I have created new maven java project in eclipse by clicking File->New->Other->Maven->New Project. I found that projects is using java 1.5. In my PC exist only java 1.4 and java 8. I need to compile project using java 1.4 JDK. I go to Project->Properties-> JRE System Library and change to java 1.4. When I run main class I have error:
java.lang.UnsupportedClassVersionError: arr/ff (Unsupported major.minor version 49.0)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:537)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:251)
at java.net.URLClassLoader.access$100(URLClassLoader.java:55)
at java.net.URLClassLoader$1.run(URLClassLoader.java:194)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)
How to make project java 1.4 compatible?
First, I'd define a property to control the value. Something like,
<properties>
<java.version>1.4</java.version>
</properties>
And then add a build stanza, like
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<verbose>true</verbose>
<fork>true</fork>
<debug>false</debug>
<source>${java.version}</source>
<target>${java.version}</target>
</configuration>
</plugin>
</plugins>
</build>
Specify source and target Java version by this way:
<project>
[...]
<build>
[...]
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.5</source>
<target>1.4</target>
</configuration>
</plugin>
</plugins>
[...]
</build>
[...]
</project>
Read offical document.
Read about Java version compatibility.
Usually IDEs use maven pom.xml file as a source of project configuration. Changing the compiler settings in the IDE not always has effect on the maven build. The best way to keep a project always manageable with maven is edit the pom.xml files and instruct the IDE to sync with maven.
Configure the maven compiler plugin in the pom.xml
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.5</source>
<target>1.4</target>
</configuration>
</plugin>
</plugins>
...
OR Set these properties (always in the pom)
<properties>
<maven.compiler.source>1.5</maven.compiler.source>
<maven.compiler.target>1.4</maven.compiler.target>
</properties>
Related
I can only use java 1.6 for my project. So maven version also has to be 2.2.1 . Cannot use maven 3.0. But while building I'm getting following error :
Error resolving version for 'org.apache.maven.plugins:maven-jar-plugin':Plugin requires Maven version 3.0
this is the pom:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
what are the version that we can use?
Changes the source and target to 1.6. If your code does not make use of java8 features then it should work just fine. This will generate a jar that is compatible with any java6 codebase.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
When I was building my project like :-
mvn clean install -DskipTests
, then it was giving some error.
After that, I just added, -Djdk.version=1.8, then it works fine.
Can someone tell what is the reason for this?
Try something like this in your pom:
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</pluginManagement>
....
</build>
It may be because you might be missing the maven-compiler-plugin.
Try the following:
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</pluginManagement>
....
</build>
From Maven 3, it defaults to JDK 1.5. So if you do not include the version, it will take JDK 1.5 as default compiler version.
Since, you mentioned that you used JDK 1.8, and the error disappeared. So if you had maven-compiler-version defined in the pom.xml, the error might be because the version would had not been defined.
So by default, it pointed to JDK 1.5 and it was trying to compile the code which would be defined for JDK 1.8 and not for JDK 1.5.
So, it is better to define the correct java version in the pom.xml
Why to specify java version in maven build?
Because Maven won't try to guess the Java version your project was created with (the one you probably only configured in your IDE).
You need to specify the earliest version supported in your pom.xml with:
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
I'm using a parent pom which establishes java version to 1.5. In my concrete project I use 1.6 so I was changing the compiler version in eclipse each time I did a Maven Update.
Looking for a solution to this I found some solutions involving overriding the behavior of the parent pom in the child one.
My question is if there are any differences between them and if so, which option should I use. The options I found (perhaps there are more) are:
In properties tag: <app.java.version>1.6</app.java.version>
In properties tag: <jdk.version>1.6</jdk.version>
In configuration tag: <source>${jdk.version}</source>
I'm very new to Maven. Thanks in advance.
You definitely want to go with:
<properties>
<maven.compiler.source>1.6</maven.compiler.source>
<maven.compiler.target>1.6</maven.compiler.target>
</properties>
It is the de facto standard Maven property for setting up Java version and it's used not only by maven-compiler-plugin but also by other standard Maven plugins (including reporting ones), so this applies your Java version globally, not only for compiling classes.
Properties are just properties, which do not mean much unless you use them somewhere.
The important thing is that you set the version in the maven-compiler-pluginconfiguration:
<properties>
<jdk.version>1.6</jdk.version>
</properties>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>${jdk.version}</source>
<target>${jdk.version}</target>
</configuration>
</plugin>
</plugins>
If your parent pom uses 1.7 jdk and you want child pom to use 1.6 java version. combine.self="override" is important use following code:
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration combine.self="override">
<verbose>true</verbose>
<fork>true</fork>
<executable>/usr/lib/jvm/java-1.6.0-openjdk-amd64/bin/javac</executable>
<compilerVersion>1.6</compilerVersion>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
I am using Eclipse as IDE. When I right click on the project, then click "Maven Update", my Java version changes to 1.5. Here is what I did so far:
I changed "Java build path" to "workspace default jre 1.8.0_25"
Then changed "java compiler" to 1.8
Then changed "project facets">java>1.8
Lastly Changed pom.xml java version to 1.8
<build>
<plugins>
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
<version>9.1.3.v20140225</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugin</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.2</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
How can I keep it to 1.8 version?
There's a typo in the groupId of the maven-compiler-plugin in your pom.xml file: it should be org.apache.maven.plugins.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.2</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
Note that the groupId actually defaults to org.apache.maven.plugins so you could also omit it.
By default, the JRE used by m2e is 1.5, see this question : Eclipse JRE System Library [J2SE-1.5]
How can I use source 5?
I tried
mvn -source 5 test
but it didn't work :-)
When I compile the file by javac, everything works.
You need to configure the maven-compiler-plugin:
<project>
...
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
...
</plugins>
...
</build>
</project>
EDIT: Changed example to use latest version of the plugin.