Error:java: System Java Compiler was not found in classpath:

今天把项目的jdk版本从1.8换成1.7，在build项目时出现一下错误：

Error:java: System Java Compiler was not found in classpath:
java.lang.ClassNotFoundException: com.sun.tools.javac.api.JavacTool
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Unknown Source)
	at org.jetbrains.jps.builders.impl.java.JavacCompilerTool.createCompiler(JavacCompilerTool.java:74)
	at org.jetbrains.jps.javac.JavacMain.compile(JavacMain.java:51)
	at org.jetbrains.jps.javac.ExternalJavacProcess.compile(ExternalJavacProcess.java:190)
	at org.jetbrains.jps.javac.ExternalJavacProcess.access$300(ExternalJavacProcess.java:32)
	at org.jetbrains.jps.javac.ExternalJavacProcess$CompilationRequestsHandler$1.run(ExternalJavacProcess.java:255)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

主要原因是在没有完全切换jdk版本：