我仍然是servlets和JDBC的新手，并希望对以下代码有所帮助：
try{
String selectSQL = "select * from product_list where category = '"+category+"'";
Statement stmt = conn.createStatement();
ResultSet rs1 = stmt.executeQuery(selectSQL);
ArrayList<Float> idList = new ArrayList<Float>();
out.println("<table border=\"1\"><tr><th>Item_ID</th><th>Item_name</th><th>Title</th><th>Category</th><th>Image_name</th><th>Price</th><th>Stock_Count</th></tr>");
while(rs1.next()){
out.println("<tr><td>"+ rs1.getFloat("item_id") + "</td>");
out.println("<td>" + rs1.getString("item_name") + "</td>");
out.println("<td>"+"<a href =\"ItemDetail\">" + rs1.getString("title")+"</a>" + "</td>");
out.println("<td>" + rs1.getString("category") + "</td>");
out.println("<td>" + rs1.getString("image_name") + "</td>");
out.println("<td> " + rs1.getFloat("price") + "</td>");
out.println("<td> " + rs1.getFloat("stock_count") + "</td>");
out.println("</tr>");
HttpSession session = request.getSession(true);
idList.add(rs1.getFloat("recording_id"));
session.setAttribute("id", idList);
}
out.println("</table>");
conn.close();
} catch(SQLException se) {
System.err.println(se);
}
我想要做的是它会在会话中存储每一个item_id，但只显示另一个servlet中用户点击其标题链接的那个（每个标题都有相同的超链接）的详细信息，我有试图将所有id存储在一个数组列表中，但是没有任何东西显示在另一个意图接收到数组列表的servlet上，那里我做错了什么，任何帮助都会受到赞赏。
以下是在不同的servlet中用于从上表
接收属性的代码HttpSession session = request.getSession(true);
ArrayList<Float> id = (ArrayList<Float>) session.getAttribute("id");
答案 0 :(得分：0)
这是一个有效的示例代码。相应地修改
//My first servlet using Java-8
try (Connection con = DriverManager.getConnection("xxxx")) {
String category = "fish";
try (PrintWriter out = response.getWriter()) {
try (ResultSet rs1 = con.createStatement()
.executeQuery("select * from product_list where category = '" + category + "'")) {
HttpSession session = request.getSession();
ArrayList<Float> list = new ArrayList<>();
out.print(
"<table border=\"1\"><tr><th>Item_ID</th><th>Item_name</th><th>Title</th><th>Category</th><th>Image_name</th><th>Price</th><th>Stock_Count</th></tr>");
while (rs1.next()) {
list.add(rs1.getFloat("item_id"));
out.println("<tr><td>" + rs1.getFloat("item_id") + "</td>");
out.println("<td>" + rs1.getString("item_name") + "</td>");
out.println("<td>" + "<a href ='" + request.getContextPath() + "/Second?id="+rs1.getFloat("item_id")+"'>"
+ rs1.getString("title") + "</a>" + "</td>");
out.println("<td>" + rs1.getString("category") + "</td>");
out.println("<td>" + rs1.getString("image_name") + "</td>");
out.println("<td> " + rs1.getFloat("price") + "</td>");
out.println("<td> " + rs1.getFloat("stock_count") + "</td>");
out.println("</tr>");
}
session.setAttribute("list", list);
out.println("</table>");
}
}
} catch (SQLException e) {
e.printStackTrace();
}
我的第二个servlet在这里
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// then just use that to get it through a GET Http Method
String id = request.getParameter("id");
HttpSession session = request.getSession();
ArrayList<Float> list = (ArrayList<Float>) session.getAttribute("list");
response.getWriter().append("item: ").append(String.valueOf(list.get(0)));
}
在屏幕上打印输出项目：45.0
希望它有所帮助。
答案 1 :(得分：0)
我认为你的问题的答案很简单，但我想帮你清理一下，因为这里有很多可以做得更好的事情。这段代码有资源泄漏，可以教你一些坏习惯。
ID没有正确显示的原因可能是这一行：
HttpSession session = request.getSession(true);
idList.add(rs1.getFloat("recording_id"));
session.setAttribute("id", idList);
} //End while
每次迭代ResultSet时都会重置idList属性。您需要在循环之外获取会话，修改ArrayList，然后将属性设置一次。
HttpSession session = request.getSession(true); //Get the session only once
ArrayList<Float> idList = new ArrayList<Float>(); //Declare output variables outside of the try block.
//Now declare your JDBC resources; always declare them as null outside of the try block.
//This allows you to close them properly later.
PreparedStatement stmt = null;
ResultSet rs1 = null;
try{
String selectSQL = "select * from product_list where category = ?";
stmt = conn.prepareStatement(selectSQL);
stmt.setString(1, category);
rs1 = stmt.executeQuery(selectSQL);
out.println("<table border=\"1\"><tr><th>Item_ID</th><th>Item_name</th><th>Title</th><th>Category</th><th>Image_name</th><th>Price</th><th>Stock_Count</th></tr>");
while(rs1.next()){
out.println("<tr><td>"+ rs1.getFloat("item_id") + "</td>");
out.println("<td>" + rs1.getString("item_name") + "</td>");
out.println("<td>"+"<a href =\"ItemDetail\">" + rs1.getString("title")+"</a>" + "</td>");
out.println("<td>" + rs1.getString("category") + "</td>");
out.println("<td>" + rs1.getString("image_name") + "</td>");
out.println("<td> " + rs1.getFloat("price") + "</td>");
out.println("<td> " + rs1.getFloat("stock_count") + "</td>");
out.println("</tr>");
idList.add(rs1.getFloat("recording_id")); //Add to the list in the loop.
}
out.println("</table>");
} catch(SQLException se) {
System.err.println(se); //This is OK, but consider 'throw new RuntimeException(se)' here instead so that the exception propagates.
} finally {
//Close the resources backwards from the way that they were opened.
//Check them all for null first in case there's an error in the middle somewhere,
//otherwise you'll get a NullPointerException from the finally block and it will "swallow"
//the original error.
if(rs1 != null) {
try {
rs1.close();
} catch(SQLException x) {
System.err.println(x); //Don't throw here; keep trying to close resources
}
}
if(stmt != null) {
try {
stmt.close();
} catch(SQLException x) {
System.err.println(x);
}
}
if(conn != null) {
try {
stmt.close();
} catch(SQLException x) {
System.err.println(x);
}
}
}
session.setAttribute("id", idList); //Set the list once and only once.