JSP already has a similar. Net dataset like the offline data access, abandon resultset, hug result!
Microsoft's. NET platform above the data access has a feature, that is, the results of data query, can be placed in memory, in the form of XML description, do not have to keep online with the database connection, with DataSet + Data adapter to achieve!
In JDBC, we usually use the Javax.sql.ResultSet class to store the data that is put back, and 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 | --+ |
| Connection lifecycle | |||||||
| ResultSet lifecycle | |||||||
We can see that this will take a long time to occupy the resources of the database connection, is a bit of a problem ...
In fact, in the JSTL provides another mechanism, let us return query results to the presentation layer, you can do offline use! 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 <% @page import= "Java.sql.Connection"%>
4 <% @page import= "Java.sql.DriverManager"%>
5 <% @page import= "Java.sql.ResultSet"%>
6 <% @page import= "Java.sql.SQLException"%>
7 <% @page import= "Java.sql.Statement"%>
8 <% @page import= "Javax.servlet.jsp.jstl.sql.Result"%>
9 <% @page import= "Javax.servlet.jsp.jstl.sql.ResultSupport"%>
Ten <%
11//For the moment, consider this below as the DAO in the multi-layer architecture okay, I'm slacking off!
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
String Strdburl
= "Jdbc:mysql://localhost/tutorial?user=tutorial&password=tutpwd";
The try {
18//Start with the database query Class.forName ("Com.mysql.jdbc.Driver"). newinstance ();
conn = Drivermanager.getconnection (strdburl); stmt = Conn.createstatement ();
String strSQL = "SELECT * from R_tut_users"; n rs = stmt.executequery (strSQL);
24//Convert resultset into Result25 result userData = Resultsupport.toresult (RS);
26//When we put the results in a model bean, we can close the database connection.
27//In order to simplify, we will consider PageContext as model Bean for now!
Pagecontext.setattribute ("UserData", userData);
29}
catch (Exception ex) {
To//handle any errors
System.out.println ("SQLException:" + ex.getmessage ());
33}
finally {
A try {
(Rs!= null) {
Panax Notoginseng rs.close ();
38}
if (stmt!= null) {
Stmt.close ();
41}
IF (conn!= null) {
Conn.close ();
44}
45}
A catch (SQLException ex) {
System.out.println ("SQL Exception:" + ex.getmessage ());
48}
49}
The logical end of//dao
Wuyi%>
<title>test</title>
<body>
<!--//below as a presentation layer bar//-->
<c:foreach items= "${userdata.rows}" var= "User" >
<c:out value= ' ${user.name} '/>
</c:forEach>
</body>
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