我正在使用我的第一个servlet程序，并且我创建了一个页面来列出数据库中表的行。
每当我点击刷新按钮时，页面都会显示重复的结果。
如何克服它，有什么建议吗？
@WebServlet("/BookList")
public class BookList extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public BookList() {
super();
// TODO Auto-generated constructor stub
}
StringBuffer string = new StringBuffer();
List<DemoBook>list=new ArrayList<DemoBook>();
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
HttpSession session=request.getSession();
if(session.getAttribute("Admin")==null)
{
response.sendRedirect("AdminLoginServlet");
}
try {
createTable(request, response);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}}
private void createTable(HttpServletRequest request,
HttpServletResponse response) throws Exception {
// StringBuffer strr=new StringBuffer();
String command = null;
PrintWriter out=response.getWriter();
System.out.println("hellowww");
response.setContentType("text/html");
System.out.println("begins");
string.append("<html>");
System.out.println("2nd html");
string.append("<head>" );
string.append("<Title>Book Collections</title><Script>");
string.append("function editBook(obj) {"
+ "document.listBook.command.value=\"editBook\";"
+ "document.listBook.BookId.value=obj.name;"
+ "document.listBook.submit();" + "}");
string.append("function deleteBook(obj) {"
+ "document.listBook.command.value=\"deleteBook\";"
+ "document.listBook.BookId.value=obj.name;"
+ "document.listBook.submit();" + "}");
string.append("</Script>");
string.append(" <style>");
string.append("#one{" );
string.append("background-image:url(\"./images/admini.jpg\");");
string.append(" width: 99.6%;");
string.append(" text-align:center;");
string.append("color:white;" );
string.append(" padding:50px;" );
string.append("}");
string.append("#two{" );
string.append("background-color:#6495ED;" );
string.append("width:100%;" );
string.append(" height:23px;");
string.append(" color:white;");
string.append("padding:3px;");
string.append("}" );
string.append(" a:link {");
string.append("color:blue; " );
string.append(" background-color:transparent;" );
string.append(" text-decoration:none;" );
string.append("}");
string.append("#four{" );
string.append(" background-color:#A0522D;");
string.append(" color:white;");
string.append("width: 100%;");
string.append(" padding:3px;");
string.append("height:30px;");
string.append(" text-align:center;");
string.append(" font-size: 1.5em;");
string.append("}");
string.append("{ table, th, td {");
string.append("border: 5px solid white;");
string.append("border-collapse: collapse; border-width: 5px;");
string.append("padding: 10px;");
string.append("}" );
string.append("h3");
string.append("{" );
string.append("color:white;");
string.append("}" );
string.append( "</style>");
string.append( "<head>");
string.append("<body>");
string.append("<div id=\"one\" >");
string.append( "<h2>Administration</h2>");
string.append("</div>" );
string.append("<div id=\"two\">");
string.append(" ");
string.append("<a href=\"Home\"><b> Home</b></a> ");
string.append("<a href=\"AdminHome\"> <b>Add Book</b></a> ");
string.append("<a href=\"\"> <b>Order List</b></a> ");
string.append("<a href\"BookList\"> <b>Book List</b></a> ");
string.append("<a href=''> <b>Change Password</b></a> ");
string.append("<a href='demo.html'> <b>Logout</b></a> ");
string.append("</div>");
string.append("<div id=\"four\"><b>List Books</b>");
string.append("</div>");
command=request.getParameter("command");
int bookId = 0;
InBookData in1=new InBookData();
List<DemoBook> bookList = in1.findAll();
if (request.getParameter("BookId") != null
&& request.getParameter("BookId") != "") {
bookId = Integer.parseInt(request.getParameter("BookId"));
}
//System.out.println(request.getParameter("BookId"));
if ("deleteBook".equals(command)) {
System.out.println("clicked:::");
InBookData in=new InBookData();
in.delete(bookId);
System.out.println(bookId);
string.append(displayBookList(bookList));
}
// else if ("editBook".equals(command)) {
//
// DemoBook book = ServiceFactory.getInBookService().findBook(bookId);
//// book.setId(bookId);
//// string.append(createUpdateForm(book));
// }
else{
string.append(displayBookList(bookList));
System.out.println("first");
}
string.append("<input type=\"hidden\" name=\"command\"/>")
.append("<input type=\"hidden\" name=\"BookId\"/>")
.append("</form></body></html>");
out.print(string);
System.out.println("--------------------helloooooooooooooo");
System.out.println(string.toString());
}
private String displayBookList(List<DemoBook> bookList) {
System.out.println("displaybook");
StringBuffer str=new StringBuffer();
str.append("<form name=\"listBook\" action=\"\" method=\"post\" >");
str.append( "<table align=\"center\">");
str.append("<tr bgcolor=\"#6495ED\"><th > Book Name</th>");
str.append("<th>ISBN</th>");
str.append("<th>Publisher</th>");
str.append("<th> Author</th>");
// +"<th> Image</th>"
str.append("<th>Edit</th>");
str.append("<th>");
str.append(" Delete");
str.append("</th>" );
str.append(" </tr>");
for(DemoBook d:bookList)
{
System.out.println(d.getB_author()+" "+d.getId());
str.append("<tr>" );
str.append( "<td>"+d.getB_name());
str.append( "</td>");
str.append( "<td>"+d.getIsbn());string.append("</td>");
str.append(" <td>" +d.getB_publisher()+"</td>");
str.append(" <td>"+d.getB_author()+"</td>");
str.append( "<td><input type=\"button\" name=" + d.getId()+ " onclick=\"editBook(this)\" value=Edit> </td>");
str.append( "<td><input type=\"button\" name=" + d.getId()+ " onclick=\"deleteBook(this)\" value=Delete></td>");
str.append("</tr>");
// string.append("<tr><td><input type=\"hidden\" name=\"BookId\" value="+d.getId()+"</td> </tr>");
}
return str.toString();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
// System.out.println("post");
}
}
答案 0 :(得分：0)
打印后删除字符串
string.delete(0,string.length());