I developed and built my Java application using Maven. I need to support Java 1.6, so I use the following properties:
<maven.compiler.target>1.6</maven.compiler.target>
<maven.compiler.source>1.6</maven.compiler.source>
Still, when I run the application I get an "Unsupported major.minor version" error and I suspect that one of my dependency jars is compiled with a Java version newer than the one I need to support.
My questions:
Is this even possible? I thought Maven would take care of this kind of dependency version problems.
Is there an easy way to find out the minor/major version of all my dependencies? (Would be awesome if it could be shown when doing mvn dependency:tree for instance.)
The problem is that every dependency (maintainer) can decide on it's own which java version is used to compile (1.5, 1.6, 1.7, 1.8 etc) so this is not solvable via Maven. But you can make sure that you don't use dependencies which are using a different Java version than you like to have.
This can be enfored by using Maven Enforcer Plugin by using extra-enforcer-rules:
<project>
[...]
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-enforcer-plugin</artifactId>
<version>1.4.1</version> <!-- find the latest version at http://maven.apache.org/plugins/maven-enforcer-plugin/ -->
<executions>
<execution>
<id>enforce-bytecode-version</id>
<goals>
<goal>enforce</goal>
</goals>
<configuration>
<rules>
<enforceBytecodeVersion>
<maxJdkVersion>1.6</maxJdkVersion>
<excludes>
<exclude>org.mindrot:jbcrypt</exclude>
</excludes>
</enforceBytecodeVersion>
</rules>
<fail>true</fail>
</configuration>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>org.codehaus.mojo</groupId>
<artifactId>extra-enforcer-rules</artifactId>
<version>1.0-beta-5</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
[...]
</project>
This will break your build if you have a dependency which is compiled with a different version of JDK than you want to have.
To answer your two questions:
Yes, this is possible. Looking at the docs, the <maven.compiler.target> and <maven.compiler.source> properties simply tells Maven which version of javac to use to compile your project. And I quote, for your reference:
Note: Merely setting the target option does not guarantee that your
code actually runs on a JRE with the specified version. The pitfall is
unintended usage of APIs that only exist in later JREs which would
make your code fail at runtime with a linkage error. To avoid this
issue, you can either configure the compiler's boot classpath to match
the target JRE or use the Animal Sniffer Maven Plugin to verify your
code doesn't use unintended APIs.
The magic number after the Unsupported major.minor version error actually tells the version of the JRE the class file is compatible with:
J2SE 8 = 52,
J2SE 7 = 51,
J2SE 6.0 = 50,
J2SE 5.0 = 49,
JDK 1.4 = 48,
JDK 1.3 = 47,
JDK 1.2 = 46,
JDK 1.1 = 45
I don't know if there is an easy way to tell the major/minor version of ALL the dependencies (and transitive dependencies) in a project though.
UPDATE: Though I haven't used it before, I wonder the Animal Sniffer Maven plugin will help to sniff out the major/minor version of your dependencies.
Related
I'm building a java project with maven.
I want to make sure several things:
the built jar CAN run on jre8.
the built jar CAN run on jre9, with module/jigsaw.
the built jar CAN be put on maven central.
How should I configure the maven-compiler-plugin?
thanks.
the original repo is at https://github.com/cyanpotion/SDL_GameControllerDB_Util
right now I can pass 2 and 3, but the output jar seems cannot run on jre8.
A multi-release jar can be used to accomplish this purpose; however, if you are only after Jigsaw module support, a dual compilation configuration of Java 8 and 9 with the maven-compiler-plugin is sufficient (demonstrated below).
The following is a build configuration that is able to maintain JRE 8 support, but is compatible with being used as a module in JRE 9+. This can be tweaked to support a project as far back as JRE 1.6, if necessary.
Overview of the following build configuration:
Enforce a $JAVA_HOME JDK 9+ so that module-info.java can be compiled and validated against the sources (ensures that all module dependencies are correctly referenced).
Changes the default-compile execution to NO-OP. By specifying <release>8</release> (or target/source flags), some IDEs during Maven auto-importation (tested with IntelliJ) will assume the language level for this project is Java 8, and produce errors about the project's module-info.java.
