Anyone that uses the M2E(maven-to-eclipse) plugin in eclipse knows the issue where you have run a build, then update maven on your project only to have it reset the JRE and throw up a wall of project errors! I noticed the issue in the post I made on running Java EE 8 with Java 9 using Open Liberty
The solution is to ensure the compiler is running the correct version you require, so –
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<failOnMissingWebXml>false</failOnMissingWebXml>
</properties>
Or –
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
There is a further point worth noting if you are using Java 9 or later, as the version number format is different. So while Java 8 has a version of 1.8, Java 9 has a version of 9 –
Java 9 vs Java 8 versions
This means you need to state the version in your pom as –
<properties>
<maven.compiler.source>9</maven.compiler.source>
<maven.compiler.target>9</maven.compiler.target>
<failOnMissingWebXml>false</failOnMissingWebXml>
</properties>
Or using the full version in my JavaEE8 project(https://github.com/farrelmr/javaee8/blob/master/pom.xml) this would be stated as –
<project
xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javabullets.javaee8</groupId>
<artifactId>javaee8</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-api</artifactId>
<version>8.0</version>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<finalName>javaee8</finalName>
</build>
<properties>
<maven.compiler.source>9</maven.compiler.source>
<maven.compiler.target>9</maven.compiler.target>
<failOnMissingWebXml>false</failOnMissingWebXml>
</properties>
</project>
This will prevent the problem in eclipse
This post may seem obvious – but it is worth stating that the change in version number for Java 9 means you must check you are using the correct version number in maven
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