servlet又出错了
情况是这样的，做了一个简单的注册功能，昨天都能运行，今天我又写了些其他页面，但是没动注册这边的
运行老是出错，我启动eclipse，第一次运行会出现这个错误：
ava.lang.Error: Unresolved compilation problem: 
The import net cannot be resolved

at myservlet.HandleRegister.<init>(HandleRegister.java:15)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at java.lang.Class.newInstance0(Class.java:374)
at java.lang.Class.newInstance(Class.java:327)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1115)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:808)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:129)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:722)


再运行一次就出现：
The requested resource (Servlet HandleRegister is not available) is not available.
  
源代码是：
package myservlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.wsc.bean.Register;
public class HandleRegister extends HttpServlet{
/**
 * 
 */
private static final long serialVersionUID = 1L;
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
doPost(request,response);
}
public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
response.setContentType("text/html; charset=UTF-8");
PrintWriter out=response.getWriter();
request.setCharacterEncoding("GB2312");
String username =request.getParameter("username");
String password =request.getParameter("password");
String email =requ