解决方法:
修改.classpath文件,重新刷新一下项目即可,在.classpath文件中,加入
<classpathentry kind="var" path="TOMCAT_HOME/lib/servlet-api.jar"/>
<classpathentry kind="var" path="TOMCAT_HOME/lib/jasper.jar"/>
<classpathentry kind="var" path="TOMCAT_HOME/lib/jsp-api.jar"/>
<classpathentry kind="var" path="TOMCAT_HOME/lib/el-api.jar"/>
<classpathentry kind="var" path="TOMCAT_HOME/lib/annotations-api.jar"/>
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下面是是myeclipse环境，把他去掉。(不去掉关系也不大)
<classpathentry kind="con" path="com.genuitec.eclipse.j2eedt.core.J2EE14_CONTAINER"/>
解决方法来自:
7楼redlotus_lyn的答案