1 Middleware (2) Nclab M.S. Jinwon Lee

2 Contents CGI, Servlet, JSP → Client Session Management JDBC (Java Database Connectivity) Connection pooling

3 Overview Client Browser Engine Supporting JSPs and Servlets Database JDBC Servlet JSP, Session Connection Pooling

4 Client Session Management

5 Stateless HTTP Protocol HTTP transaction is independent to each request. Problems at Data Tracking, User Identification. Ex) website login, shopping cart. Need to mange state information between transaction requests and Web Application → Session Tracking

6 Session Tracking Manage states information Client-side : Cookie Server-side: HttpSession (Servlet API)

7 Cookies A cookie is a piece of information that a site hands to your browser The browser hands the site the cookie on each subsequent request Unless the cookie is deleted, expired, modified..

8 Servlet/JSP support Cookies Javax.serlvet.http package support Cookie class Send to Client (HttpServletResponse class) Cookie myCookie = new Cookie(“key”, “value”) // Create cookie and Set attribute response.addCookie(myCookie); // Send Cookie to Client(Cookie is part of the HTTP response header.) Receive from Client(HttpServletRequest class) Cookie [] allCookie = request.getCookies(); // Receive allCookie from Client String value = myCookie[i].getValue(); // Find the specific one you are interested in

9 Cookies don’t always taste good Cookies can only contain small amounts of data (all cookie data are strings) Cookies might not be accepted by the browser Cookies can get stale → Use Object in Server-side (HttpSession)

10 HttpSession A session is a continuous connection from the same browser over a fixed period of time. Default is 30 minutes for Servlet Container To maintain session information, Use session with browser cookies or encodeURL Javax.servlet.http package support HttpSession interface

11 HttpSession How to obtain HttpSession object HttpSession session = request.getSession(true); // read session id from cookie or encodeURL,and // if there are valid session object, return object. // else create new session with cookie You can maintain a set of (key, value) paired information in the HttpSession object. To store session-specific information, use the putValue(key, value) & getValue(key).

12 encodeURL If the browser doesn’t accept cookies, session id is appended to each URL in the HTML response When the rewritten URL is accessed, the server extracts the appended session id String URL encodeURL(String URL); session id is append to URL and return URL [URL] [After encodeURL] xxxxxxx

13 Session Implemention Informations of HTTP transaction are managed by using HttpSession → Security, efficiency To track the HttpSession, it is the best way that user accept cookie

14 JDBC

15 JDBC Application 개발시 Database system 과의 연동이 필수적 → JDBC (Java Database Connectivity) JDBC API Java 로 작성된 Program 을 일반 Database 에 연결하기 위한 API 제공

16 JDBC Overview DB 와 User 사이에 Abstract Layer 제공. 한가지 API 만을 이용하여 서로 상이한 DB 사용 가능. 대부분의 DB Vendor 가 JDBC Spec. 에 따 라 JDBC Driver 를 구현하여 제공.

17 Java Application JDBC Driver Manager (java.sql.*) JDBC Driver JDBC API JDBC Driver API DB

18 JDBC Driver Type I : JDBC-ODBC bridge plus ODBC driver DataBase JAVA 어플리케이션 JDBC-ODBC Bridge 기존의 ODBC 드라이버 Native API( C/C++) DataBase protocol

19 Type II : Native-API partly-Java driver ( JDBC 의 호출을 각 DB Client API 로 변환하여 호출 )

20 Type III: JDBC-Net pure Java driver

21 Type IV: Native-protocol pure Java driver

22 장점 JDBC 호출을 DBMS 의 고유한 Protocol 로 직접 변환해 처리하기 때문에 처리 속도가 가장 빠르다. Internet/Intranet 에 가장 적합한 방식 단점 DB 고유의 Protocol 을 알고 있어야만 하므로 JDBC Driver Vendor 가 만들기에는 어렵고 주로 DBMS Vendor 에 의해 제공된다.

23 java.sql package JDBC 2.0 core API Major interface Making a connection with a data source DriverManager class Connection interface Sending SQL statements to a database Statement interface Retrieving and updating the results of a query ResultSet interface Throwing exceptions SQLException

24 Programming with JDBC API 1. DriverManager 에 해당 DBMS driver 등록 Class.forName(String className ); “com.jk.jdbc.Driver” 2. 해당 Driver 로부터 Connection 객체 획득 String 1433"; String user=“scott”; String passwd=“tiger”; Connection conn=DriverManager.getConnection( jdbcURL, user, passwd);

25 3. Connection 객체로부터 Statement 객체 획득 Statement stmt=conn.createStatement(); 4. Statement method 를 이용하여 SQL 실행 ResultSet rset=stmt.executeQuery(“SELECT id, name FROM emp”); 5. 결과를 ResultSet 으로 받아서 처리 while(rset.next()) { System.out.println(“ 사번 :” + rset.getInt(“id”)); System.out.println(“ 이름 :” + rset.getString(“name”)); } 6. 종료 rset.close(); stmt.close(); conn.close();

26 Problems Accessing the database can be slow Lots of years and tears are spent optimizing database access An obvious optimization is to reuse the JDBC connections

27 References Books Professional Java server programming Website (servlet/jsp lecture 7 ~ 9)