Eclipse JRE System Library [J2SE-1.5]

artbristol gave the correct answer (and I upvoted him).

That was in 2012. Here is an update more appropriate for today (2016, Java 8, Spring 4.x/Servlet 3.x):

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-compiler-plugin</artifactId>
   <version>3.0</version>
   <configuration>
      <source>1.7</source>
      <target>1.7</target>
   </configuration>
</plugin>

The problem is not with Eclipse, but with the projects you're importing. m2e will set the project's JRE to match the maven project. The POM specifies the JRE version, and this is defaulted to 1.5 if not present. You need this in the POM:

<build>
     <plugins>
        <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.0</version>
                <configuration>
                   <source>1.7</source>
                   <target>1.7</target>
                </configuration>
        </plugin>
    </plugins>
</build>