IDEA: javac: source release 1.7 requires target release 1.7

Most likely you have incorrect compiler options imported from Maven here:

Also check project and module bytecode (target) version settings outlined on the screenshot.

Other places where the source language level is configured:

• Project Structure | Project

• Project Structure | Modules (check every module) | Sources

Maven default language level is 1.5 (5.0), you will see this version as the Module language level on the screenshot above.

This can be changed using maven-compiler-plugin configuration inside pom.xml:

<project>
  [...]
  <build>
    [...]
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
    [...]
  </build>
  [...]
</project>

or

<project>
  [...]
  <properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
  </properties>
  [...]
</project>

IntelliJ IDEA will respect this setting after you Reimport the Maven project in the Maven Projects tool window:

IntelliJ 15, 2016 & 2017

Similar to that discussed below for IntelliJ 13 & 14, but with an extra level in the Settings/Preferences panel: Settings > Build, Execution, Deployment > Compiler > Java Compiler.

IntelliJ 13 & 14

In IntelliJ 13 and 14, check the Settings > Compiler > Java Compiler UI to ensure you're not targeting a different bytecode version in your module.

In IntelliJ IDEA 14.1 the "Target bytecode version" is in a different place.

The following change worked for me:

File > Settings... > Build, Execution, Deployment > Compiler > Java Compiler : change Target bytecode version from 1.5 to 1.8