Compiles all sources (including module-info.java) for Java 9; this ensures that the module-info.java includes any dependencies used without the project sources.
Compile all sources (excluding module-info.java) for Java 8, overwriting all previously compiled Java 9 classes with Java 8 classes; this means the only Java 9 class (class level 53+) will be module-info.class. All other classes should now be executable on a compliant JRE 8.
Notes:
A caveat is this will compile sources twice, once for Java 8 and another for Java 9. This may significantly increase build times for larger projects (but negligible for smaller projects). This may resolved by placing module-info.java in another source directory (e.g. src/main/java9) and configuring a multi-release JAR (see the first link at the beginning of this message). Note that for proper IDE auto-importation and marking this additional Java 9 source directory correctly, a NO-OP execution with org.codehaus.mojo:build-helper-maven-plugin can be used.
Only module-info.java will have Java 9 support, all other classes are limited to classes/methods/fields/code available in JDK/JRE 8.
Some tooling may need to be updated in your project configuration if it does not support Java 9 module-info.class. Some older variants of the default Maven plugins do not have sufficient support for modules.
<build>
<plugins>
<!-- ensure the project is compiling with JDK 9+ -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-enforcer-plugin</artifactId>
<version>3.0.0-M3</version>
<executions>
<execution>
<id>enforce-jdk9</id>
<goals>
<goal>enforce</goal>
</goals>
<configuration>
<rules>
<requireJavaVersion>
<version>[1.9,)</version>
<message>JDK 9+ is required for compilation</message>
</requireJavaVersion>
</rules>
</configuration>
</execution>
</executions>
</plugin>
<!-- compile sources -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<executions>
<!-- disable default phase due to fixed id and position in lifecycle -->
<execution>
<id>default-compile</id>
<phase>none</phase>
<!-- specify source/target for IDE integration -->
<configuration>
<release>9</release>
</configuration>
</execution>
<!-- compile sources with Java 9 to generate and validate module-info.java -->
<execution>
<id>java-9-module-compile</id>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<release>9</release>
</configuration>
</execution>
<!-- recompile sources as Java 8 to overwrite Java 9 class files, except module-info.java -->
<execution>
<id>java-8-compile</id>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<!-- specify JDK 9+ release flag to ensure no classes/methods later than Java 8 are used accidentally -->
<release>8</release>
<!-- exclude module-info.java from the compilation, as it is unsupported by Java 8 -->
<excludes>
<exclude>module-info.java</exclude>
</excludes>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
I've done it. See my project, the IPAddress Java library. You compile with Java 9 compiler level, then you recompile everything except the module-info.java with Java 8 compile level.. So you have a Java 8 jar with a Java 9 module-info. You can see the compile commands in my ant xml script on GitHub.
There was originally an issue with Android studio that has since been resolved, it would not ignore the module-info. More recent Android studio versions are fine, and so are all Java platforms and environments. Java 9 jres and up will recognize the module-info, Java 8 will not, Java 8 and earlier will ignore it.
My jar is also in maven central, so it is satisfying your 3 requirements. Try it out in your dev environment to see it work, using Java 8 or later jres.
Multi-release jars are not necessary and not worth the trouble.
When I was researching this same question I found this same solution in use with an Apache project, so I am not the only one doing it.
I'm experiencing an odd behavior in maven as well as in eclipse itself.
Even though i configured my project to be compiled in Java 1.8, I can compile and run (eclipse) a piece of code that was introduced in Java 9
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
The code line in question:
LocalTime.ofInstant(cal.toInstant(), cal.getTimeZone().toZoneId());
I'm using Oracle's JDK 11 locally for compiling and running in eclipse without any errors. When i package it into a docker container using openjdk:8-jdk-alpine it will boot up, but throw the following Exception when I call the method:
java.lang.NoSuchMethodError: java.time.LocalTime.ofInstant(Ljava/time/Instant;Ljava/time/ZoneId;)Ljava/time/LocalTime
How can I avoid and identify these situations before they go to testing? Am I doing something wrong or is it a bug in the build system or in JDK11?
thanks in advance
The source option specifies that the source code must be compatible with Java 8, the target option that the classes should be compatible with Java 8. However, you will still compile with the Java 11 class library if you build with Java 11 and then you can get errors like the one you have.
