin>
<groupId>sample.plugin</groupId>
<artifactId>hello-maven-plugin</artifactId>
<version>1.0-SNAPSHOT</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>sayhi</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
to access project properties inside your Mojo
/**
* The Maven project.
*
* #parameter expression="${project}"
* #required
* #readonly
*/
private MavenProject project;
and then
project.getProperties("build.directory")
and read other properties to determine your jar file packed
See
maven: guide-java-plugin-development
I agree on creating a custom maven plugin seems like a better option. I dont know about an existing plugin provides solution for what you asked.
md5 checksum (or sha-1 in my repository) is generated with install plugin, so seems like you need to extend this or write a new plugin which works after install phase.
I have 2 suggestions about this plugin:
1) When thinking simple, this plugin should:
Read generated jar:
Extract all entries.
Exclude some entries (e.g. MANIFEST.MF).
Sort remaining entries .
Extract md5s for each in memory.
Generate a single md5 from all of those extracted.
However when considering about where & when independency: Accordig to .class file structure Java_class_file there is minor, major versions entries are held in compiled class files. So if compiler changes, .class files will be changed. In this case we need a check on source code level from this point :( So this solution become useless if there is no guarantee on copiler version.
2) As very dirty but easy solution, this plugin may only extract your module's pom.xml file's md5 code. But you must guarantee each change in your jar reflects to a minor version (or built number) manually.
Instead of writing your own plugin you can write a Groovy script that is executed by groovy-maven-plugin:
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>groovy-maven-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<source>
import java.util.jar.*
String fileName = '${project.build.directory}/${project.build.finalName}.jar'
println "Editing file ${fileName}"
JarFile file = new JarFile(fileName);
// do your edit
</source>
</configuration>
</execution>
</executions>
</plugin>