How to specify Java version in Spring/Spring Boot pom.xml?

What is the correct way of specifying Java 11 as the version to be used in Spring (or Spring Boot) pom.xml file?

I.e., what value do I need to put in the java.version property of the pom?

For Java 8 we use 1.8, just like the documentation shows, for Java 9 it's 1.9.

I'm not sure if Java 11 would be 1.11 (although it seems unlikely), and I've seen it specified as just 11 when using maven-compiler-plugin, however I'm not using the compiler plugin.

e.g.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <release>11</release>
    </configuration>
</plugin>

I've searched around and couldn't find the answer, as pretty much any documentation I've read as well as blog posts related to the Java version only show versions 8 or 9.

So what should I use? 1.11 or just 11?

I tried both and my web server seems to start correctly and compile correctly (IntelliJ shows Information:javac 11.0.2 was used to compile java sources) however I'm not entirely convinced that changing the java.version value is doing anything, because I can set it to e.g. 100 and everything works fine.

The only related questions I could find are: Minimum Spring version compatible with Java 11, Spring Boot fails due to a Hibernate error after migrating to JDK 11 and Spring 4.3.x with OpenJDK 11, but they don't really shed any light.

Short Answer:

The correct way is to use the followings values in <java.version> for different Java versions:

• Java 8 : 1.8 or 8
• Java 9 : 9
• Java 10 : 10
• Java 11 : 11
• Java 12 : 12
• .....
• .....
• Java 16 : 16
• Java 17 : 17

So for Java 11 , it should be:

<properties>
   <java.version>11</java.version>
</properties>

> However I'm not sure if Java 11 would be "1.11" (seems unlikely), and > I've seen it specified as just "11" when using maven-compiler-plugin, > however I'm not using the compiler plugin.

Actually , at the end it still uses maven-compiler-plugin to compile. Springboot just configures a <java.version> property such that by changing this value , you are implicitly changing maven-compiler-plugin 's <source/> and <target/> to the same value as what specified in the <java.version> :

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <source>11</source>  <!-- same as <java.version> -->
        <target>11</target>    <!-- same as <java.version> -->
    </configuration>
</plugin>

---

Detailed Answer:

Seem like you want details to convince you.

It is because every spring boot project will extend the parent pom spring-boot-starter-parent which defines <java.version> as follows:

<properties>
    <java.version>1.8</java.version>
    <maven.compiler.source>${java.version}</maven.compiler.source>
    <maven.compiler.target>${java.version}</maven.compiler.target>
</properties>

From the maven-compiler-plugin docs, maven.compiler.source and maven.compiler.target are the user property for the <source> and <target> config parameters. Due to the behaviour of the user property, setting these two properties to 11 means to set the following :

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <source>11</source>   <!-- maven.compiler.source  -->
        <target>11</target> <!-- maven.compiler.target -->
    </configuration>
</plugin>

From the maven-compiler-plugin docs again, <source> and <target> are the -source and -target argument for the Java compiler (javac). Then, from javac docs, we can see that these two arguments are allowed to have the following values:

> - 1.6 : No language changes were introduced in Java SE 6. However, encoding errors in source files are now reported as errors instead of > warnings as was done in earlier releases of Java Platform, Standard Edition. > - 6 : Synonym for 1.6. > - 1.7 : The compiler accepts code with features introduced in Java SE 7. > - 7 : Synonym for 1.7. > - 1.8 : The compiler accepts code with features introduced in Java SE 8. > - 8 : Synonym for 1.8. > - 9 : The compiler accepts code with features introduced in Java SE 9. > - 10 : The compiler accepts code with features introduced in Java SE 10. > - 11 : The compiler accepts code with features introduced in Java SE 11. > - 12 : The compiler accepts code with features introduced in Java SE 12.

Hence, <java.version> should be set to 11 for Java 11.

If any one looking to specifying Java 11 as the version to be used in Spring (or Spring Boot) in a gradle project, then use either sourceCompatibility = '11' or sourceCompatibility = '1.11' in your build.gradle file

plugins {
id 'org.springframework.boot' version '2.1.4.RELEASE'
}

apply plugin: 'io.spring.dependency-management'

group = 'au.com.ranuka'
version = '0.0.1-SNAPSHOT'

sourceCompatibility = '11'
//or 
sourceCompatibility = '1.11'

repositories {
   mavenCentral()
}

dependencies {

}

I am adding it as an answer so it can be helpful to more people:

Since Java 9 the versions are specified as 9, 10, 11, and so on, instead of 1.8, 1.7, etc. Some further reading here.

The way you are specifying the JDK version with <release>11</release> is correct. It was introduced with maven-compiler-plugin 3.6 and is equivalent as the old way, as below:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
      <source>11</source> -- Using JDK 11 to compile
      <target>11</target> -- Using JDK 11 as target
    </configuration>
  </plugin>
</plugins>

This post can be helpful on using maven-compiler-plugin with JDK 11.

You should not need to mention the maven-compiler-plugin in your POM file, if you only want to specify the compiler version. Instead, add these properties to your pom file

<properties>
  <maven.compiler.source>1.8</maven.compiler.source>
  <maven.compiler.target>1.8</maven.compiler.target>
</properties>

Edit: My bad, it looks like the version number properties have changed starting with the 3.6 release of the maven-compiler-plugin. The example above is fine for java 8 and lower. For java 9, add this property:

<properties>
    <maven.compiler.release>9</maven.compiler.release>
</properties>

Check out the accepted answer to this question: https://stackoverflow.com/questions/38882080/specifying-java-version-in-maven-differences-between-properties-and-compiler-p