详解 问题：HttpServlet cannot be resolved to a type

DescriptionResourcePathLocationType
HttpServlet cannot be resolved to a typeSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 15Java Problem
HttpServletRequest cannot be resolved to a typeSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 22Java Problem
HttpServletResponse cannot be resolved to a typeSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 22Java Problem
ServletException cannot be resolved to a typeSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 22Java Problem
The import javax.servlet cannot be resolvedSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 5Java Problem
The import javax.servlet cannot be resolvedSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 6Java Problem
The import javax.servlet cannot be resolvedSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 7Java Problem
The import javax.servlet cannot be resolvedSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 8Java Problem
The import javax.servlet cannot be resolvedSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 9Java Problem


WebServlet cannot be resolved to a typeSimpleServlet.java/JavaHelloWorldApp/src/main/java/wasdev/sample/servletline 14Java Problem