Microsoft. one feature of data access on the NET platform is that the data query results can be stored in the memory and described in XML format, without the need to keep online connections with the database, use DataSet + Data Adapter!
In JDBC, we usually use the javax. SQL. ResultSet class to store the stored data. Its Process and lifecycle are as follows:
| Use ResultSet to return database query results |
| Client |
--> |
Connection |
--> |
Statement |
--> |
JDBC Driver |
-- + |
| |
Database |
| Client |
<-- |
Parsing |
<-- |
ResultSet |
<-- |
JDBC Driver |
-- + |
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Connection lifecycle |
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ResultSet lifecycle |
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We can see that this will occupy the database connection resources for a long time, which is a bit uncomfortable...
In fact, another mechanism is provided in JSTL, so that we can use it offline when returning the query results to the presentation layer! It is the javax. servlet. jsp. jstl. SQL. Result class!
1 <% @ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "c" %>
2 <% @ page contentType = "text/html; charset = UTF-8" %>
3 <% @ pageImport = "java. SQL. Connection" %>
4 <% @ pageImport = "java. SQL. DriverManager" %>
5 <% @ pageImport = "java. SQL. ResultSet" %>
6 <% @ pageImport = "java. SQL. SQLException" %>
7 <% @ pageImport = "java. SQL. Statement" %>
8 <% @ pageImport = "javax. servlet. jsp. jstl. SQL. Result" %>
9 <% @ pageImport = "javax. servlet. jsp. jstl. SQL. ResultSupport" %>
10 <%
11 // now I think of the following content as a DAO in a multi-layer architecture. I am lazy!
12 Connection conn =Null;
13 Statement stmt =Null;
14 ResultSet rs =Null;
15 String strDbUrl
16 = "jdbc: mysql: // localhost/tutorial? User = tutorial & password = tutpwd ";
17Try {
18 // start querying the database
19 Class. forName("Com. mysql. jdbc. Driver"). NewInstance();
20 conn = DriverManager. getConnection(StrDbUrl);
21 stmt = conn. createStatement();
22 String strSql = "SELECT * FROM R_TUT_USERS ";
23 rs = stmt.exe cuteQuery(StrSql);
24 // convert ResultSet to Result
25Result userdata = resultsupport. toresult (RS );
26 // when we put the result into a Model bean, we can close the database connection.
27 // to simplify the process, we can now regard pageContext as the Model Bean!
28 pageContext. setAttribute("UserData", userData);
29}
30Catch (Exception ex) {
31 // handle any errors
32 system. Out. println("Sqlexception:" + ex. getmessage());
33}
34Finally {
35Try {
36If (RS! =Null) {
37 Rs. Close();
38}
39If (Stmt! =Null) {
40 stmt. Close();
41}
42If (Conn! =Null) {
43 conn. Close();
44}
45}
46Catch (Sqlexception ex) {
47 system. Out. println("SQL exception:" + ex. getmessage());
48}
49}
50 // logic end of Dao
51%>
52 <HTML>
53 54 <title> test </title>
55 56 <body>
57 <! -- // The following is the presentation layer. // -->
58 <c: forEach items = "$ {userData. rows}" var = "user">
59 <c: out value = '$ {user. name}'/>
60 </c: forEach>
61 </body>
62 |
