java Web问题

这到底是啥错啊？
public void doPost (HttpServletRequest req,
HttpServletResponse res) throws ServletException, IOException {

HttpSession session = req.getSession();
Member member = (Member)session.getAttribute("member");

HoldSet heldBooks = null;

try {
    heldBooks = LibraryMember.getMemberHolds( member );
} catch( Exception e ){
    sendErrorRedirect(req, res, e);
}

BookTitleSet books = new BookTitleSet();

try {
    for( int i=0; i<heldBooks.getHoldCount(); i++ ) {
books.addBookTitle(LibraryBookTitle.getBookTitle(heldBooks.getHoldAt(i).getCallNumber()));
    }
} catch( Exception e ){
    sendErrorRedirect(req, res, e);
}

session.setAttribute("books", books);
res.sendRedirect("/library/viewheldbooks.jsp");
return;

    }

public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
     {
doPost(req, res);
     }

The server encountered an internal error () that prevented it from fulfilling this request.

exception

java.lang.IllegalStateException
org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:435)
MemberViewonholdController.doPost(MemberViewonholdController.java:40)
Controller.doGet(Controller.java:39)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.

Java Web 异常 Apache --------------------编程问答--------------------

--------------------编程问答-------------------- 在sendErrorRedirect(req, res, e);方法后加return语句即可，如下：
sendErrorRedirect(req, res, e);
return;
原因是：在程序中两次调用了response.sendRedirect()方法。

jdk5.0文档中很清楚地介绍了出现IllegalStateException异常的可能情况:

1）同一个页面中再次调用response.sendRedirect()方法。
2）提交的URL错误，即不是个有效的URL。

--------------------编程问答--------------------

--------------------编程问答-------------------- 在程序中两次调用了response.sendRedirect()方法。，同意楼上的说法 --------------------编程问答-------------------- Controller.doGet(Controller.java:39) 39行；

贴完整代码

补充：Java ,  Web 开发