Class 'java.io.' is not present in JRE Emulation library INTELLIJ IDEA - gwt

Question

I am working on a GWT project in IntelliJ IDEA 15.0.4. This project compileds and runs. But IntelliJ keeps telling me that java class files are not present in JRE Emulation Library.
Please help me! Is there something missing in my maven pom.xml?
Here are the error messages:
My pom.xml:
<properties>
<maven.compiler.target>1.8</maven.compiler.target>
<maven.compiler.source>1.8</maven.compiler.source>
</properties>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<verbose>true</verbose>
<fork>true</fork>
<executable>/Library/Java/JavaVirtualMachines/jdk1.8.0_73.jdk/Contents/Home/bin/javac</executable>
<compilerVersion>1.8</compilerVersion>
</configuration>
</plugin>
Here are my IntelliJ project config:
Timesheet.gwt.xml
<?xml version="1.0" encoding="UTF-8"?>
<module rename-to='Timesheet'>
<!-- Inherit the core Web Toolkit stuff. -->
<inherits name='com.google.gwt.user.User' />
<inherits name="com.vaadin.polymer.Elements"/>
<!-- Inherit the default GWT style sheet. You can change -->
<!-- the theme of your GWT application by uncommenting -->
<!-- any one of the following lines. -->
<inherits name='com.google.gwt.user.theme.standard.Standard' />
<!-- <inherits name='com.google.gwt.user.theme.chrome.Chrome'/> -->
<!-- <inherits name='com.google.gwt.user.theme.dark.Dark'/> -->
<!-- Other module inherits -->
<!-- Specify the app entry point class. -->
<entry-point class='com.campus.client.Timesheet' />
<!-- Specify the paths for translatable code -->
<source path='client' />
<source path='shared' />
<!-- <inherits name="com.google.gwt.user.theme.standard.Standard"/> -->
<inherits name="com.google.gwt.user.theme.clean.Clean"/>
<!-- For production, most teams prefer to set the default log level to `OFF` -->
<inherits name="com.allen_sauer.gwt.log.gwt-log-OFF" />
<!-- For development, a default of `DEBUG` is recommended -->
<!-- <inherits name="com.allen_sauer.gwt.log.gwt-log-DEBUG" /> -->
</module>

Answer 1

Unless you have the full version of IntelliJ I would strongly suggest you to use Eclipse + GWT Plugin for GWT development.
This is the reference for GWT Jre emulated class, all that is in here will work on the client side:
http://www.gwtproject.org/doc/latest/RefJreEmulation.html#Package_java_io
In your particular case seems like IntelliJ cannot find the String class either, that points out to a deeper configuration issue than a GWT related one.

Answer 2

I seemed to have this problem when I installed Oracle JDK 9 in Arch Linux and used that as the project SDK. After I uninstalled Oracle JDK 9 and installed OpenJDK 8, and set that as the project SDK, no errors occurred anymore. I wonder if either Java 9 or Oracle JDK is just not very nicely supported by GWT.
Another possible cause of error is that maybe I set up the SDK incorrectly. First I pointed the SDK path to /usr/lib/jvm/default-runtime, but later I changed it to the actual path (/usr/lib/jvm/java-8-openjdk).

Answer 3

This will help you solve your issue.. I had same issue and tried to add the dependencies..
<gwt.version>2.7.0</gwt.version>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-servlet</artifactId>
<version>${gwt.version}</version>
</dependency>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-user</artifactId>
<version>${gwt.version}</version>
</dependency>