There are two good solutions. One is to use the Maven toolchains plugin and build with Java 8. Then you can have multiple Java versions installed and Maven will use the configured one on a per-project basis.
The other is to use the new release and testRelease options. They will build with API classes from the given release. Just add <release>1.8</release>.
If you are using JDK 11, configure your maven pom.xml like that:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-release-plugin</artifactId>
<version>2.5.3</version>
</plugin>
</plugins>
</build>
I was trying to install the dependency packages into my location maven repository with running mvn clean install from my maven project.
But unfortunately. I got a compile error for some source files which said :annotations are not supported in -source 1.3(use -source 5 or higher to enable annotations)#override.
After researching. I found I need to specify the source version of my maven project.
So I add the following configuration in the POM.
<build>
<defaultGoal>install</defaultGoal>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
</plugins>
</build>
Actually. It does work fine. But what makes me confused is where does the JDK1.6 comes from and make the Maven compile work ? I didn't have the JDK1.6 install in my computer(Currently, the available JDK installed in my computer is JDK1.8), Thanks.
Later versions of Java allow you to compile your program as earlier versions. Since you have Java 8 installed you can compile your program as a Java 6 one that will run on a machine with only the 1.6 JRE. The limitation is that you can't use any of the language features added in the Java 7 and 8 releases.
I'm not very experienced with Maven and while experimenting with multi-module project I started wondering how can I specify Java version for all my child modules in parent Maven pom. Until today I was using just:
<properties>
<java.version>1.8</java.version>
</properties>
...but when researching I found that you can also specify Java version in Maven compiler plugin, like that:
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
And then wrap this into plugin management tag to enable child poms usage of this. So the first question is this:
What are the differences beetwen setting Java version in properties and in Maven compiler plugin?
I couldn't find clear answer but in process of researching I found that you can also specify Java version in this way:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
...which suggest that compiler plugin is there even if I don't explicit declare it. Running mvn package outputs with
maven-compiler-plugin:3.1:compile (default-compile) # testproj ---
...and some other plugins that I didn't declare.
So are those plugins default, hidden part of Maven pom? Are there any differences between setting source/target in properties and in Maven plugin configuration element?
Some other questions are - which way should be used (and when if they are not equal)? Which one is best for multi-module project and what happens if Java version specified in pom is different than version pointed in JAVA_HOME?
How to specify the JDK version?
Use any of three ways: (1) Spring Boot feature, or use Maven compiler plugin with either (2) source & target or (3) with release.
Spring Boot
<java.version> is not referenced in the Maven documentation.
It is a Spring Boot specificity.
It allows to set the source and the target java version with the same version such as this one to specify java 1.8 for both :
1.8
Feel free to use it if you use Spring Boot.
maven-compiler-plugin with source & target
Using maven-compiler-plugin or maven.compiler.source/maven.compiler.target properties are equivalent.
That is indeed :
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
is equivalent to :
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
according to the Maven documentation of the compiler plugin
since the <source> and the <target> elements in the compiler configuration use the properties maven.compiler.source and maven.compiler.target if they are defined.
source
The -source argument for the Java compiler.
NOTE: Since 3.8.0 the default value has changed from 1.5 to 1.6. Since 3.9.0 the default value has changed from 1.6 to 1.7
Default value is: 1.7.
User property is: maven.compiler.source.
target
The -target argument for the Java compiler.
NOTE: Since 3.8.0 the default value has changed from 1.5 to 1.6. Since 3.9.0 the default value has changed from 1.6 to 1.7
Default value is: 1.6.
User property is: maven.compiler.target.
