How to change compiler compliance level to 1.8 in eclipse

Maven JDK 1.8 use in Eclipse

A reminder of this rocky relationship is the fact that Eclipse and Maven have a habit of forcing Java 5 compliance on new applications, even if JDK 1.8 is the only JVM installed on the development machine. The Java 1.5 compliance issue means Lambda expressions, stream access or newer language features besides generics won’t compile.

Some developers try and change the Java compiler setting within Eclipse from Java 1.5 to Java 1.8, but that only works temporarily. As soon as a new Maven build takes place, the JDK version reverts back to 1.5. The only way to make this a permanent change is to edit the Maven compiler plugin POM entry and force Eclipse and Maven to use Java 1.8.

Eclipse Maven JDK 1.8 compliance and support

Of course, there is a fairly simple answer to this problem. That’s why everyone loves Maven. The build tool always has a simple resolution on offer. To force Eclipse and the Maven compiler plugin  to have JDK 1.8 compliance on your new projects, simply add the following to your POM file:

<!-- Force Eclipse and Maven to use a Java 8 JDK compiler-->
<properties>
  <maven.compiler.target>1.8</maven.compiler.target>
  <maven.compiler.source>1.8</maven.compiler.source>
</properties>

Maven Java 1.8 plugin support

An alternate, albeit slightly more verbose approach to tell Eclipse and Maven to use Java 8 or newer compilers is to configure the Apache Maven plugin:

<!-- Build plugin to force Maven JDK 1.8 compliance -->
<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>
  </plugins>
</build>

Maven compiler plugin and Java 11

Note that since the 3.8.0 version of the Maven compiler plugin, you can actually specify the release version of Java rather than source and target:

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

Eclipse Java 1.8 compiler setting

Once the maven-compiler-plugin change is made to the POM, you can open up Eclipse’s Java compiler properties page and notice that JDK compliance has changed from JDK 1.5 to 1.8.

When the POM updates to Maven JDK 1.8 support, the Eclipse Java compiler page reflects the change.

It’s a tedious problem but it’s also one that is easily fixed by a quick edit to the Maven compiler plugin. Furthermore, you only need to edit the POM file once on a project to force Eclipse and Maven to use Java 8 or Java 11. It’s really not all that big an inconvenience to overcome.