利用Servlet緩存技術連接tomcat6.0數據源

今天是禮拜天，閒來無事想起加強一下自己的Servlet基礎。做了一個簡單是應用:利用Servlet中的init()方法緩存數據源DataSource對象，已達到提高提高系統性能的目的.

首先需要強調一下的是,tomcat6.0數據源的配置方法和以前tomcat5.x是不同的,tomcat6.0以前我們的數據源一直是配置在

%CATALINA_HOME%/conf/server.xml中,而tomcat6.0中我們一般不需要在server.xml中配置，而是直接在context.xml文件中配置

下面就需要在應用程序WEB_INF目錄下面的web.xml文件中配置數據源參考

<resource-ref> <description>Database for Portal</description> <res-ref-name>jdbc/portal</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> <res-sharing-scope>Unshareable</res-sharing-scope> </resource-ref>

這裏再強調一點：不要忘記加入你的數據庫驅動包,這樣我們的環境基本上就準備好了,下面就開始開發了...

我們的流程是這樣的，首先訪問一個jsp頁面，通過form表單提交，調用ControllerServlet，在ControllerServlet查找數據源，得到DataSource對象，並將其緩存在ServletContext中,爲了簡單起見直接在Servlet中查詢數據庫(並沒有使用後臺的業務類).將查詢出來的數據封裝到List中返回到jsp頁面顯示出來。最後在頁面中繼續調用一個Controller_Servlet將數據在控制檯打印出來.

1、ControllerServlet.java

@SuppressWarnings("serial") public class ControllerServlet extends HttpServlet { private javax.sql.DataSource testDS = null; //創建DataSource對象 public void destroy() { } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //============================================================================== //============================================================================== System.out.println("============================================"); ResultSet rs = null; Connection conn = null; PreparedStatement ps = null; List<UserInfo> list = null; DataSource ds = this.getTestDS(); //GetUsers g = new GetUsers(); //g.getUsers(ds); try { if(ds !=null){ conn = ds.getConnection();//獲取Connection對象失敗 }else{ System.out.println("獲取DataSource失敗!DataSource==null"); return ; } ps = conn.prepareStatement("SELECT * FROM T_TEST_CHEN"); rs = ps.executeQuery(); list = new ArrayList<UserInfo>(); while(rs.next()){ UserInfo userInfo = new UserInfo(); userInfo.setT_id(rs.getString("t_id")); userInfo.setT_name(rs.getString("t_name")); userInfo.setT_score(rs.getString("t_score")); userInfo.setDescription(rs.getString("t_description")); list.add(userInfo); } } catch (SQLException e) { e.printStackTrace(); System.out.println("doPost()方法異常!"); }finally{ try { if(rs!=null){ rs.close(); rs = null; } if(ps!=null){ ps.close(); ps = null; } if(conn!=null){ conn.close(); conn = null; } } catch (SQLException e) { e.printStackTrace(); } } if(list!=null){ System.out.println("list集合中元素數量--"+list.size()); //HttpSession session = request.getSession(); //session.setAttribute("list", list); request.setAttribute("list", list); //留下疑問：爲什麼使用request頁面就無法得到數據呢? } response.sendRedirect("/testCompany/login/TestDB.jsp"); } public void init(ServletConfig config) throws ServletException { super.init(config); Context ctx = null; try { ctx = new InitialContext(); //構造一個初始上下文 testDS = (javax.sql.DataSource) ctx .lookup("java:comp/env/jdbc/portal"); System.out.println(testDS);// ok this.getServletContext().setAttribute("testDS", testDS); //使用ServletContext保存數據對象 } catch (NamingException ne) { ne.printStackTrace(); System.out.println("jndi沒有找到數據源!"); } catch (Exception e) { e.printStackTrace(); System.out.println("不明異常"); } } public DataSource getTestDS(){//獲得DataSource對象 return testDS; } }

2、TestDB.jsp

<body> <table cellpadding="0" cellspacing="0" border="0" align="left"> <tr> <td>學號</td> <td>姓名</td> <td>成績</td> <td>評論</td> </tr> <c:forEach items="${list}" var="list"> <tr> <td>${list.t_id }</td> <td>${list.t_name }</td> <td>${list.t_score }</td> <td>${list.description }</td> </tr> </c:forEach> </table> <form action="/testCompany/servlet/Controller_Servlet" method="post"> 調用Servlet <input type="submit" value="提交"/> -------查看控制檯是否打印數據---------------- </form> </body>

3、Controller_Servlet

@SuppressWarnings("serial") public class Controller_Servlet extends HttpServlet { ServletConfig config; public void init(ServletConfig config) throws ServletException { this.config = config; } public void destroy() { //Input something code here } private Connection conn = null; private PreparedStatement ps = null; private ResultSet rs = null; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("------------Enter into Controller_Servlet"); //Servle上下文中獲取DataSource對象 DataSource ds = (DataSource) config.getServletContext().getAttribute("testDS"); try { conn = ds.getConnection(); ps = conn.prepareStatement("SELECT * FROM T_TEST_CHEN"); rs = ps.executeQuery(); while(rs.next()){ System.out.print(rs.getString("t_id")); System.out.print(rs.getString("t_name")); System.out.print(rs.getString("t_score")); System.out.print(rs.getString("t_description")); } } catch (SQLException e) { e.printStackTrace(); }finally{ try { if(rs!=null){ rs.close(); rs = null; }if(ps!=null){ ps.close(); ps = null; }if(conn!=null){ conn.close(); conn = null; } } catch (SQLException e) { e.printStackTrace();} } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request, response); } }

哎~時間又不早了，吃飯去了...

利用Servlet緩存技術連接tomcat6.0數據源

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