About the default values for source and target, note that
since the 3.8.0 of the maven compiler, the default values have changed from 1.5 to 1.6.
maven-compiler-plugin with release instead of source & target
The maven-compiler-plugin 3.6 and later versions provide a new way :
org.apache.maven.plugins
maven-compiler-plugin
3.8.0
9
You could also declare just :
<properties>
<maven.compiler.release>9</maven.compiler.release>
</properties>
But at this time it will not work as the maven-compiler-plugin default version you use doesn't rely on a recent enough version.
The Maven release argument conveys release : a new JVM standard option that we could pass from Java 9 :
Compiles against the public, supported and documented API for a
specific VM version.
This way provides a standard way to specify the same version for the source, the target and the bootstrap JVM options.
Note that specifying the bootstrap is a good practice for cross compilations and it will not hurt if you don't make cross compilations either.
Which is the best way to specify the JDK version?
The first way (<java.version>) is allowed only if you use Spring Boot.
For Java 8 and below :
About the two other ways : valuing the maven.compiler.source/maven.compiler.target properties or using the maven-compiler-plugin, you can use one or the other. It changes nothing in the facts since finally the two solutions rely on the same properties and the same mechanism : the maven core compiler plugin.
Well, if you don't need to specify other properties or behavior than Java versions in the compiler plugin, using this way makes more sense as this is more concise:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
From Java 9 :
The release argument (third point) is a way to strongly consider if you want to use the same version for the source and the target.
What happens if the version differs between the JDK in JAVA_HOME and which one specified in the pom.xml?
It is not a problem if the JDK referenced by the JAVA_HOME is compatible with the version specified in the pom but to ensure a better cross-compilation compatibility think about adding the bootstrap JVM option with as value the path of the rt.jar of the target version.
An important thing to consider is that the source and the target version in the Maven configuration should not be superior to the JDK version referenced by the JAVA_HOME.
A older version of the JDK cannot compile with a more recent version since it doesn't know its specification.
To get information about the source, target and release supported versions according to the used JDK, please refer to java compilation : source, target and release supported versions.
How handle the case of JDK referenced by the JAVA_HOME is not compatible with the java target and/or source versions specified in the pom?
For example, if your JAVA_HOME refers to a JDK 1.7 and you specify a JDK 1.8 as source and target in the compiler configuration of your pom.xml, it will be a problem because as explained, the JDK 1.7 doesn't know how to compile with.
From its point of view, it is an unknown JDK version since it was released after it.
In this case, you should configure the Maven compiler plugin to specify the JDK in this way :
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
<compilerVersion>1.8</compilerVersion>
<fork>true</fork>
<executable>D:\jdk1.8\bin\javac</executable>
</configuration>
</plugin>
You could have more details in examples with maven compiler plugin.
It is not asked but cases where that may be more complicated is when you specify source but not target. It may use a different version in target according to the source version. Rules are particular : you can read about them in the Cross-Compilation Options part.
Why the compiler plugin is traced in the output at the execution of the Maven package goal even if you don't specify it in the pom.xml?
To compile your code and more generally to perform all tasks required for a maven goal, Maven needs tools. So, it uses core Maven plugins (you recognize a core Maven plugin by its groupId : org.apache.maven.plugins) to do the required tasks : compiler plugin for compiling classes, test plugin for executing tests, and so for... So, even if you don't declare these plugins, they are bound to the execution of the Maven lifecycle.
At the root dir of your Maven project, you can run the command : mvn help:effective-pom to get the final pom effectively used. You could see among other information, attached plugins by Maven (specified or not in your pom.xml), with the used version, their configuration and the executed goals for each phase of the lifecycle.
In the output of the mvn help:effective-pom command, you could see the declaration of these core plugins in the <build><plugins> element, for example :
...
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>2.5</version>
<executions>
<execution>
<id>default-clean</id>
<phase>clean</phase>
<goals>
<goal>clean</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>2.6</version>
<executions>
<execution>
<id>default-testResources</id>
<phase>process-test-resources</phase>
<goals>
<goal>testResources</goal>
</goals>
</execution>
<execution>
<id>default-resources</id>
<phase>process-resources</phase>
<goals>
<goal>resources</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<executions>
<execution>
<id>default-compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>default-testCompile</id>
<phase>test-compile</phase>
<goals>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
</plugin>
...
