java - servlet类中throws抛出异常出错？

package servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class ServletSample extends GenericServlet {

public void service(ServletRequest request,ServletResponse response){
    throws ServletException,IOException  {
        response.setCharacterEncoding("gbk");
        PrintWriter out=response.getWriter();
        out.println("");
        out.println("head");
        out.println("");
        out.print("");
        out.println("");
        out.println("");
        out.println("
这是第一个servlet的例子
");
        out.println("");
        out.print("");
        out.println("");
        out.close();
    }
}

}

帮帮忙，我是初学者，请多多指教，谢谢