Warning - Build path specifies execution environment J2SE-1.4

Question

In Eclipse from your project:

1. Right-click on your project
2. Click Properties
3. Java build path: Libraries; Remove the "JRE System Library[J2SE 1.4]"
4. Click Add Library -> JRE System Library
5. Select the new "Execution Environment" or Workspace default JRE

Whether you're using the maven eclipse plugin or m2eclipse, Eclipse's project configuration is derived from the POM, so you need to configure the maven compiler plugin for 1.6 (it defaults to 1.4).

Add the following to your project's pom.xml, save, then go to your Eclipse project and select Properties > Maven > Update Project Configuration:

<project>
 <build>
  <pluginManagement>
   <plugins>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>          
        <configuration>
            <source>1.6</source>
            <target>1.6</target>
        </configuration>
    </plugin>
   </plugins>
  </pluginManagement>
 </build>
</project>

The above solutions fix the project or work around the problem in some way. Sometimes you just don't want to fix the project and just hide the warning instead.

To do that, configure the contents of the warning panel and make sure to toggle-off the "build path"->"JRE System Path Problem" category. The UI for this dialog is a bit complex/weird/usability challenged so you might have to fiddle with a few of the options to make it do what you want.

In eclipse preferences, go to Java->Installed JREs->Execution Environment and set up a JRE Execution Environment for J2SE-1.4

The actual cause of this warning is that you have configured your project to run with an earlier JRE version then you have installed. Generally this occurs whenever you use old projects with newer JREs.

This will likely cause no trouble at all. But if you want to be really on the save side, you should install the correct, old JDK. You can find them here: http://www.oracle.com/technetwork/java/archive-139210.html

If you then restart eclipse you can go into Window > Preferences > Java > Installed JREs > Execution Environments and set for in your case J2SE-1.4 the [perfect match] as eclipse calls it.

If you have Java 1.8 then

You need this xml part in pom.xml and update project.

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