You can have more information about it in the introduction of the Maven lifeycle in the Maven documentation.
Nevertheless, you can declare these plugins when you want to configure them with other values as default values (for example, you did it when you declared the maven-compiler plugin in your pom.xml to adjust the JDK version to use) or when you want to add some plugin executions not used by default in the Maven lifecycle.
None of the solutions above worked for me straight away. So I followed these steps:
Add in pom.xml:
<properties>
<maven.compiler.target>1.8</maven.compiler.target>
<maven.compiler.source>1.8</maven.compiler.source>
</properties>
Go to Project Properties > Java Build Path, then remove the JRE
System Library pointing to JRE1.5.
Force updated the project.
The below steps work for me like charm! so thought to share with everyone.
These are the lines i added in the pom.xml file to work with a basic project. I am using Java 12 (you can replace yours 11, 10, 1.8 etc).
<properties>
<maven.compiler.source>12</maven.compiler.source>
<maven.compiler.target>12</maven.compiler.target>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<release>12</release>
</configuration>
</plugin>
</plugins>
</build>
After changing the pom file please reload your project so that IDE can download/fetch the plugin to the project. (For IntelijIDEA: Right-click on pom.xml -> Go to maven -> Reload project).
please make sure to configure the desire version in your IDE as well.
if you are using IntelliJ idea maven build.
Consider the alternative:
<properties>
<javac.src.version>1.8</javac.src.version>
<javac.target.version>1.8</javac.target.version>
</properties>
It should be the same thing of maven.compiler.source/maven.compiler.target but the above solution works for me, otherwise the second one gets the parent specification (I have a matrioska of .pom)
For NetBeans IDE, changing project properties - (Jersey Service) - Categories > Sources >
Selected 'Source/Binary Format' as 1.8.
Afternoon all,
I am receiving the above error when trying to build my project. I'm pretty sure this has something to do with Maven's latest update being compiled using Java 1.6 and the project we are trying to build is a 1.4 project. The plugin prior to this worked without problems, so I have added the following to the POM.xml file to try to force the existing plugin to be used.
<dependency>
<groupId>org.codehaus.plexus</groupId>
<artifactId>plexus-archiver</artifactId>
<version>1.2</version>
</dependency>
But it continues to fail.
Any help would be much appreciated
Thanks
Try to add the following plugin for maven. It works for me:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
The error you are experiencing means that org/codehaus/plexus/archiver/jar/JarArchiver was compiled against Java 1.5 whilst you are trying to load using older Java version.
1.2 version of plexus-archiver works under Java 1.4. However 2.0 requires Java 1.5. Are you sure you are using 1.2?
If this is a plugin, it should be defined under <plugins>.
Use:
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</pluginManagement>
I was getting this error till I changed my maven-source-plugin version to 2.2.1. I was getting the error with 2.1.1.
Including the 'old' version of a plugin in the pom.xml is solving part of the problem. you also need to make sure you are using the right jvm to match.
For a current project i'm working on I had to set JAVA_HOME to java 1.4 with maven 2.0.8. Problem with maven is that it looks for updates in the local and remote repositories (if there is a remote repository set in the maven settings.xml), than tries use version 2.5 for the 'clean' and 'install' plugins for example causing the major.minor 49.0 error (clean and install plugins version 2.5 are compiled with java 1.5 or greater while I tried to execute them in a java 1.4 environment).
With adding in the plugin snippet in the pom.xml of the project forcing it to use version 2.2 combined with the old java version on my path:
(set path=c:\youroldjavadirectory\bin;c:\youroldmavendirectory\bin) everything started working.
Check versions of java before running the maven command:
java -version
mvn -v
According to Fred from the m2e-mailing list, this has been fixed with m2eclipse-mavenarchiver 0.17.0. You can install it from http://repo1.maven.org/maven2/.m2e/connectors/m2eclipse-mavenarchiver/0.17.0/N/LATEST/
Just add the repo as an update site, and then upgrade the mavenarchiver component.