How to Resolve the Maven Error: “Invalid target release: 21”

In the world of Java development, Apache Maven stands as a pivotal tool for project management and comprehension. It simplifies the build process like compiling and packaging, and also manages project dependencies. However, Maven users occasionally face issues that can hinder their development workflow, one of which is the “Invalid target release: 21” error. This error can occur for several reasons, but it primarily signals a discrepancy between the Java version used for the project and the version recognized by Maven. This article will delve into the causes of this error and offer practical solutions to resolve it effectively.

Understanding the Error

The “Invalid target release: 21” error typically arises when attempting to compile a Java project with Maven, specifying Java 21 as the target release in the Maven configuration. This error indicates that the Java compiler version being used by Maven does not support the specified target version. The reasons for encountering this error can include but are not limited to:

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• The installed JDK (Java Development Kit) version is lower than 21.
• Maven is not correctly configured to use the appropriate JDK version.
• Environmental variables point to a different JDK version.

Causes and Solutions

1. JDK Version Mismatch

• Cause: You might have an older version of the JDK installed, which does not support compiling to Java 21.
• Solution: Verify and update your JDK installation to version 21 or higher. You can check your current JDK version by running java -version and javac -version in the terminal. If needed, download and install the latest JDK from the official Oracle website or adopt an OpenJDK distribution.

2. Maven Configuration

• Cause: Maven uses the JDK version specified in its configuration files or environment settings, which might not match the project’s requirements.
• Solution: Ensure Maven is configured to use the correct JDK version. You can specify the JDK version in the pom.xml file using the maven-compiler-plugin:

  
  <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.8.1</version> <!-- Use the latest version -->
      <configuration>
          <source>21</source> <!-- JDK source version -->
          <target>21</target> <!-- JDK target version -->
          <release>21</release> <!-- Use this for JDK 9+ to ensure API compatibility -->
      </configuration>
  </plugin>
  
  

3. Environmental Variables

• Cause: The JAVA_HOME environment variable or PATH might be set to an older JDK version.
• Solution: Update the JAVA_HOME environment variable to point to the JDK 21 installation directory. Also, ensure the updated JAVA_HOME is correctly reflected in your system’s PATH. You can verify the settings by running echo %JAVA_HOME% on Windows or echo $JAVA_HOME on Unix/Linux/MacOS systems.

• How to Set JAVA_HOME on macOS
• How to Set JAVA_HOME on Windows
• How to Set JAVA_HOME on Ubuntu/Linux Mint

Verifying the Solution

After addressing the potential causes, you can verify the solution by running the Maven build again with the mvn clean install command. If the configuration is correct, Maven should successfully compile the project using Java 21 without throwing the “Invalid target release: 21” error.

Conclusion

Resolving the “Invalid target release: 21” error in Maven involves ensuring that the JDK version matches the project’s requirements, correctly configuring Maven, and setting environmental variables appropriately. By following the outlined solutions, developers can overcome this hurdle and continue with their Java development tasks smoothly. Remember, keeping the JDK and Maven updated is crucial for leveraging the latest language features and ensuring compatibility.